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Gray Mouse Lemur, microcebus murinus
Gray Mouse Lemur, microcebus murinus

Lemurs with Brains 1/200 the Size of Chimps’ Pass Same IQ Test

This new finding about mouse lemurs also makes human exceptionalism more exceptional

Researchers were surprise to discover recently that the mouse lemur, a tiny primate whose brain is 1/200th the size of a chimpanzee’s brain, did as well as great apes on a primate intelligence test:

Conducting systematic tests with identical methods revealed that cognitive abilities of lemurs hardly differ from those of monkeys and great apes. Instead, this study revealed that the relationship between brain size and cognitive abilities cannot be generalized and it provides new insights into the evolution of primates.

Deutsches Primatenzentrum (DPZ)/German Primate Center, “Primate brain size does not predict their intelligence” at ScienceDaily (September 25, 2020)

The test subjects included ring-tailed lemurs, black-and-white ruffed lemurs, and grey mouse lemurs, which vary greatly in diet, brain size, and social organization, both among themselves and with Old World monkeys and great apes.

The study, using the Primate Cognition Test Battery (PCTB), provides further evidence that brain size alone is not a predictor of intelligence, though that doesn’t mean there were no differences at all: Larger primates did better on spatial reasoning tests.

There have been hints of this earlier. Research in 2004 found lemurs to be smarter than generally thought:

Until now, primatologists believed lemurs to be primitive, ancient offshoots of the primate family tree, with far less intelligence than their more sophisticated cousins, monkeys, apes and humans. But at the Duke University Primate Center, with the gentle touch of his nose to a computer screen, the ringtail lemur called Aristides is teaching psychologist Elizabeth Brannon a startling scientific lesson — that lemurs are, indeed, intelligent creatures.

Such research could offer important evolutionary insights into the nature of intelligence in primates, Brannon said, since lemurs are living models for the ancient primate mind. “Prosimians,” including lemurs and related species split off from the primate line some 55 million years ago, evolving independently from the line that led to anthropoids and humans.

Duke University, “Experiments reveal startling insights into lemur intelligence” at Eurekalert

Although the Deutsches Primatenzentrum (DPZ) study is said to provide “provides important insights into the evolution of cognitive abilities in primates,” these insights are not spelled out. The obvious conclusion from the research is that all primates show a more similar level of intelligence than expected—except for humans, who are highly exceptional. And it’s not clear how to account for that according to conventional theories of evolution.

In that sense, the study is reminiscent of two that we looked at yesterday, in which smart birds were found to have brains more like the brains of mammals than expected.

For some reason, the researchers thought that this finding was an argument against human exceptionalism. But it is quite the opposite.

If, as believed, the last common ancestor of birds and mammals lived 320 million years ago, life forms back then may have been smarter than we think. But such findings only accentuate the vast gap in intelligence between humans and lemurs, chimpanzees, or ravens today. Efforts to account for this gap in evolutionary terms have not been particularly successful.

Note: The paper, Claudia Fichtel, Klara Dinter, Peter M. Kappeler. The lemur baseline: how lemurs compare to monkeys and apes in the Primate Cognition Test Battery. PeerJ, 2020; 8: e10025 DOI: 10.7717/peerj.10025, is open access.

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Denyse O'Leary

Denyse O'Leary is a freelance journalist based in Victoria, Canada. Specializing in faith and science issues, she is co-author, with neuroscientist Mario Beauregard, of The Spiritual Brain: A Neuroscientist's Case for the Existence of the Soul; and with neurosurgeon Michael Egnor of the forthcoming The Human Soul: What Neuroscience Shows Us about the Brain, the Mind, and the Difference Between the Two (Worthy, 2025). She received her degree in honors English language and literature.

Lemurs with Brains 1/200 the Size of Chimps’ Pass Same IQ Test