Male mountain gorillas in Rwanda care for all of the young in their social group regardless of paternity. The care extended towards non-related young poses a conundrum to scientists. Males who care for their own children are protecting their genetic investment, but the effort spent caring for infants fathered by other males doesn’t add to their genetic success. In evolutionary terms, caring for kids fathered by another male is a not a good use of resources.

Traditional thinking holds that paternal care can only evolve in social systems such as monogamy in which males can be certain of paternity. Without other males around, males could safely assume that they were caring for their own kids. Otherwise, the risk of putting resources towards protecting individuals who are not carrying their genes is too high.

The observations of gorillas providing paternal care to all the young in groups with multiple males surprised scientists. That is very unusual behavior in mammals and the goal of a recent study was to find out why males were doing this. The assumption is that males would only do this if it benefits them in some way, which from an evolutionary perspective means that it adds to their ability to pass on their genes to the next generation. But how?

Males have limited resources in the game of life, where the winners are those who have the most surviving offspring. In order to succeed, males can pursue mating opportunities with females and they can care for their own young, as both of these can add to the number of surviving babies that they have.

The recent study to determine why mountain gorilla males care for offspring regardless of who the father is revealed something new about the evolution of paternal care. This study showed that there is an entirely different pathway for paternal care to evolve in a species because paternal care can offer a benefit to the males even if they are caring for unrelated offspring.

That benefit is the opportunity to sire more offspring. Males who are among the most active third of caregivers sire more than five times as many offspring over their lifetime as the males who are in the lower third as measured by amount of caregiving behavior. Females choose to mate with males who care for the young, and it is that female preference for caregiving males that confers a huge benefit to those males. Caregiving males are getting more of their own genes into the next generation not by focusing their efforts exclusively on their own infants but by increasing their opportunities to father more of them.

In summary, mountain gorillas have greater mating success if they spend time with kids, even if they are not the father, an astounding result reported in the recent scientific paper Caring for infants is associated with increased reproductive success for male mountain gorillas.

As Father’s Day approaches, remember that when males care for offspring other than their own, this valuable behavior can enhance their evolutionary success.

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Karen B. London, Ph.D. is a Certified Applied Animal Behaviorist, Certified Professional Dog Trainer, author, and an Adjunct Faculty in NAU’s Department of Biological Sciences.


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