This summer, in the introductory course I teach on the evolution and biology of human and animal behavior, I showed my students a website that demonstrates how to identify frog “genders.” I explained that this was a misuse of the term “gender”; what the author meant was how to identify frog sexes. Gender, I told the students, goes far beyond mere sex differences in appearance or behavior. It refers to something complex and abstract that may well be unique to Homo sapiens. This idea is nothing new; scholars have been saying for decades that only humans have gender. But later that day I began to wonder: Is it really true that gender identity is totally absent among nonhuman species — even our closest evolutionary relatives, chimpanzees and bonobos?
Before tackling this question, it is necessary to define “sex” and “gender.” Sex refers to biological traits associated with male and female bodies. Sex isn’t a perfect binary, but it is relatively simple compared to gender.
Gender is multifaceted, complex, and a little abstract, and not everyone agrees on exactly what it means. That said, there are a couple of aspects of gender that most experts say are essential. The first is the existence of socially determined roles. Gender roles refer to the range of behaviors that society deems normal or appropriate for people of a particular gender based on their designated sex — the norms that (at least in many Western cultures) cause us to expect men to be assertive and brave, and women to be caring and accommodating, for instance.
It’s common for people to believe that gender roles are natural or innate, ranging from religious claims that they are God-given to the argument made by evolutionary psychologists that they are the biological result of natural selection. On the contrary, while some aspects of gender-correlated behaviors are probably largely genetic in origin (researchers don’t have a great sense of which are and aren’t), most experts agree that many gender-related expectations, such as that girls play princess and boys pretend to be soldiers, are socially determined — that is, we learn them from our culture, often without even being aware of it. This socially learned aspect is as fundamental to gender as the roles themselves.
