Many species can even change sex, with fish topping the gender-bender list.26 That might be acceptable for animals, but a transgender human who decides to have a sex change operation is abhorrent to most people—because transgender individuals violate our natural view of humans as being either male or female, a property fixed from birth. In truth, many of our intuitive biological boundaries, such as gender, are more apparent than real. There is much more shared similarity and common origins than we appreciate. And if you don’t believe me, ask yourself this: why do men have nipples?27
