Major human races. Racial differences in intelligence
Race classification. All people living at the present time belong to the same species; any marriages between them produce fertile offspring. It is impossible to get a reliable answer to the question of whether any ancient forms of man, such as Neanderthal man, were representatives of the species Homo sapiens. The species Homo sapiens is divided into populations, which are commonly referred to as races. A race is a large population of individuals who have a significant part of their genes in common and which can be distinguished from other races by their common gene pool. In ancient times, members of the same race often lived together in similar sociocultural conditions. The concept of "race" overlaps with other concepts used to refer to smaller population units, such as the concept of "dem". The classification and history of races constituted one of the main directions of research in the field of classical anthropology, carried out in the 19th and especially at the beginning of the 20th centuries. Previously proposed classifications were based on the corresponding visual impressions and on the analysis of statistical distributions of anthropometric features. With the development of human genetics, data on the frequencies of polymorphic genetic markers have been increasingly used for this. The classifications of different authors differ somewhat in detail; however, the division of mankind into Negroids, Mongoloids and Caucasians is beyond doubt. To these three great races are often added two smaller groups, namely the Khoisanids or Capoids (Bushmen and Hottentots) and the Australoids (Australian Aborigines and Negritos).
Genetic differences between races. The definition of race given here is genetic, and therefore it would be desirable to build a racial classification on the basis of traits well studied at the gene level. Several groups of such signs can be distinguished.
Many genes function in all human beings, showing perhaps only small quantitative differences in the level of expression. For example, each person has genes that determine the structure of enzymes necessary for the implementation of many basic metabolic processes. Unusual individuals - carriers of rare mutations that alter these genes - suffer from inborn errors of metabolism. Many of the genes belonging to this group are also found in other living beings.
There are traits and, consequently, genes that determine them, common to all or almost all representatives of any one race; they are absent in individuals of other races. The number of such features seems to be very small; from a genetic point of view, they are poorly characterized. One example of signs of this kind is the vertical fold of the upper eyelid in Mongoloids.
The third group of signs should include those that are found only in one of the three main races, while representatives of the other two are absent. This group includes big number markers of genes that make up many well-characterized systems of genetic polymorphism (Table 7.5). One of these signs is the Diego factor detected in a blood test. This blood type was discovered in 1953 in representatives of four generations of one Venezuelan family; while it was shown that most white people lack the Diego factor. The phenotypic frequencies of this factor obtained in the study of American Indian populations vary from 0.025 to 0.48. In populations of whites and blacks, the corresponding allele was not found at all. On the other hand, among Mongoloids, such as the Japanese and Chinese, it occurs, although with a lower average frequency. These data confirm the assumption put forward in classical anthropology, according to which the American Indians are part of a large Mongoloid race.
There is another class of traits that are more common in some populations than others. These include traits and alleles that are present in all human races, but found in them with different frequencies. This class includes, for example, alleles of most systems of genetic polymorphism and genes that determine quantitative traits such as height, body proportions and physiological functions. Polymorphic alleles are increasingly being used in studies undertaken to characterize different populations from a genetic point of view. This made it possible to fairly objectively classify populations. The results of works devoted to this problem are summarized in Murant's monograph. The available data indicate the similarity of the frequencies of some homologous genes in different populations and that the construction of racial classifications is not an easy task: within-group differences between representatives of any racial group often exceed the differences between representatives of different large races (Mongoloids, Negroids and Caucasians).
How did evolution proceed, leading to the emergence of genetic differences between races? The main factor in the evolution of phenotypes and, in particular, the main factor in racial genesis is natural selection, which determines adaptation to various environmental conditions. In order for selection that leads to the emergence of genetic differences (for example, between large races) to be effective, significant reproductive isolation of subpopulations is necessary. Was there a period in early human history when the human population was subdivided into three more or less isolated subpopulations?
During most of the last ice age (about 100,000 years ago), a huge area of the Earth's surface was covered with ice (Figure 7.11). The Himalayan and Altai mountains with glaciers located on them divided the Eurasian continent into three regions, thus creating conditions for the separate evolution of whites in the west, Mongoloids in the east and Negroids in the south. The modern areas of settlement of the three great races do not coincide with those areas in which they were formed; this discrepancy can be explained by migration processes.
Genetic differences due to the action of certain selective mechanisms: skin pigmentation and radiation. The most notable differences between the great races are differences in skin pigmentation. Most modern primates are dark-pigmented, and so there is reason to believe that ancient human populations also consisted of dark-skinned individuals, especially considering that the first humans arose in Africa. Why, then, is the skin of whites and Mongoloids so poorly pigmented?
According to one plausible hypothesis, in the places of settlement of these two races, people have adapted to low levels of ultraviolet (UV) radiation. UV light is involved in the conversion of provitamin D to vitamin D in human skin (Fig. 7.12). Vitamin D, in turn, is necessary for the classification of bones; its deficiency leads to rickets. One of the most dangerous manifestations of rickets is a deformity of the pelvis that disrupts normal childbirth, which in the conditions of life of primitive people often led to the death of the mother and child. This effect obviously creates a strong selection pressure. On fig. Figure 7.13 is a map showing the degree of human skin pigmentation and the intensity of exposure to UV light in different parts of the world.
Rice. 7.13. The intensity of ultraviolet light and the degree of pigmentation of the skin of the native population in various parts of the world. The numbers given are the average values of the intensity of solar radiation incident on a horizontal plane on the earth's surface (annual averages over 24 hours, expressed in mW × cm -2)
From this hypothesis, it follows that UV radiation penetrates lightly pigmented skin more easily than highly pigmented skin, and therefore, at the same doses of UV radiation, more vitamin D is formed in light skin than in dark skin. This conclusion is supported by data obtained in pigs. There is a breed of pig in which the middle part of the body is highly pigmented, while the rest of the skin is almost devoid of pigment. The formation of vitamin D after in vitro UV irradiation in unpigmented skin was higher than in pigmented areas of the same animal (Fig. 7.14). The relationship between the geographical localization of the population and the pigmentation of the skin of its members is not confirmed in two cases - for the Eskimos and the African pygmies. Both populations, especially the last one, consist of dark-skinned individuals, although in the Arctic regions and on the ground under the canopy of a tropical rainforest, UV radiation is relatively weak. Eskimos seem to get their vitamin D from fish and seal livers, while Pygmies get their diet from insect larvae.
Rice. 7.14. Vitamin D formation (mg/cm 2 skin: ordinate) in pigs after exposure to UV light (S 300; distance 50 cm). The abscissa shows the exposure time. Parentheses indicate the standard deviations of the mean values
The discovery that Duffy's blood type is related to the functioning of the receptors for Plasmodium vivax is of great importance. In this case, the elucidation of the biological role of the erythrocyte polymorphism system occurred after its discovery. Virtually all Africans are Duffy-negative. It can be assumed, therefore, that due to its selective advantage, this allele has spread throughout the population.
An alternative hypothesis has recently been developed. According to her, the preexisting high frequencies of the Duffy-negative allele prevented P. vivax malaria from becoming an endemic disease in West Africa. The thesis is substantiated that malaria caused by P. vivax appeared in an ancestral primate and could not spread across Africa due to the presence of a Duffy-negative allele in it.
Absorption and malabsorption of lactose. Lactose is a nutritionally essential carbohydrate in milk (Fig. 7.15). In order for lactose to be absorbed in the small intestine, it must be hydrolyzed by a special enzyme, lactase, which is localized in the brush border of intestinal epithelial cells. Lactose is found in the milk of almost all mammals; lactase activity is high in newborns and infants of any population and race, and decreases with weaning. Subsequently, lactase activity is maintained at a low level, usually accounting for less than 10% of the activity of this enzyme in a newborn.
Until a few years ago, there was an idea that in “normal” people, high lactase activity persists into adulthood. Persons with high lactase activity can tolerate large amounts of lactose; after a lactose load in their blood, the concentration of glucose and galactose, the sugars that make up the lactose molecule, increases significantly.
Malabsorption of lactose. In persons with low lactase activity, after drinking milk, an increase in blood glucose either does not occur at all, or it is insignificant. In such people, after taking 25-50 g of lactose (1 liter of cow's milk contains 45-50 g of lactose), clinical symptoms of intolerance appear. They include diarrhea, cramping abdominal pain, flatulence. Small amounts of milk and dairy products in which most of the lactose is hydrolysed (yogurt or curdled milk) are tolerated without any unpleasant consequences. A comparative analysis of lactose tolerance in black and white Americans found that blacks were much more likely to be milk intolerant than whites. Currently, many populations have been studied in this regard (Fig. 7.16). The most reliable results can be obtained by measuring lactase activity in intestinal biopsies. It is clear that such a method is not suitable for population or family studies. For them, standard tests have been developed based on the measurement of H 2 content in the exhaled air after oral administration of a certain dose of lactose.
In most Mongoloid, Indian, and Eskimo populations, retention of lactase activity in older children and adults is very rare or non-existent. An equally low frequency of lactose tolerance is recorded in most Arabs and Jews, as well as in the populations of tropical Africa, Australian Aborigines and Melanesians. A significant predominance of individuals who retain lactase activity in adulthood (> 75%) is typical only for residents of Northern and Central Europe and for their descendants on other continents. Note, however, that a high frequency of lactose tolerance was also noted in a number of groups of African pastoral nomads. Intermediate frequencies (30-70%) were found in the population of Spain, Italy and Greece. The peoples of South Asia show high variability in this trait; it is possible that its appearance among the population of this region is due to migration. In the population of American blacks, the frequency of this trait is somewhat higher than in Africans.
What condition should be considered normal? In most human populations, after weaning children from the breast, they experience a decrease in lactase activity; this feature is common to two of the three great races (Negroes and Mongoloids). Preservation of lactase activity in the adult state is typical only for whites, and even in them this trait is not found in all populations. Therefore, for humans, as well as for other mammals, the loss of this specific activity is quite a "normal" phenomenon.
However, the scientists who conducted these studies considered lactose tolerance to be the norm, since this particular trait is common in European populations. This conclusion had certain economic consequences. It is known that in order to improve the protein nutrition of children from African and Asian countries, a large amount of milk powder was supplied to these regions; the initiators of this action proceeded from the logical hypothesis that what is good for European children should also be good for children in developing countries. In light of our current knowledge of the population distributions of lactose tolerance, these programs appear to require revision. Of course, it is unwise to completely ban the consumption of lactose-containing foods in populations consisting of lactose intolerant individuals, since otherwise they will suffer from protein malnutrition.
Enzyme induction or genetic variation? There are two possible biochemical explanations for lactose malabsorption.
1. Lactose malabsorption may be due to low lactose intake in most individuals after breastfeeding is stopped. We know that the activity of many enzymes can be increased by the addition of a substrate (substrate-specific induction). This hypothesis was initially widely accepted, but its subsequent testing in animals and humans gave negative results.
2. Family studies testified to the genetic conditionality of this trait, or rather, to the autosomal recessive type of inheritance of lactose malabsorption.
Autosomal recessive inheritance of lactose malabsorption has been demonstrated in a large-scale study of matched marriage types in Finland. This result was confirmed in the study of many other populations. Lactose "absorbers" are either homozygous or heterozygous for the lactose absorption gene, while individuals with malabsorption do not have this gene.
Multiple allelism? A decrease in lactase activity to a certain level (recessive trait) in different populations occurs in different ages. In Thailand and the Bantu, all children over 4 years of age show no rise in blood glucose after a lactose load. The proportion of children of American blacks who are unable to digest lactose out of the total number of peers increases with their age up to 14 years, and in Finland the full expression of the corresponding genes is delayed and occurs between 15 and 20 years. Such phenotypic variability may be due to multiple alleles or differences in the quantity and properties of milk consumed during childhood, and requires further study.
genetic mechanism. We have already said that residual lactase activity is also present in adults who are unable to digest lactose. It is still unknown whether there are differences in the structure of lactase in persons with impaired absorption and in "absorbers". The switch from high to low activity is somewhat reminiscent of the transition from hemoglobin γ-chain production to β-chain production, followed by a transition from HbF to HbA production; the maintenance of lactase activity in adults can be compared to the maintenance of fetal hemoglobin (section 4.3).
