In the old days, it seemed simple: Men hunted and women bore and raised kids. Then we moved out of caves, invented gender studies, and learned a thing or two about genetics. Now nothing is clear cut. While social and biological analyses of gender offend some, they have freed others to finally feel comfortable in their own skin. Whether you're gay or straight, transgender or cisgender, or just curious about why men and women treat each other the way they do, there's something in here for you.