Why is a modern person’s chin sharper than that of his ancestors?

Today, humans can afford to eat processed foods that do not require powerful, strong jaws to chew.
Our ancestors could not afford such a luxury, since they often ate what they could get directly from nature. There could be no talk of any kind of food processing several thousand years ago. The need for a strong lower jaw was vital. Over time, it disappeared, and a sharp chin began to indicate relatively weakened chewing muscles.