Ape tool curation skills

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...


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