The bad trend is that scientists and laypeople both think that there is something more impressive about biological markers—a trait that one can measu… - J. Michael Bailey

When most people hear “environment,” they automatically think of the social environment, such as how children are raised or what kind of interpersonal experiences they have. But to a geneticist “environment” means anything not encoded in DNA, and this includes biological factors as well as social factors: diet, germs, and random biological events might also affect development. For example, when one identical twin is born with a major brain defect such as anencephaly (lack of a cerebral cortex, or outer brain) or microcephaly (a very small cortex), the other twin is usually normal. Only environment can cause identical twins to differ, but the environmental problem in this case is biological.

Another environmental hypothesis that has received some enthusiasm on the political right is the idea that gay people seduce and recruit. I have never understood how this is plausible. A boy with no interest in homosexual activity wouldn't find it pleasant even if he agreed to it. How is this supposed to turn him gay?

The fact is that we don't know enough about hormonal effects on the human brain to have a very specific theory of how Danny's brain could have developed in a feminine direction while his body developed masculine. If Danny's body also showed signs of feminine development, this would support nature theory, but the lack of anatomical femininity does not disprove it. There has been essentially no research on boys like Danny that is directly biological. Short of dissecting the brain of a feminine boy and comparing it with normal boys' and girls' brains, it is unclear what we would even look for. However, the best conceivable direct test of nurture theory has been tried, and it failed. Amanda became Jason again.