Lemur Logic May Provide Clues to Primate Intellect Evolution

John Pickrell in England
for National Geographic News
June 4, 2004

We already know that monkeys and apes have remarkable levels of intelligence. Chimps and gorillas have been taught to use complex sign languages, Rhesus macaques demonstrate knowledge of basic math, and baboons are known to commonly deceive one another to their own ends.

But lemurs— monkeys' primate cousins—were thought to possess few of these abilities. Scientists had all but written them off as a cognitive dead end in the primate family tree.

Now, Aristides, an 11-year-old ring-tailed lemur with fluffy gray fur and enquiring brown eyes, may be about to turn that idea on its head.

With the help of his trainer, psychologist Elizabeth Brannon, Aristides selects sequences of images by pressing his nose against a computer screen. In return for fruit-flavored sugar pellets, Aristides and his eager classmates at the Duke University Primate Center are providing Brannon's team with compelling clues about how our earliest primate ancestors developed mental capabilities that we all share today.

Ancestral Brainpower

Fossils suggest that lemurs, bush babies, lorises, aye-ayes, and their relatives (the prosimians) spilt off from the ancestors of monkeys and apes around 55 million years ago. Therefore studying the brainpower of these seemingly primitive animals might offer insights into the earliest primates' mental abilities.

"Anthropologists are interested in discovering how human intelligence evolved and how we differ to other species," said Brannon of the Durham, North Carolina-based university. "By pinpointing which cognitive abilities all primates share, including prosimian primates, we hope to determine what aspects of intelligence are general primate adaptations."

Much of Brannon's research has focused on understanding how humans became so sophisticated numerically. Her studies of human infants, monkeys, and now lemurs are helping to piece together a picture of whether primates possess a special predisposition to math.

Despite the huge quantity of literature on all aspects of intelligence in chimpanzees, rhesus macaques, and a handful of other primates, there has been very little work on lemurs. Brannon's work may now go someway to filling that frustrating data hole.

However, she started the pilot project with low expectations. Lemurs—which are found exclusively on the African island of Madagascar—are much less curious than the average monkey. The handful of existing cognitive studies suggested that the animals had little capacity to learn or complete simple tasks.

List Learning

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