Human

Human. Contents: Origin of human ............ 5 24 Heredity of human........... 530 Human in terms of its systematic position in the organic world belongs to the animal kingdom (Animalia), to the subkingdom of multicellular organisms (Metazoa), to the phylum of chordates (Chordata), to the subphylum of vertebrates (Vertebrata), to the class of mammals (Mammalia), to the subclass of placentals (Placentalia), to the order of primates (Primates), to the suborder of apes (Pithecoidea), being the only species and genus of the family hominids (Hominidae). To this family, in addition to modern H., belong extinct ancestors of H., which were characterized by upright walking, opposition of the thumb, underdevelopment of the hair cover, relatively large brain, and predominance of the cerebral part of the skull over the facial. Origin of human. The first scientific solution to the problem of anthropogenesis was given by Darwin. Based on extensive material, he showed the idea of the natural development of H. from an ape-like ancestor, common with currently living anthropoid apes. I At present, the view of the animal origin of H. is universally recognized; the statement made by C. Linnaeus about the systematic affiliation of H. to the order of primates does not cause any objection. But regarding the placement of H. in smaller taxonomic units, there are conflicting points of view. Most phylogenetically connect H. with anthropoids, but there are attempts to derive the trunk of H. from lower primates independently of the trunks of anthropoids. Such is the tarsoid hypothesis of Wood Jones, leading the line of H. directly from tarsiers, a relict representative of which is the tarsier - a small nocturnal animal from S.E. Asia, with a fairly large round head, poorly developed facial skeleton, with close-set, straight-forward large eyes, placed in completely closed rounded orbits, with proportions of limbs close to human, and with a long tail serving as support in the vertical position of the body. A bright representative of such a view is Osborn. Emphasizing the minor distinguishing features of H. from apes and explaining its striking similarity to anthropoids by convergence, Osborn asserts that for the development of human features - by analogy with the development of known paleontological phylogenetic series of ungulates, proboscids, etc. - significantly more time was required than is allocated by the hypothesis of phylogenetic closeness of H. and anthropoids. In the question of phylogenetic closeness of H. with one or another species of modern anthropoids, supporters of the latter hypothesis also have no unity. Klaatsch connects some races with orangutan-like, others with gorilla-like ancestors. Attempts were made to derive H. from gibbon-like ancestors, but comparative anatomy, embryology, parasitology, physiology, etc. prove the genetic closeness of H. to the gorilla-chimpanzee group and its separation from their common trunk in relatively recent times. Paleontology points to the extinct group of anthropoids-dryopithecus (Dryopithecus) as the common ancestor of H. and African anthropoids. Various species of dryopitheci are known from the Miocene of Europe, S.E. Asia and N. Africa. The preserved remains of these animals, mainly fragments of jaws and individual teeth, allow, for example, to speak of the fact that Darwin's dryopithecus from the upper Miocene deposits of Europe can be considered as the common ancestor of H. and chimpanzee. The lack of paleontological material will hardly ever give us the opportunity to accurately establish the species of extinct anthropoids that gave rise to H. Of 1,065 characteristics studied by Keith on H., only 312 are exclusively characteristic of H., while 396 are common with chimpanzee, 385 with gorilla, etc. The dryopithecus ancestors of H. differed even less from other species of dryopithecus, and therefore each new discovery of dryopithecus brings new data to our understanding of this stage of development of H. The already available facts of evolutionary anatomy and embryology speak in favor of the fact that H. in its development passed sequentially through the stages of arboreal, semi-arboreal and terrestrial life, when the hand finally freed itself from the functions of locomotion. Apparently the stage of dryopitheci corresponds to the second of the listed stages. As a representative of a fully terrestrial bipedal stage of pre-human development, many are inclined to consider australopithecus (Australopithecus africanus), the remains of which were found in S. Africa in Bechuanaland in 1924 by Dart. The remains (almost a complete facial skeleton with teeth, with zygomatic arch and lower jaw, base of the skull, internal cast of the entire right and anterior part of the left side of the cerebral skull, damaged bones of the left side of the skull and some bones of the skeleton of limbs and trunk) were found in a cave in a semi-desert area, transitioning to the north and west into deserts. According to geologists, the climate of this and surrounding areas has not noticeably changed since the Tertiary period, to which the remains of australopithecus belong, and therefore the latter lived in an area separated from the habitat of modern anthropoids by a wide impassable desert barrier. Obviously the group of australopithecuses that overcame this barrier had advanced significantly compared to the development of African anthropoids. The fact that the remains belong to a juvenile animal (1 molar is just erupting, which corresponds to the age of a 6-year-old child H. or a 4-year-old chimpanzee) indicates complete acclimatization of the group to these conditions. Morphol. features of the skull and brain confirm the view of the evolutionary advancement of the animal, but at the same time indicate its significant specialization, excluding it from the ancestral trunk of hominids, and do not allow to separate it from the group of anthropoids. An indisputable representative of hominids is Pithecanthropus erectus (upright ape-man), the remains of which - skull cap, femur and molar - were found by Dubois in 1891 on the island of Java. The conditions of occurrence of the remains indicate the existence of pithecanthropus at the very beginning of the Quaternary period, the time of the beginning of glaciation of W. Europe. The shape and structure of the femur are fully human and speak of upright walking, while the skull cap by its shape rather resembles the cap of a large ape. The frontal bone seems especially striking. Instead of the convex, rising almost vertically frontal squama of modern H., here we have a flat, devoid of any hint on frontal tubercles, obliquely receding backward forehead; instead of supraorbital arches here is a continuous torus, continuously extending from one zygomatic process to another (torus supraorbitalis), overhanging like a balcony over the orbit and forming a significant part of its roof. The anterior part of the squama is strongly narrowed, forming directly behind the edges of the orbits the so-called "constriction". The parietal bones are flattened, the squama of the occipital bone is very low, sloping down and backward from the lambdoid suture. The overall dimensions of the skull are very small (length 184 mm, width 131 mm, height above the glabella-inion line 62 mm) and characterize the skull as dolichocephalic (index 73.4), very low, with a volume of about 900 cm³. Despite the discrepancy between the skull and femur, their belonging to one individual is considered an indisputable fact, proving that the evolution of the brain preceded the evolution of methods of movement, in particular the freeing of the hand for labor processes. The skull cap of Sinanthropus, found in 1929 near Beijing, slightly exceeding in size the skull cap of Pithecanthropus, is very close to it in shape, although it shows some evolutionary advancement. Stone tools and remains of a hearth found together with it confirm its belonging to H., who knew how to use fire and make tools. The lower jaw of Sinanthropus, judging by its fragment, is very close in shape to the Heidelberg jaw, found in 1907 near Heidelberg in Germany. In shape, the Heidelberg jaw very much resembles an enlarged chimpanzee jaw, but the teeth are completely human. Its belonging to H., who lived in the second interglacial, is not disputed by anyone. The remains of pithecanthropus, Sinanthropus and Heidelberg man indicate the existence of a pithecanthropoid stage of H., on which it had already spread widely over the earth (Java, China, W. Europe) and existed for many millennia (from the beginning of the Quaternary period to the second interglacial). During this time, the ancestors of H. continued to evolve, and already Sinanthropus, who lived much later than pithecanthropus, shows such features that give some scientists grounds to single it out from this stage and consider it as a primitive member of the next stage - Neanderthal (Homo neanderthalensis, s. primigenius). This species Homo is known by a large number of paleoanthropological finds and remains of its culture. Traces of its existence have been found in W. and E. Europe, in E. and Asia Minor, in Australia, in Africa. To this species belong the following most famous finds of skeletal remains: Neanderthal, Spy, La Chapelle-aux-Saints, Moustier, Rhodesian, Krapina, Palestinian.

