On Monday, Piers Morgan was owned by the internet after he called actor Daniel Craig an #emasculatedbond for carrying his own child in a baby carrier. In response, hundreds of dads tweeted photos of themselves proudly carrying their young, asserting that fatherhood reinforced male identity. According to a new Scientific Reports article, proud and involved fatherhood is a behavior that human males — well, most of them, anyway — uniquely share with gorillas.

According to the study, released Monday, male mountain gorillas take care of kids, just like humans. They don’t do so out of any sort of cultural obligation. They do it because it ensures their reproductive success. In the study, the male gorillas that spent more time taking care of kids were also more likely to more offspring, even if the kids weren’t theirs.

“Humans and mountain gorillas are the only species of great apes in which males regularly form strong social bonds with infants,” co-author Stacy Rosenbaum, Ph.D. tells Inverse. In other words, gorillas show that paternal childcare isn’t emasculating. It’s a key to survival.

Rosenbaum, a postdoctoral fellow at Northwestern University, and her colleagues studied the 23 male gorillas, observed in Rwanda’s Volcanoes National Park, to understand why and how male care for children evolved. Caring fathers are quite rare among mammals, and even among primates. It’s been observed in a few species of Old World monkeys, like baboons and macaques, and in South America some small, tree-dwelling New World male monkeys care more for their children than females. Still, gorillas and humans are the most caring fathers and, because of our genetic bond, understanding why gorillas are good dads could explain why paternal care evolved to be so prominent among humans.

To assess the evolutionary upside to being a good dad, Rosenbaum and her team analyzed data on how often the gorillas, observed between 2003 to 2014 by the staff of the Dian Fossey Gorilla Fund’s Karisoke Research Center, mated and sired newborns and interacted with infants. These interactions weren’t so different than those between a human father and a child, consisting of of playing, hugging, and grooming.

gorilla family
A family of mountain gorillas in Volcanoes National Park, Rwanda.

“They do all kinds of things [when interacting] but in this paper we specifically measured grooming and ‘resting in contact,” Rosenbaum explains. “That is when two animals sit or lie so close that their bodies are touching. It’s kind of like being cuddled up next to someone on the couch — you usually only do that with people you are very close to and trust.”

They found that the male gorillas who interacted more with infants — whether their own or those of others — had more offspring than those who were less hands-on with kids. An additional analysis of behavioral data provided a simple explanation for this evolutionary upside: Females were really into the males that cared for infants, and because of this, good dads typically sired five times more than their less fatherly counterparts.

male gorilla
A male gorilla nurtures an infant.

The findings suggest it’s evolutionarily advantageous for gorillas to be involved in parenting, even if they’re a non-monogamous species. This is a unique characteristic for a male in the animal world because childcare is usually costly — thwarting mating opportunities, expending energy, and exposing busy fathers to predators. In many other species, a male animal is evolutionarily better off being a deadbeat dad, looking out for himself and siring new kids, but there seems to be something different about gorilla society that makes hands-on fatherhood a better choice.

“One possibility for why we see this in mountain gorillas is that maybe it doesn’t actually cost the males all that much,” Rosenbaum speculates. “Here we have a situation in which the animals don’t appear to discriminate their own offspring from those of other males, yet the males who are doing the care-taking are leaving behind more infants than the males who aren’t.”

Rosenbaum and co-author Chris Kuzawa, Ph.D. plan to study the role that hormones might play in facilitating good fatherhood in gorillas. Previous research on hormones in human men demonstrated that their testosterone levels decline as they become fathers, helping them focus their attention on the needs of the newborn. If the team finds that gorilla testosterone also declines with fatherhood, it will strongly suggest that there’s an evolutionary reason that pathway was conserved, suggesting that being a good dad comes with other benefits — perhaps attracting mates.