A comparison of seven nonhuman primate species has found both similarities and differences among the effects of age on female reproduction.

The work, which was published in the May 9, 2022, issue of the Proceedings of the National Academy of Sciences (PNAS), contributes to sorting out two distinct contributors to the reduced fertility that accompanies aging.

Reproductive senescence has two components. One is fertility senescence, which refers to the biological aging that makes it less likely that conception will occur and lead to a live birth. The other is parental-effect senescence, which is a collection of factors that make the offspring of older mothers less healthy, and less likely to have offspring themselves, than those of younger mothers. (In some primate species, the youngest mothers, too, have offspring that are less likely to survive to adulthood.)

The team found evidence of fertility senescence in six of the seven primate species they studied, and argued in their paper that the lack of fertility senescence in the seventh – capuchin monkeys – may have more to do with sample size and specifics of the study population than with a true absence of such an effect.

The authors wrote that "our cross-species approach provides a comparative landscape in which the evolution of human aging and reproduction can be situated and allows us to test for both components of reproductive senescence: fertility senescence and parental-effect senescence."

For now, little is known about the biology of fertility senescence. But Jennifer Garrison, an assistant professor at the Buck Institute for Research on Aging who was not involved in the work now published in PNAS, wants to change that.

At the Buck Institute, Garrison is the faculty director of the global consortium for female reproductive longevity and equality.

She is tackling not just diseases through the lens of aging, but aging through the lens of female reproductive aging. Her reasons have to do with both science and equity.

"As we are moving forward in extending healthy longevity, if we don't tackle female reproductive span, it's going to make gender equality worse," she said. Already, women live longer than men but spend significantly more time in poor health, in part because menopause accelerates aging.

Additionally, the comparatively early onset of menopause makes fertility a much more salient part of general decision-making for women than for men.

Despite the fact that females are more affected by the health consequences of aging across their lifespan, a lopsided amount of what is known about aging comes from the study of males.

"We've been using the male body as biology's baseline for pretty much all of the last century," Garrison told BioWorld Science. "Everything about female sex is woefully understudied."

The National Institute on Aging's Intervention Testing Program (ITP) is a laudable exception – it has been using both male and female mice since its inception. Several of the interventions it has identified – for example, aspirin – increase longevity only in one sex in mice.

Garrison thinks that ironically, leaning into the complexities of female biology is an overlooked opportunity for scientific insights.

"The ovaries -- you can think of them like an accelerated model for human aging," she said.

In industry, "the big hurdle is that there's no good way to test interventions" in humans.

But the ovaries provide "a unique, wondrous opportunity to study aging in a human on a timescale that's feasible... three years, maybe five at the outside."

At the Buck Institute, Garrison is currently starting up the world's first ovarian biology core facility. Her goal is to collaborate with other academics, and with industry, doing aging experiments in human ovarian tissue, and model organisms from rodents to nonhuman primates.