Such a wide territorial distribution of Neanderthals is associated with the significant variability of their traits, which precludes the possibility of asserting their complete uniformity. European Neanderthals are characterized by a very long (200 mm and more) and wide (150 mm) skull, with a low flattened vault, a narrow receding forehead, a strongly developed supraorbital ridge, a flat and as if broken at the border of the upper and main scales occipital bone, on which a powerful torus occipitalis transversus develops. In the facial skeleton, the large round orbits with a thickened edge attract attention, and the bottom of the orbital cavity without a sharp border passes into the small bones; alveolar prognathism of both jaws. A massive lower jaw without a protruding chin, with a rough 'sublingual ridge' on the inner side and without an internal chin crest. All Neanderthal finds are associated with the period of the 3rd interglacial and are characterized by the Mousterian stone culture. Non-European Neanderthal finds represent rather significant deviations from this type, sometimes approaching individual traits of the modern H. Thus, the child's skull from Galilee in its anterior part 'has a Neanderthal structure, while the posterior part of the skull represents a completely new type of structure, more resembling what is found in modern man' (Keith). From later European deposits, the so-called transitional or intermediate forms are known, to which must be attributed the skulls from Brux, Galley Hill, etc., which possess weakened Neanderthal traits and traits of Homo sapiens. The type of modern man, Homo sapiens, first appears in Western Europe in the deposits of the last ice age, in the so-called Aurignacian cultural epoch, and persists to our day without significant changes. Its remains testify to significant morphol. diversity of the population of this period. The most ancient form of Homo sapiens in Europe is the so-called Cro-Magnon race. Under this term is usually united a group of more or less morphologically homogeneous bone remains, and as a typical representative of the race is considered 'the old man of Cro-Magnon' (Dordogne). This race possessed a rounded, dolichocephalic skull with moderate height, a well-developed forehead, strong supraorbital ridges, often taken for a typical torus, a low and wide face, a protruding nose, low and wide rectangular orbits, with slight alveolar prognathism, with a well-developed chin and wide branches of the lower jaw. Sometimes under the term Cro-Magnon race are united a number of smaller taxonomic units (Chancelade, Obercassel, Barma Grande races), opposing it to another fossil race Homo sapiens fossilis, which in turn is composed of the Brünn and Negroid (Grimaldi) races. In general, there is no universally accepted classification of Upper Paleolithic races. Therefore, in relation to most skeletons, the most diverse views exist. Thus, some create a special Brünn race for the skulls which we. called transitional; others include the Galley Hill skull in the Brünn race; sometimes they speak of an Aurignacian race on the basis of a single skeleton from a cave of the same name, while others consider it a hybrid of two neighboring races; two skeletons (male and female) from Obercassel are by some attributed to the Cro-Magnon race, others assign the female skeleton to the Brünn race, and for the male create the Obercassel race. Unification of the systematics of fossil races is the next task of anthropology. Apart from this coherent scheme of development of H. stands the famous Piltdown (England) find of 1911, consisting of separate fragments of the cranial box and lower jaw. The bones were found in river deposits, their exact geological age cannot be established. With equal foundation one can speak of both a pre-Mousterian and an Upper Paleolithic or even more recent age of the find. The find itself is extremely unusual. While the braincase is of almost modern type, the jaw is clearly chimpanzee-like. However, the assumption that the jaw and skull belonged to two different individuals must be rejected, all the more so since in 1915 at some distance from the place of the first find, parts of the skull and lower jaw were found, possessing the same characteristics and belonging to a second specimen of the same type of H. Anthropologists, mainly English, consider the Piltdown man as an eoanthropus (Eoanthropus)-ancestor of Homo sapiens, living before or simultaneously with the Neanderthal, already possessing a highly developed brain but retaining a monkey-like jaw and teeth. In his 1933 work, Weinert comes to diametrically opposite conclusions. He believes that the skull belongs to a relatively recent time and undoubtedly belongs to Homo sapiens, and the ape-like jaw is simply an anomaly, quite possible given the extremely wide variability of this bone. At the same time, he notes that the reconstruction of the skull was not done quite correctly, and on it one can note a number of primitive features not previously noticed. In 1932, Elliot Smith declared the presence of a certain similarity of individual traits of Piltdown and Sinanthropus. Both statements refute the myth of the eoanthropus, assigning a place to Piltdown among one of the three known stages of development of H.-pithecanthropic-Neanderthal-modern. Attempts to find factors driving the evolution of H. were made by many scientists, starting with Darwin, but none of the hypotheses they put forward is acceptable. Only Engels succeeded in scientifically solving this task on the basis of applying the method of dialectical materialism. 'Labor created man himself.' Some highly developed breed of monkeys, due to changed climatic. conditions, was forced to switch from a tree-dwelling to a terrestrial way of life. Accustomed to using hands differently than feet on trees, it on the ground intensified the rudiments of division of labor between the limbs, completely freeing the hands from the functions of locomotion-'the hand became free', thanks to this it became possible for its further improvement, the development of new and new movements associated with obtaining new types of food, '...the decisive step was taken, the hand became free and could be perfected in dexterity and skill, and the greater flexibility thus acquired was transmitted by inheritance and multiplied from generation to generation. The hand is thus not only an organ of labor, it is also its product. Only thanks to labor, thanks to adaptation to ever new operations, thanks to the transmission by inheritance of the special development of muscles, ligaments and, over longer periods of time, also bones, as well as thanks to the ever new application of these inherited improvements to new, ever more complex operations-only thanks to all this did the human hand reach that high degree of perfection at which it could, as if by magic, bring to life the paintings of Raphael, the statues of Thorvaldsen, the music of Paganini. But the hand was not something self-sufficient. It was only one member of an extraordinarily complex organism. And what was good for the hand was also good for the whole body...' (Engels, Dialectics of Nature). The introduction of new types of food (in particular animal), changing the biochemical. composition of protoplasm, contributed to further changes in the body. Being by its nature a social animal, the monkey ancestor of H. in the process of labor activity developed its social instincts; in connection with labor activity articulate speech was born, further increasing the social ties of people. On the basis of production relations, the primitive herd grew into a primitive communist society, which subsequently disintegrated into classes. On the basis of ever more complicated production relations, legal and ideological superstructures-religion and others-were created. Regarding the place of the initial separation of H. from the trunk of monkeys, there are as many opinions as there are researchers who have dealt with this question. As the most probable homeland of H. are named Central Asia, S.E. Asia, Africa, Europe, W. Asia, Polar regions, etc. Engels, in agreement with Darwin, speaks of land that has sunk to the bottom of the ocean.

