Separation is a global phenomenon of human sexuality. Sexual dimorphism is manifested in a wide range of morphophysiological and behavioral differences between a man and a woman, but its essence is in the peculiarities of the reproduction process. Sexual reproduction provides the most progressive type of reproduction in the evolutionary series. There is a rapid emergence of new genetic combinations that greatly facilitate their carriers to adapt to changing environmental conditions, and the males and females perform different functions in this process. According to the theory of V.A. Geodakyan, the process of self-reproduction of any biological system includes two opposite trends: heredity and variability. Heredity is a conservative factor that seeks to keep all parental characteristics in the offspring unchanged.

Variability is a quality due to which each next generation, in order to adapt to a changing life, has new signs, that is, a person evolves. Moreover, individuals of the female form a kind of “golden pantries” of heredity, ensuring the continuity of offspring from generation to generation. On the contrary, males are the vanguard of the population, which takes on a collision with extreme situations, new conditions of existence, as a result of which new genetic tendencies arise. Thus, in the process of phylogenesis, that is, the historical development of the human population, the male sex plays the main role in its change, and the female sex in preservation.

Geodakyan’s theory well explains some facts of natural sexual selection, for example, increased mortality among males, who account for maximum external influences, which is why they are much more likely to become victims of unsuccessful “experiments” of nature and man himself, summarizing numerous data, notes that the sex ratio at the zygote level (fertilized egg) is 1.2–1.7 (120–170 male fruits per 100 female), and the secondary (at birth) 1.03– 1.07. Male fetus is more vulnerable in the first trimester of pregnancy. The tertiary sex ratio, on the contrary, changes in the direction of women, since among men there is a higher mortality rate due to congenital defects and various diseases.

American sexologist D. Mani (1955) identified a number of patterns of sexual differentiation, which he presented in the form of the following principles.

The principle of differentiation and development means that the development of an organism is at the same time a process of its differentiation, during which the initial bipotential embryo becomes an individual male or female. This principle is directed against the notions of linear evolution, according to which, in the course of development, only one – the only set of possibilities inherent in the embryo is realized. He also refutes the theories according to which the sexual and sexual identity of an individual is determined primarily by the characteristics of the environment and upbringing.

The principle of stadial (sequential) differentiation: the process of individual development has its own natural stages, where each subsequent differentiation is based on the previous one (the genetic dimorphism of the sex chromosomes precedes the differentiation of the gonads, which in turn determines the hormone sex of the embryo, etc.).

The principle of critical periods emphasizes that each stage of sexual differentiation corresponds to a certain period of development, when the body is most sensitive to specific effects. If the critical period is missed for any reason, then the consequences are usually irreversible.

Thus, the differentiation of the embryonic gonads, which is controlled by the sex chromosomes, occurs normally only in cases where the genetic code recorded in the chromosomes can fully manifest itself during the critical period set aside for this (6-7 weeks of intrauterine development). Violations of the genetic code can change the entire process of sexual differentiation at this stage.

The principle of Adam (complementarity of masculine differentiation) means that nature is primarily concerned with the creation of the female individual. Therefore, at all critical stages of development, if the organism does not receive additional signals or commands, differentiation automatically proceeds according to the female type. In order for a man to be born, it is necessary to suppress the initial feminine principle at different stages of fetal development. Initially, it is N-Y-antigen, which helps the transformation of the germinal genital glands into the testicles. They, in turn, begin to produce testosterone, which converts the wolf ducts to the male genitals. In addition, a special SRY-gene activates the embryonic testicles to produce an anti-Mullerian hormone, which inhibits the conversion of Mullerian ducts into female genitals. Since the creation of the male individual requires additional efforts, it often makes mistakes, that is, the male path of development is more vulnerable to changes and environmental impacts. It is known, for example, that mental retardation, learning problems, some forms of speech pathology and deviations in sexual behavior are found in men significantly more often than in women. In addition, this is another explanation for the increased mortality of men and their susceptibility to a variety of diseases.

Sexual dimorphism explains the higher adaptability (plasticity) of females, their better learning, reducibility, conformity. Men are distinguished by ingenuity, ingenuity, ingenuity. Therefore, the tasks that are set for the first time, but in solving them, are the main requirements for novelty, and not for perfect execution, more on the shoulder of men, whereas with familiar tasks that require a minimum of novelty, but the maximum of perfection, women cope better. Sex differences also appear in polodimorphic (sex-role) behavior. It is well known that boys, as a rule, are more mobile, pugnacious, less affectionate, more often participate in power-based competitive games, toys are preferred by designers, cars, weapons, etc. At the same time, girls are calmer, love to play the dolls, the family, are more likely to help the mother with the housework, take care of the younger children, etc.

Subsequently, sex-role differences persist. Men choose professional activities more often associated with technology, abstract concepts, career, prestige, high earnings. They are more rational in their actions, not inclined to sentimentality. Women are much more likely to need to satisfy their emotional needs: tenderness, love, respect, etc. However, it would be wrong to associate the formation of people’s behavior exclusively with biological differences between men and women. For example, the laws of the social division of labor and the associated psychological characteristics of the sexes are historical and do not follow from the characteristics of their psychophysiology. For a long time M. Mead explored the lives of three tribes in New Guinea and convincingly showed that in each of them men and women performed completely different roles, sometimes diametrically opposed to generally accepted stereotypes. Apparently, sex roles are formed not only and not so much due to the biological differences between men and women, but based on the cultural and social characteristics of the era and society.

Modern biology states the presence of gender differences at all levels of development and functioning of the body. At the same time, it would be a great simplification to divide all human properties into two polar categories: male or female. Along with mutually exclusive properties (the same subject cannot normally have both male and female genitalia) there are many bisexual qualities inherent in persons of both sexes. This is true for both somatic and behavioral properties, which do not always coincide.

The concept of “sexual dimorphism” did not at first distinguish between genetic, hormonal, morphological, behavioral, and psychological differentiation of individuals, since it was assumed that all these measurements coincide and are determined by the same reasons. Until now, according to the physique of the individual, they are trying to determine his sexual preferences. However, sex differences in the psyche may not coincide with morphological signs. You should also not absolutize the psychological characteristics of the carriers of a particular sex. Sexual dimorphism allows and even assumes a variety of individual psychological variants of masculine and feminine character and lifestyle.