THE LEFT OVERS

A lot has happened for modern humans to get to this point. We lost most of our hair, learned how to make tools, established civilizations, sent a person to the Moon, and invented artificial intelligence. Whew! With all of these changes, our bodies have changed, too. It’s only taken us about six million years.

- Charles C. Hofer

It all comes back to one key idea: evolution.

In 1859, Charles Darwin published his book On the Origin of Species, in which he explained his theory of evolution. He described the process of “descent with modification,” where physical parts— and even behaviors—of animals may change over multiple generations due to natural selection. If certain traits—such as sharp teeth or thick fur—helped the animal survive in the wild, then these favorable traits would be “selected for” and passed down to the next generation. Then that generation would pass them on. And so on.

And while favorable traits are passed on, other traits are sometimes phased out altogether. Unused parts are called vestiges. This word comes from the Latin vestigium, or “footprint.” These vestiges are our body’s evolutionary leftovers.

Chew on This

Modern humans (Homo sapiens) and our ancestors are all referred to as hominins. There have been many different types of hominins over the millennia.

Starting about three million years ago, hominins created simple tools that could cut, pound, and grind food materials like raw plants. They also harnessed the power of fire, which could be used to cook meats and other foods, making them more digestible. Soon hominins consumed less cellulose, a strong structural material found in plants that is difficult for many animals to digest. Then something funny happened along the six million years’ march toward modern Homo sapiens: Our jaws grew smaller, and our brains grew bigger. As our ancestors’ eating habitats changed, over time the hominin jawbone shrank. Our teeth grew smaller, too.