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April 17, 2008
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
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Live human experiment in the Balkans - ethnic Albanian minority in Kosovo province were risking their lives for independence from Serbia, and now ethnic Serbian minority are risking their lives for independence from new country Kosovo.
Robyn Dawes wrote about this in her book years ago:
"Rational Choice in an Uncertain World: The Psychology of Judgement and Decision Making."
She gave a very interesting explanation of the phenomenon, related to the brain's sensory processing. Even if inexact, the explanation allows making predictions about the choices people are likely to make in the face of risk.
I'm not so sure about the lion example. It might well be that killing the young/wounded wildebeest (first caught one) is the strategy that minimizes effort per unit food, independent of risk aversion.
Likewise, the loss example based on food rather than utils says nothing about risk aversion. Would you prefer to fall 100 feet, or have a 10% chance of falling 1000 feet? What about a 9% or 11% chance? Do you think your answers reveal anything about risk aversion? (You may assume that the fall of 100 feet is fatal.)
These preferences may also be observed in investment decisions, were investors generally try to avoid risks (unless influenced by testosterone, as recently published articles show), but sometimes choose to bet bigger and bigger as an reaction to an initial (small) loss - finally rather betting the house, than accepting a loss. See Jerome Kerviel. --JAN
I'm not so sure that theory is true. Think about lotteries. Your chance of hitting the jackpot is virtually nil, but people spend money on it anyway, hoping to get that huge reward. Likewise, slot machines and other gambling. What about the old prospectors going west to dig for gold?
When people see a large reward, they are more likely to overlook the risk, and turn off their better judgement. Con artists often take advantage of this; just to name one example, the Nigerian 419ers. "We're foreign strangers who have picked you -- out of 300 million other Americans -- to give $$ millions to if you just transfer some cash for us. Oh, but we need some money from you up front..."
"Mature and healthy prey would probably be more nutritious..."
Says who? Young, healthy prey have less damage to internal organs, and the more tender meat can be digested more easily.
Additionally, the digestive systems of the predators will have tended to have evolved to better use the nutrients of the younger, weaker prey.
The easier choice, which is less risky, becomes, over millennia, the better one.
@Seth "Would you prefer to fall 100 feet, or have a 10% chance of falling 1000 feet?"
In a nutshell. The other side is "would you prefer to get a good pair of climbing boots, or a 10% chance of 10 pairs?"
More generally, if you have just about enough food (or whatever) to get by (as most creatures generally do). Then losing half of it is just as bad as losing all of it, but getting ten times as much really isn't much better than getting, say, twice as much.
What interests me about this is the social aspect of it. A hermit is better off foraging for berries than hunting elk, but a band of hunters who share their meat live better than a band of foragers. So I predict that creatures in equitable social networks will be bolder than loners, and conversely creatures in risky niches will be more social than those in steady ones.
When providing security recommendations for customers, I categorize them by their visible risk-taking characteristics. I really believe if humans had not made it easier to survive, a lot of my customers would have been weeded out by natural selection.
This post is anonymous, right?
Chimps ... risk aversion ... what if they have no choice? This is an off-shoot from security, but interesting in the fact that chimps, 40+ years ago, were instrumental in the US's space program. Have a look:
"Says who? Young, healthy prey have less damage to internal organs, and the more tender meat can be digested more easily."
That would be true, if lions went for young and healthy prey. But reportedly, they tend to go for young and sickly prey, making Bruce's argument more probable.
"making Bruce's argument more probable."
No. Lions catch and kill as more young and healthy prey than young and sickly prey. There are many more young and healthy prey than sickly ones, and they make up a much larger portion of these big cats' diet.
No member will turn down a live, sickly animal as prey. But there's not enough of them to sustain the pride.
So, your info is true, but it's not the whole truth, and it leaves out the most pertinent part.
Bruce's overall argument will do better without his use of a poor example.
Some of the work by an ecologically-minded group called the "Resilience Alliance" might be of interest, specifically their work on poverty and rigidity traps. A poverty trap can be thought of as simulated annealing without finishing the first phase; constantly jumping around, i.e., taking risks. Rigidity can be interpreted as risk-adverse. A paper currently in review by SR Carpenter et al will be presenting this train of thought soon, in the context of environmental management. It's interesting stuff. Risk is everywhere in ecology, ask any ecologist.
Oh, and I forgot to mention in my previous post - the main idea is that being too risk adverse or too risk-prone is damning on both ends, but there may exist some sweet spot in the middle.
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