Editing Sexual orientation (section)

==== Hormones ====
{{Main|Prenatal hormones and sexual orientation}}

The hormonal theory of sexuality holds that just as exposure to certain hormones plays a role in fetal [[sex differentiation]], hormonal exposure also influences the sexual orientation that emerges later in the adult. Fetal hormones may be seen as either the primary influence upon adult sexual orientation or as a co-factor interacting with genes or environmental and social conditions.<ref name="BornGay-passim">Wilson, G., & Q. Rahman, ''Born Gay: The Psychobiology of Human Sex Orientation'', ''op. cit.''</ref>

For humans, the norm is that females possess two X sex chromosomes, while males have one X and one Y. The default developmental pathway for a human fetus being female, the Y chromosome is what induces the changes necessary to shift to the male developmental pathway. This differentiation process is driven by [[androgen]] hormones, mainly [[testosterone]] and [[dihydrotestosterone]] (DHT). The newly formed testicles in the fetus are responsible for the secretion of androgens, which will cooperate in driving the sexual differentiation of the developing fetus, including its brain. This results in sexual differences between males and females.<ref>{{cite journal|last=Siiteri|first=PK|author2=Wilson, JD |title=Testosterone formation and metabolism during male sexual differentiation in the human embryo.|journal=The Journal of Clinical Endocrinology and Metabolism|date=Jan 1974|volume=38|issue=1|pages=113–25|pmid=4809636|doi=10.1210/jcem-38-1-113}}</ref> This fact has led some scientists to test in various ways the result of modifying androgen exposure levels in mammals during fetus and early life.<ref name=Levy>{{cite book|last1=LeVay|first1=Simon|title=Gay, Straight, and the reason why. The science of sexual orientation.|date=2011|publisher=Oxford University Press|isbn=978-0-19-993158-3|pages=45–71, 129–56}}</ref>