chimpanzees

Victoria Horner and colleagues (2006) set up two "diffusion chains" of chimpanzees, to see if a learned task could be transmitted faithfully from one chimp to another for several iterations.

Using a powerful three-group, two-action methodology, we found that alternative methods used to obtain food from a foraging device ("lift door" versus "slide door") were accurately transmitted along two chains of six and five chimpanzees, respectively, such that the last chimpanzee in the chain used the same method as the original trained model. The fidelity of transmission within each chain is remarkable given that several individuals in the no-model control group were able to discover either method by individual exploration. A comparative study with human children revealed similar results. This study is the first to experimentally demonstrate the linear transmission of alternative foraging techniques by non-human primates. Our results show that chimpanzees have a capacity to sustain local traditions across multiple simulated generations (Horner et al. 2006:13878)

Essentially, they trained one individual in each of two chimpanzee groups to open a box with a reward inside -- but there were two ways to open the box, and each of these models was taught a different method. Another chimpanzee was given a period of time, with several trials, to observe one of these models opening the box. Then when the learner acquired the method, another chimp became the learner observing the second. And so on.

They found that the two methods were transmitted essentially intact across as many chimpanzees as they tried, with a couple of limits -- some chimpanzees couldn't be paired as model-learner pairs because they were aggressive toward each other, and some just didn't watch the model and learned the task independently. As the paper notes, these cases are interesting because they present limits on the ability of groups to maintain such traditions:

Side branches occurred in both chains because either the model was unsuccessful/unmotivated (RN in FS1, AM in FS2) or aggression occurred bet ween the model and observer (KT to BO in FS1, CY to VV in FS2). The latter highlights the importance of tolerance and reinforces the hypothesis that opportunities for social learning in the wild may be restricted by the level of tolerance between individuals (50) and that not all individuals within a population may be good models for social learning (51) (Horner et al. 2006:13881).

For me, this study helps to clarify some of the constraints on social learning:

It is not the function of diffusion studies to dissect in depth the underlying mechanisms of transmission, although these must be sophisticated enough to ensure the replication of behavior across the generations. However, some limited inferences are suggested by the contrasts deriving from the three-group design. The no-model control condition indicates that for about half the chimpanzees (and children), opening an object like the Doorian fruit can be said to be within their untutored competence. Therefore, it seems reasonable to assume that half the participants from the diffusion chains would also have been able to open the Doorian fruit in a control condition. Their exclusive use of only one of the two available techniques may represent a form of "canalization" (46), whereby a chimpanzee's potentially limitless exploration of a problem is focused around only a subset of behaviors that they see performed by others. Similarly, it is likely that half of the participants in the chains would have failed the control condition, and hence their behavior suggests a more complex social learning mechanism, such as emulation or imitation (28), but further experiments will be required to establish this (Horner et al. 2006:13881).

Of course this is an artificial situation -- with two possible solutions -- but it suggests several of the balancing factors in the learning and transmission of natural behaviors. Simple things ought to be transmitted very readily. But then, if an adaptive behavior is really that simple, then maybe it should be genetically assimilated. One wonders also whether the chimpanzees who failed to pick up the behavior independently would have ever been able to figure it out, or whether they would just remain oblivious to an adaptive resource in the wild. There is also, after all, a possible reason to be bad at trying new things -- that being, that sometimes new things will kill you.

References:

Horner V, Whiten A, Flynn E, de Waal FBM. 2006. Faithful replication of foraging techniques along cultural transmission chains by chimpanzees and children. Proc Nat Acad Sci USA 103:13878-13883. PNAS online

An accessible story by Bjorn Carey discusses the paper by Mulcahy and Call, titled "Apes save tools for future use." From the story:

To determine if apes can also perform this type of "mental time travel," Nicholas Mulcahy and Josep Call, researchers at the Max Planck Institute for Evolutionary Anthropology in Germany, enlisted five bonobo chimpanzees and five orangutans for an experiment.

The researchers first led the animals into a room and taught them how to use a tool to get a food reward. Then the apes were directed to a "tool shed" containing tools for reaching grapes and juice bottles. Two of the tools were well suited for the task, while six were not.

After an ape made its selection, it was not allowed access to the goodie dispenser for an hour, so the animal hauled the tool back to a waiting room for storage.

When the researchers allowed the animals to have a go at the dispenser, the apes returned with a suitable tool and retrieved their treat in less than five minutes about 30 percent of the time.

With one bonobo and one orangutan, they ran the test overnight -- they had to take the tool back to their sleeping room and return with the tool in the morning to get the reward.

