Humans are generally highly cooperative and often impressively altruistic, quicker than any other animal species to help out strangers in need. A new study suggests that our lineage got that way by adopting so-called cooperative breeding: the caring for infants not just by the mother, but also by other members of the family and sometimes even unrelated adults. In addition to helping us get along with others, the advance led to the development of language and complex civilizations, the authors say.
In the late 1990s, Sarah Blaffer Hrdy, now an anthropologist emeritus at the University of California, Davis, proposed the cooperative breeding hypothesis. According to her model, early in their evolution humans added cooperative breeding behaviors to their already existing advanced ape cognition, leading to a powerful combination of smarts and sociality that fueled even bigger brains, the evolution of language, and unprecedented levels of cooperation. Soon after Hrdy’s proposal, anthropologists Carel van Schaik and Judith Burkart of the University of Zurich in Switzerland began to test some of these ideas, demonstrating that cooperatively breeding primates like marmosets engaged in seemingly altruistic behavior by helping other marmosets get food with no immediate reward to themselves.
The researchers suggest that cooperative breeding might have developed when our earliest ancestors, who evolved in Africa, first moved from life in the trees to a more precarious existence in savanna and woodland environments, several million years ago. “From other species, such as birds, we know that [cooperative breeding] is typically associated with adverse environmental conditions where it is difficult to survive,” Burkart says. “Once they moved into those savannah habitats, it may simply have become impossible for mothers to rear and provision their offspring alone.” Among the advantages of cooperative breeding, Burkart adds, is that mothers can give birth to new offspring while the previous ones are still dependent on adult care, thus increasing their reproductive success.