Natural selection. The persistence of individuals capable of absorbing lactose in most human populations, the presence of this feature in other mammals indicates that the gene responsible for maintaining lactase activity arose from time to time in the course of human evolution as a result of a mutation and that the high frequencies of this gene in some populations are due to its selective advantage. What is the nature of this advantage? Two main hypotheses have been put forward in this regard.
1. Cultural-historical hypothesis.
2. Hypothesis according to which lactose promotes better absorption of calcium.
According to the first hypothesis, the domestication of dairy cattle during the Neolithic period (about 9,000 years ago) resulted in a selective advantage for individuals who could meet most of their dietary protein requirements from milk. Indeed, there are a number of populations made up of milk consumers; for example, the pastoral tribes mentioned above. This hypothesis is quite applicable to them. However, the assertion of its universal significance raises certain doubts. For example, noteworthy is the lack of parallelism between the habit of drinking milk and the predominance of persons capable of absorbing lactose. Large populations in Africa and Asia are made up of milk consumers, but have very low rates of lactose digestion. Nevertheless, in any population there are always several individuals who are able to digest lactose; therefore, this gene was present before and could experience a favorable effect of selection. In Europe, the highest frequency of the lactose absorption gene was found in the south of Scandinavia (0.7-0.75), where dairy cattle breeding began to develop relatively recently. Before people learned how to artificially cool milk or get it in a dry form, people who were unable to digest lactose easily found that they digested sour milk much better than fresh milk. All of the above convinces us that the alternative assumption about the specific advantage of dairy nutrition in the natural conditions of Northern Europe deserves attention.
It is known that vitamin D deficiency in the northern regions is due to reduced levels of UV radiation. It is currently hypothesized that lactose may replace vitamin D, improving calcium absorption. For this hypothesis, the key issue is the question of the mechanism of the possible antirachitic effect of high levels of lactose absorption. Is there a phenomenon of a specific increase in calcium absorption associated with lactose hydrolysis? Animal experiments cannot give a definitive answer because adult animals are unable to absorb lactose. Recent human studies have shown that lactose absorption does enhance calcium absorption.
Regardless of whether the calcium hypothesis is confirmed or refuted, it can be stated that it has a number of features characteristic of heuristic hypotheses. It is specific, suggests a mechanism of action, and provides an idea for experiments by which it can be tested.
Vitamin D and serum genetic markers (GC system). Genetic polymorphism of the β 2 protein fraction of human blood serum has been detected by immunological methods and has been known since 1959: many alleles of this system are currently described, but most populations are polymorphic in only two of them, namely GC 1 and GC 2; Australian Aborigines have a third allele, GC Ab0, and Chippewa Indians have a fourth, GC Chip. The first data on the frequencies of these genes showed that the GC 2 allele is rare in very dry areas. This result became clear when the function of GC proteins, which turned out to carry vitamin D, was established.
More recently, data have emerged that indicate a relationship between the intensity of sunlight and polymorphism of GC alleles; in most populations living for a long time in areas with low intensity of sunlight, high frequencies of GC 2 are found.
This geographical distribution is indicative of the selective advantage of GC 2 . This may be due to the fact that this allele provides more efficient transport of vitamin D (which is especially important when the supply of this vitamin is limited). This, in turn, can lead to a decrease in the frequency of rickets either in individuals heterozygous for the GC 2 allele, or in individuals homozygous for it, or both. The precise selection mechanism operating in this case, remains to be seen.
Possible selective mechanisms in case of other racial characteristics. Apart from the examples given in the preceding paragraphs and used in the chapter on population genetics, very little is known about the selective advantage or disadvantage of racial traits.
It can be assumed that the small stature and dense physique of the Eskimos, as well as the relatively thick layer of subcutaneous fat characteristic of them, provide certain advantages in cold climates, and the wide chest of the South American Indians living high in the Andes is associated with respiratory adaptation to life in high altitude conditions.
Representatives of different racial groups in the US and other developed countries show differences in susceptibility to multifactorial diseases. For example, American blacks are more likely to suffer from hypertension than whites. It has also been shown that some groups of Indians, such as those living in Trinidad, have a higher proportion of diabetic patients than other population groups. Undoubtedly, the reason for such differences will become clear when researchers with medical education and good knowledge of specific diseases become interested in population genetics.
Several hypotheses have been proposed to explain the current incidence of diabetes and atherosclerosis, such as the concept of "parsimonious genotype" and rapid lipid mobilization. It is assumed that under conditions of starvation, the diabetic genotype provides more efficient mobilization of carbohydrates, and genes predisposed to atherosclerosis contribute to more rapid mobilization of fats.
It is believed that such selective mechanisms, which operated in the past, when for many generations starvation was a common human condition, explain the high incidence of diabetes and atherosclerosis at the present time. Unfortunately, none of these hypotheses is consistent with current pathophysiological concepts of carbohydrate and lipid metabolism.
05/20/2003, Tue, 14:05, Msk
Races - groups of people with clearly distinguishable features - have long symbolized the many attempts to divide people into lower and higher categories. Until recently, it was believed that the observed differences between races were due not to genetic, but to purely external causes, including social ones. But there is evidence that populations and races still differ from each other in DNA. That is, race is a genetic reality. But what then determines human behavior - antisocial or non-traditional sexual orientation - special genes or upbringing?
“The DNA of all people, regardless of their skin color and hair texture, is 99.9% the same, so from a genetic point of view, the concept of race is meaningless,” says Sally Lerman on the pages of the authoritative Scientific American. According to this point of view, the observed differences between races are not due to genetic, but purely external reasons, including social ones. “Research shows that the concept of race at the genetic level is bullshit,” she continues. - Races are subject to change - both geographically and historically. … By giving too much importance to DNA, we turn the health problem into a biological inevitability. There is also a great temptation to use the same tool when talking about the genetic background of criminal tendencies or intelligence.”
In general, the conclusion about the great influence of living conditions on personality development in different ethnic and racial groups is fair. However, genetic differences do exist. Moreover, we undertake to assert that populations and races differ from each other in DNA - this is the subject of a comment (provided by the editors from the June issue) by Lev Zhivotovsky, professor, doctor of biological sciences.
One can fully agree with most of her (Sally Lerman's article) provisions. Indeed, the concept of race, as a group of people with clearly distinguishable morphological features, has long been a symbol of the division of people into lower and higher categories. Differences between races in the pigmentation of hair, skin and accompanying features in recent centuries have become the basis of the thesis of the biological inequality of people.
Eugenics and psychology, relying on test data (intellectual development quotient IQ), tried to prove the genetic nature of race inequality. However, population genetics has shown the failure of this view. It turned out that the differences between representatives of the same race far exceeded the differences between races. And recently it was found that people of even different races differ from each other in DNA less than different individuals of chimpanzees in the same herd. However, we are not genetically identical to each other (only identical twins have almost the same DNA) - we are all slightly different from each other.
Sally Lerman argues that the observed differences between races are not due to genetic, but purely external causes, including social ones. In general, the conclusion about the great influence of living conditions on personality development in different ethnic and racial groups is fair. However, genetic differences also exist. Based on the data of recent years, we undertake to assert that populations and races still differ from each other in DNA. But their genetic difference alone cannot serve as a measure of the hereditary inequality of people of different origins. Genetic differences between populations and races are not biological inequalities: they evolved and are able to change evolutionarily.
“The DNA of all people, regardless of their skin color and hair texture, is 99.9% the same, so from a genetic point of view, the concept of race is meaningless.”
The argument made against the existence of genetic differences between races is not really an argument. Indeed, the human genome consists of three billion nucleotides (more precisely, they speak of pairs of nucleotides, because DNA consists of two complementary chains). Therefore, 99.9% agreement, or 0.1% difference, means that people differ from each other in three million base pairs. Probably, most of these differences occur in informationally “silent” regions of the genome, but the remaining functionally significant differences are enough to ensure the individuality of each of us. It is known that human and chimpanzee DNA coincide by 98-99% - the figure is also large at first glance. However, humans and chimpanzees are different zoological species, separated by at least five million years since the separation of their evolutionary branches from a common ancestor.
“As research shows, the concept of race at the genetic level is nonsense.”
Now we can say that this is not so - these three million base pairs are enough to determine the genetic differences between races. More than fifty native populations from various regions of the world have recently been surveyed ( South Africa, Western Eurasia, East Asia, Oceania, America) for almost four hundred genetic loci of different parts of the genome. These geographical groups of populations correspond to the main human races (the term "race" was not used in these publications, since for many decades it turned out to be emotionally overloaded and causing associations far from science). It turned out that among these loci there are no such ones that would clearly “mark” one or another race. However, for each of them, an interracial difference that was practically indistinguishable by statistical methods was revealed. These meager differences were accumulated by all four hundred loci until complete racial identification - according to the genetic "profile" each individual could be unambiguously assigned to one of the geographical groups.
Races are subject to change, both geographically and historically.
The above data confirm this conclusion: statistically significant differences were found between populations (ethnic groups) from the same geographic region (same race). However, these differences were not 100%: an individual could not always be unambiguously assigned to one or another population1. The differences themselves between geographical groups and between populations within the region have evolved over many tens of thousands of years under the influence of mutations and population-genetic processes, and the degree of difference corresponded to the time elapsed after humans left Africa and settled on different continents.
The time of genetic isolation between regions turned out to be sufficient for the accumulated genetic differences between them to become identificationally significant. However, the division of populations within the region occurred much later, and therefore there was not enough evolutionary time for the development of significant differences within the region. True, this does not exclude the possibility that the involvement in the analysis of, say, several thousand loci accumulates additional differences and makes it possible to identify populations within a race. Mass migrations, interracial marriages and miscegenation can quickly, within a few generations, destroy the evolutionary established genetic differences. This suggests that race is a real, but not a frozen category that does not absolutely separate people on biological grounds. Race, like ethnicity, is a historical, evolutionary concept.
This is confirmed by another fact. In terms of DNA, we are quite close to the Neanderthal, much closer than to the chimpanzee, but we represent various evolutionary branches that diverged from a common ancestor much earlier than human races from each other, about 500-700 thousand years ago. For the purposes of the discussion, we and Neanderthal man are simply very different races that have reached the status of subspecies of Homo sapiens: according to modern nomenclature, we are Homo sapiens sapiens, and Neanderthal man is Homo sapiens neanderthalensis. However, the genetic differences between modern human races are much smaller, than the differences between us and Neanderthal man.
“Race exists at least as a difference factor from a medical point of view. It is impossible to abandon this concept without abandoning, along with it, all the epidemiological data known today.
The different prevalence of hereditary pathologies in different races is also associated with evolutionary processes. Hereditary diseases arise as "harmful" mutations - "breakdowns" of functionally important genes, which are then passed on to descendants if the carriers of such mutations survive to reproductive age. Therefore, a certain mutation, if it does not disappear, spreads mainly among close populations and further through migrations. So, on the basis of a purely random process of the appearance of harmful mutations, over time, regional differences arise in one or another hereditary pathology. This process leads to differences in the spectrum of hereditary diseases not only between races, but also between populations within a race. Of course, the prevalence of a particular hereditary disease can be restrained or, conversely, enhanced by specific environmental factors. And in this sense, we can agree with the author's phrase: "Race is part of the environmental background of the human genome."
