In the new and excellent sci-fi film Ex Machina, Ava (Alicia Vikander), an android with a marvelous chin, admires the chin on the face of a former operating android. An android is a robot in the form of a human.
In the new and excellent sci-fi film Ex Machina, Ava (Alicia Vikander), an android with a marvelous chin, admires the chin on the face of a formerly operating android. An android is a robot in the form of a human. A24 Films

Humans are the only ape with a protruding bone that forms the facial feature we call a chin. Even extinct apes like the Neanderthals did not have them. What can this mean? The answer appears to be found not in the mechanics of the mouth, or as an adaptation for the pressing needs of chewing. (Quick note: In the book Catching Fire: How Cooking Made Us Human, Richard Wrangham, a British primatologist, points out that one of the consequences of cooking is that humans spend a short amount of time, 30 minutes per day, chewing; chimpanzees, an animal that's mostly confined to raw food, can spend up to six hours a day just chewing tough stuff.)

The answer for the chin is found, researchers and an anthropologist at the University of Iowa contend, in the development and refinement of human sociality. As we became more social, we became less aggressive. This reduction in aggression, particularly among males, led to a hormonal shift that reduced, over time, the size of our face. As our faces got smaller, chins emerged. This socializing process, which is not old, must also have played a role in reducing and removing weapons from the human body. Even our nails are useless for fighting and killing. Our nails are indeed often made to look pretty. But we substituted our lack of bodily weapons with very deadly cultural ones.