Size may matter, at least when it comes to parenting

Maryland.gov

Having both parents care for a child not only increases its survival, but also improves its mental health, social skills, and educational prospects. Obviously, it’s best for both parents to be involved. But not all dads are great ones. There are a lot of reasons why a father may not invest in his kids—he may work long hours, live far away, or just not care. In this week’s PNAS, researchers from Emory University raise another possibility: maybe bad dads are the product of a life history tradeoff.

From a biological perspective, life is all about passing on one’s genes, and there are different ways to do that; one way is to invest heavily in a few precious offspring to make sure they survive, while another is to invest a whole lot of time and energy in mating and hope something pans out. Do human males exhibit this tradeoff? To address this question, the Emory researchers turned to testicles.

Yep, you read that right—testicles. Testes size has been linked to reproductive effort in several species; big ones generally mean increased sperm production, which increases the likelihood of mating success. Perhaps men with large testicles would be naturally predisposed to sow their seed rather than stay home with the kids. Guys who are less well-endowed, then, might be more likely to be the nurturing sort.