“By giving too much importance to DNA, we turn the health problem into a biological inevitability. There is also a great temptation to use the same tool when talking about the genetic background of criminal tendencies or intelligence.”
These fair phrases touch upon the most important problem: how the contributions of genes and environment correlate in the development of the traits and characteristics of each person. Is antisocial behavior or non-traditional sexual orientation really determined by special genes, or is it due to upbringing? Now it has become fashionable to refer to the genetic fatality of the extreme manifestations of personality that are spreading today. However, there is no strong evidence for this, except in cases where marginal behavior is caused by serious hereditary defects. On the contrary, there are a large number of facts confirming the leading role of perception, imitation and motivation in the development of personality traits.
Races are the main groups of human beings. Their representatives, differing from each other in many small aspects, form one whole, containing certain features that are not subject to change and inherited from their ancestors, as well as their essence. These certain signs are most evident in the human body, where one can both trace the structure and make measurements, as well as in the innate abilities for intellectual and emotional development, as well as in temperament and character.
Many people believe that the only difference between races is the color of their skin. After all, we are taught this in school, and in many television programs that promote this idea of racial equality. However, as we get older, and seriously thinking about this issue and considering our life experience (and calling for help from historical facts), we can understand that if the races were really equal, then the results of their activities in the world would be equivalent. Also, from contacts with representatives of other races, it can be concluded that their way of thinking and acting is often different from the way of thinking and acting of white people. There are definitely differences between us and these differences are the result of genetics.
There are only two ways for people to be equal. The first way is to be the same physically. The second is to be the same spiritually. Consider the first option: can people be the same physically? No. There are tall and small, thin and fat, old and young, white and black, strong and weak, fast and slow, and a host of other signs and intermediate options. No equality can be seen among the multitude of individuals.
As for the differences between races, they are many, such as head shape, facial features, degree of physical maturity at birth, brain formation and cranial volume, visual acuity and hearing, body size and proportions, number of vertebrae, blood type, bone density, duration pregnancies, number of sweat glands, degree of alpha wave radiation in the brain of newborns, fingerprints, ability to digest milk, structure and arrangement of hair, smell, color blindness, genetic diseases (such as sickle cell anemia), galvanic resistance of the skin, pigmentation of the skin and eyes, and susceptibility to infectious diseases.
Looking at so many physical differences, it is foolish to say that there is no spiritual differences, and even vice versa, we dare to suggest that they not only exist, but are of decisive importance.
The brain is the most important organ in the human body. It takes up only 2% of a person's weight, but absorbs 25% of all the calories we consume. The brain never sleeps, it works day and night, supporting the functions of our body. In addition to thought processes, it controls the heart, respiration and digestion, and also affects the body's resistance to disease.
In his epic book, The History of Man, Professor Carlton S. Kuhn (former President of the American Anthropological Association) wrote that the average black brain weighs 1249 grams compared to the 1380 grams of the average white brain, and that the average black brain size 1316 cu. cm., and a white man - 1481 cu. see He also found that the size and weight of the brain is largest in white people, then come the inhabitants of the east (Mongoloids), after them blacks, and lastly the Aborigines of Australia. Differences between races in brain size are largely due to the structure of the skull. For example, any anatomist, looking at the skull, can determine whether a person belonged to the white or black race, this was discovered as a result of crime investigations, when it turned out that it was possible to determine the racial identity of the body found, even if it was almost completely decomposed and only the skeleton remained.
The Negro's skull is narrower with a low forehead. It is not only smaller but thicker than the average white skull. The hardness and thickness of the Negro skull is directly related to their success in boxing, as they can take more blows to the head than their white opponents.
The part of the brain enclosed in the cerebral cortex is the most developed and complex part of it. It regulates the most essential types of mental activity, such as, for example, mathematical abilities and other forms of abstract thinking. Dr. Kuhn wrote that there is a big difference between the brain of a Negro and a white man. The anterior lobe of the Negro's brain is less developed than that of the white. Thus, their abilities in the areas of thinking, planning, communication and behavior are more limited than those of whites. Professor Kuhn also found that this part of the brain in blacks is thinner and has less convolutions on the surface than in white people, and the development of this area of \u200b\u200bthe brain in them stops at an earlier age than in whites, thereby limiting further intellectual development.
Dr. Kuhn is not alone in his conclusions. The following researchers in the years listed, using various experiments, showed a difference between blacks and whites ranging from 2.6% to 7.9% in favor of whites: Todd (1923), Pearl (1934), Simmons (1942) and Connolly (1950) . In 1980, Kang-cheng Ho and his assistants, working at the Case Western Institute of Pathology, determined that the brains of white men are 8.2% larger than the brains of black men, while the brains of white women are 8.1% larger than the brains of black women ( A woman's brain is smaller than a man's, but larger percentage to the rest of the body).
Black children develop faster than white children. Their motor functions develop quickly along with their mental ones, but later there is a delay and by the age of 5 years, white children not only catch up with them but also have an advantage of about 15 IQ units. The larger brains of white children by age 6 are further evidence of this. (Whoever was tested for IQ, they all showed the results of differences from 15% to 23%, with 15% being the most common result).
The studies of Todd (1923), Vint (1932-1934), Pearl (1934), Simmons (1942), Connolly (1950) and Ho (1980-1981) showed important differences between races and in brain size and development, and hundreds psychometric experiments confirmed these 15 units of difference in intellectual development between blacks and whites more and more. However, such research is now discouraged, and such initiatives would be met with frenzied suppression efforts if they took place. Undoubtedly, the study of biological differences between races seems to be one of the first topics that is forbidden to speak in the United States today.
The findings of Professor Andrey Shuya in a monumental 50-year work on IQ tests called "Testing the Intelligence of Negroes" indicate that the IQ of blacks is on average 15-20 points lower than whites. These studies were recently confirmed in the bestselling book The Bell Curve. The amount of "overlap" (cases-exceptions when blacks score the same number of points as whites) is only 11%. For equality, this value must be at least 50%. According to Professor Henry Garrett, author of Children: White and Black, for every gifted black child, there are 7-8 gifted white children. He also found that 80% of gifted black children are of mixed blood. In addition, researchers Baker, Eisnek, Jensen, Peterson, Garrett, Pinter, Shuey, Tyler, and Yerkes agree that blacks are inferior in logical and abstract thinking, numerical calculation, and speculative memory.
It should be noted that people of mixed ancestry score higher than full-blooded blacks, but lower than full-blooded whites. This explains why light-skinned blacks are more intelligent than those with very dark skin. An easy way for you to check whether this is true or not is to look at black people shown on TV, famous hosts or artists. Most of them have more white blood than black blood, and thus are more capable of dealing with whites.
The argument has been made that the IQ test is related to the culture of a certain society. However, this is easily refuted by the fact that Asians who have just arrived in America and are far from the specifics of American culture (which, of course, cannot be said about American blacks) are ahead of blacks in tests. Also, the American Indians, who, as everyone knows, are a group of society that is not in the best social position, outstripped the Negroes. Finally, poor whites narrowly outperform even the upper class blacks, who have become fully integrated into American culture.
Besides, each US Department of Education IQ test, all levels armed forces, state, county and city education departments, always showed that blacks are on average 15% weaker than whites. Even if this test were related to white culture, it would be practically impossible for every test containing a huge number of different questions to end up striving for the same number with such accuracy.
Below is a chart from the Society for Research on Child Development USA, which shows that the majority of black children are in the low IQ region. Since an IQ of 85 to 115 is considered normal, it can be seen that most black children have lower IQs. It can also be seen that many more white children than black children have an IQ greater than 100.
The difference in mental strength is not the only mental difference between whites and blacks.
According to J.P. Rushton's analyses, Negroes are more excitable, more violent, less sexually reserved, more impulsive, more prone to crime, less altruistic, less inclined to follow rules, and less cooperative. Crime statistics, the impulsive and violent nature of the crimes that blacks commit, the fact that schools with mixed students require more discipline and police presence than schools with only white students, and the willingness of a certain part of blacks to take part in the perpetration riots, all this was confirmed by the observations of Mr. Rushton.
"Education, sir, is the development of what is. From time immemorial, the Negroes owned the African continent - wealth beyond poetic fantasies, lands crunching with diamonds under their feet. But they never raised a single diamond from the dust until the white man showed them to them shining light.. Their lands were crowded with powerful and obedient animals, but they did not even think to harness a wagon or sleigh. Hunters out of necessity, they never made an ax, a spear or an arrowhead to save them after the moment of use. They lived like a herd of bulls, happy to pluck grass for an hour.On a land full of stone and forest, they did not bother to saw a plank, carve a single brick, or build a house not from sticks and clay.On an endless ocean coast, next to seas and lakes, for four thousand years they observed ripples from the wind on their surface, heard the roar of the surf on the beaches, the howling of the storm above their heads, peered into the misty horizon calling them to the worlds beyond, and not once did the dream of sailing seize them!"
At one time, when there was more free-thinking expression and the media were not completely under Jewish control, scholarly books and reference books unequivocally interpreted the above facts. For example, "Scientifically popular collection" volume 11, edition of 1931, p. 515, states the following in the "Section of primitive peoples": "The conclusion is that the Negro really belongs to an inferior race. The possibilities of his brain are weaker, and his device is simpler. In this respect, alcohol and other drugs that can paralyze self-control are his enemies." Another example is a direct quote from the "Negro" section of Encyclopædia Britannica, 11th edition, p.244:
"The color of the skin, which is also recognized by the velvety of the skin and a special smell, does not exist due to the presence of any special pigment, but a large amount of coloring matter in the Malpighian mucosa between the inner and outer layers of the skin. Excessive pigmentation is not limited to the skin, pigment spots are often they are also found in internal organs, such as the liver, spleen, etc. Other features found are modified excretory organs, a more pronounced venous system and a smaller brain volume compared to the white race.
Of course, according to the above characteristics, the Negro should be attributed to a lower stage of evolutionary development than the white, and being closer in terms of kinship with the higher anthropoids (monkeys). These characteristics are: the length of the arms, the shape of the jaw, a heavy massive skull with large superciliary arches, a flat nose, depressed at the base, etc.
Mentally, the Negro is inferior to the white. F Manetta's notes, collected after many years of studying Negroes in America, can be taken as the basis for describing this race: "Negro children were smart, quick-witted and full of liveliness, but as the period of maturity approached, changes gradually set in. Intelligence seemed to cloud over, revival gave way a kind of lethargy, energy was replaced by laziness.We must certainly understand that the development of blacks and whites occurs in different ways.While on the one hand, with the growth of the brain, there is an expansion of the cranium and its formation in accordance with the shape of the brain, on the other hand, there is a premature closure of the cranial sutures and subsequent compression of the brain by the frontal bones. This explanation makes sense and may be one of the reasons..."
Why was this information removed? Simply because it did not correspond with the plans of the government and the media. Please remember that prior to 1960, racial differences between whites and blacks were world-famous and accepted.
Here are the biological facts about races. We understand that they may be "politically incorrect", but the facts do not cease to be facts. There is no more "hate speech" in saying the biological facts that the white race is more intelligent than it is in saying that human beings are more intelligent than animals, or some animals are more intelligent than other animals. Science has nothing to do with "hate speech", it has to do with reality.
Are there genetic differences between races and peoples? Yes, and this is a fact long established by science. Thanks to genetic mutations, in some parts of the world they are poisoned by milk and do not tolerate alcohol at all, while in others, beans threaten people with sudden death. But the same genetic diversity allows science to look into the distant past of mankind and provides important clues to medicine.
Data of ethnogenomics and ethnogeography. They make it possible to visualize by what branches and migration flows humanity settled from its African ancestral home. For some stages in the history of homo sapiens, ethnogenomics data can be supplemented with data from paleoanthropology, archeology, and linguistics. Thus, the sciences, complementing each other, draw a more detailed picture of the history of mankind.
