...femininity in boys and homosexuality in men are probably caused by incomplete masculinization of the brain during sexual differentiation. - J. Michael Bailey

Once you've learned about autogynephilic and homosexual transsexuals and seen several of each, distinguishing them is easy.

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.

The bad trend is that scientists and laypeople both think that there is something more impressive about biological markers—a trait that one can measure with a ruler or a blood test or complicated electronic equipment (I'm serious, there is no better definition of “biological marker”)—than there is about psychological or behavioral markers. This is a mistake.