A. Yuaefoshsh. Heredity of humans. The phenomena of human heredity and the methods of their study have their specific peculiarities, however this by no means means that the basic regularities established in animals and plants are not applicable to humans. On the contrary, everything known about the mechanism of human heredity is splendidly explained by the same scientific principles of genetics common to the entire organic world. As the history of the study of human heredity convincingly shows, attempts to discover the regularities of the latter were fruitless until the application of Mendelism and the basic principles of genetics. Everything known about the biology of humans leads to the conviction that in him all the material, morphological, and physiological structures and regularities are present on the basis of which the phenomena of heredity are realized, and they are common to other animals and plants. Non-recognition in humans of the regularities of segregation, independent combination of genes, dominance, chromosomal theory of heredity (see Heredity, Mendelism) means refusing to extend to humans such unquestionably established phenomena as reduction division and maturation of gametes, the doctrine of individuality and constancy of the number of chromosomes, and a number of others. In general, it should be considered that all genotypic regularities, i.e., those related to the transmission and distribution of genes from generation to generation (chromosomal theory of heredity), are fully realized in humans. As for phenotypic regularities, i.e., the realization of the characteristics of an organism as a result of the interaction of the genotype and the specific environment, although all known regularities in this field (dominance, 'intermediate heredity', lethal factors, polymericity, epistasis, pleiotropy, etc.) are also undoubtedly realized in humans (see below), the concept of environment in him acquires a special specific character due to the presence of super-biological, social regularities. If usually under environment, which is a necessary and determining condition for the specific realization of an organism's characteristic, one understands first, external conditions (temperature, food, infection, etc.), second, the conditions of development of the organism as a whole and the interaction of its parts, and third, the genotypic environment, i.e., the aggregate of genotypic influences besides the specific genes determining the characteristic, then in humans a fourth factor of environment is added—social-class conditions. The significance of each of these developmental conditions separately should be determined each time specifically for each particular characteristic. Thus, if one takes such indisputable hereditary anatomical-morphological characteristics as claw-like extremity, brachydactyly, color of eyes and hair and many others, then the modifying influence of external conditions on them is very insignificant, and only the genotypic environment can play a greater or lesser significant role. On the other hand, a whole series of hereditary diseases are of the nature of predispositions, i.e., for their realization certain external conditions are necessary. Thus, there are diseases that have a hereditary basis, however for their manifestation they require infection. An example of the role of conditions of development of the organism as a whole can serve all so-called limited sex-linked characteristics, as for example sporadic goiter, which for some physiological reason can manifest itself mainly in persons of the female sex. Social-class conditions play a huge role in the manifestation and content of mental and psychopathological hereditary characteristics. The content and direction of talent and psychoses depend to such a degree on social factors that one should exercise extreme caution in evaluating the hereditary elements in them. In no way can one speak of the heredity of specific conditioned-reflex connections, but only of a certain norm of reaction, within which there is apparently a great variation in the occurrence of conditioned-reflex connections. In addition, the repetition from generation to generation of certain mental and professional tendencies in specific cases can be explained not so much by hereditary transmission as by property-class or professional continuity. How complex the influence of the social environment is is shown by the fact cited by S. Davidenkov that 'hysteria in Azerbaijani women usually has a severe, convulsive character'. This 'medieval' hysteria is most likely to be connected not with the accumulation of special genes, but with the circumstance that the Azerbaijani Muslim woman until recently was often forced to live in conditions of closed alienation from the outside world, covered by a veil, under which the most whimsical, suppressed affects and demonological fantasies can nest. Numerous studies on the 'heredity' of criminality, asociality, altruism, suicidal predisposition, 'nomadism' and other socially conditioned characteristics, especially characteristic of researchers of capitalist countries and the fascist, racist direction in genetics, need serious scientific criticism. It is not possible to sharply delimit the role of social-class conditions from mental and psychopathological characteristics. A whole series of factors of nutrition, housing, sanitary conditions depend on social-class affiliation. It is therefore not surprising the existence in relation to some diseases of a 'social predisposition'. All the above shows what difficulties in known cases are encountered in establishing hereditary characteristics in humans. Methods of studying heredity. The first task in studying a particular characteristic of humans is to establish whether it is a hereditary peculiarity. Erroneous is the criterion of 'innateness' of a characteristic, i.e., its presence at birth. Even an undoubtedly hereditary characteristic can often be realized only in the post-embryonic period. It is completely obvious that this is determined by the nature of the characteristic and its dependence on the general development and the various conditions of