Menopause more about boosting fertility than you thought, study suggests

As any working Israeli parent of young children knows, during the summer school vacation, grandmothers are irreplaceable. Menopause apparently evolved so women – who live many years after they are able to bear children – can use their cognitive abilities to care for their grandchildren, according to research that has just appeared in PLOS Computational Biology.

According to computer simulations performed at the Institute of Evolutionary Sciences of Montpelier in France, directing resources to one’s adult children and their children provides an evolutionary edge. Instead of having more children, a grandmother may pass on her genes more successfully by using her cognitive abilities to directly or indirectly aid the next two generations, said Carla Aimé and colleagues at the institute.

Women lose their fertility long before the end of their expected lifespan. Researchers have long hypothesized that menopause and long post-reproductive lifespan provide an evolutionary advantage; that is, they increase the chances of a woman passing on her genes. However, the precise nature of this advantage has still been still up for debate.

To investigate the evolutionary advantage of menopause, the team developed computer simulations of human populations using artificial neural networks. Then they tested which conditions were required for menopause to emerge in the simulated populations. Specifically, the research team used the simulations to model the emergence and evolution of resource allocation decision-making in the context of reproduction. Menopause can be considered a resource allocation strategy in which reproduction is halted so that resources can be reallocated elsewhere.

The researchers found that emergence of menopause and long post-reproductive lifespan in the simulated populations required the existence of cognitive abilities in combination with caring for grandchildren. The importance of cognitive abilities rather than physical strength lends support to a previously proposed hypothesis for the evolution of menopause known as the Embodied Capital Model.

“Cognitive abilities allow accumulation of skills and experience over the lifespan, thus providing an advantage for resource acquisition,” Aimé said. “Stopping reproduction during aging allows allocating more of these surplus resources to assist offspring and grand-offspring, thus increasing children’s fertility and grandchildren’s survival.”