Hm, I believe that most socially induced gender-specific behaviours have a natural, physical basis. Of course, many, if not all, of them are exponentially reinforced by culture, some of them probably having such a little difference that they would often overlap without the effects of culture, but becoming very distinct in reality... But hormones, and perhaps genetics, play an undeniable role, I'd say.
Also, even though putting any trace of placebo effect aside is impossible, I'm pretty sure that my aggressive behaviours were greatly reduced with starting HRT. There are surely many similar (and reverse for FTMs) experiences in other trans people.
But anyway, I'm almost sure that testosterone is associated with risk taking.
...But aren't we -really- derailing the thread?