In the 80s of the last century, the world was seized by a wave of panic associated with the discovery of the AIDS virus. Humanity has felt completely unprotected in the face of a deadly disease that can occur as a result of infection with the immunodeficiency virus. The slogans of “free love” of the previous era were forgotten: now people were talking about “safe sex” more and more often, dangerous razors disappeared from hairdressers, and in medicine everything was relied on disposable.
Later it turned out, however, an interesting thing: there are people who are resistant to HIV infection. In these people, the mutation turned off the gene for the chemokine receptor, which encodes a protein that is a kind of "landing pad" for the virus. No site, no infection. Most of these people are in Northern Europe, but even there they are no more than 2-4%. And the “landing site” for the virus discovered by scientists has become the target of developed therapeutic drugs and vaccines against HIV.
Anti-AIDS - no AIDS
The most striking thing in this story is not even that, for some reason, it was in Northern Europe that a certain number of people were found who were not afraid of the "plague of the 20th century." Another thing is more interesting: the mutation, and practically with the modern frequency, was present in the genome of the Northern Europeans even ... 3000 years ago. How could this happen? After all, according to the data of modern science, the AIDS virus mutated and "moved" from African monkeys to humans no earlier than the 20s of the last century. In the form of HIV, he is not even hundreds of years old!
Peoples and genes
A population is a biological concept, and it can be studied by biological methods. The people is not necessarily a genetic unity, but is a cultural and linguistic community.
Nevertheless, it is possible to isolate populations comparable to individual ethnic groups and identify genetic differences between them. It is only necessary to understand that the differences between people within the same ethnic group will always be greater than the differences between the groups themselves: only 15 percent of the total number of differences will fall on interpopulation differences. Moreover, these differences can be harmful, neutral, and only in a certain case useful, adaptive.
If we take genetic differences over large areas, then they will line up in some geographical patterns associated, for example, with climate or the intensity of UV radiation. An interesting question is the change in skin color. In the conditions of the African ancestral home of mankind with its scorching rays of the sun, all mutations that create fair skin invariably were rejected by selection. When people left Africa and ended up in geographic areas with a large number of cloudy days and low UV radiation intensity (for example, in the North of Europe), on the contrary, selection supported such mutations, since dark skin under such conditions prevents the production of vitamin D, which is necessary for calcium metabolism. Some peoples of the Far North, however, retained relatively dark skin, since they replenish the lack of vitamin D from venison and the liver of marine animals. In areas with varying UV intensity, another genetic mutation made it possible for the skin to develop a temporary tan.
Africa is the cradle of mankind, and the genetic differences between Africans from each other are much greater than Europeans from Asians. If you take the genetic diversity of Africa for 1000, then the rest of the world accounts for 50 of this thousand.
Obviously, the mutation of the chemokine receptor gene that once arose was fixed by selection in the northern European region, as it gave the advantage of survival against the background of the spread of some other viral infection. Its penetration into the human body occurred using a molecular mechanism similar to AIDS. What kind of infection it was is now not known exactly, but it is more or less obvious that the selection that gave an advantage to the owners of the mutation went on for thousands of years and was recorded already in the historical era. How did you manage to install it?
As already mentioned, as early as 3000 years ago, among the inhabitants of the region, the “anti-AIDS” mutation already had an almost modern frequency. But exactly the same frequency is found among Ashkenazi Jews who first settled in Germany and then migrated to neighboring areas of Central and Eastern Europe. Jews began to settle massively in Europe 2000 years ago after the defeat of the anti-Roman uprising in the 1st century AD. and the fall of Jerusalem. In addition to the Ashkenazi (Germanic) branch, there was also a southern, "Sephardic" branch, with localization mainly in Spain.
In the homeland of the Jews, in Western Asia, a mutation of the chemokine receptor gene also occurred, but with a frequency of no more than 1–2%. It remained so among the Jews who lived for generations in Asia (Palestine, Iran, Iraq, Yemen), in North Africa, as well as among the Sephardim. And only Jews living in a region close to Northern Europe acquired a locally high mutation rate. Another example is the gypsies who came from India to Europe about 1000 years ago. In their homeland, the mutation rate was no more than 1%, but now among European Gypsies it is 15%.
Of course, both in the case of Jews and in the case of gypsies, there was an influx of genes from outside due to mixed marriages. But the estimates existing in science do not allow attributing such an increase in frequency to this factor alone. Natural selection is clearly at work here.
Humanity clock
It is known that mutations in the human genome occur constantly, they work as a kind of biological clock, according to which it is possible to establish how the distant ancestors of mankind migrated: first they settled in Africa, and then, leaving their native continent, to the rest of the world, except for Antarctica. In these studies, mitochondrial DNA, which is passed down the female line, and male Y chromosomes, which are passed down the male line, are of the greatest help. Neither the gene information of mitochondria, nor the part of the genome stored in the Y-chromosome, practically participate in the recombination of genes that occurs in the sexual process, and therefore go back to the genetic texts of the foremother of mankind - "mitochondrial Eve" - or some African "Adam", Y- whose chromosomes were inherited by all men on Earth. Although mtDNA and Y chromosomes did not recombine, this does not mean that they came from the ancestors unchanged. It is precisely the accumulation of mutations in these two repositories of genetic information that most reliably demonstrates the genealogy of mankind with its endless branching and settlements.
Innate Vulnerability
Obviously, there are regional populations on earth, or even an entire ethnic group, in the genome of whose representatives mutations have developed that make these people more vulnerable.
And not only when drinking alcohol, but also in the face of certain diseases. From this, the idea may arise of the possibility of creating a genetic weapon that would strike people of one race or one ethnic group, and leave representatives of others unharmed. To the question of whether this can be done in practice, modern science answers “no”. True, one can jokingly talk about milk as an ethnic weapon.
Considering that about 70% of the Chinese population suffers from a genetically predetermined lactase deficiency, and digestion is disturbed by drinking milk in most Chinese adults, it is possible to disable the PRC army by sending it to latrines, if, of course, you can find a way to give it milk to drink - More serious an example is legume intolerance among residents of a number of Mediterranean countries, which is described in the article. However, even the pollen of leguminous plants will not allow to incapacitate, say, only all Italians in a multinational crowd, and in fact it is precisely this kind of selection that is meant when they talk about fantastic projects of ethnic weapons.
However, mutations that occur in the part of the genome subject to recombination, that is, in the X chromosomes, are much more significant for humans and humanity. In the study of adaptation, more attention is paid to mutations that have arisen in the part of the genome subject to recombination - that is, all chromosomes except the Y chromosome. Moreover, the age of these mutations can also be tracked. The fact is that next to the mutated part of the DNA there are other quite recognizable sections of the chromosome (possibly bearing traces of other, older mutations).
During recombinations, fragments of parental chromosomes are mixed, however, at the first stages, the environment of the mutation of interest to us will be preserved. Then new recombinations will gradually break it up and bring new "neighbors". This process can be estimated in time and get the approximate time of occurrence of the mutation of interest to us.
Ethnogenomics data make it possible, on the basis of the history of accumulation of mutations, to trace the history of the exodus of mankind from the African ancestral home and distribution across all inhabited continents. These data at certain time intervals can be supplemented with data from linguistics and archeology.
From the point of view of an individual organism or a community in which one or another frequency of mutations is observed, mutations can be neutral or negative, or they can carry an adaptive potential. It can manifest itself not in the place of origin of the mutation, but where its effect will be most in demand and will be supported by selection. And this is one of the important reasons for the genetic diversity of peoples on the ethnological map of the world.
And this applies not only to alcohol consumption, but also to certain diseases. From this, the idea may arise of the possibility of creating a genetic weapon that would strike people of one race or one ethnic group, and leave representatives of others unharmed. To the question of whether this can be done in practice, modern science answers “no”. True, one can jokingly talk about milk as an ethnic weapon.
Sobriety mutation
In the example already given, the mutation conferring resistance to AIDS is present at low frequencies in India, the Middle East, and Southern Europe. But only in the north of Europe did its frequency rise sharply. There is another similar example - a mutation leading to alcohol intolerance. In the 1970s, when studying liver biopsy preparations from the Chinese and Japanese, it was found that representatives of these Far Eastern peoples have a very active alcohol dehydrogenase enzyme produced by the liver, which converts alcohol into acetaldehyde, a toxic substance that does not give intoxication, but poisons the body.
In principle, the processing of ethanol into acetaldehyde is a normal stage in the body's struggle with ethanol, but this stage should be followed by the second stage - the oxidation of acetaldehyde by the enzyme aldehyde dehydrogenase and the production of harmless, easily excreted components. But this second enzyme was not developed at all in the examined Japanese and Chinese. The liver quickly turned alcohol into poison, which was not excreted from the body for a long time.
Hence, instead of a “high”, a person after the first glass received a tremor in his hands, reddening of the skin of the face, nausea and dizziness. It is very unlikely that such a person could become an alcoholic.
As it turned out, the mutation that gives rise to the rejection of alcohol arose around the beginning of agriculture somewhere in the Middle East (there is still about 30% of its frequency among Arabs and Asian Jews). Then, bypassing India (through the steppes of the Black Sea and Southern Siberia), it ended up in the Far East, where it was supported by selection, covering 70% of the population. Moreover, in Southeast China, its own version of the “anti-alcohol” mutation appeared, and it also spread over a large territory up to the steppes of Kazakhstan.
All this means that in the Far East there was a high demand for such a mutation among local populations, that's just ... we must remember that this happened several thousand years ago, and alcohol was practically not present in human culture. Where did the anti-alcohol genes come from?
Obviously, at one time they also came to the court as a means of combating some kind of infection, and then - lo and behold! - it so happened that in the Far and Middle East there are now many people who genetically do not accept drunkenness. This whole story, as well as the story of the AIDS resistance gene, perfectly shows that this or that mutation could in the past be supported by selection not at all according to the trait on which it was discovered in our time.
But what about Russia? In Russia, the mutation responsible for the aversion to drinking has a frequency of 4%, that is, no more than 10% of the population are its carriers. Moreover, we are talking about both mutations - both in the Middle East and in the Chinese versions. But they didn’t take root with us together, so genes can’t help us in the fight against drunkenness.
Medicine or Achilles heel?
During the Korean War, soldiers american army who suffered from malaria were given a drug called primaquine. The pharmacological action of this drug was to destabilize the erythrocyte membrane. The fact is that the malarial plasmodium, penetrating into the blood, “captures” the erythrocyte and develops inside it. To make it more convenient to develop, plasmodium destabilizes the erythrocyte membrane.
It was then that the primachin appeared, who literally knocked out a wedge with a wedge. He additionally "softened" the membrane, weakened by plasmodium, and it burst. Further, the causative agent of malaria could not develop, the disease receded. And what happened to the rest of the erythrocytes that were not captured by plasmodia? But nothing. The action of the drug passed, the membrane stabilized again. But this was not the case for everyone.
A number of soldiers who took primaquine died from hemolysis - the complete destruction of red blood cells. When they began to investigate the issue, it turned out the following. First, all the deceased were deficient in the enzyme glucose-6-phosphate dehydrogenase, which is responsible for stabilizing erythrocyte membranes, and this deficiency was due to a genetic mutation. And secondly, the soldiers who died had either African-American or Mediterranean ancestry. The mutation, as it turned out, was found only in some peoples.
Today it is known that approximately 16-20% of Italian men (women do not have this effect) are at risk of death from hemolysis, and not only after taking primaquine (which weakens the already weak membranes of red blood cells and leads to their massive death).
