Julio Torres, Intern.
Ancient Bodies, Modern Lives: How Evolution Has Shaped Women’s Health written by Wenda Trevathan, Ph.D., a Regents Professor of Anthropology at New Mexico State University, we learn about a range of women’s health issues. Trevathan’s hypothesis is that many of the health challenges faced by women today result from a mismatch between how our bodies have evolved and the contemporary environments in which we live. In the following excerpt, Trevethan draws from Jane Goodall’s observations of primates to illuminate how grandmothers, by virtue of being present in the family, contribute to the growth of prosperity of the grandchildren and the family unit as a whole.
Grandmothers and Reproductive Success
Most long-lived, group-living mammals have in their social groups as many as three generations present at any one time. Examples include elephants, whales and many primates. For primates who live in matrilocal groups, that usually means three generations of females: Infants, their mothers, and their grandmothers. A famous example comes from Jane Goodall’s studies of a Tanzanian chimpanzee social group in which Flo, her adult sons Faben and Figan, and her daughter Fifi lived together. Flo was a high-ranking female and her presence had a number of positive effects on her offspring. For example, Fifi was able to stay in the troop into which she was born, whereas the more typical pattern among chimpanzees appears to be for young females to leave their birth troops at maturity. By staying with her mother, Fifi was also able to rise to a high status. She began reproducing much earlier than most chimpanzee females and not only set the record for reproductive success at Gombe, but one of her sons became the largest male ever recorded at Gombe. Two of Fifi’s sons rose to high status in the dominance hierarchy and her daughter began reproducing much earlier than Fifi did. There is little doubt that grandmother Flo’s status had an effect on her daughter’s (and thus her own) reproductive success. There is no evidence, however, that Flo contributed directly to the care and feeding of her grandchildren, although it is true that she was not in good health at the time Fifi’s first infant was born in 1971.
Anthropologist Sarah Hrdy notes that despite her reproductive success, Flo serves as a good example of why having offspring at later ages may not be a good way to achieve this success or why “stopping early” might be selectively advantageous. Flo reproduced for the last time when she was very old and in poor health, but that infant did not live long. Goodall proposes that this last pregnancy was so draining for her that she was unable to mother her other young offspring, Flint, and when Flo died, Flint died also, even though he as at an age when he should have been able to survive on his own. In fact, if Flo had stopped reproducing after Flint, he probably would have lived, perhaps going on to sire another offspring and increasing Flo’s reproductive fitness through her grandchildren.
Similar evidence that the presence of grandmothers has positive effects on reproductive success comes from observations of a number of other primate species. Again, it is not usually resources and direct care that older female grandmothers provide; rather, they help to defend the infants from other troop members (including infanticidal males) whose behaviors endanger them. In fact, observers report that grandmothers will often act even more vigorously in defense of infants than younger kin. Grandmother Japanese macaques make a significant difference in survival of their grandchildren through the first year of life. Furthermore, females have much greater reproductive success if they have living mothers, even when those older females are still r