A dramatic example, consider social insect colonies, and in particular, the Hymenoptera (bees, ants and wasps).
In these colonies we find such an extreme degree of cooperation—division of labor (queen, workers, soldiers, etc.), food-sharing, information sharing—that it is tempting to view the entire colony as a single functioning organism.
Indeed, in the case of stinging worker honey bees, there is not only cooperative labor but also, when necessary, the ultimate sacrifice in defense of the hive (at least where the invader is a mammal, stinging of which proves fatal to the bee as the barbed sting is torn out upon being deposited in the victim). How can such striking cooperation and self-sacrifice be explained in evolutionary terms?
To explain how worker on helping the queen took precedence over personal reproduction, and it explains how even suicidal behavior could have been selected for propagating the genes that cause it (Dawkins 1989, 174–75).