development. Thus, chorea usually does not manifest itself before 30 years. Clinically very close, but completely different in hereditary nature, cerebellar ataxia and Friedreich's ataxia usually also differ in the age of manifestation: while the first begins at 30 years, the second at 10 years. Xeroderma pigmentosum, which requires for its occurrence an impulse from external conditions, begins already after the first insolation. On the other hand, 'congenital' characteristics very often represent the result of intoxication or other influences in the embryonic period. To this type belong all cases of blastophthoria and such congenital diseases as for example 'hereditary' syphilis. In general, the embryonic and post-embryonic periods of development should be considered as fundamentally not differing and being separate segments of a single process. Equally unreliable is the coincidence of the property of a characteristic with a previously established undoubtedly hereditary characteristic. Completely similar in their properties characteristics can be of completely different origin. Thus, there exists sporadic goiter—hereditary—and endemic goiter, to a large extent dependent on special external conditions. Similarly, there apparently exists hereditary premature graying and non-hereditary, connected with hyperfunction of the thyroid gland. Also known is genotypic and paratypic deaf-mutism. In recent years, much attention has been paid to the method of studying twins (see); since monozygotic twins have an identical genotype, their similar characteristics should, under otherwise equal conditions, be genotypic. Siemens especially considers it important to establish by this method the hereditary nature of characteristics determined by many genes, for example of some diseases. This method has received wide distribution, and to the present time a huge factual material has been accumulated. Nevertheless, there are no unconditional criteria for proving monozygosity of twins. The most reliable is the use of a set of characteristics already known as undoubtedly hereditary, for example color of eyes, hair, etc. However, even undoubtedly hereditary characteristics can show noticeable phenotypic variation in monozygotic twins. In addition, one should bear in mind that monozygotic twins are similar not only genotypically, but there is much probability that their conditions of development, especially post-embryonic, are very similar. The similarity of environmental conditions of course leads to similarity of characteristics of undoubtedly non-genotypic nature. To decide the question of what determines the similarity of specific characteristics in monozygotic twins—genotypic identity or similarity of conditions of development—the method of comparing monozygotic twins with dizygotic is used. The latter are not necessarily genotypically similar; on the contrary, they are usually genotypically different, but their conditions of development are identical with those for monozygotic twins. Therefore, the similarity of the studied characteristics in dizygotic twins speaks in favor of their non-genotypic determination. Conversely, for genotypically determined characteristics, their non-coincidence in dizygotic twins is characteristic.

In view of this, an important condition for applying the twin method is the study of all both monozygotic and dizygotic twins; this is also important to avoid the possible influence of conscious or unconscious selection of case material on the research results. In general, the twin study method, being one of the most promising, contains great difficulties and requires a high level of scientific research. A good indirect proof of the heritability of a trait is the case of double marriage of a possessor of the trait being studied: in the case of a hereditary nature of the latter, the offspring in both marriages should equally give individuals with the trait being studied. However, this will be observed only for dominant genes or, if the subject who had two spouses is a woman, for genes located in the X chromosome (see below). The most common way to establish the heritability of a trait is to discover its 'familial' nature and to study the genealogies of such families. But one must always keep in mind the constant source of scientific errors—the selective nature of the genealogies studied. There is an extremely widespread tendency in the literature on human genetics to search for the most 'typical' genealogies, i.e., those in which the maximum number of carriers of the trait being studied is observed or which can be more easily 'fitted' into a certain inheritance pattern. To avoid this danger, one resorts to comparing the frequency of the trait being studied in the researcher's selective genealogies with the frequency in an arbitrary group of representatives of the human population. The frequency established for the latter serves as a control: if it is similar to that calculated in the case material, one cannot assert the heritability of the trait being studied, and conversely, it must be lower than in genealogies of truly hereditary traits. In the event that it is possible to give a factually satisfactory explanation for the type of gene transmission observed in the genealogy in successive generations and to explain the observed numerical relationships from the standpoint of known patterns of heredity, the heritability of the trait can be considered reliable. However, one must always keep in mind that the further accumulation of facts relating to the trait being studied must constantly confirm and satisfy the proposed interpretation. If the opposite occurs, e.g., it later turns out that the repetition of the trait being studied in individual members of the same family can be explained by an infection that took place or by the same influences of certain factors of the external environment, then the explanation of the heritability of the trait must of course be discarded. Thus, if deaf-mutism is observed as a result of syphilitic intoxication, then it is not surprising that it will be observed in a number of individuals. Or, if we study the genealogy of families with endemic goiter living in an area where goiter is a common phenomenon, then we will obtain in the pedigree a resemblance to 'transmission' by inheritance. In view of this, it is always necessary to clarify as much as possible all data on the influence of the environment on the trait being studied. It is quite obvious that when collecting genealogical information, maximum accuracy must be observed and only in extreme cases should one be limited to information provided by relatives. When studying individuals with respect to the trait of interest, it is necessary to apply as deeply as possible the qualitative and quantitative research methods possessed by those disciplines to whose competence the trait being studied belongs (X-rays, photographs, biochemical analysis, tests, etc., etc.). In addition, it is necessary not to limit oneself as much as possible to only the trait being studied, but to record everything that may turn out to be in interaction with the genes or developmental conditions of the trait being studied. All this is