FRIDAY, Aug. 4 (HealthDay News) -- Great apes -- chimpanzees , orangutans and gorillas -- consistently outperform monkeys and lemurs on a variety of intelligence tests, which proves they're the smartest of nonhuman primates, say researchers who reviewed hundreds of studies.

The findings may help scientists better understand the link between intelligence and human evolution.

"It's clear that some species can and do develop enhanced abilities for solving particular problems. But our results imply that natural selection may favor a general type of intelligence in some circumstances. We suspect that this was crucial in human evolution," study leader Robert O. Deaner, an assistant professor of psychology at Grand Valley State University in Michigan, said in a prepared statement.

He led the study as part of his doctoral dissertation at Duke University Medical Center.

The findings were published online this week in the journal Evolutionary Psychology.

"The fact that great apes performed better than other primates in these laboratory tasks is reassuring," study co-author Carel van Schaik, director of the Anthropological Institute and Museum at the University of Zurich, Switzerland, said in a prepared statement.

"After all, in absolute terms, their brains are the largest, and they show the most sophisticated behavior under natural conditions -- deception and culturally transmitted behavior, including tool use," van Schaik said.

More information

Learn more about primates at the University of Wisconsin's National Primate Research Center.