Chimpanzees and bonobos – our closest living relatives – both live in similar environments, and yet they show incredibly diverse behavioral differences. Chimps, for example, are prolific tool users, whereas bonobos are not. Previous research has shown that young chimps spend more time playing with objects from an early age, and that this primes them to develop more complex tool use behavior as they age. But new research has found that it might not be as simple as more play leads to more tool use.
“In numerous mammalian species, sex differences in immatures foreshadow sex differences in the behaviour of adults, a phenomenon known as 'preparation',” explains Dr. Kathelijne Koops, who co-authored the study published in PLoS One. And yet even though young male chimps spend more time playing with objects when compared to young females, which one would expect to ultimately lead to more advanced object manipulation later in life, it’s actually the females who are more avid and competent tool users when they reach adulthood.
In order to work out what it is that makes these two animals so behaviorally different, the researchers spent several months studying a community of wild chimpanzees in Uganda and one of wild bonobos in the Democratic Republic of Congo. They found that while immature male chimps spent a lot of time simply playing with objects – not necessarily tools – the female chimps were far more selective with how they interacted with these objects.
Interestingly, this is a parallel of what’s been observed in humans. “The finding that in immature chimpanzees, like humans, object-oriented play is biased towards males may reflect a shared evolutionary history for this trait dating back to our last common ancestor,” write the researchers, who are from Cambridge, Zurich and Kyoto.
The younger females showed lower rates of object manipulation, but rather than simply playing with any object they came across, they displayed a greater diversity of manipulation behavior – such as biting, breaking, and carrying objects. So it seems that it’s not necessarily the time the apes spend handling objects, but more the type of manipulations the young apes perform that prime them for tool use as adults.
The researchers go on to suggest that the apparent similarities between human children and immature chimpanzees with regards to male-bias could mean that object play in males has some other function in developing motor skills for male-specific behavior, such as dominance displays. “It seems that not all object manipulation in immatures prepares for subsistence tool use. It is important to take the types of manipulation into consideration,” says Koops.
Considering just how closely related chimps, bonobos and humans are, Koops hopes that understanding how species and sexes differ in “preparation” for tool use among chimps and bonobos might shed some light on gender differences observed among human children.