especially important for establishing the degree of constancy of the trait or the presence of several types of it, etc. Mendelian heredity. The simplest case of heritability in H. will be the presence of such an alternative constancy when one can speak of a definite, clearly defined trait—yes, no—with respect to individual family members. This is usually observed in monomeric inheritance, i.e., when a difference is found in the genealogy only with respect to one pair of allelic genes. In this case, the analysis is comparatively simple. It is first necessary to establish which of the traits of the allelic pair of genes is dominant or recessive. Usually, one speaks of dominance or recessiveness only with respect to the trait 'changed' in relation to the 'norm'. However, one should remember that this is quite arbitrary, since the changed trait, determined by a dominant gene, is opposed in a 'normal' individual by a recessive gene and vice versa. In the case of traits such as skin pigmentation (Negro, white), hair, eyes, etc., the meaninglessness of the expression 'norm' is quite clear. Dominant traits. If the trait being studied is dominant, then in the offspring it should be observed in all marriages where at least one of the parents manifested it. In view of this, the dominant gene should not show 'skipping' no matter how many generations we study: if at least one parent carries it, it will be revealed in the offspring. Another proof of the dominance of a gene is Mendelian splitting of the offspring in certain numerical ratios (see Mendelism). Since the probability of homozygosity for the dominant gene is very small, heterozygotes (DR) are usually observed. Therefore, the offspring, without showing 'skipping', by no means should all be carriers of the trait being studied. Theoretically, it is expected: in the case of both parents possessing the trait—splitting 3D : 1R; in the case of the trait being present in only one of the parents—splitting 1D : 1R. Finally, in the genealogy of a dominant gene, all marriages of individuals not manifesting the trait being studied should show no splitting, i.e., the offspring should always be completely devoid of the dominant trait (German 'einmal frei-immer frei'). In H., many dominant genes have been studied: brachydactyly, claw-like extremities, epidermolysis bullosa traumatica, keratosis, polyuria (diabetes insipidus), cataract, hemeralopia (night blindness), Huntington's chorea, cerebellar ataxia, and many others. When obtaining sufficiently large numbers of splitting, they must be subjected to mathematical processing to determine the reality of deviations from theoretically expected ratios (methods of calculating errors—see Variational statistics). Sometimes violations of the picture of the supposed dominant heredity are observed. Such violations include 'skipping'—entirely normal offspring from a subject who manifested the supposed dominant trait. At the same time, another rule of dominant inheritance can be violated: in such externally 'normal' individuals, splitting will be observed in their offspring, i.e., the appearance of two types of individuals. In addition to possible errors in compiling the genealogy, skipping can be explained by the following circumstances: 1) too late age of manifestation of the trait—then individuals who did not die in old age or are still alive may not have had time to show the trait; 2) incorrect and variable manifestation of the trait—when the trait strongly depends on external conditions or the genotypic environment. Thus, polydactyly, although it is undoubtedly a hereditary dominant trait, often manifests itself in a smaller number of individuals than expected, and sometimes does not manifest itself at all. Recessive traits. A recessive trait is characterized by the fact that it can always be observed in the offspring from normal parents. Another essential condition for the recessiveness of a trait is that in a marriage of two subjects who have equally manifested the trait, all offspring without exception must carry the recessive trait (RR). Due to the fact that in the offspring of subjects who have not manifested the trait, recessive forms can appear only as a result of splitting that has occurred, a characteristic feature of genealogies of a recessive gene is the relative frequency of consanguineous marriages in them. Finally, when recessive individuals appear in the offspring of subjects who have not manifested the trait, certain numerical relations must always be observed—3D : 1R, i.e., there should be 25% recessive forms. In the experience of counting numerical relations in the splitting of recessive genes, a number of researchers have often found significant deviations from theoretically expected ratios—3:1, namely—an 'excess of recessives' (Recessiven-Uberschuss) is often observed. As it turns out, this happens due to the small number of offspring in H. In view of this, the probability of the appearance of a recessive child in a family with 2, 3 children is extremely small. Thus, for every 16 two-child marriages, theoretically only 7 marriages are expected to have recessive children (in the amount of 1-2), and in the other 9, no recessives are expected at all. Correspondingly for three-child marriages, for every 64 marriages only 37 of them will give recessives (from 1 to 3).

Thanks to this, the researcher when collecting material will not pay attention to families that have not shown recessives, and will select only families in which there is at least one recessive. As a result - an excess of recessives. Thus, in our example with two-child and three-child marriages, even if all families with the presence of at least one recessive are taken into account, instead of the ratio 3:1, the ratios will be 3:4 for two-child families and 21:16 for three-child families. Weinberg proposed methods of calculation, thanks to which it is possible to avoid this distortion as a result of unconscious selection of material. Later, Lenz, Bernstein and others proposed even more perfect methods. The numbers obtained by the mentioned methods must be subjected to mathematical processing to calculate the deviation of these numbers from theoretically expected numbers (see Variational Statistics).-A large number of recessive genes in H. are also known. These include, for example, xeroderma pigmentosum, ichthyosis congenita, universal albinism, alkaptonuria, myoclonus epilepsy and others.' Intermediate traits. In all the above-mentioned types of monomeric heredity, complete dominance and recessiveness are assumed, i.e., heterozygous forms (DR) do not show any phenotypic transitions to recessive forms (RR). Theoretically, this means that heterozygotes are completely phenotypically indistinguishable from dominant homozygotes (DD, so-called pea type--Pisum typus). However, it is usually not possible to confidently specify DD and DR forms for their comparison in H. Usually only BR and RR types are known. Therefore, very recently it has been proposed (by S. Levit) to call such traits 'conditionally dominant,' and only after establishing the phenotype of individuals homozygous for such a trait (DD) can it be classified as one of the two types of dominance. In cases where transitions between dominant and recessive forms are observed with clear monomeric heredity, it is possible to assume that we are dealing with 'intermediate' heredity, i.e., when homozygotes are externally different from heterozygotes. Thus, if we are talking about a disease, heterozygotes will also not be completely healthy, but will show it in a transitional or slightly expressed form, so-called forme fruste. This type of phenotypic regularity is sometimes called the corn type (Zea typus). In this case, as is known, the observed phenotypic splitting coincides with the genotypic and occurs in the ratio 1DD : 2DR : 1RR, and in cases where there are reasons to assume that DD is not observed (see below about lethal factors), the ratio of recessives to dominants will be 1RR : 2DR instead of 1:3.