Cooking

No, it was not the division of labour that made us.

Cooked food, by contrast, is easier to digest, gives you more energy, and
takes no time to eat. Cooking also kills bacteria and renders many natural
poisons inactive. So the simple expedient of heating food gave us access to many
more safe calories every day, which was a survival jackpot. Once we started to
eat soft, cooked food, our jaws and teeth were no longer required to munch
ceaselessly, and they became smaller and more delicate. That is why we don't
look like apes anymore. Similarly, the more cooked food we ate, the less
industrial-strength digestion we had to do, and the smaller our guts became. In
the same way that our bodies evolved to better walk on two legs, our bellies
changed to better handle well-done over rare.