We Interbred

When modern humans reached Europe, they and Neanderthals had children together. The proof is in your cells. Most people with roots outside Africa carry a small slice of Neanderthal DNA, usually between 1 and 4 percent. Neanderthals are not distant cousins on the family tree. They are literal ancestors.

That inherited DNA still shapes us. It tweaks immune defenses, skin and hair color, pain sensitivity, and even whether you are a morning person. Some of those genes once fought off local diseases. Today, a few of the same variants nudge up the risk of conditions like lupus and type 2 diabetes.