An evolutionary biologist at Purdue University named William Muir studied chickens. He was interested in productivity—I think it's something that concerns all of us—but it's easy to measure in chickens because you just count the eggs. He wanted to know what could make his chickens more productive, so he devised a beautiful experiment. Chickens live in groups, so first of all, he selected just an average flock, and he let it alone for six generations. But then he created a second group of the individually most productive chickens—you could call them superchickens—and he put them together in a superflock, and each generation, he selected only the most productive for breeding.

After six generations had passed, what did he find? Well, the first group, the average group, was doing just fine. They were all plump and fully feathered and egg production had increased dramatically. What about the second group? Well, all but three were dead. They'd pecked the rest to death.