These people are also contraindicated in beans and some other foods and medicines that contain strong oxidants. Even the smell of bean pollen can cause a fatal reaction. The strange character of this mutation ceases to be strange when one considers that it was supported by selection precisely in the places of distribution of malaria and was a kind of "natural" primaquine.
In addition to Italy, a relatively large number of carriers of the mutation was noted in Spain, and its frequency is about 2% in North Africa and Azerbaijan. In Soviet times, it was even decided to ban the cultivation of legumes in the Azerbaijan USSR, so frequent were cases of favism, that is, the occurrence of hemolysis from contact with beans.
Winners are everything!
The science of ethnogenomics, which has been actively developing in recent years, studies the genetic characteristics of races and ethnic groups, as can be seen at least in the examples given, is a completely applied discipline. Closely related to it is pharmacogenomics, which studies the effect of drugs on people with different genetic characteristics, including those characteristic of certain ethnic and racial groups.
Indeed, for some of them, some drugs can be harmful (for example, primaquine), and some, on the contrary, are much more effective. In addition, ethnogenomics has been of great help in drawing up a picture based on scientific data, and not on myths, of the pre-literate history of mankind and its languages.
And one of the main conclusions that we can draw today from research on ethnogenomics is that, with all the diversity of mankind, there are no grounds to talk about genetically more or less developed peoples. All living generations are champions of life, because their ancestors managed to survive the harsh whims of nature, epidemics, long migrations and give a future to their offspring. And genetic diversity is just a memory of exactly what biological mechanisms different parts of humanity managed to adapt, survive and win.
Language can be learned. The child of French-speaking parents living in France is not born with the ability to speak French. However, as soon as he reaches the age of five, this child will easily learn to speak French. The child of German-speaking parents living in Germany will just as easily learn to speak German.
And it's not because any child is born with a special aptitude for the language of their parents. If children from a French and German family were exchanged in infancy, then little Pierre would learn to say "Auf Wiedersehen", and little Hans could say "Ai revoir" with equal ease. And if little Pierre and Hans ended up in America in the first years of their lives and grew up with American children, then they would both learn to say “Good bye” without any accent.
Any normal child will learn any language spoken by the people around him, regardless of what his father's and mother's native language was.
As you can see, language thus cannot be a mark of race. If you close your eyes and hear the voice of a man speaking perfect English language, then you cannot say for sure where this person's parents come from, from New York, Shanghai or Timbuktu. Just by hearing a person's voice, you cannot tell what the color of their hair, the shape of their head, or their height is.
The same applies to the food that a person loves, and to the clothes that he prefers to wear. These taste preferences depend on what he is used to from childhood. The children of immigrants in America are just as easily addicted to hamburgers and fried beans as the children of native American parents.
Differences between people that are the result of learning are called cultural differences. Cultural differences cannot be taken into account to divide people into races. It would be like trying to classify dogs into different breeds according to the tricks they could do. Imagine such a division: all dogs that can "play dead" belong to one breed, and all who can "sit and beg" belong to another!
What we have to do is find the characteristics of the person that are not the result of learning. We must find those traits that each person is born with or develops as he grows, but without any outside interference. For example, a child is born with ten fingers and ten toes. And this is long before his hair grew and his eyes took on a certain color. By the time of his maturation, a person reaches a certain height and acquires an individual physique. Differences in such characteristics, including the size, shape, and color of various parts of the body, are all physical differences. These differences have been used by anthropologists (scientists who specialize in the study of humans) to divide people into different races.
Leather
One way to divide people into races is to determine the color of the skin. We can find a good example in America - in the case of the Negro and the white man. Most Negroes are different from most white people, and you could easily tell one from the other.
In addition, skin color is determined from birth. A Negro child may grow up to be a recognized writer, an excellent lawyer or scientist, perhaps even a member of Congress or a Nobel laureate, but his skin color will not change. He will always belong to the Negroid race.
The color of normal human skin depends on the presence of three types of coloring substances, or pigments. The most important of these pigments is melanin, a dark brown substance. The skin of all healthy people contains melanin. Some people, however, have more melanin than others. Whites generally have a small amount of melanin in their skin. People with more melanin are darker. Blacks naturally have much more melanin in their skin than whites. The question is not in the difference in skin color, but only in larger or smaller amounts of melanin, which determine one or another shade.
The second of the three pigments is carotene. This is a yellow substance that is present in carrots (from the English carrot - carrots), in the yolk of an egg, or in human skin. Like melanin, carotene is present in the skin of all people. Due to its light color, the presence of a significant amount of carotene in the skin of people is not so clearly visible. Melanin hides it. Among people with a small amount of melanin in the skin, some have more carotene, others less. East Asian peoples with large amounts of carotene have somewhat yellowish complexions.
The third pigment is hemoglobin, which colors blood red. Naturally, it is present in all people. However, hemoglobin is found in the blood vessels under the skin, so it is hardly visible. Its presence is completely blocked by the proper amount of both melanin and carotene in the skin. Hemoglobin can only be seen in the skin of white people, especially those with fair complexions. And it is hemoglobin that makes the cheeks pink and allows you to blush.
Based on these differences in coloration, humanity is sometimes divided into
1) black race - determined by the high content of melanin;
2) yellow race - low in melanin, but high in carotene;
3) the white race - with a low content of both melanin and carotene.
Such a division would seem quite satisfactory were it not for some difficulties. On the one hand, the described differences are not so clear-cut. All kinds of intermediate skin colors are available. Southeast Asians and Native Americans - the Indians - are darker, for example, than the Chinese and Japanese - members of the yellow race. On the other hand, they don't look like blacks. Sometimes the inhabitants of Southeast Asia, as well as the inhabitants of many of the Pacific islands, are referred to as the Melanesian race, while the American Indians are referred to as the red race. (This description is perhaps incorrect, as the Indian has a brownish tinge, but not red.) In other respects, these peoples are known to fit rather with the yellow race; so that perhaps the best solution would be to classify them with the yellow Melanesian race, which includes all these groups.
Another source of doubt is that groups of people can have the same skin color and yet differ in many other ways. There are the dark-skinned peoples of Africa, called Negroes, and there are the dark-skinned Aborigines of Australia. The average native is more obscure than the average black, but it would not be entirely correct to consider both of them only as representatives of the black race. In many other physical characteristics, besides skin color, the African Negro and the Australian Aborigine are quite different. There is a third group of dark-skinned people called Dravidians, they were among the earliest inhabitants of India and now live compactly in the southern regions of this country. Despite their dark complexion, in many ways they are different from both the blacks of Africa and the Australian Aborigines.
And not all black Africans are as dark-skinned as we might imagine. Americans are used to seeing black blacks because the ancestors of most black Americans were brought to America from West Africa. And this is the region where the most dark-skinned peoples live. There are blacks whose skin is much lighter. Some East African tribes, for example, are slightly brown, almost yellowish.
Skin color does not remain completely unchanged. Although the skin cannot become lighter, at the same time it often becomes darker, tanned by natural sunlight. UV rays can be quite harmful to the skin if they penetrate the outer layer of the skin. (Many of us know from experience the pain of sunburn.) Melanin protects the skin by blocking ultraviolet rays. Many whites, who do not have enough melanin in their skin to protect themselves, can get extra melanin over time if they work or play while exposing their body to the sun. (This is a slow process, and so too much exposure to the sun first causes a burn.) Very fair-skinned people, no matter how hard they try, often cannot produce enough melanin. They "burn" and do not get a tan.
The darkness of a tanned person's skin will slowly disappear if he is no longer exposed to the sun. However, many tanned whites actually have more melanin in their skin than many black Africans.
Hair
Hair color, unlike skin color, was not used to divide mankind into races. The most important pigment found in hair, as well as in skin, is melanin. Most people's hair contains enough melanin to give it a dark brown or black color. Some representatives of the white race are brown-haired or blond, because they have a small amount of melanin in their hair. Some people have red pigment in their hair. Its color appears in fair-haired people in the form of various shades of red hair. As we age, the ability to form melanin for the new hair that continuously replaces the old hair is often lost. The result is gray, or white, hair.
In Europe and North America, where modern racial theories have been developed, people have such different shades of hair that people no longer pay much attention to it. To be sure, the German-speaking peoples who invaded Western and Southern Europe in the sixth century had fairer complexions than the Romance peoples they conquered. Until complete mixing occurred, blond hair was more common among the aristocratic descendants of the invaders than among the descendants of the conquered peasants. Perhaps it is for this reason that blond princesses are often found in fairy tales (many of which were created during the Middle Ages).
Hair color aside, however, some anthropologists have tried to classify people into races according to the shape of their hair. Hair can be straight, wavy or curly.
Virtually all members of the yellow Melanesian race, for example, have straight hair without a hint of waves or curls. The Eskimos, whom most scholars would classify as yellow, also have straight hair, but so do the Turkic peoples of Central and Western Asia, and many of them, especially in Western Asia, are considered white.
Curly or finely curled hair is characteristic of the black race living in Africa and New Guinea and neighboring islands.
Wavy hair is found among the white race, as well as among the dark-skinned Dravidians of India and the Aborigines of Australia.
Here, not everything is as simple as it seems at first glance. Many Europeans or European Americans have perfectly straight hair, although they belong to the wavy hair group. On the other hand, there are at least three types of curly hair. There is short curly hair that evenly covers the entire scalp, like most Negro peoples. There are short curly stripes that grow in strands that create pomp, as in some East African groups. There are also longer curly hair among the peoples of the southwestern Pacific islands. Australian Aboriginal hair is generally curly or wavy, with the exception of one small group in Queensland who have what is called curly hair.
Eyes
Eye color, like hair color, is not used to distinguish between races. The iris (which is the colored part of the eye), like hair and skin, contains the pigment melanin. In people with brown eyes, the iris contains enough melanin. Those with very little melanin have blue eyes.
There is one feature of the structure of the eye that has been used in determining racial differences - the epikaitic section of the eyes. This is the fold of skin that covers the upper eyelid and sometimes even the upper row of eyelashes when the eyes are wide open. It makes the eyes narrower and is sometimes incorrectly called "narrow-eyed". The epicanthic section of the eyes is characteristic of many representatives of the yellow Melanesian race, such as the Chinese, Japanese, Mongols and Eskimos, but, however, not all. It is not commonly seen in the other groups of people we have already mentioned.
Skeletal system
Along with skin color, the skeletal system is most often used in determining the differences between people. The bones form the skeleton of the human body, it is the skeletal system that is responsible for the fact that one person is tall and narrow-shouldered, while the other is squat and has short fingers. (Of course, the fat layer also affects the appearance of a person, but this is easily changed by diet.) Height is usually a distinguishing feature of different peoples. In all groups of people there are short and tall individuals. However, the average height of the Scandinavians is significantly greater than the average height of the Sicilians. Residents of northern France are on average slightly taller than residents of southern France.
Representatives of the yellow and black races can also be divided into different groups depending on their height. The Chinese are taller than the Japanese. Great diversity is also observed among African peoples. Representatives of some Negro tribes are as tall as the Scandinavians, or even taller than them. On the other hand, the Pygmies of the Congo are the shortest people.
However, the growth criterion has its own difficulties. First, the growth of an individual cannot be known until he has finally grown; so the growth rate is useless in classifying children. In addition, a single Sicilian can be taller than a single Scandinavian. In addition to this, height also depends on the sex of the person, usually males are taller than females of the same group. Finally, human growth is partly dependent on the food system. Children of European immigrants in America often grow up taller than their parents, which is probably because their nutrition has improved.
head shape
Head shape is often used for racial classification. When viewed from above, the head is oval in shape, and its length (forehead to occiput) is greater than its width (distance from ear to ear). If the length from the forehead to the back of the head is taken as 100, then the width of the head from ear to ear will be equal to some smaller value. If the width is three quarters of the length, this indicator will be equal to 75, if four fifths of the length, then the indicator will be 80.
