Today’s Herald carried a story from the UK’s Telegraph, which looked at some research into the social behaviour of chimpanzees & bonobos (‘pigmy’ chimanzees). And – as usual – extrapolated from this to people… Grumpiness, it told is, was a sign of a more ‘advanced’ nature, whereas the happier, more peaceable bonobos were ‘less evolved’.
The article doesn’t begin well: Researchers looked at two different kinds of monkey — the familiar chimpanzee and the less evolved but much more easy going bonobo. Chimps are monkeys??? Arrggghhh! And the ‘less evolved’ really grates. Humans & chimps last shared a common ancestor around 5-7 million years ago and, as the recent swag of publications about ‘Ardi’ have shown, the two lineages have followed different evolutionary paths since then. (Bonobos & chimps subsequently diverged from each other 0.85-2.5 million years ago – & are as ‘evolved’ as each other.) I did wonder if there was a bit of wish-fulfillment there – chimps can be grumpy, & chimps are ‘more evolved’ than bonobos, so grumpiness is a ‘more evolved’ state – good news for all those grumpy human prima donnas :-)
The newspaper story was based on a paper in Current Biology entitled Bonobos exhibit delayed development of social behavior and cognition relative to chimpanzees (Wobber et al. 2010). The researchers compared chimpanzees (Pan troglodytes) & bonobos (Pan paniscus), looking at differences in the animals’ social behaviour & also their cognition in order to test the hypothesis that certain aspects of behaviour or cognition in adult bonobos represent developmentally delayed forms of the traits found in chimpanzees (Wobber et al, 2010:1). In other words – that differences in behaviour could be related to differences in development: adult bonobos show some ‘juvenile’ behaviour patterns (eg play, & non-reproductive sex) compared to adult chimps, & also show a degree of paedomorphism in their cranial structure.
In particular, the team looked at behaviours to do with sharing/competing for food: for each species they gave the animals a food-sharing task, using male:male, male:female & female:female pairs, for a total of 30 chimps and 24 bonobos. The results: older bonobos were as tolerant as juvenile animals when it came to sharing food, but adult chimps were much less so. The adult bonobos were also more playful (including sexual play), which the authors thought might affect their tolerance for sharing food. A subsequent trial of infant & juvenile bonobos & chimps found that pre-weaning bonobos were less adept at social behaviours related to feeding competition than pre-weaning chimps. And finally they looked at the ability of the two species to adapt to ‘role reversal’, where human experimenters switched roles in terms of which possessed a hidden food reward: young bonobos were slower than juvenile chimps, and adults of both species, to adapt each time a researcher switched roles. (It would be nice, though, to see some data from observational field work here – using a human experimenter does introduce new variables that might not apply in the wild.)
Overall, the authors concluded that [u]nderstanding the evolutionary processes by which ontogenetic changes occurred in bonobos may provide insight into our own species’ evolution. [It's been] proposed that the crucial cognitive adaptation of humans relative to other apes is the accelerated development of social skills in infants. Althought the genetic changes that produce such developmental shifts are not well understood, if we can determine the process by which the ontogeny of bonobos evolved, inference can be made regarding analogous evolution in our own species (Wobber et al. 2010: 4) In other words, having an understanding of the control of behaviour development in bonobos may tell us something about the evolution of our own social behaviour.
But it’s a big jump to suggest (as the Telegraph does) that the heightened intolerance for food sharing shown by adult chimps is a ‘higher’ form of behaviour (with the implication that grouchy behaviour in humans is somehow a ‘more evolved’ trait). After all, like bonobos, humans show a reasonable level of paedomorphism in their general appearance, resembling young chimps in their relative facial proportions & in their lighter body hair. But this apparent similarity between humans & bonobos is the result of parallel evolution. Similarly, humans & P.troglodytes have an equally long history of separate evolutionary development, such that any apparent similarities in behaviour (eg grouchiness as a successful food-competition strategy) may well be more perceived than actual.
V.Wobber, R.Wrangham & B. Hare (2010). Bonobos exhibit delayed development of social behaivour and cognition relative to chimpanzees current biology, 20 : 10/1016/j.cub.2009.11.070