The longer a woman lives, the fewer grandchildren she is likely to have, according to a recent paper in the American Journal of Anthropology by a USF professor.

Lorena Madrigal, a biological anthropology professor, conducted research in Costa Rica that primarily focused on the whether longevity is inherited.

After Madrigal and her colleagues pored through stacks of church records dating back 500 years, they found a connection between a woman’s longevity and the number of children she has.

Madrigal’s findings raise questions about hypotheses explaining why women live long after they are able to produce children, a trait unique to humans.

There are two hypotheses accepted by the scientific community that Madrigal’s findings contradict.

One, known as the “mother” hypothesis, suggests that menopause allows women to focus their energy and resources into raising the children they already have. It also increases the likelihood of the mother’s living longer by removing the danger of death during childbirth.

The “grandmother” hypothesis, on the other hand, proposes that post-reproductive longevity is a way of allowing a woman’s children to receive additional help in raising their own offspring. After the childbearing years a woman will live longer so she can help her daughters raise their children and thus promote her genetic descent. This hypothesis stems from research conducted in Africa showing that grandmothers increase the overall health of their grandchildren.

Madrigal said she doesn’t think her research entirely contradicts the grandmother hypothesis, but she doesn’t think the hypothesis is universally applicable, either.

“My conclusion is that we are not saying that the grandmother hypothesis is totally wrong in every single culture,” she said, “but what I am asking for is that we question the universality of the grandmother hypothesis. There are populations where the grandmother is actually detrimental.”

She said it’s not possible to determine the cause of the phenomenon from her research, but she believes it might have something to do with the amount of resources available to families. A grandmother who lives longer will require more care in addition to her daily food requirements. This would mean daughters would have fewer available resources to provide to newborn children. Madrigal said one of the more interesting aspects of the research is that the pattern continues into modern times, when resources are much more abundant. This would suggest that there is a genetic correlation between childbirth and longevity, she said.

She said her next step is to increase the overall sample size and analyze the participants’ genetic makeup to determine whether there are any identifiable traits.

Elizabeth Bird, chair of the anthropology department at USF, said applied research like this is the type the anthropology department likes to emphasize. Bird said this research raises the profile of the department – and the University as a whole – by being published in a prestigious journal.

Madrigal said she didn’t think her research necessarily applied to the U.S.

“I think in the U.S. we are actually likely to see the opposite – the grandmother hypothesis works in some situations where the mothers are unable to take care of the children. So I would think that in the U.S. the grandmother hypothesis would work.”