Mammalian brain development and our grandmothering life history

Among mammals, including humans, adult brain size and the relative size of brain components depend precisely on the duration of a highly regular process of neural development. Much wider variation is seen in rates of body growth and the state of neural maturation at life history events like birth and weaning. Large brains result from slow maturation, which in humans is accompanied by weaning early with respect to both neural maturation and longevity. The grandmother hypothesis proposes this distinctive combination of life history features evolved as ancestral populations began to depend on foods that just weaned juveniles couldn't handle. Here we trace possible reciprocal connections between brain development and life history, highlighting the resulting extended neural plasticity in a wider cognitive ecology of allomaternal care that distinguishes human ontogeny with consequences for other peculiarities of our lineage. •Order and rate of neural maturation are stable in eutherian mammals, including humans.•Developmental duration, brain size, and longevity are all closely correlated.•But human infants are weaned notably early with respect to neural development.•The grandmother hypotheses links the evolution of human longevity to earlier weaning.•Grandmothering puts infants into unique social ecology at early neural development.