Understanding Sexual Dimorphism and Gender in Humans
28. Inducing Levels of Sexual Dimorphism and Female Pattern Endogenous in Humans
Sexual dimorphism is defined as variations in external appearance related to sex, such as shape, color, or size between males and females of the same species. Sexual dimorphism has implications for concepts of sex and gender in humans. Sex is a variable that involves some sexual differentiation processes that extend throughout the life cycle, involving biological, psychological, and social factors that are in constant mutual interaction, resulting in what we call men, women, or individuals with an ambiguous situation of sex. On the other hand, gender refers to those characteristics considered socially appropriate for females and males within each given society (Fernández, 1996).
The components of both concepts, sex and gender, are gradually revealed throughout this century: the genetic, hormonal conditioning, control brain mechanisms of sexual offense, and the impact of social factors, just to highlight some of those that have received more attention from researchers (Money and Ehrhardt, 1972). You can set a three-pronged approach/level for proper analysis of both realities, sex and gender (Fernández, 1991):
1. Structural Level
This level enables a detailed analysis of the components of each domain, thanks to contributions from each and every one of the disciplines engaged in its study: genetics, endocrinology, neurology, psychology, sociology, anthropology, and sexology.
2. Functional Level
From this level, you can concatenate all this knowledge from the previous level, which is usually juxtaposed.
3. Interactive Level
This level tries to realize the general idea of these concepts and highlights the need for interaction of both domains (sex and gender) in the evolution of the individual.
The development of sex through the prenatal period is performed in three stages or levels: genetic, gonadal, and genital.
At the Genetic Level / Chromosome
Human development begins with the fertilization of gametes, when a male gamete or sex cell penetrates the membrane of a female gamete. Each gamete contains half the genetic information from each parent. Every human being has 46 chromosomes, 23 inherited from each parent. The 23rd pair determines the individual’s biological sex. The karyotype is 46, XY in males and 46, XX in females. Therefore, the mother always transmits X, while the father transmits either an X or Y, which determines the sex of the fetus.
At the Embryonic Stage
This stage refers to the period from fertilization to 6-7 weeks. During this period, the development is equal for both XX and XY configurations. The embryo has a primitive pair of gonads that can develop into testicles or ovaries, and two sets of sexual ducts that coexist: the Wolffian and Müllerian ducts, precursors of the male and female reproductive tracts, respectively. From the 6th week, if no changes occur, a morphogenesis will take place that consists of regression and the persistence and differentiation of the other. The Y chromosome genetic entity, called the testis differentiation factor (TDF), promotes the primitive gonad to develop into testicles.
Hormonal Levels
The fetal testis synthesizes a variety of hormones, particularly androgens, which induce somatic differentiation. The most important of these hormones is testosterone, which causes maturation of the Wolffian ducts and inhibits the Müllerian ducts, leading to the development of the seminal vesicles, prostate, and deferent ducts. Testosterone is also responsible for the formation of male external genitalia, such as the penis and scrotum.
The pattern of human endogenous development suggests that nature defaults to female unless the Y chromosome is present or functioning correctly. This development does not require female hormone intervention to induce this process. From the primitive gonads, the ovaries and Müllerian ducts develop into the fallopian tubes, uterus, and outer third of the vagina. It is possible for an individual to have a female appearance despite having a Y chromosome if the testis has not formed or due to other causes. If, by week 12, there is no differentiation, even with a Y chromosome, the embryo will develop into a female fetus. Therefore, the XY configuration is fragile, revealing stronger female characteristics embryologically speaking.
This contrasts with the Freudian theory of psychoanalysis, which proposed a so-called castration complex in women, as if they were missing something that men possess. Further investigation has shown that the penis is an enlargement of the basic female sex organ.
In the brain, there is greater dimorphism in more evolved species. Animal experiments have discovered the effect of androgens on sexual differentiation. For instance, the application of testosterone to females born after birth had a significant effect. When androgens were injected into pregnant mothers, as demonstrated by Phoenix in 1959, the female offspring of rats exhibited fewer female behaviors, such as lordosis, and demonstrated greater male behaviors, such as mounting. Additionally, Whalen in 1963 found that estradiol administration to genetic females neonatally suppressed ovulation and female behavior patterns. This is because testosterone, when it reaches the brain, is transformed into estradiol, which is responsible for defeminization.
Androgenization in humans is difficult to study and can only be done in exceptional cases. The success of synthetic progestin, a hormone that was used in the 1950s for pregnant women and later banned, is one such case. The progestin caused fetal androgenization in XX individuals during pregnancy. It did not affect identity or gender role but produced nuances in behavior: more intense physical activity (stronger physically), rougher play, and competitive games with less use of dolls, as well as less attention to personal appearance.
On the other hand, there is androgen insensitivity, which affects the XY configuration. Individuals with this condition lack receptors for androgens. They develop testes that secrete testosterone and antimüllerian hormone, thus having a male karyotype, but their bodies do not respond to the androgens secreted. Externally, they acquire a female physiognomy, developing breasts during puberty, but they may not have a vagina or may only have the outermost third. Their phenotypic traits are female, but genotypically they are male.
“Sexual orientation is not chosen; you choose sexual experiences. There are few people in something unique to their orientation.” (Torres, Classes of Psychology Degree, 2010)