-All the types described above are characterized by complete independence in their inheritance from sex, i.e., inheritance does not change depending on which sex is the carrier of such a gene. In other words, we are dealing with genes located in autosomes (see Heredity). The chromosomal complex of H. and sex determination. According to modern data by Painter (1923), as well as by Evans and Swezy (1929), confirmed by many other researchers, the chromosomal complex of H. consists of 24 pairs of chromosomes. The type of sex determination in H. is identical to that in Drosophila and belongs to the so-called Lygaeus type (see Heredity). Consequently in H. the male sex is digametic, which possesses heterochromosomes x and y; the female sex carries two x-chromosomes. Sex-linked heredity. I. Sex-linked heredity. Cytological data are in complete agreement with the heredity of traits linked to sex. This type of heredity includes diseases such as hemophilia, color blindness (see), atrophy of the optic nerve (atrophia nervi optici) and others. In this type of heredity, a male who receives an x-chromosome with the disease gene from his mother is always diseased (both with dominance and recessiveness of the trait), since the y-chromosome is apparently genetically inactive and does not carry alleles for the genes of the x-chromosome. Since the x-chromosome of such a diseased male cannot be passed to his sons (except in the case of 'non-disjunction' of the x-chromosome in the wife, which has never been described in humans), all sons will be healthy, unless their mother was heterozygous for the same gene. The daughters, however, will all receive one x-chromosome from the father, and although they will be externally healthy, since (in the case of recessiveness of the trait) the other x-chromosome received from the mother has a dominant allele of the same gene, they will be so-called conductors of this disease, i.e., its carriers. Therefore, the rule of Lossen is incorrect, according to which diseased males do not pass the disease to the next generation. The usually observed false limitation by sex, i.e., the absence of diseased women, perhaps can be explained by the extreme improbability of a marriage between a diseased male and a woman heterozygous for the same gene. According to another point of view (S. Levit), the possibility of limiting the hemophilia trait to the male sex is not excluded; then it is this, and not the recessiveness of hemophilia, that explains its non-manifestation in women. From the above it is obvious that in sex-linked heredity, in the case of marriage between two individuals who equally do not show the observable trait, the recessive gene located in the x-chromosome can be in a hidden state (x^Dx^R) only in women. In this case, in the offspring all women will be phenotypically normal (50% of the offspring), and among males only half will show the recessive trait (25%), while the other half of males will also not show it. Thus, the usual splitting (75% : 25%) will be observed, but the recessive trait will only affect the male sex (in 50% of it). In the case where the trait is present only in the father, if the wife is not a conductor of the recessive gene, i.e., her formula is x^Dx^D, all offspring without exception are normal; in the case where the wife is a conductor of the gene (x^Dx^R), the usual ratio of 1:1 is obtained, and the distribution of DR and RR is equally probable by sex. Finally, when the trait is manifested only by the mother (x^Rx^R), all daughters will be normal (x^Dx^R), and all sons will be recessive (x^Ry). Establishing the recessiveness or dominance of traits linked to sex genes is sometimes more difficult than for autosomal genes. In addition to the already mentioned frequent impossibility of comparing homozygous and heterozygous forms (so-called 'conditionally dominant' traits), another difficulty is added - in the absence of women showing the studied trait (hemophilia, myopic hemeralopia, etc.), i.e., with complete limitation of the trait to the male sex, it is impossible to distinguish a recessive trait from a dominant one. Therefore, it has been proposed (by S. Levit) to call such traits 'indeterminate.' And only upon finding women who have manifested the trait determined by a sex-linked gene in a heterozygous state (x^Dx^R) will it be possible to classify such a trait as dominant (fully dominant, intermediate or 'conditionally dominant'). Perhaps these difficulties of analysis determine the predominance among the studied traits linked to sex genes - recessive ones. However, the existence of dominant traits linked to sex genes is indisputable. II. Sex-limited heredity is observed in the case where the manifestation of a trait determined by such a gene is limited to one sex for physiological reasons. Thus, hypospady, although it is a dominant trait, manifests only in males. Unlike sex-linked genes, sex-limited genes can be located both in the sex chromosomes and in the autosomes. Recessive genes inherited with sex limitation are not yet known. The difficulty of finding such a recessive autosomal gene here is aggravated by its manifestation in only one sex. The third theoretically possible type of sex-influenced inheritance is so-called sex-influenced heredity. Such heredity can be observed in H. only if the gene is located in the y-chromosome. The only known case is the syndactyly of the feet described by Schofield (1922) - the formation of webs between the fingers. Syndactyly manifested only in males obviously because the y-chromosome with the supposed dominant gene in it is passed only to the male sex. However, this case cannot be considered proven and is recently being questioned. Heredity fixed for the female sex is obviously not possible. However, if cases of non-disjunction or association of x-chromosomes were observed in H., the so-called matroclinal heredity observed in these cases would be externally similar to heredity fixed for the female sex; at the same time patroclinal heredity would be observed. A possible case of this kind is the genealogy described by Cunier as early as 1838. In this genealogy, the trait of night blindness manifested exclusively in women, and all without exception. Very recently, an interpretation of this genealogy was proposed (by S. Levit and A. Serebrovsky) by analogy with a case known in Drosophila.

