How Prehistoric Grandmothers Promoted Family Values

Your Grandma wants you to settle down and get married already, and she’s wanted that since at least prehistoric times, according to a new study published in PNAS. The findings are the latest addition to the so-called “Grandmother Hypothesis,” a controversial theory about human families that suggests early hominid grandmothers stuck around to pitch in with child care, and in doing so promoted family values.

The human family has long baffled scientists. Apes, our closest relatives, don’t invest in long-term, monogamous relationships, and even animals that mate for life typically appear to lack the level of emotional investment that humans have in their significant others. Traditionally, researchers have explained our odd family structure as a sort of deal between male hunters and childbearing females—men agreed to hunt and feed one exclusive, female mate in exchange for undisputed paternity over her offspring. But recently, anthropologists have begun touting a new explanation for the human family: grandmothers. The Grandmother Hypothesis suggests that women with good genes for long life survived to help raise their grandchildren, which allowed young mothers and fathers to build larger families. Women who did not live to see their grandchildren left behind sons and daughters who, without any help around the house (or cave, or mud hut), ended up producing fewer children. Eventually, genes for long life—and a grandmother’s touch—began favoring bigger families, and so humans began living longer.

Now, in a new study of the Grandmother Hypothesis, researchers from the University of Utah have found not only that grandmothers fostered bigger families, but that their influence may have been what first encouraged male hominids to forsake their bachelorhood for committed relationships and parenting responsibilities.

For the study, scientists ran 60 computer simulations of 300,000 years of human evolution, 30 with grandmothers and 30 without. They found that grandmothers appeared to increase the ratio of fertile males to females from 77 men for every 100 women to 156 men for every 100 women. The results, for which the researchers didn’t have an explanation, imply that having grandmothers around increases the overall number of fertile men in a population.

At this point, the study turns a bit speculative. In virtually every animal population, the scientists note, there are more fertile females than males. But computer simulations suggest that when there are more fertile males than females, men begin guarding their mates to ensure the survival of their genetic information. Given thousands of years, the hypothesis goes, mate guarding turned into love, marriage, and the societal requirement that men buy overpriced roses and mediocre chocolates every February. “This male bias in sex ratio in the mating ages makes mate-guarding a better strategy for males than trying to seek an additional mate, because there are too many other guys in the competition,” University of Utah anthropologist Kristen Hawkes, coauthor on the study, said in a prepared statement. “Mate-guarding and pair bonds are not necessarily the same,” she cautioned. “But they have in common the tradeoff between paying attention to the current partner and seeking another.”

The idea that grandmothers may have been the evolutionary “first step” toward pair bonding and, eventually, the human family structure is for now a bit of a stretch, and the anthropology community is sure to respond strongly to the new hypothesis. In the meantime, it does make you think. Also, would it kill you to call your grandmother more often? She just wants to know how you’re doing, and to be thanked for human longevity, pair-bonding and the abundance of fertile males in modern society.

Last Modified: Apr 12, 2019