Humans, it seems, are not unique in this regard. According to new research, our close relatives, the chimpanzees, also need help from their extended families when rearing their youngsters.
In 1960, Jane Goodall began documenting the day-to-day activities of chimps at Gombe in Tanzania. Records of dawn-to-dusk observations, she and her successors made, are held at Duke University’s Jane Goodall Research Institute. There are detailed life-histories of over 200 chimps.
Using these Kara Walker, an evolutionary anthropologist at Duke, examined the maternal behaviour of 36 individuals. She found striking parallels between the problems faced by the wild mothers and daughters and those encountered by their human equivalents.
Chimps live in large hierarchical social groups, dominated by alpha males and alpha females. Youngsters inherit their place in the social order from their mothers. When a daughter grows up, the age at which she starts breeding depends largely on her status in the community; if her mother is high-ranking, she may breed for the first time when 13 years old.
Low-ranking females, on the other hand, are slower to breed. Also, chimps, whose mothers had been present throughout their childhoods, began breeding earlier than ones orphaned before the age of eight. These findings are hardly surprising; a well connected youngster, pampered and cosseted, will have better access to food.
With a privileged start in life, surrounded by supportive relatives and friends, she will tend to be healthier and come into breeding condition sooner.
Not all females remain in their natal communities throughout their lives. Some adolescents choose to leave and seek their fortunes elsewhere. These emigrants must seek out, and apply to join, other chimp groups.
A newcomer chimp risks rejection and victimisation. Not knowing the ropes in an alien group, an immigrant must struggle to gain acceptance. Lacking the support of family and friends, she will lose out to the native youngsters and take longer to climb up the social pecking order.
As a result, the research showed, blow-in chimps don’t start breeding until they are about 16 years old.
With a three-year headstart in becoming mothers, stay-at-home females get to raise more young in the course of their lives than under-privileged blow-ins. So what prompts a young female to emigrate?
The most likely explanation is that, by leaving her natal colony, she reduces the risk of consanguinity. If breeding always took place at home, incest would become rife. This would, in time, lead to an impoverished gene pool.
By emigrating, a female’s offspring will be less exposed to defects resulting from inbreeding. And it’s not just the wanderer who benefits; new genes also favour the adopting community.
The differences between human and chimp DNA may be as little as 1%. In his controversial 1991 book The Third Chimpanzee, Jared Diamond argued that chimps are so closely related to humans that they should be placed with us in the genus Homo.
The parallels between human and chimp maternal behaviours, identified in the Gombe research, seem to support Diamond’s thesis.
Like the wandering young chimps, we too are driven by curiosity, a tendency which made us the world’s most widely distributed and adaptable species.
Our youngsters have very long childhoods, during which we transfer vital knowledge skills and culture to them. That young chimps take equally long to mature raises an intriguing question; did we and they each evolve this tendency independently, or was it inherited from our common great ape ancestors?