If we assume that in the original carrier of the gene for night blindness, located in the X-chromosome, during the maturation of the sex products the usual divergence of X-chromosomes does not occur, perhaps due to their constant connection (the so-called 'linked' X-chromosomes), then such a double X-chromosome will invariably be found in all female offspring. Thus, the matroclinical nature of the inheritance of night blindness in the case of Cunier can be explained. Inevitably, the single X-chromosome present in all male offspring will, contrary to the usual case, originate exclusively from the father. Therefore, all male offspring will exhibit traits determined by genes located only in this X-chromosome, and conversely, they will never exhibit any traits of the maternal X-chromosome. Consequently, patroclinal inheritance will be observed in them. Up to the present time, for humans there are no precisely established facts of linkage between genes located in the same chromosome. This is explained by the extremely high number of linkage groups in humans. Multiple allelomorphism. In all described cases of monomeric inheritance, we always deal with two states of one gene-dominant and recessive. As is known, in modern genetics it has been established that the same gene can give not only two allelomorphic changes, but theoretically many different allelomorphs. These series of multiple allelomorphs (or, as is now customary to say, alleles) usually give a whole range of expressions of the trait. Therefore, it is understandable that the finding of multiple allelomorphs in humans has great fundamental importance, as this way it may become possible to explain the so often observed diversity of 'family forms' of what seems to be the same hereditary disease. The phenomenon of multiple allelomorphism in humans is very little studied, but several more or less reliable facts in this area have already been established. Thus, in regard to color blindness, it has apparently been possible to establish two series of multiple allelomorphs. Color blindness manifests in the form of a series of distinct forms-protanopia, protanomaly, deuteranopia, deuteranomaly. Just (1925), Waaler (1927), and some others have established that these anomalies should be considered as following 2 series of allelomorphs: 1) normal vision > protanomaly > protanopia; 2) normal vision > deuteranomaly > deuteranopia. The allelomorphs are arranged in order of dominance. Thus, if in one X-chromosome of a woman the gene for normal vision is located, and in any other gene for color blindness, this woman will be phenotypically normal. However, if a woman carries simultaneously the genes for protanomaly and protanopia, she will be phenotypically protanomalous. Similarly, the same is observed with deuteranomaly and deuteranopia. That we are dealing not with one series of allelomorphs, but with two, follows from the fact that a woman carrying simultaneously one gene from each series, for example protanopia and deuteranomaly, will be phenotypically normal. This happens because these genes are located at different points of the X-chromosome, and therefore for each of them there will be in the other chromosome the gene for normal vision dominating over them. Another example of a series of multiple allelomorphs is the group of genes determining the agglutination properties of blood. Lethal factors. In general genetics, a large number of genes are known that phenotypically in the homozygous state prove to be lethal for the organism. Such factors are called lethal, and their action can theoretically occur at any stage of development. If the lethal stage falls on the embryonic period, then often such homozygous individuals for such a gene cannot be observed, and their presence can only be judged by the complete absence of homozygous forms and the change in numerical relations in segregation (2D : 1R instead of 3D : 1R). Usually such factors, the external manifestation of which remains unknown, are recessive, because in the case of partial dominance of the lethal factor, it is possible, however only partially, to judge its phenotypic manifestation by the heterozygotes. That recessive lethal genes do have phenotypic signs, speak the cases observed in domestic animals, when organisms containing such recessive lethal factors died after birth. If the lethal stage is shifted further into the post-embryonic period, then one usually speaks of semi-lethal genes, i.e. more or less less viable. Obviously, there is no fundamental difference between lethal and semi-lethal genes. Any trait, no matter how it is phenotypically expressed, can, for some physiological reasons, disrupt the viability of the organism. No clear lethal factors in humans have been discovered. Bauer (K. Bauer) believes that the absence of women with hemophilia, i.e. homozygous for the recessive gene of hemophilia, is explained precisely by the lethality of this gene in the homozygous state. However, this cannot be considered proven, since from this point of view it is surprising that recessive males do not show lethality. Meanwhile, this is generally observed in other animals (Drosophila). Mohr and Wridt (1919) discovered a special dominant gene for brachydactyly: in the marriage of two heterozygous parents, out of 2 children born, 1 was barely viable, a monster in whom fingers were absent on hands and feet and the entire skeleton was anomalous. They consider this child as homozygous for the brachydactyly gene. Although at present science possesses only negligible information about lethal factors in humans, their great role in human heredity is theoretically indisputable. Perhaps this will help to explain cases of high mortality of children in some families and genealogies. Theoretically, it should also be expected that a recessive lethal gene in the sex chromosome can lead to an abnormal sex ratio in the offspring (2♂ : 1♀). Polygenic inheritance. In the case of a more complex picture of segregation and the presence of a whole series of intermediate forms, it is usually assumed that we are dealing not with one pair of allelomorphic genes, but with two or more. More or less conditionally, three possible cases of polygenic inheritance are distinguished: 1) univocal factors or polymeria in the narrow sense of the word (according to another terminology: multiple factors, 'wheat type'-Avenatypus), when individual polymer genes act qualitatively and quantitatively more or less similarly; 2) polyhybridity, when polymer genes affect related traits, but the action of each of them is specific; 3) modifiers or as an extreme limit-pleiotropy, when genes affecting some basic trait for them are also related to another trait changed by them only indirectly and little specifically. As an example of univocal factors in humans, we can cite the inheritance of skin pigmentation. In crossing a white person and a Negro, melanistic skin dominates; however, a series of transitions between white and black skin is observed. For a long time, the opinion existed that in crossings of Negro and white, no segregation is observed, i.e. recessive white forms do not reappear in their pure form. However, Davenport managed to prove that such segregation is observed, but for its explanation it is necessary to assume at least 2 pairs of genes. Each pair of genes determines the presence or absence of a special pigment. The existence of another gene for skin thickness, which also affects the color, is also possible. Due to the observed dimery, a whole series of forms with two dominant pigment genes and with each separately is possible; the pure recessive form, i.e. white, should obviously be observed only in ¹/₁₆ of the offspring, which satisfactorily explains the rarity of such recessives. Polyhybridity. It is quite clear that simultaneously in a genealogy a whole series of genes can be transmitted and they form any combinations and segregations (see Genetic analysis). Thus, if non-allelomorphic genes affecting similar traits are encountered, their mutual combination can give rise to various complex traits, again breaking down in the offspring. Moreover, usually when two or more genes acting on close traits are combined, not a simple summation of their traits is obtained, but some new specific interaction. An example of an attempt to explain a hereditary disease by dimery is Rudin's interpretation of dementia praecox as a double recessive. This explanation was necessary for him to explain the rarity in the offspring of individuals with dementia praecox (about ¹/₁₆). In addition, dementia praecox is distinguished by great variability. However, at present it seems completely impossible to decide which phenotype corresponds to each formula of digybrid segregation in dementia praecox-form of double dominant, dominant for each gene separately, double recessive. Therefore, it is not surprising that other researchers interpret the formula of dementia praecox differently, considering it sometimes as one dominant and recessive, sometimes as homozygote in contrast to heterozygote.