The ratio of the width of the head to its length is known as the cephalization index. Naturally, the cephalization index in different people unequal. People with a cephalization index of less than 75, when viewed from above, have narrow, oblong skulls, since their skull is less than three-quarters wide in relation to its length. People with skulls of this shape are called dolichocephals, which means in Greek "long-headed". With a cephalization index of more than 80, the head appears shorter and broader when viewed from above. People with similar skulls are called brachycephals, which in i-i means "short-headed." A cephalization index between 75 and 80 gives us mesocephals, which in Greek means "average annuals".
Groups of people can also differ from each other in the shape of the head. The peoples of northwestern Europe, including the inhabitants of Scandinavia, Great Britain, Holland, Belgium, as well as the northern parts of France and Germany, are most often mesocephalic. People living further south - in Central France, Southern Germany and Northern Italy (as well as almost all the peoples of Eastern Europe) - are brachycephalic. Further south, among the inhabitants of the Mediterranean, in Portugal, Spain, southern France, Italy and the Balkans, live mesocephals. There are many dolichocephals in North Africa and the Middle East.
Using the size of the skull as the main criterion, some researchers have tried to divide the white race into three subdivisions.<ы. Жителей Северо-Западной Европы они называют скандинавами. Скандинавы имеют i-иетлую кожу и являются мезоцефалами. Жителей Центральной и Восточной Европы относят к альпийцам. Они имеют темную кожу и являются брахицефалами. Наконец, жителей Южной Европы и Северной Африки называют средиземноморцами. Они имеют темную кожу и являются долихоцефалами.
With such a classification, some European countries would be inhabited mainly by one such iodra. For example, Norway would be almost entirely Scandinavian, Hungary almost entirely Alpine, and Portugal almost entirely Mediterranean. Other countries would be made up of two or even three sub-races. There are both Scandinavians and Alyts in Germany. Both Alysh and Mediterranean people live in Italy. France, which has a highly culturally homogeneous population, is represented by all three sub-races.
Head shapes also change outside the white race. Most of the black race are dolichocephalic or mesocephalic, and most of the yellow Melanesian race are brachycephalic.
Head shape, like height, can change with diet. Children born during the long northern winter are deprived of sunlight in the early months of their lives. If they are not given fish oil or vitamin supplements, they are deficient in vitamin D. Such children suffer from a disease known as rickets, in which the bones do not strengthen properly. The soft, malleable skulls of such children can also be deformed by the pressure of the cradle, and the size of the skull at a later age will no longer mean anything.
droplets of life
The smallest living organisms are called protozoa, or protozoa. Some of them are barely visible to the naked eye, but most are microscopic in size. That is why they are studied under a microscope.
A protozoan, such as an amoeba, consists of a tiny drop of a jelly-like liquid called protoplasm. This drop of protoplasm is separated from the water in which the amoeba lives by a very thin membrane. Protoplasm separated by a membrane from the external environment is called a cell.
Although the amoeba is microscopic in size, it performs all the essential functions of life. It can capture food particles that are smaller than itself in volume, digest them and throw out undigested residues. She can detect danger and in this case move to avoid it. It can grow, and when it grows to a certain size, it can split in two so that in place of one amoeba two will form. When the amoeba splits in two, the new daughter cells that appear will have all the characteristics of the old parent cell.
It would be reasonable to believe that if we could understand how a cell divides into two cells while retaining all of its features, then this could be a starting point for studying how these features are transmitted in larger organisms, creatures, such as humans.
The protozoa are made up of a single cell. Animals larger than protozoa are composed of many cells closely adjacent to each other. Since each of these cells is approximately the same size as a protozoa cell, it takes quite a lot of them to form a large animal. Man, for example, is made up of trillions and trillions of microscopic cells. Every human cell is made up of protoplasm; each surrounded by a cell membrane. Animals made up of many cells are called metazoa. Man also belongs to the metazoa.
A single protozoa cell is a kind of jack-of-all-trades. She can do a little of everything. In the metazoa, cells have different specializations. In humans, for example, there are long thin cells that make up muscle tissue, which become short and thick when the muscle is tensed. There are jagged nerve cells that carry messages from one part of the body to another. There are skin cells that serve as elastic protection for the rest of the body.
Some of these various cells, such as those that make up the brain and nerves, have become so specialized that they have lost the ability to divide. Other types of cells, however, continue to divide throughout life, or at least can divide whenever it becomes necessary. For example, the outer skin cells gradually wear out throughout life. For this reason, the cells in the deeper layers of the skin continuously grow and divide to replace the lost cells.
The process of human cell division is almost the same as that of protozoa cells. Human cells retain their characteristics after division in the same way as kayu and protozoa cells. In fact, the division process is approximately the same in all cells. To explore this process, let's take a closer look at the cell.
In the beginning, all cells that grow and divide are made up of two parts. Somewhere within the cell, often near its center, there is a small patch of protoplasm, separated from the rest of the cell by a membrane even thinner and more delicate than the outer membrane of the cell. This inner part of the cell is called the nucleus. The protoplasm surrounding the nucleus is called the cytoplasm.
Of these two parts of the cell, the nucleus is the most important. Suppose an amoeba is divided in two by a microscopic needle point in such a way that one half contains a whole nucleus, while the other half does not contain a nucleus. The half with the core will be able to restore the missing part and will then continue to live a normal life, growing and dividing. The half without a nucleus lives only for a short time, but after that it dries up and dies. It does not grow and never divides.
So now let's take a closer look at the core itself. If we take very thin sections of tissue from certain organs and place them under a microscope, we can see individual cells and even perhaps cell nuclei within cells. If we confine ourselves to viewing only, then we will not see anything special in the core. But we will not be limited to this.
The nucleus, like the cell as a whole, is made up of a large number of different substances. Some chemicals, when added to the water in which the cloth plate is placed, can enter the cells and combine with some, but not all, of the substances that are there. The resulting chemical compounds are sometimes colored in one color or another. By adding the right chemical to the cell tissue, we stain some parts of the cell and leave other parts untouched. When, for example, a drug called Feulgen's reagent is added to a cell, the scattered parts of the nucleus turn bright red (Felgen's stain). These parts are called chromatin (from the Greek word for "color"). If a drug is added to cells at various stages of division, the behavior of chromatin can become visible to us, and it is this behavior that is the key to the situation of interest to us.
How cells divide
At the very beginning of the process of cell division, the chromatin of the nucleus begins to assemble into small filamentous forms. These strands of chromatin are called chromosomes. The number of chromosomes is different in the cells of different animal species. A fly, for example, has only eight chromosomes in its cells, while a spiny lobster has more than a hundred. All cells of any animal of the same species have the same number of chromosomes. In human cells, for example, chromatin is assembled into exactly 48 chromosomes during the process of cell division.
Because chromatin is assembled into small thread-like forms during cell division, the process of cell division is called mitosis, from the Greek word for thread.
After the chromosomes have formed, the nuclear membrane disappears and substances from the nucleus mix with the cytoplasm. Chromosomes meanwhile stretch across the cell in the middle.
This is the decisive moment. It's called metaphase. The chromosomes remain in the middle of the cell, and after a while each chromosome is suddenly duplicated by a companion chromosome lining up next to the original chromosome. In a dividing human cell, the number of chromosomes thus increases from 48 to 96 in metaphase.
After metaphase, everything happens pretty quickly. First, the chromosomes separate from each other. One set of 48 chromosomes (in human cells) moves to one end of the cell. Another set of 48 chromosomes is at the other end of the cell.
The chromosomes at each end of the cell are then enveloped by new nuclear membranes. Within a short time, the cell has two nuclei at once. Within each nucleus, the chromosomes begin to unfold and lose their threadlike form. But they do not disintegrate and do not dissolve. This can be compared to how if a strongly stretched string, after being released, suddenly weakened and became long and twisted. This is how chromosomes unfold into chromatin and wait for the next cell division when they once again form chromosomes.
After these two nuclei have formed at opposite ends of the cell, the cell begins to narrow in the middle. The middle becomes narrower and narrower until the cells separate. In the protozoa, the two resulting cells detach from each other and become two separate individuals. In the metazoa, two daughter cells remain in place. The new cell membrane, however, now separates the two parts of what was once a single cell.
Now back to metaphase. One unusual thing that may interest us in the process of mitosis is the doubling of chromosomes. Everything else is just a matter of dividing the substance of the cell into two equal parts and separating them from each other by a membrane.
You may ask, “Isn't the same thing happening with chromosomes? Doesn't each chromosome simply divide along its length, becoming two chromosomes?
To answer this question, it is not enough for us to consider only the cell itself, or even the nucleus. We must turn our attention to the chromosome itself.
Inside the chromosome
Now we're dealing with objects that are so tiny that we have to pause to consider how small we can possibly get anyway. As all of us living in the age of the atomic bomb probably know, the whole world is made up of atoms. Atoms are extremely small objects. A chromosome that is large enough to be seen with a microscope contains many billions of atoms.
Atoms come in a hundred different types, some more simple than others. With rare exceptions, atoms are bound together in groups. Sometimes such a group consists of atoms of only one kind. More often, a group consists of two or more different kinds of atoms. Sometimes these groups can be made up of only two atoms each, sometimes half a dozen, sometimes several million. In any case, a group of atoms, whether it consists of one kind or many, whether it contains two atoms or two million, is called a molecule.
Each of the various types of substances known to us (and there are many hundreds of thousands of them) consists of molecules of its own kind. Each of the different kinds of molecule has its own set of properties and characteristics.
For example, if you cut a piece of a substance, such as sugar, in two, each piece will still be sugar. If you keep dividing the sugar into smaller and smaller pieces, each piece is still sugar. Even if it were possible to divide sugar so precisely as to separate it into individual molecules (billions and trillions of molecules), each molecule would still be sugar. A molecule, however, is the smallest particle that can retain the characteristics of the substance it makes up. If you were to split a sugar molecule in two, you would be left with two groups of atoms, each one half the size of the original molecule. One of the new bands, however, would no longer be sugar.
It's the same as if you took a class of 16 students and split it into two. You would then have two classes of 8 students each. You could go ahead and do 4 classes with 4 students each, 8 classes with 2 students each, or even 16 classes with 1 student each. But you should have stopped there. If you tried to continue this fascinating process and form 32 classes with half a student each, you would end up with no classes at all, no students, but serious trouble with the police.
Now let's get back to the chromosome. The chromosome is made up of a substance called a nucleoprotein. The nucleoprotein molecule is huge compared to most molecules. It is a million or more times larger than, for example, a sugar molecule. (Even so, still too small to be seen under normal microscopes.) A chromosome is a string of several thousand of these giant nucleoprotein molecules strung together.
Now imagine what would happen if each chromosome were to split in the middle at metaphase and become two chromosomes. It would be like breaking a pearl necklace. You wouldn't have more than two pearl necklaces, just two sets of bunches of pearls and nothing else.
Now we can answer the question with which we ended the previous section. Chromosomes don't just split in the middle, becoming two chromosomes in metaphase. If the chromosome were split down the middle, every nucleoprotein molecule would be destroyed. Instead of having two chromosomes, we would have none.
Therefore, in order for each chromosome to become two chromosomes in metaphase, one of them must be created anew from simpler materials.
How it's done? Nobody knows for sure. Many scientists are studying this process. Once they have a complete answer, they will have at their disposal one of the important keys to knowing the nature of life itself.
