In another test, the researchers showed the animals where to find a treat hidden in one of three cups placed upside down on a table, then moved the treat to a different cup while the animals looked on. To get it right, the animals had to suppress the urge to keep looking under the first cup and search under the new cup instead.
Bonobos, gorillas and orangutans performed well on both tests, picking the correct cup or reaching for the right opening more than 90% of the time. But squirrel monkeys and a lesser-known primate called the Coquerel's sifaka did miserably, getting it right less than half the time.
Led by MacLean and Brian Hare and Charlie Nunn of Duke University, the researchers looked at a range of factors that could explain why some species excelled and others floundered.
Overall, the species with the highest scores on the self-control tests had bigger brains. Absolute brain size mattered, but relative brain size did not -- suggesting that species differences in self-control may be due to differences in how the brain is wired, rather than having big brains for their bodies per se.
In addition to brain size, the researchers also looked at whether lifestyle factors might play a role. One of the most widely accepted ideas is that animal intelligence evolved to deal with the demands of living in a group. The bigger the group, the better an animal needs to be at keeping track of social relationships and managing the delicate balance between competing and cooperating.
Surprisingly, group size didn't seem to matter for self-control, but within primates the researchers found support for another idea: Primat
|Contact: Robin Ann Smith|
National Evolutionary Synthesis Center (NESCent)