Male Gorillas Who Care for Kids Are Five Times More Successful at Reproducing

Gorilla Parents
N'Yaounda holds her one-day-old gorilla baby beside father Golo at a zoo in Budapest. Male gorillas who spent the most time with baby gorillas sired five times as many children as the gorillas that spent the least amount of time with baby gorillas. ATTILA KISBENEDEK/AFP/GETTY IMAGES

Wild male gorillas may be more successful at reproducing if they spend more time caring for their offspring—or even other gorillas' offspring.

Researchers at Northwestern University, the Max Planck Institute for Evolutionary Anthropology and the Dian Fossey Gorilla Fund studied why wild male mountain gorillas in Rwanda spent so much time with the kids in their group even when they didn't know who the father was. Published in Nature Scientific Reports on Monday, the study showed how much more successful these male gorillas were at reproduction and challenged assumptions on paternal care in primates.

"About 15 years ago, I worked as a research assistant for the Dian Fossey Gorilla Fund, studying male gorilla behavior. I was very struck by how much time males and kids spent together, even in large groups where multiple males might be the father," Stacy Rosenbaum, a postdoctoral fellow at Northwestern University and lead author on the study, told Newsweek. "It looked very much like fathering in humans, which just isn't something that we really think of apes engaging in."

In a study she'd published a few years ago, Rosenbaum found that male gorillas weren't treating their own biological children any differently from other kids in their group, so she decided to figure out why they interacted so differently from many other mammals.

The new study found that the male gorillas who groomed and rested more with the young in the group had more reproductive opportunities with the female gorillas. Male gorillas who spent the most time with kids sired five times as many children as the gorillas who spent the least amount of time with kids. That could be because the females chose to mate with the male gorillas because of the interactions they had with the young.

"We actually first found this result more than three years ago. I was pretty skeptical that it was real, so we waited until we had more paternity results, and sure enough, not only was the relationship still there, it got stronger," Rosenbaum said.

It is known that male mountain gorillas compete for reproductive opportunities, but this research shows that competition might be more complex than previously thought. Even after the researchers controlled their results for age, dominance ranks and the number of reproductive chances the males had, the male gorillas who formed bonds with the kids in the group were significantly more successful.

In humans, studies have shown that males' testosterone drops when they become fathers. If this is also true in gorillas, then those male gorillas with lower testosterone might have trouble competing for another chance at reproduction, and scientists would be able to find even more reason for their behavior.

"Our results really speak to a route by which the kind of fathering behavior we see in modern humans might have gotten a toehold amongst our extinct relatives," Rosenbaum explained. "Human fathering is unquestionably costly—men invest a lot in their children, in cultures across the globe. But this research shows a path that selection might have taken to help establish social bonds between males and infants, among our fossil relatives."