Cooperation is the key to the evolution of life, even though natural selection favors genetic selfishness. Since all complex life, whether it's a tree or a whale, reproduces through sex, genes have only a 50 percent chance of getting into an egg or a sperm. This means that even genes have to cooperate, because any gene that cheated and found itself a greater than 50 percent chance of success would prosper -- and sex and complex life wouldn't work.
Without such genetic cooperation, the only life on earth would be simple, single-celled bacteria.
Animals in groups must also work together to build and run the societies in which they live. In an ant nest, for example, there may be millions of workers, foraging, building and maintaining the nest and defending it against predators and other ants. An ant colony is often referred to as a superorganism because it is composed of a single individual who reproduces, the queen, and thousands or even millions of other ants, all sterile, working to raise the queen's offspring. An ant colony is, in effect, a single cooperative unit, albeit one of huge size.