Great apes, our closest living relatives, live longer and mature later than most other mammals and modern humans are even later‐maturing and potentially longer‐lived. Evolutionary life‐history theory seeks to explain cross‐species differences in these variables and the covariation between them. That provides the foundation for a hypothesis that a novel role for grandmothers underlies the shift from an ape‐like ancestral pattern to one more like our own in the first widely successful members of genus Homo. This hypothesis links four distinctive features of human life histories: 1) our potential longevity, 2) our late maturity, 3) our midlife menopause, and 4) our early weaning with next offspring produced before the previous infant can feed itself. I discuss the problem, then, using modern humans and chimpanzees to represent, respectively, genus Homo and australopithecines, I focus on two corollaries of this grandmother hypothesis: 1) that ancestral age‐specific fertility declines persisted in our genus, while 2) senescence in other aspects of physiological performance slowed down. The data are scanty but they illustrate similarities in age‐specific fertility decline and differences in somatic durability that are consistent with the hypothesis that increased longevity in our genus is a legacy of the “reproductive” role of ancestral grandmothers. Am. J. Hum. Biol. 15:380–400, 2003. © 2003 Wiley‐Liss, Inc.