DNA has an expiration date. But proteins are revealing secrets about our ancient ancestors we never thought possible.

A red double-helix DNA strand is breaking up against a black background.

The moment a creature dies, its DNA begins to break down. Half of it degrades every 521 years on average. By about 6.8 million years, even under ideal preservation conditions in cold, stable environments, every meaningful trace is gone.

That's a huge challenge when trying to understand our evolutionary history more deeply: Two-legged primates emerged 7 million years ago in Africa, and our genus showed up around 2.6 million years ago. But DNA breaks down fast in the places our distant ancestors roamed. As a result, many of the key adaptations that make us uniquely human date to a period in which ancient DNA is indecipherable.