In a rough approximation, however, this seems to work in the following way: the protoplasm in the cell contains various simple substances that can be combined to form a chromosome. (It's like the pieces of a jigsaw puzzle when you see which one, when properly combined with the others, can make up the big picture.) Some of these substances are called amino acids. Others are called purines, pyrimidines, pentoses, and phosphate ions. In some way these simple substances are pulled out of the protoplasm and lined up around the various chromosomes. The arrangement of substances is such that each amino acid in each chromosome has a similar amino acid next to it; each purine is adjacent to a similar purine, and so on. When the building is complete, all these little molecules and ions are connected together, and in the end we have a second chromosome next to the first. Since the second chromosome is made up of exactly the same molecules and ions as the first, and lined up in the same order, we have an exact duplicate of the first chromosome. The first chromosome acted as a kind of model, but by which the second was molded.
The process by which a chemical structure forms another structure solely and directly from materials in protoplasm is known as self-reproduction.
Summing up, therefore, what happens in a dividing human cell in metaphase, we see that each of these forty-eight chromosomes in the cell reproduces itself. The formed second set of chromosomes is an exact duplicate of the first set. The two sets move to opposite ends of the cell, and as the cell divides, each daughter cell has its own set of chromosomes.
Enzymes and genes
We have seen that the cell contains many different substances that can be used as raw materials in the manufacture of complex chromosome structures. Each cell, in fact, contains many thousands of different chemicals within its microscopic structure. These chemicals are constantly colliding and combining with each other, exchanging atoms, splitting and separating, rearranging atoms within their own structure, etc. Actions of this kind are called chemical reactions.
As you might imagine from this description, events within a cell must be very intricate, with molecules scurrying back and forth like people bumping into each other in a crowded train station. However, there is one type of molecule that brings order and meaning to the chemical reactions that take place within a cell. These are enzymes. Enzymes are relatively large molecules that can influence the course of some chemical reactions. Each enzyme can influence one specific chemical reaction, since only this one takes place near it, and no other.
Within a single cell, various enzymes appear to be arranged in an orderly manner. For example, a variety of enzymes are parts of small structures within the cytoplasm of a cell. These structures are called mitochondria. Like chromosomes, mitochondria are made up of a nucleoprotein. The mitochondrial nucleoprotein, however, is chemically different from the chromosomal type.
We can look at the cell as something like a microscopic factory. Molecules of all kinds enter our body from the air and from the food we eat, and are carried to individual cells by blood streams. This is reminiscent of the way in which coal, steel, rubber and other raw materials are brought to factories by trains and ships.
In the cell, these molecules break down to give up energy as a result, or they line up to form more complex molecules. It's like how factories burn coal for energy, or use steel and other materials to create complex structures like a car or an airplane. Every chemical reaction in a cell is controlled by an enzyme, just as every action in a factory is controlled by a worker. Enzymes are organized in mitochondria in the same way that workers are placed along assembly lines.
Just as a factory couldn't do anything significant if all the workers went on strike, for example, so a cell can't create anything without its thousands of enzymes. But then where do the enzymes themselves come from? This is an important question. The best answer we know so far is this: Enzymes are formed by nucleoprotein molecules within chromosomes.
As we said, the chromosome is not made up of a single nucleoprotein molecule, but of thousands of such extended molecules. Each nucleothyroid molecule is called a gene.
Genes have two important properties. The first is the ability to reproduce itself during mitosis, a process explained in How Cells Divide and Within the Chromosome. The second is the ability to produce an enzyme. The exact process by which the enzyme is produced is not yet known. Perhaps the whole gene is used as a model for another gene, and only some part of the gene is used as a model for an enzyme.
Some scientists believe that each gene has the ability to form one specific enzyme and no other. Others are not entirely convinced that genes are so specialized. It seems fairly reasonable, however, that the nature of the genes present on a cell's chromosomes determines the nature of the enzymes in the cell. Since enzymes control chemical reactions, genes control the chemistry of the cell. After cell division, each daughter cell has identical genes and therefore an identical chemical composition. This is the result of self-reproduction in mitosis: both daughter cells have identical genes.
Genes and physical characteristics
Now that we have shown how cells retain their characteristics after division, you may wonder how all this relates to the problem of human races. The application of all this is this: the physical characteristics that we mentioned in the previous section are determined by the chemistry of the cell. Anything that affects the chemistry of the cell in some way can affect the bodily physical characteristics in one way or another.
Let's take skin color as an example.
The large pigment molecule melanin is formed in skin cells from a much smaller molecule called tyrosine. (Tyrosine is colorless and is present in all cells.) The specific steps in this process are still unknown, but one of the first steps we know of requires the presence of an enzyme called tyrosinase. In the skin cells of most people there is at least one gene, the work of which should lead to the formation of tyrosinase. If the gene is of the kind that can produce significant amounts of tyrosinase, the skin cell is like a well-equipped factory. Significant amounts of melanin are formed, and a person with this gene therefore has dark brown skin, black hair, and dark brown eyes. If the gene is of a species that produces only a small amount of tyrosinase, the opposite will be true. Only a small amount of melanin will be formed and the person will have pale skin, blond hair and light eyes. In addition, there are some people whose genes do not form tyrosinases at all. Since their cells don't even have a small amount of tyrosinase, they can't have melanin either. Such people have very fair skin, white hair, and they have no iris pigmentation at all. (Their eyes look reddish because small blood vessels show through the clear, colorless iris.) These people are called albinos. If you have ever met an albino, you could see for yourself what an amazing effect on the physical condition of a person can have the presence or absence of only one gene.
There are other enzymes, and therefore many other genes are involved in the formation of melanin. The color of the skin, for this reason, is more complex than it might appear from what we have so far talked about.
Another physical characteristic we might consider is height. One of the chemical factors that affect human growth is known as growth hormone. This substance is formed in the cells of a small structure called the pituitary gland, which is located just below the brain. Growth hormone passes from the pituitary gland into the blood stream. The blood carries it to all parts of the body, somehow (again we don't know the exact details) encouraging the cells to grow and divide.
Unless there are other factors that could be considered in conjunction with it (such as diet or disease), a person with more HGH in their blood will grow more rapidly than a person with less HGH. He will probably get big and very tall. There are people in whom, for some reason, only a very small amount of growth hormone is produced by the pituitary gland. Such a person hardly grows at all, and as a result he remains a dwarf. On the contrary, some people have excessive production of growth hormone, and as a result they turn into giants. The dwarfs and giants we see in circus performances are the result of too little or too much growth hormone.
Growth hormone is formed in the pituitary gland under the control of enzymes. The amount of growth hormone therefore depends, at least in part, on the amount of certain enzymes formed in the cells. This, in turn, depends on the nature of the genes responsible for the formation of these enzymes. So height, like skin color, depends on the nature of the genes that a person possesses.
Similar arguments can be made for any physical characteristic. It's always a matter of genes. For this reason, it is logical to assume that if we are to succeed in dividing people into racial groups, we must first study everything we can learn about how genes are passed from parents to children.
egg and sperm
All but the simplest animals produce specialized cells that, under favorable circumstances, have a way of developing into new individuals. Such cells produced by female animals are known as ova. The ovum is often called the Latin word ovum, which means "egg". A hen's egg is an ovum that we are all very familiar with. In this example, you can immediately see how much the egg differs from other cells. Look at a chicken egg and remember that it is just a single cell. Now compare it to cells that are so small that they can only be seen with a microscope. In fact, only a microscopic speck on the surface of the egg yolk is alive. Everything else is just a supply of food. It will take three weeks for a chicken to grow from this microscopic speck into a small creature that fills the shell. The egg should contain all the calories, vitamins and minerals that the chick will need during those three weeks.
In humans (as well as other mammals) the situation is somewhat different. The egg develops inside the mother's body. Shortly after the fertilized egg begins to grow, an organ known as the placenta is formed. In the placenta, the developing baby's blood vessels come very close to the mother's blood vessels. Nutrients, vitamins, oxygen - in general, everything necessary to sustain life - pass from the mother's blood into the child's blood. This is the way a mother feeds a child. (Note that the blood vessels of the mother and baby do not connect. There is no mixing of blood!)
Since it is the mother's blood that nourishes the developing fetus, there is no need for a human egg to contain many nutrients. Therefore, it is much smaller than a chicken egg. In fact, the size of a human egg is only "/.75" in diameter. But even so, it is still the largest cell in the entire human body.
Males also produce special cells that contribute to the development of new individuals. They are called spermatozoa, or semen. They are much smaller than eggs. 600 or more sperm weigh the same as a single egg.
The human sperm cell is a very unusual kind of cell because it can move on its own. It does this with its long tail, swinging it in all directions. This tail is approximately ten times the size of the rest of the cell. When viewed under a microscope, a spermatozoon looks very much like a tiny tadpole.
Both eggs and sperm are all produced in special organs. The eggs are formed in the ovaries. All normal women have two ovaries. In them, they produce one egg every four weeks. Sperm cells are produced in the testicles, all normal men have two testicles. The testicles continuously produce vast amounts of sperm. The drop of fluid produced by the testicles contains many, many millions of spermatozoa.
When the sperm is released near the egg, many spermatozoa randomly rush to it. Only one of the sperm enters the egg through the layer of small cells surrounding it. Once a sperm enters an egg, no other sperm can do the same. The combination of an egg and a sperm is called a fertilized egg, or a zygote.
The difference between an egg formed in the ovaries and a fertilized egg is extremely large. If the formed egg is not fertilized by the sperm, then it will soon be destroyed. The fertilized egg, however, immediately begins to divide and divide again, grow and develop into an embryo. Finally, if everything goes smoothly, a human baby is born.
Now we can ask ourselves many questions at once. Why exactly two cells are required to produce a new individual? Why does he have to have both father and mother? Does it matter that a spermatozoon is so different in appearance from an egg?
To answer these and other similar questions, let's turn our attention back to chromosomes.
Earlier we said that human cells contain 48 chromosomes. These 48 are lined up in pairs. Each human cell therefore contains 24 pairs of chromosomes. The genes on any chromosome are like the genes on the chromosome that is paired with it. If one chromosome contains the gene that forms tyrosinase, so does its twin chromosome. This gene is even located in the same place on each chromosome. The genes may not be identical; that is, one of them, for example, may be capable of generating more tyrosinase than the other. However, both of them are associated with the same enzyme.
In other words, a human cell contains 24 different chromosomes, plus spare parts for each of those 24, for a total of 48.
You may remember that in the previous chapter we mentioned one exception to the rule that all human cells contain 48 chromosomes. This exception is the female egg and sperm.
Eggs and sperm cells are formed from parental cells containing the usual 48 chromosomes. The parent cells, however, undergo an unusual form of cell division known as meiosis. Chromosomes do not reproduce themselves. Instead, these 48 chromosomes simply split into two groups and travel to opposite ends of the cells. At one end there are 24 different chromosomes, and at the other end there are 24 "spare parts".
The result of this is that both eggs and sperm are only "semi-cells", at least in terms of the number of chromosomes. They have but 24 chromosomes.
A small sperm cell contains the same number of chromosomes - 24 - as a much larger egg. A sperm cell, however, contains almost nothing else: just 24 chromosomes, tightly packed together and driven back and forth by a wagging tail. The egg, on the other hand, contains a significant amount of nutrients, due to which the embryo can live until the placenta is formed.
When a sperm cell enters an egg (leaving its tail outside), it becomes a nucleus, much like the small nucleus in an egg. These two nuclei approach and dissolve into each other. Now the fertilized egg is already a full-fledged cell. It contains all 48 chromosomes. This is why a fertilized egg can develop into an embryo while an unfertilized egg cannot. This requires the total number of chromosomes - namely 48.
