Chimp Cheetah talks on the phone, understands language and is nearly as clever as Tarzan. But Great ape intelligence is not just a movie story: A number of scientific studies have explored the cognitive capacities of chimpanzees, orang-utans and gorillas. Three scientists of the German Primate Center (DPZ) in Göttingen have now shown that monkeys perform similarly to apes in a set of intelligence tests, designed to make the performance of apes and monkeys directly comparable. These results indicate that the mere size of the brain is less predictive for cognitive abilities than previously thought, and underline the assumption that humans are special when it comes to cooperatio and communication (PLoS ONE, 04/02/2012, doi:10.1371/journal.pone.0032024).
In order to understand the evolution of human intelligence, comparative psychologists are frequently using intelligence tests with nonhuman primates, more specifically apes, our closest relatives. While great apes’ understanding of physical aspects of the environment such as space, quantities and causality is similar to that of human toddlers, they fare less well in the social domain, when it comes to understanding communicative intent or the knowledge state of others. These abilities have been related to the cooperative nature and cultural developments of humans. What remained unclear was how monkeys compared to apes in such tests. Would they do generally less well, as predicted by their relatively smaller brains, or is the human excellence in the social domain a result of accelerated evolution? A team led by Vanessa Schmitt from the DPZ’s Cognitive Ethology Laboratory has now tested baboons and macaques at the German Primate Center. They compared their data with the results reported by a team at the Max Planck Institute for Evolutionary Anthropology, and found that great apes and monkeys differ little in these tests. „The results of our research suggest that differences in brain size do not translate into different results in these tests“, Vanessa Schmitt, the first author of the study, said. Schmitt and her colleagues conducted a range of tests, known as the “primate cognition test battery” (PCTB), with 18 baboons and long-tail macaques in the animals’ habitual environment at the DPZ. In order to test their understanding of causality, for instance, the monkeys were shown two cloths covered by raisins, one of which was cut in two pieces. The monkeys could choose to pull one of the two cloths and thus reach the food, but had to choose the uncut one to succeed. Both species solved the test in which the great apes had also done well. One example for a test of the social intelligence of the animals is a situation where the experimenter points at one of two cups that were turned upside down. This cup contained a food reward while the other one was empty. Neither apes nor monkeys were able to understand that the pointing was a clue for finding the food. „Our data call question the assumption of a large gap in intelligence between great apes and monkeys – at least in these kinds of tests“, Vanessa Schmitt explains. „Our upcoming studies will focus on the question why nonhuman primates don’t understand certain causal relations and also which conditions enable them to do better in such tests“, adds Julia Fischer, the head of the research group.
Vanessa Schmitt, Birte Pankau, Julia Fischer: „Old World Monkeys Compare to Apes in the Primate Cognition Test Battery”, PLoS ONE online, 04/02/2012, doi:10.1371 journal.pone.0032024.
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