The Foundations of Cooperative Breeding

Alloparenting, or the investment in young by individuals other than the biological parents, occurs among a wide array of insects, birds, and mammals – including humans. Human reproduction is characterized by notable features that distinguish it from the general mammalian pattern and that of apes, our closest living relatives. Comparatively, we wean our infants early, before they are nutritionally independent. Despite this practice of early weaning, we maintain relatively short inter-birth intervals (IBI), or the space between births. This association between short IBI and early weaning is hypothesized to have evolutionary roots, allowing hominid mothers to resume ovarian cycling more rapidly, facilitating the birth of new infants while maintaining care for older (and still highly dependent) children. Given the high estimates of the nutritional input required for a hominid mother to successfully feed herself and only one of her offspring, it is unlikely that she would have been able to do it alone - she likely relied on assistance from others. This practice of allomothering unfolded in the larger social context of cooperative breeding and includes nurturing, caregiving, and/or provisioning. It likely allowed our Pleistocene ancestors to successfully rear energetically expensive, large brained offspring in an unpredictable ecological environment. Allomothering, while considered to be one of the hallmarks of human evolutionary history, also has a strong contemporary resonance. It is currently the most widespread cross-cultural practice of child rearing, not only normative among small-scale non-industrial populations such as foraging communities, but also commonplace in the post-industrialized cultural west. Despite changes in demography and residence patterns throughout the world, allomothers continue to provide for and nurture children, underscoring not only how central this practice is to the anthropology of reproduction, but also to what makes us (and our reproductive lives) human.