There is one important difference between a fertilized egg and all other cells in the female body in which it exists. Chromosomes are different! Only 24 of the chromosomes of the fertilized egg were obtained from the cells of the woman, that is, from the mother. The other 24 chromosomes entered the cell from outside, i.e., from "the father's sperm. Now that the fertilized egg divides and divides again, each new self-replicating cell has chromosomes that are identical to the chromosomes of the original, fertilized egg. The cells of every person on earth therefore contain 24 chromosomes which he received from his mother, and 24 chromosomes received from his father.In addition, in each pair of chromosomes, one received from his mother and one from his father.Now we can go further.Every person has two genes responsible for each specific enzyme , and in each case one gene is from the mother and one from the father (There are some exceptions to this rule, as we shall see later.)
It does not matter that the mother seems to sacrifice much more than the father for the development of the child. She donated an egg that is much larger than her father's sperm cell. And then, for nine months, only the mother's blood feeds the growing embryo. However, as far as chromosomes are concerned, each parent makes an equal contribution. And it is the chromosomes that determine the specific inheritance of physical characteristics.
Man and woman
The first question anyone asks about a newborn baby is "Boy or girl?" You may wonder when exactly the sex of a baby is determined. The answer to this may surprise you. The sex of the baby is determined when the sperm cell fertilizes the egg.
Let's see why this is so. As we have already said, all human cells (except eggs and sperm cells) contain 24 n chromosomes. In fact, this is not entirely correct. A woman's cells do contain 24 perfect pairs. The male's cells, however, contain 23 perfect pairs plus a 24th pair, which is a bit unusual. The 24th pair in males consists of one perfect chromosome and one stunted little partner. A complete chromosome is called an X chromosome. The stunted partner is called the Y chromosome. In other words, the 24th pair in men does not have a proper "spare part". What does this mean for the maturation process? When an egg is formed, the 24 pairs of chromosomes in a woman divide evenly. Each egg receives 24 perfect chromosomes. Therefore, all eggs are similar in this respect and each contains an X chromosome.
However, when a spermatozoon is formed, the 24 pairs of chromosomes divide so that one cell of 1 sperm gets 24 perfect chromosomes and the other gets 23 perfect chromosomes plus a Y chromosome. Therefore, two types of sperm cells are formed - one type with a Y chromosome, the other without it. Both of these species are formed in equal proportions.
Now, if an egg is fertilized by sperm without a Y chromosome, the fertilized egg is found to have 24 perfect pairs of chromosomes, and the embryo automatically develops as a female. If the egg is fertilized by sperm with a Y chromosome, the fertilized egg is found to have 23 perfect pairs of chromosomes and the 24th pair with a Y chromosome. The embryo then automatically develops as a male1.
Since both types of sperm cells are formed in equal proportions, there are equal chances for one of the first or second type to fertilize an egg, and for this reason there are as many men in the world as women.
In fact, the distribution of iols is somewhat different from the 50/50 ratio. Eggs fertilized by sperm with a Y chromosome are somewhat more common than eggs fertilized by sperm with an X chromosome. The reason for this is still unknown. But there is another factor that requires our consideration. Having a spare for each chromosome is very helpful. If something wrong happens to a gene on a particular chromosome, then the gene on its part can be in perfect order, and the organism can get out of a difficult situation in this way. With respect to 23 pairs of chromosomes, both sexes are equal. On chromosome 24, however, females have an advantage. They have a spare part, but men do not. If women have an imperfect gene on the X chromosome, the spare part saves them. If men have an imperfect gene on the X chromosome, they are very unlucky.
It is for this reason, perhaps, that male embryos encounter more difficulties than female embryos. Fewer of them live to the moment of birth. In addition, more male infants die at an early age than female infants, and in general men live less than women. Thus, despite the fact that there are more conceptions of boys than girls, the general population has a slightly higher percentage of women.
In short, men may be taller, heavier, and more muscular than women, but as far as their chromosomes are concerned, they are in fact the weaker sex.
Variations among genes
As we have said, genes control the development of enzymes and thus govern the nature of physical characteristics. Unfortunately, our knowledge of cell chemistry is very limited. We can hardly ever know exactly which enzyme or enzymes govern ordinary physical characteristics. In fact, we know that the enzyme tyrosinase is necessary for the formation of melanin, and it determines the color of the skin, hair and eyes. We believe, however, that other enzymes are also required for this process.
For this reason, one can skip the details of the enzyme and only connect the gene to a physical characteristic. For example, we could talk about a baldness gene, a five-finger gene, or an eye color gene. Sometimes it would be convenient for us to talk about different genes that affect the same physical characteristic, but in different ways. Eye color is a good example. We could talk about the brown eye gene and the blue eye gene.
Each place on a chromosome can only be occupied by one gene at a time. However, there may be several genes that can take this place. When different genes are able to occupy a certain place on a chromosome, they are said to form alleles, that is, specific forms of the same gene. Usually, different allele genes affect the same physical characteristic, but in different ways. For example, a gene that produces tyrosine and is capable of generating a significant amount of tyrosinase will cause a child to have brown eyes. Another similar gene, which is capable of generating only minute amounts of tyrosinase, and which will thus cause blue eyes, may be in the same place on the chromosome in some other individuals. The brown eye gene and the blue eye gene are two alleles of the same gene.
Except for the genes on the X and Y chromosomes in males, all genes exist in pairs because all chromosomes exist in pairs. For every gene that exists at a certain place on the chromosome, there is a second gene that controls the same physical characteristic and is in the same position on the other paired chromosome. These two genes may or may not be identical, but they both affect the same physical characteristic - they may affect it in the same way or in different ways.
Each cell has two genes that are responsible for eye color through the formation of tyrosinase. One is on some chromosome and the other is on the same spot on the twin chromosome. One might be the brown eye gene, and so might the other; or it could be the blue eye gene, and the other one too. Whenever these two genes are identical, the person is said to be homozygous for that characteristic. He is homozygous for the brown eye gene in the first case, and homozygous for the blue eye gene in the second case.
But these two genes do not have to be identical. They may be different alleles of a specific gene. A person can have the gene (allele) for brown eyes on one chromosome and the gene for blue eyes on the twin chromosome. Such a person is heterozygous for the genes that determine eye color.
"Homozygous" and "heterozygous" are difficult words. Sometimes people talk about "pure lines" when the two genes are similar, and "hybrids" when they are not. These are much simpler terms, and also more familiar. You may wonder why we don't use them instead of "homozygous" and "heterozygous". Unfortunately, too many people think that there is something good about being "pure" and something bad about being a "hybrid". To avoid getting into trouble with these prejudices (in fact, as we shall see, there are good and bad sides to both of these conditions), we will stick with the words "homozygous" and "heterozygous" in this book.
Let's continue our topic with eye color genes. Consider, for example, eggs that are produced by a woman who is homozygous for hazel eyes. The pairs of chromosomes divide, and since a woman only has the brown eye gene, each egg will have one brown eye gene. With regard to the eye color gene, all eggs will be identical.
A man who is homozygous for brown eyes will in the same way produce sperm cells that have one gene for brown eyes.
Suppose this homozygous man and the homozygous woman are married and have a child. The child will have an eye color that depends on the nature of the genes in the sperm cell and in the egg that combined to form the fertilized egg. But, as we have already explained, all eggs contained one gene for brown eyes, and all sperm cells contained one gene for brown eyes. Therefore, no matter which sperm cell fertilizes an egg, that fertilized egg will always have two genes for brown eyes. Like both parents, the child will be homozygous for brown eyes. All other children from this marriage will be the same.
If the mother and father are both homozygous for blue eyes, then, reasoning in the same way, all their children will be homozygous for blue eyes.
But - and this is a very big but - does it often happen that one parent is homozygous for brown eyes and the other is homozygous for blue eyes? Suppose the mother is homozygous for brown eyes. Then each egg she produces will contain one gene for brown eyes. Father is homozygous for blue eyes; so every sperm cell he produces will contain one gene for blue eyes. No matter which sperm fertilizes the egg, the fertilized egg will contain one gene for blue eyes and one gene for brown eyes. The child will be heterozygous.
If not the mother had brown eyes, but the father, and the mother had blue eyes, the result would be the same. Each egg would have one blue eye gene, and each sperm cell would have one brown eye gene. Again, a fertilized egg would have both genes, and the child would be heterozygous.
What happens to a child who is heterozygous for eye color? The answer is: he (or she) has brown eyes. The child has one gene that can produce a large amount of tyrosinase and a gene that can produce a small amount of tyrosinase. However, a single gene can generate a relatively large amount of tyrosinase, and it may be enough to color the eyes brown.
As a result, two parents, one homozygous for brown eyes and the other homozygous for blue eyes, have children who are heterozygous and at the same time have brown eyes. The blue eye gene does not appear. He is invisible. It seems to be disappearing.
When a person has two different genes for some physical characteristic at identical locations on a pair of chromosomes, and only one gene is expressed, that gene is called dominant. A gene that does not show up is recessive. In the case of eye color, the brown eye gene is dominant in relation to the blue eye gene. The blue eye gene is recessive to the brown eye gene.
It is impossible to tell just by looking at a person whether they are homozygous or heterozygous for brown eyes. Either way, his eyes are brown. One way to say something definite is to find out something about his parents. If his mother or his father had blue eyes, he must be heterozygous. Another way to know something is to see the color of his children's eyes.
We already know that if a homozygous brown-eyed man marries a homozygous brown-eyed woman, they will have homozygous brown-eyed children. But what happens if he marries a heterozygous girl? A homozygous male would only form sperm cells with genes for brown eyes. His heterozygous wife would produce two types of eggs. During meiosis, since her cells have both a brown eye gene and a blue eye gene, the brown eye gene will travel to one end of the cell and the blue eye gene to the other. Half of the formed eggs will contain the gene for brown eyes, and the other half - the gene for blue eyes.
The chance of a sperm cell fertilizing a brown-eyed egg or a blue-eyed egg is therefore 50/50. Half of the fertilized eggs will be homozygous for brown eyes, and half will be heterozygous. But all children will have brown eyes.
Now suppose that. both father and mother are heterozygous. Both would have brown eyes, but both at the same time have the gene for blue eyes. The father would form two kinds of sperm cells, one with the blue eye gene and the other with the brown eye gene. In the same way, the mother would form two kinds of eggs.
Several combinations of sperm and egg cells are now possible. Suppose one of the sperm cells with the brown eye gene fertilizes one of the eggs with the brown eye gene. The child in this case will be homozygous for brown eyes and will naturally have brown eyes. Suppose a sperm cell with the gene for brown eyes fertilizes an egg with the gene for blue eyes, or a sperm cell with the gene for blue eyes fertilizes an egg with the gene for brown eyes. Either way, the baby will be heterozygous and still have brown eyes.
But there is another option. What if a sperm cell with a blue eye gene fertilizes an egg with a blue eye gene? In this case, the child will be homozygous for blue eyes and will have blue eyes.
Thus, two brown-eyed parents can have a blue-eyed child. The gene that seemed to have vanished reappeared. In addition, you can, by looking at the child, say something about the parents. Although their eyes are brown, just like a homozygous person, you know that they both must be heterozygous or the blue eye gene would not be expressed.
When two people are similar but in some specific physical characteristics, they are said to belong to the same phenotype. All people with brown eyes have the same phenotype in terms of eye color. The same is true for people with blue eyes. When two people have the same combination of genes for some specific physical characteristic, they belong to the same genotype. Since all blue-eyed people are homozygous and have two genes for blue eyes in their cells, they all have the same combination of genes and all belong to the same genotype in terms of eye color. Brown-eyed people, however, can be either homozygous or heterozygous. For this reason, they belong to two different genotypes in terms of eye color. One genotype includes people with two genes for brown eyes; the other includes people with one gene for brown eyes and one for blue eyes.
You can determine a person's phenotype just by looking at them, but you can only determine a person's genotype by examining their parents, or their children, or both. Sometimes, as we will see, you will not be able to determine the genotype of a person even in this case.
