Sexual Differentiation and its Effects on Sexual Orientation
What controls a human's sexual orientation? The long-standing debate of nature versus nurture can be extended to explaining human sexual orientation. Is it biological or environmental? The biological explanation has been gaining popularity amongst the scientific community although it is only based on speculations. It is argued that sexual orientation is linked to factors that occur during sexual differentiation. The prenatal exposure to androgens and their affect on the development of the human brain play a pivotal role in sexual orientation (2). Heredity is also part of the debate. Does biology merely provide the slate of neural circuitry upon which sexual orientation is inscribed? Do biological factors directly wire the brain so that it will support a particular orientation? Or do biological factors influence sexual orientation only indirectly?
Gender is determined by the sex chromosomes, XX produces a female, and XY produces a male. Males are produced by the action of the SRY gene on the Y chromosome, which contains the code necessary to cause the indifferent gonads to develop as testes (1). In turn the testes secrete two kinds of hormones, the anti-Mullerian hormone and testosterone, which instruct the body to develop in a masculine fashion (1). The presence of androgens during the development of the embryo results in a male while their absence results by default in a female. Hence the dictum "Nature's impulse is to create a female" (1). The genetic sex (whether the individual is XX or XY) determines the gonadal sex (whether there are ovaries or testis), which through hormonal secretions determines the phenotypic sex. Sexual differentiation is not driven by the sex chromosomes directly but by the hormones secreted by the gonads (3).
Hormones are responsible for sexual dimorphism in the structure of the body and its organs. They have organizational and activational effects on the internal sex organs, genitals, and secondary sex characteristics (1). Naturally these effects influence a person's behavior not only by producing masculine or feminine bodies, but also by causing subtle differences in brain structure. Evidence suggests that prenatal exposure to androgens can affect human social behavior, anatomy, and sexual orientation.
Androgens cause masculinization and defeminization of developing embryos. Masculinization is the organizational effect of androgens that enables animals and humans to engage in male sexual behavior in adulthood. This is accomplished by stimulating the development of neural circuits controlling male sexual behavior (1). Defeminization is the organizational effect of androgens that prevents animals and humans from displaying female sexual behavior in adulthood. This is accomplished by suppressing the development of neural circuits controlling female sexual behavior (1). For example if a female rodent is ovariectomized and given an...