When monkeys play dumb

Science News, Nov 6, 1999 by B.B.

Rhesus monkeys jockey fiercely for power and social position in their colonies. Some become big shots, while others end up as small fry. When individuals in a colony face experimental challenges in front of their comrades, big shots exhibit what looks like much greater intelligence than small fry.

However, the big shots aren't blessed with a surplus of smarts, a new study finds. Their advantage lies in intimidation.

Low-ranking monkeys display as keen a learning capacity as their social superiors when the two groups undergo separate testing, report Christine M. Drea of Duke University in Durham, N.C., and Kim Wallen of Emory University in Atlanta. Small fry do poorly on a learning task only if they see dominant monkeys hanging around, the researchers hold.

They suspect that low-ranking monkeys selectively play dumb, probably to avoid rising above their humble social status and attracting retaliation from dominant animals.

People behave in similar ways, Drea and Wallen argue. For example, evidence suggests that many teenage girls do better academically in same-sex rather than co-ed classrooms. Also, black college students score lower on standardized tests after being prompted with a negative stereotype (SN: 10/30/99, p. 280).

Drea and Wallen studied a colony of 55 rhesus monkeys housed in an outdoor research facility. The researchers identified 27 dominant and 28 subordinate animals.

All of them first had opportunities to learn that they could dig up peanuts buried in four blue boxes but not in four red boxes. Each monkey got a chance to check out the boxes undisturbed as the test of the colony waited nearby. Animals then were split into high- and low-status groups for individual assessment. In further trials, members of the two social groups separately explored yellow boxes with peanuts and green boxes with none. Learning tests then occurred in the presence of the entire colony.

In these joint learning and testing sessions, dominant monkeys retrieved the most peanuts and spent the most time near peanut-holding boxes, the researchers report in the Oct. 26 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. In split groups, small fry got as many peanuts as big shots did. Still, higher-ranking monkeys in each group did better than the rest.

Drea and Wallen say that dominant animals rarely threatened subordinates in joint trials, indicating that low-ranking monkeys were not overtly bullied into playing dumb.