Interestingly, LeVay’s finding builds
on the group discovery of the neuroscientist Dick Swaab’s, at the Netherlands Institute for Brain Research in Amsterdam. Swaab’s
team found that the suprachiasmatic nucleus (SCN), a part of the brain that governs daily rhythms, is twice as large in homosexual
men as it is in the typical heterosexual brain. At the same time, another scientist, Laura S. Allen made a similar discovery
in the hypothalamus as well. She found that the anterior commissure (AC) of the hypothalamus was also significantly larger
in the homosexual subjects than that of the heterosexuals. However, while it might be influenced by the same factors that
cause homosexuality, it is less likely than the anterior hypothalamus to be part of the cause. Then the question is, what
causes the difference in the development of this part of the brain? A possible answer comes from studies in rats, which also
have a sexually dimorphic area in their anterior hypothalamus, larger in males than in females, that governs sexual behavior.
In rats, the development of the area is dependent on testosterone levels before and immediately after birth. Male rat pups
that are castrated at birth have reduced testosterone levels and have a smaller sexually dimorphic nucleus than normal males;
when they grow up they show less male-type sexual behavior, such as mounting. Testosterone injections enlarge the nucleus
in female pups. The resulting adults show more “male” sexual behavior.
Another research conducted to support the
biological argument is the neuroendocrine studies. The neuroendocrine viewpoints’ basic hypothesis is that sexual orientation
is determined by the early levels (prenatal) of androgen on relevant neural structures. If highly exposed to these androgens,
the fetus will become masculinized, or attracted to females. This research was conducted on rats at Stanford
University. The adult females rats that received male-typical levels of androgen
sufficiently early in the development exhibited male symptoms of attraction. The same was true in the reverse when applied
to the male subjects. The female exposed to high levels of the hormone exhibited high levels of aggression and sexual drive
toward other females, eventually trying to mount other females in an attempt to simulate the act of reproduction. In males,
the subject who received deficient level of androgen became submissive in matters of sexual drive and reproduction and were
willing to receive the sexual act of the other male rat.
Another interesting finding
from McMaster University has found that lesbians are twice as likely as heterosexual women to show left hand preference on
a variety of tasks (gay men show such tendency as well). Studies of people with abnormal sex-hormone levels suggest that handedness
is a brain feature that can be influenced by sex hormones during brain development. Furthermore, depending on levels and timing,
sex-hormones could influence handedness, sexual orientation, or other characteristics.