“When speaking about humans, I find it's helpful to distinguish between social categories and biological categories. "Men" and "women" are social categories. We have the freedom to decide who counts as a man and who counts as a woman. The criteria change from time to time. In some circles, a "real man" can't eat quiche. In other circles, people seize on physical traits to define manhood: height, voice, Y chromosome, or penis. Yet these traits don't always go together: some men are short, others are tenors, some don't have a Y chromosome, and others don't have a penis. Still, we may choose to consider all such people as men anyway for purposes like deciding which jobs they can apply for, which clubs they can join, which sports they may play, and whom they may marry. For biological categories we don't have the same freedom. "Male" and "female" are biological categories, and the criteria for classifying an organism as male or female have to work with worms to whales, with red seaweed to redwood trees. When it comes to humans, the biological criteria for classifying an organism as male or female don't coincide 100 percent with present-day social criteria for man and woman. Indeed, using biological categories as though they were social categories is a mistake called "essentialism." Essentialism amounts to passing the buck. Instead of taking responsibility for who counts socially as a man or woman, people turn to science, trying to use the biological criteria for male to define a man and the biological criteria for female to define a woman. However, the definition of social categories rests with society, not science, and social categories can't be made to coincide with biological categories except by fiat.”