The clever part of the experiment was one of the controls:

Experiment 4 established the baseline probability of transporting tools in the absence of a future task but using identical reinforcement contingencies as in experiment 3. Two bonobos and two orangutans received the same treatment as in experiment 3, except that no apparatus was set up upon their return to the test room although they were rewarded if they brought the suitable tool back. Subjects solved the task significantly less often (mean = 1.8, SEM = 1.2) than did those in experiment 3 (t6 = 3.91, P = 0.008). In fact, only two of the four subjects brought back the suitable tool at all, and they behaved differently from other successful subjects because after their first successful trial, they failed the next 11 and 14 trials, respectively (Table 1). Subjects in experiment 4 also solved the task significantly less often than those in experiment 1 (t8 = 2.81, P = 0.023), thus ruling out the possible confounding effects of practice, because both groups of subjects were naïve when their respective experiments began.

It seems that if they didn't have to use the tool, they didn't bother to bring the tool.

A question: Why are these kinds of stories always about "how smart" apes are instead of "how dumb" people are? I mean, it would be fairly hard to train people to do this task without talking to them. I think that there would be a good fraction of people who wouldn't get it.

At least, not without a better reward. I guess that even though students pretty consistently fail to bring number 2 pencils on evaluation day, they rarely fail to bring them when there's an exam...

References:

Mulcahy NJ, Call J. 2006. Apes save tools for future use. Science 312:1038-1040. DOI link

I was discussing animal (and plant) rights in class yesterday, and now I see that the Spanish Socialist Party wants to make apes legal persons (via Althouse):

The Spanish Socialist Party will introduce a bill in the Congress of Deputies calling for "the immediate inclusion of (simians) in the category of persons, and that they be given the moral and legal protection that currently are only enjoyed by human beings." The PSOE's justification is that humans share 98.4% of our genes with chimpanzees, 97.7% with gorillas, and 96.4% with orangutans.

This is precisely the problem with using the "percent similarity" -- should baboons be included? What about chickens? Should they have rights according to their "percent similarity" to us? Mushrooms?

A pox on everyone who repeats the "percent similarity" meme!

UPDATE (4/26/2006): A reader writes:

Sorry to bother you, but the chimp story is not true. Just media making a story more interesting:

[This linked story] contains words from the minister Cristina Narbona (environment cabinet):

"En ningún caso ni se crean ni se defienden derechos humanos para los simios; en ningún momento se habla de otorgar derechos humanos a los grandes simios", reiteró.

Which can be translated as: "In no case we will create or support human rights for the simians; at no time do we talk on giving human rights to the big apes", she said.

A pox on sensationalist simian stories!

Another piece of Google archaeology: this 1947 piece from Natural History:

By this time Moos and Bimba were definitely money-mad. When permitted to operated the Work Machine as often as they wished, these two apes amassed great piles of poker-chip wealth.

Oh, yes, it's an article about early psychology experiments on chimpanzee economics!

The most touching part is this:

It might have been anticipated that the introduction of money into chimpanzee society was bound to make trouble sooner or later. Perhaps it is too much to say that the profit motive could wreck ape economy. And as far as the scientific report goes, there is no absolute proof that the Yale Colony succumbed to an irreversible process of moral decay as a result of these experiments. Nevertheless, it is just as well that they came to an end when they did, for certain ominous trends were rapidly becoming apparent.

Despotism and cruelty are not unknown among man's nearest living relatives, but usually they take simple and straightforward forms such as wife-beating or commandeering of the food supply. New and subtle kinds of treachery are possible when wealth is involved.

When Bula and Bimba were living in the same cage, a large supply of white poker chips was offered to the two females. Bula promptly assumed ownership of nearly every one, and Bimba was left with a very small hoard. She protested vocally and with gestures, whining and holding out an empty hand. Like a rich man tossing a coin to a beggar, Bula impatiently selected one chip from her huge pile and dropped it negligently in Bimba's palm. When the vending machine was wheeled up to their cage, both animals rushed to spend their windfalls. Bula roughly shouldered Bimba away and took complete possession of the machine. The menu that day was slices of unpeeled oranges. Bula calmly bought and devoured one slice after another, and when Bimba started to complain, Bula handed her the peels!

It's a pretty entertaining read -- not because it seems hopelessly out of date, but surprisingly, because it seems like it could have been written last year! Current experiments like these in primates are more sophisticated in subtle ways, but at the level of description for a popular article they look almost indistinguishable.

I suppose that should be depressing. But then, I'm used to seeing every new fossil described as a "missing link", a chestnut that's been with us since the 1870's, so finding a 60-year-old psychology article that looks current doesn't surprise me!