Chapter 10 Summary and Analysis

The author explains that he has discussed parents, sexuality, and fighting behavior between animals of one species, and now he plans to consider animals that live in unrelated mixed groups, like zebras and gnus. He promises to tie up loose ends brought up in chapter one, to explain away other behavior that's not really altruistic but appears to be, and to look at social insect behavior.

First, most group behavior helps the individual. Hyenas hunt bigger prey as a pack, penguins keep warm, and fish and birds move more smoothly together. W.D. Hamilton explains the idea of how groups form. Hamilton says that if each animal has a bigger chance of being eaten by a stalking predator if it is isolated, it will naturally crowd closer into the center of a group. This is how herds are formed.

Bird calls...