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Young adult male Haden, 19, grooms his mother, Lita, who is his “best friend,” at Kibale National Park in Uganda.

Kevin Lee

Even as young adults, male chimps are ‘mama’s boys’

Even tough male chimps need their moms. Chimpanzees live in a male-dominated society, where most of their valuable allies are other males. However, as young male chimpanzees become adults, they continue to maintain tight bonds with their mothers, a new study reveals. And for about one-third of them, this mother-son relationship is the closest one they have.

The dramatic changes of adolescence are difficult for chimps, just like they are for humans, says Elizabeth Lonsdorf, a primatologist at Franklin & Marshall College who was not involved in the study. And “sure enough,” she says, “their moms remain a key social partner during this turbulent time.”

Previous research has shown chimpanzee mothers provide their sons support that goes far beyond nursing. Young male chimps that are close with their moms grow bigger and have a greater chance of survival. What’s more, losing their mothers after weaning, but before age 12, hinders the ability of young chimps to compete with other males and reproduce.

To see whether this bond extends later into life, researchers followed 29 adolescent (9 to 15 years old) and young adult (16 to 20 years old) male chimpanzees at a research site in Kibale National Park in Uganda. For 3 years, they observed the chimps from a distance, recording any social interaction they witnessed. These included grooming, comforting behaviors such as holding hands or shoulder pats, looking back for or waiting for other individuals, offering support during conflicts, and sitting near each other.

The team found that young adult males spent less time with their mothers than adolescents did—26% versus 76%. As the male chimps grew older and more independent, they began to travel over wider ranges and spent more time away from their moms. And unlike adolescents, they no longer cried for their mothers or sought reassurance after fighting.

However, when these young adult males happened to be in the company of their mothers, they acted just like the adolescents, the researchers report this month in Behavioral Ecology and Sociobiology. They groomed their moms just as often and kept track of them. Many mothers remained the males’ “best friends,” or the social partner they associated with most frequently, even though chimpanzee communities are dominated by male interactions, says study co-leader Rachna Reddy, a biological anthropologist at Harvard University.

The support offered by mothers to their sons may reduce stress, especially in the competitive world of male chimps, the team speculates. In future studies, Reddy hopes to learn more about how these bonding behaviors are linked to health benefits in male chimpanzees.

Such persistent ties are also prevalent in humans after sons leave their mothers and live on their own—especially now, Reddy says. “With COVID happening, we really feel what it’s like to not be able to see our parents when we want to,” she says. “The importance of those bonds in our lives and the comfort we get from them have deep evolutionary roots.”