Species have to keep evolving just to avoid falling behind, not to get ahead

Leigh Van Valen noticed that a species' odds of going extinct stay roughly constant no matter how long it's existed, as if age gave no safety margin. His explanation: predators, prey, parasites and hosts are all evolving in response to each other at once, so running faster just keeps everyone in the same relative position. He named it after the Red Queen in Through the Looking-Glass, who tells Alice it takes all the running you can do just to stay in the same place.

— Leigh Van Valen, A New Evolutionary Law — Evolutionary Theory, 1, 1–30 (1973)