The androgen receptor gene, which dictates how the body responds to hormones like testosterone and DHT, is located on the X chromosome. Since men (XY) inherit their X chromosome from their mother, their genetic predisposition for androgen sensitivity is maternally inherited.

The 2D:4D finger length ratio is a marker for prenatal testosterone exposure. On average, lesbians exhibit a more masculine ratio (shorter index finger relative to ring finger) than straight women, suggesting a biological influence on sexual orientation established in the womb.

Unlike personal trauma, generational trauma has a biological component passed down via epigenetics. A mother's chronic stress can alter her gene expression, creating a predisposition for stress vulnerability that is genetically transmitted to her child.

Studies on 2D:4D finger ratios, a proxy for prenatal androgen exposure, found no average difference between gay and straight men. This challenges the "under-androgenized" stereotype and suggests orientation differences may stem from the brain's response to testosterone, not the hormone level itself.

Otoacoustic emissions, tiny sounds produced by the inner ear, show a sex difference at birth. Studies found lesbians have fewer emissions than straight women, a pattern closer to males. This suggests prenatal testosterone, which influences these emissions, also plays a role in shaping sexual orientation.

Scientific evidence suggests that a mother's feelings toward her fetus can imprint a core sense of self before birth. This is demonstrated by a case where a newborn rejected its mother's milk because the mother secretly had not wanted the child.

The "rich gay uncle" hypothesis suggests homosexuality persists by shifting reproductive effort. Instead of having their own children, gay men may invest heavily in their siblings' offspring, promoting the survival of shared genes through kin selection. This is supported in some, but not all, cultures.

It's a myth that all cells are a 50/50 blend of parental DNA. Neuroscientist Catherine Dulac's work shows that entire brain areas can be genetically identical to either the mother or the father. This explains why certain behaviors and traits are so strongly inherited from one parent.

Hormones shape brain circuits not just for attraction but also for aversion. This is seen in some male sheep ("gay rams") that consistently refuse to mount females, suggesting a powerful aversive component to their sexual preference, rather than just a lack of attraction.