Biology and sexual orientation INAH3 weight for the heterosexual male brains was significantly larger than for the heterosexual female brains, while the results for the gay male group were between those of the other two groups but not quite significantly different from either. The neuron count also found a male-female difference in INAH3, but found no trend related to sexual orientation. A 2010 study, Garcia-Falgueras and Swaab asserted that "the fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge.
Male reproductive system during puberty causes the male secondary sexual characteristics to be manifested. the manifestation of secondary sexual characteristics include the growth of: Secondary development includes the increased activity of the eccrine sweat glands and sebaceous glands along with the darkening of the skin in the scrotal region. Chromosomal abnormalities can occur during fertilization impacting the development of the male reproductive system. The genotype of the male consists of a Y chromosome paired with an X chromosome. Female gender is determined by the absence of a Y chromosome. Some individuals are male who have the XX male syndrome and androgen insensitivity syndrome.