Let's open up the discussion, shall we?
Epigenetics and evolution: ‘the significant biological puzzle’ of sexual orientation | Science | The Guardian
A taster, taken from the article:
"I cheerfully taught it in my first-year biology classes for more than two decades, in full knowledge that the story is more complex. For example, if an individual’s testosterone production is defective, a genetic male (based on their possession of a Y chromosome and SrY gene) will develop as a female. Indeed, such individuals may be hyper-female, since they do not produce or respond to testosterone, whereas genetic females do both.
"Even more extraordinary is a rare syndrome caused by a deficiency of the enzyme 5α-reductase. This enzyme converts testosterone to a more potent male-determining hormone. These kids, who are chromosomally male, are born with female-like genitalia and are often raised as girls. They then change to the male phenotype at puberty with its associated release of testosterone. Not only do male foetuses produce more androgens than female foetuses, they respond to it more strongly due to sex-specific epigenetic marks in genes that code for androgen receptors. Conversely, female foetuses produce less androgen and have reduced responsiveness to it. It is even possible for a genetically female foetus to have levels of circulating androgens in the male range but still develop as a female. So, while the primary cause of male bodies from female bodies is indeed SrY, other genes on the sex chromosomes can modify its effects."