英语时差：生存策略（上）

Beneath the surface of a pond or stream it’s a fish-eat-fish world, and the tiny minnow is often lunch for larger fish such as pike. You’d think a tasty minnow would try to remain inconspicuous, but this isn’t always the case. If a minnow’s skin is damaged by an attacking pike, it releases a chemical that attracts more pike. Why would a minnow that’s already being attacked want to attract more trouble? Do injured minnows have some kind of crazy death wish? This seemingly suicidal behavior is actually a clever survival strategy. The minnow’s chemical has two distinct functions. First, it warns other minnows about the danger. Minnows travel in schools with close relatives, so this chemical alarm warns the others away from potentially dangerous waters. Even if the original minnow is eaten, its brothers and sisters will live to reproduce. From a genetic standpoint, this self sacrifice makes sense.