The units of selection - Does natural selection ever favor groups, rather than individuals?
Group selection describes natural selection operating between groups of organisms, rather than between individuals. This would produce adaptations that benefit the group, rather than the individual. Darwin's theory of evolution was based upon individual selection, and he rejected the idea of group selection.
The idea was brought to prominance in 1962 by British zoologist Wynne-Edwards, who argued that animals restrain their reproduction in order not to over-eat the local food supply. If all the individuals in a group reproduce at the maximum rate, their offspring might over-eat the food supply, and the group would then go extinct. This could be avoided by collectively restraining their reproduction.
Of course, natural selection on individuals doesn't favor reproductive restraint. An individual that increases its reproduction will automatically be favored relative to individuals that produce fewer offspring. Within a group, if some individuals produce more offspring than others, the former will proliferate. For Wynne-Edwards theory to be correct, selection on groups must be weaker than selection on individuals.