This long-term study, from 1993 to 1998, grew out of my belief that meerkats might offer vital insights into the evolution of mammalian cooperation. According to evolutionary logic, an individual's success is usually measured by the number of offspring it raises, but some meerkats spend part or all of their lives helping others raise young rather than breeding themselves. Such seemingly altruistic behavior can be found in very few mammals, but even within this select group, which includes mole rats, marmosets, wild dogs, and some other mongooses, meerkats are unique in the extent and coordination of their cooperative activities.