What Is the Definition of the Word Human?

What defines humanity? Is it the fact that we can walk upright on two legs? That we have brains big enough to use tools? That we can organize our societies well enough to find wonderful ways of exploiting the resources of the planet — and each other?

While the answer may seem clear enough to anyone who doesn’t think too closely about it, anthropologists — the scientists who actually study humans — aren’t necessarily so certain.

“We’re using this term and it’s not quite colloquial and it’s not quite scientific either,” says Sheela Athreya, a biological anthropologist at Texas A&M University. It also depends on what exactly you’re talking about when you use the word “human.”