GOING SOLO: The mystery of why female chimps leave their groups
Most female chimps suddenly leave home entirely, just before puberty. There one day and gone the next. She heads off into regions unknown, alone, and finds a community of strangers to join.
SARAH DUNPHY-LELII: When animals live together in bonded communities, there needs to be some mechanism to maintain healthy genetic diversity—incest avoidance, essentially… Typically, some of the community members will depart in early adolescence to seek their fortunes (and their mates) elsewhere, but who, and how?
Chimpanzees know very well who their mother is, and also know well their siblings through their mother, both younger and older. Like us, chimpanzee mothers raise their infants very carefully for a long time. For the first five years, juveniles are rarely out of her sight: she grooms and watches them constantly, and they sleep together each night. Since males remain forever in the community where they were born, sons typically maintain lifelong relationships with their mothers. Garbo, a 64-year-old chimp, spends much of her time in the company of her three grown boys…
Paternity is another story. Chimpanzees live in large, very social groups and are promiscuous in their mating: when a female is fertile, she mates with a number of males, and males regularly mate with many different females. Nobody knows who their father is, and fathers do not know their daughters; it’s a risky situation from an incest point of view. Chimpanzees have solved this problem in a particular way: Most females suddenly leave home entirely, just before puberty. There one day and gone the next. She heads off into regions unknown, alone, and finds a community of strangers to join. She is never seen again by either her own mother or the researchers who had grown attached to her. She begins her adult life knowing no one at all.
We don’t know very much about these life-changing departures. What, exactly, prompts her to leave? How does she choose where to go? How long does it take her to find a new home? In situations where females could emigrate—they are free to range, there are available neighboring communities and unimpeded travel between them—and still don’t, it is something of a mystery why… Genetic tests via fecal samples, combined with personal observations, tell us that… there may be an alternative incest-avoidance mechanism in place for them.
Jane Goodall once suggested it might be the daughters of high-ranking females that stay, since they can expect status and resources right where they are, and this seems true in some cases, but not all. Relatedly, those very few females who don’t depart at puberty might start having kids earlier than those of their peers who wander in from elsewhere—they’re comfortable, they have their mother’s support, they know people. SOURCE…
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