Growing a human being inside you for nine months, and then expelling it with a force that can fracture your pelvis can take its toll on the body. (So can, you know, raising it.)
According to a branch of evolutionary biology called life-history theory, there should be a tradeoff for all this effort—namely, that having kids should speed up the aging process. Energy invested in reproduction, after all, is energy that isn’t being used toward keeping the body’s tissues all shiny and new.
Studies in other species—fish, birds, mice—have found this to be the case. These studies measured the length of the animals’ telomeres, the protective DNA caps at the ends of chromosomes. Telomeres are often compared to the plastic coverings at the end of shoelaces, in that they protect the ends of chromosomes from getting frayed or mucked up. And as organisms age, their telomeres shorten. If life-history theory holds, having more offspring should be associated with shorter telomeres and accelerated aging.
But a new longitudinal study published in PLOS One found just the opposite. It followed 75 women, all Kaqchikel Maya who lived in rural areas of southwest Guatemala, for 13 years. The Kaqchikel Maya tend to marry within the community, and all the women in the study had similar lifestyles, which helped limit possible confounding factors.