Chimps prefer to copy others with prestige

There is no action so stupid that you can’t persuade someone to do it by getting celebrity endorsement. Even the barmiest advice on everything from medical decisions to diets will have happy idiots queuing up to listen, if it comes from the mouth of someone who was once on TV. Such recommendations can be disastrous, but they can be beneficial if the people in question are wise and knowledgeable, from village elders to community leaders. This is all part of the same trend – the human penchant for apeing individuals with high status. And now, it seems that we aren’t the only species that does this. Chimpanzees have the same inclination for apeing those with prestige.

We know that chimps can pick up new traditions from one another, with different groups enjoying rich and diverse cultures. Much of this understanding is thanks to work from scientists like Victoria Horner, Andrew Whiten and Frans de Waal at the Yerkes National Primate Research Center. Now, the same team have found that when it comes to passing on traditions, some chimps are more influential than others. Given a choice between two individuals, chimps tend to copy the actions of the older, higher-ranking one.

The Yerkes Center is, incidentally, a shining paragon of ape research. The chimps live in spacious outdoor enclosures, full of grass, climbing frames, swings, and toys to stimulate their mind. The researchers call each chimp by name and ask them to take part in studies, giving them the choice to interact with equipment.

So far, the center’s researches have focused on whether chimps pass on traditions to one another but they’ve now started to look at why a chimp might decide to copy another chimp’s behaviour. Horner gave two groups of chimps a chance to learn a new set of skills from one of two different tutors. In each tutor pair, one animal was a high-ranking older female who has successfully passed on cultural traditions before, and the other was a younger subordinate who had no such experience.

In the first group, Horner trained the older female to collect plastic tokens and put them in a spotted box in exchange for food. Meanwhile, she trained the younger female to do the same with a striped box. In the second group, the box assignments were reversed. Over ten days, the other chimps watched as their demonstrators enacted their token-collecting actions during 20-minute sessions.

When the onlookers were given tokens of their own, they were far more likely to stick them in the box favoured by the older, high-ranking female, whether it was striped or spotty. As groups, they opted for her choice on around 70% and 90% of the time. As individuals, they also showed the same favouritism.

This bias must stem from differences between the two tutor chimps, for neither action was harder than the other nor did either one earn a greater reward. The tutors demonstrated in parallel sessions for the same number of times at the same distance from their audience. And the dominant chimp didn’t make any more aggressive advances than the subordinate.

Horner thinks that chimps, like humans, gain “prestige” as they demonstrate their skills and knowledge, and with it comes a disproportionate influence over their peers. The effect is probably even more pronounced in the wild, when low-ranking individuals may be more concerned about aggressive rebukes from their peers and stay on the periphery of their groups. But for the moment, it’s not clear what exactly contributes to this prestige: age; social status; past successes; or a combo of the above? Having only studied two pairs of demonstrator chimps, Horner can’t tell which yet.

This might seem obvious but it’s never been tested before and it casts our knowledge of chimp culture in a different light. Groups of wild chimps certainly have cultural differences but equally, field researchers have found that the vast majority of innovations never spread. Chimps also get ‘stuck’ on familiar techniques. They’re reticent to adopt a new strategy, even if it’s more efficient.

Horner’s new results could help to explain why. It seems that in chimp societies, subordination is the mother of invention. Most innovations are the work of low-ranking individuals, trying to avoid competition from their superiors. Ironically, these individuals are the least likely to be aped by their fellow apes. Only if they rise through the ranks do they stand a chance of significantly passing on their new behaviours to their colleagues.

Reference: PLoS ONE http://dx.doi.org/10.1371/journal.pone.0010625

Photo: by Matthew Hoelscher

More on chimp behaviour:

• How chimpanzees deal with death and dying
• Culture shapes the tools that chimps use to get honey
• Chimps use Swiss army toolkit to rob beehives
• Cultured chimps pass on new traditions between groups
• Chimpanzee collects ammo for “premeditated” tourist-stoning
• Chimpanzees make spears to hunt bushbabies

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