Transsexuals and transgendered people can often tell us a great deal about our society because they've experienced what most of us never will: being perceived as a man or a woman in the same lifetime.

A worthy read on this topic is Kate Bornstein's Gender Outlaw, which chronicles some of her experiences as a transsexual woman. One memorable passage describes the first time Kate walked into a store after being able to successfully pass as a woman. She was shocked to find that nobody was treating her with any respect. A so-called "normal" woman who's been a woman her entire life would never know the difference.

Ben A. Barres, a neurobiologist who happens to be a transsexual man, wrote a commentary for Nature about sex differences in scientific ability. Barres started out his career as a female scientist and then transitioned to being male. Consequently, he personally experienced how differently people treat male and female scientists. Largely spurred by the Larry Summers controversy, Barres' article makes a convincing case against purely biological explanations for gender differences. If you're interested, the full article can be viewed here.