Risk Preferences in Chimpanzees and Bonobos
I've already written about prospect theory, which explains how people approach risk. People tend to be risk averse when it comes to gains, and risk seeking when it comes to losses:
Evolutionarily, presumably it is a better survival strategy to -- all other things being equal, of course -- accept small gains rather than risking them for larger ones, and risk larger losses rather than accepting smaller losses. Lions chase young or wounded wildebeest because the investment needed to kill them is lower. Mature and healthy prey would probably be more nutritious, but there's a risk of missing lunch entirely if it gets away. And a small meal will tide the lion over until another day. Getting through today is more important than the possibility of having food tomorrow.
Similarly, it is evolutionarily better to risk a larger loss than to accept a smaller loss. Because animals tend to live on the razor's edge between starvation and reproduction, any loss of food -- whether small or large -- can be equally bad. That is, both can result in death. If that's true, the best option is to risk everything for the chance at no loss at all.
This behavior has been demonstrated in animals as well: "species of insects, birds and mammals range from risk neutral to risk averse when making decisions about amounts of food, but are risk seeking towards delays in receiving food."
A recent study examines the relative risk preferences in two closely related species: chimanzees and bonobos.
Human and non-human animals tend to avoid risky prospects. If such patterns of economic choice are adaptive, risk preferences should reflect the typical decision-making environments faced by organisms. However, this approach has not been widely used to examine the risk sensitivity in closely related species with different ecologies. Here, we experimentally examined risk-sensitive behaviour in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), closely related species whose distinct ecologies are thought to be the major selective force shaping their unique behavioural repertoires. Because chimpanzees exploit riskier food sources in the wild, we predicted that they would exhibit greater tolerance for risk in choices about food. Results confirmed this prediction: chimpanzees significantly preferred the risky option, whereas bonobos preferred the fixed option. These results provide a relatively rare example of risk-prone behaviour in the context of gains and show how ecological pressures can sculpt economic decision making.
The basic argument is that in the natural environment of the chimpanzee, if you don't take risks you don't get any of the high-value rewards (e.g., monkey meat). Bonobos "rely more heavily than chimpanzees on terrestrial herbaceous vegetation, a more temporally and spatially consistent food source." So chimpanzees are less likely to avoid taking risks.
Fascinating stuff, but there are at least two problems with this study. The first one, the researchers explain in their paper. The animals studied -- five of each species -- were from the Wolfgang Koehler Primate Research Center at the Leipzig Zoo, and the experimenters were unable to rule out differences in the "experiences, cultures and conditions of the two specific groups tested here."
The second problem is more general: we know very little about the life of bonobos in the wild. There's a lot of popular stereotypes about bonobos, but they're sloppy at best.
Even so, I like seeing this kind of research. It's fascinating.
EDITED TO ADD (5/13): Response to that last link.
Posted on April 17, 2008 at 6:20 AM • 14 Comments