A more reliable example of polyhybridism is the system of genes determining eye and hair color in humans. The presence of several eye color genes is assumed, for example, the gene for yellow pigment, the gene for intensity, the gene for gray eye color, and the gene for black eye color. However, it is important that, for example, the gene for black eyes can only exert its effect only with the simultaneous presence of both the gene for yellow pigment and the gene for intensity. Thus, if one of the latter is absent, then despite the presence of the black eye gene, the eyes will not be black but gray or blue. This explains the mysterious fact that sometimes dark-eyed children are born from light-eyed parents—different genes from both parents, which are in a latent state, will come together and a complex combination will arise in which the genes will manifest their effect. Thus, here we observe a complex interaction of genes, usually denoted by the terms 'epistasis' and 'hypostasis.' A gene that exerts its effect only in the presence of a number of others is called epistatic, as it masks the action of all the other interacting genes individually. If a hypostatic gene, i.e., the masked one, is absent, the epistatic one cannot manifest. In this case, another hypostatic gene, most epistatic to the others present, will manifest. Thus, epistatic and hypostatic genes can be arranged in a series of increasing epistatic strength (see also Genetic analysis). Pleiotropy and modifiers. Generally, it should be assumed that a certain gene is only conditionally a specific representative of a given trait. In any case, the gene does not determine the trait as a whole. Each trait is only conditionally isolated from the organism as a whole. Just as the latter developed in a unified process, the special influences of individual genes cannot be broken down into a simple sum of individual components. In view of this, the current point of view has come to be that of pleiotropy (see), which consists in the fact that the effect we observe of this or that gene is by no means its only influence. On the contrary, it is possible that we have not discovered the most important trait of this gene. In any case, practically at the present time it is not possible to establish all the traits for which this or that gene is responsible. Finally, it may be that every gene participates in the realization of all other genes and vice versa. In view of this, a whole gradation of genes can be found from extremely 'specific' to completely non-specific. The latter are usually called modifiers. The significance of modifiers in human heredity, although great, especially in heredity of diseases_?, however, at present there are no more or less satisfactory methods for their study. The mutation process. There is no reason to doubt that human genes did not exist eternally, but appeared at one time or another through mutation. Unfortunately, there are very few precise observations of the first occurrence of mutations in humans. A completely reliable observation of the first appearance of a mutation can be made only in the case of a properly dominant gene. Thanks to the absence of skips in the genealogy for such a gene, its appearance can be reliably attributed to the generation in which the mutant occurred from normal parents, usually in a single case. At present, a larger number of genealogies traced over several centuries are known. Thus, Heck traced the heredity of the dominant trait of prognathic jaw in the Habsburgs. He found a continuous transmission of this trait, starting from one duke who died in 1424. Drinkwater reports the genealogy of an Englishman with the dominant gene for fusion of the finger joints, who is a descendant of John Talbot, killed in 1453; upon examination of the latter's skeleton, the same anomaly was found. Night blindness (hemeralopia) has been traced by Netlship to Jean Nougare, born around 1637. Weil traced the inheritance of diabetes insipidus to Schwarz, born in 1772. As we see, in all these cases, despite establishing the antiquity of dominant genes for almost 500 years, it was not possible to reliably establish the time of the first appearance of the genes. More or less reliable cases refer to the appearance of a claw-like limb—a dominant gene. This is all the more plausible as several such cases apparently of completely independent origin have been described, for example in England and in the USSR. The first appearance of the gene refers to 4-5 generations before the present time. Also apparently reliable is the case described by S. Levit and N. Malkova, of the appearance of a special dominant, autosomal gene for bleeding—haemophilia—a. The mutation manifested in one woman (4 generations ago), born from normal parents. Subsequently, the gene shows no skips. The first appearance of a gene in the X chromosome can be established with relatively certainty, since when it appears in a male, it will immediately manifest the traits of this gene even in the case of its recessiveness. In the case of the appearance of a gene in one of the X chromosomes of a woman, in the very next generation half of her sons will manifest the gene. However, if the offspring of such a woman contains no sons at all or all of them turn out to be carriers of only one unchanged maternal X chromosome, the mutation will not be detected immediately but after one or more generations in the offspring of daughters. Genes of the sex chromosome have also been traced very far back, for example, color blindness was already known in the 18th century. However, a reliable case of first appearance is apparently unknown. The first occurrence of an autosomal recessive trait cannot be established with certainty, since for the manifestation of such a gene, segregation as a result of a related marriage is necessary. Before the moment when such a related marriage between heterozygotes would become probable, a long period of greater or lesser 'saturation' of the population with the recessive gene, remaining all the time in a latent state, must have passed. Cases of centuries-long transmission of recessive genes in a latent state are known. In view of this, it is impossible to reliably establish the first heterozygous form with a latent recessive gene. Hanhart claims that he has traced the gene of recessive Friedreich's ataxia to its first carrier, a heterozygote in 1640, however this claim cannot be proven. In any case, the amplitude of the mutation process in humans is quite high. This is evidenced by the very large number of independent recurrent or similar genes found in individual genealogies. Thus, a huge number of different forms of brachydactyly are known—shortening, fusion, absence of individual phalanges of all or certain fingers. Several cases of independent origin of the gene for claw-like limbs have already been mentioned above. The phenomenon of recurrent mutations is of considerable theoretical interest, especially for pathology, since very diverse familial forms of the same disease are often observed. Similar mutations can be attributed to one of the following three types: 1) Recurrent mutations, i.e., cases when a gene localized in the same point of the same chromosome mutated two or more times, and their phenotypic traits completely coincide. 2) Series of multiple allelomorphs, i.e., cases similar to the previous one, however with the difference that the phenotypic manifestation (including the nature of dominance) does not coincide; all multiple allelomorphs usually represent different degrees of expression of similar traits. 3) Phenotypically similar mutations—cases of similarity of two mutations that occurred with different genes in one or different chromosomes; the similarity of such genes can reach the practical (and perhaps theoretical) indistinguishability of their effect. As an example of the latter type, hemeralopia can be cited, which is known in dominant, recessive, and sex-linked forms. It goes without saying that when two such forms, similar only phenotypically, enter a genealogy, they will not behave as allelomorphs and a complex, confused picture of inheritance will be observed. The question of the causes of the mutation process in humans is even less developed than in animals (see Mutation). In any case, the role of external factors causing mutational changes directly in the sex cells is fundamentally assumed (see Heredity). The discovery by Müller of the induction of mutations by X-rays and radium rays raises a serious question about the influence on humans of therapy with X-rays. It must be kept in mind that the doses that cause mutations do not give an external effect in the irradiated individual, and therefore one cannot in any way speak of the harmlessness for offspring of irradiations that have not caused an external effect. Apparently, with increasing hardness of the rays, their influence on the sex cells also increases. Careful observations of the influence on offspring of X-ray therapy need to be established.