Gay brains structured like those of the opposite sex - life - 16 June 2008 - New Scientist
Brain scans have provided the most compelling evidence yet that being gay or straight is a biologically fixed trait.
The scans reveal that in gay people, key structures of the brain governing emotion, mood, anxiety and aggressiveness resemble those in straight people of the opposite sex.
Psychiatry and LGB people
Despite almost a century of psychoanalytic and psychological speculation,
there is no substantive evidence to support the suggestion that the nature of parenting or early childhood experiences have any role in the formation of a persons fundamental heterosexual or homosexual orientation (Bell and Weinberg, 1978).
It would appear that
sexual orientation is biological in nature, determined by genetic factors (Mustanski et al, 2005) and/or the early uterine environment (Blanchard et al. 2006). Sexual orientation is therefore not a choice, though sexual behaviour clearly is.
Epigenetics may be a critical factor contributing to homosexuality, study suggests
The study solves the evolutionary riddle of homosexuality, finding that
"sexually antagonistic" epi-marks, which normally protect parents from natural variation in sex hormone levels during fetal development, sometimes carryover across generations and cause homosexuality in opposite-sex offspring. The mathematical modeling demonstrates that genes coding for these epi-marks can easily spread in the population because they always increase the fitness of the parent but only rarely escape erasure and reduce fitness in offspring.
"Transmission of sexually antagonistic epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality," said the study's co-author Sergey Gavrilets, NIMBioS' associate director for scientific activities and a professor at the University of Tennessee-Knoxville.