Monkeys, Brains, and Human Evolution: New Findings


Monkeys, Brains, and Human Evolution: New Findings

Dan McLerran  

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Two recently conducted studies may add some possible new revelations related to our understanding of human or primate evolution. In one, researchers have concluded that certain monkeys, like humans, have the ability to recall or remember things and then even apply those memories to novel situations, suggesting the possibility that recollection did not necessarily depend upon language and that this ability may have been present in a common primate ancestor 30 million years ago. In another, researchers are suggesting that a single gene mutation may have controlled or directed the evolution of the cerebral cortex of the human brain over the last 5 million years.

Study No. 1

Having a memory like a monkey may not be quite as bad as it sounds. A recent study conducted by Benjamin Basile and Robert Hampton of Emory University shows that rhesus monkeys are capable of not only recognizing things they have seen before, but can also recollect or recall images and impressions from the past by recreating them in a new situation. Up until now, this was thought to be a uniquely human trait, making it possible to imagine, plan, and perform other cognitive skills necessary for greater social complexity and survival. Basile and Hampton tested the monkeys by having them "draw" or reproduce shapes they saw in the past on a computer touch screen.  "The ability of monkeys to recall these shapes flexibly suggests that they might be able to recollect other types of information that would be useful to them in the wild," said Basile. "It's exciting to speculate that they may be able to recollect the appearance of monkeys they know, what favorite foods look like, or the path they would have to take to get to a water source."

Like humans, the monkeys remembered less during tests when required to recall something, as compared to simply recognizing something, but the most important finding suggested that the monkeys, again like humans, were able to transfer their memories to novel shapes. Their ability was not limited only to shapes to which they had been exposed during earlier tests or training. 

What are the implications for human evolution? The researchers suggest that the ability to recall did not necessarily depend upon the development of language and other advanced cognitive abilities, functions attributed to early and modern humans. Say Basile and Hampton in their report, "The presence of recollection in rhesus monkeys suggests that ancestors common to humans and Old World monkeys evolved under selection pressures favoring the ability to recall as well as recognize. For example, familiarity does not support detailed memory for context, but it is quick and resistant to distraction. Recollection is slower and more vulnerable to distraction but supports a more detailed and flexible use of memory. Familiarity might better allow rapid responses to foods and predators under distracting conditions, whereas recollection might be necessary to access knowledge of distant food locations or past social interactions for planning future behavior."

Study No. 2

A collaborative team of researchers have found that the shape and size of the cerebral cortex of the human brain is primarily determined by mutations of a single gene. The cerebral cortex is the outer layer of the cerebrum of the brain, responsible for such functions as perceptual awareness, thought, language, and consciousness. It's functionality is, in other words, one of the factors that has made humans uniquely intelligent and creative, set apart from most mammals. 

The findings were based on a genetic analysis of children who were born with a severe form of microcephaly, a neurodevelopmental disorder where the circumference of the head is significantly smaller than normal. The test subjects had brains only 10 percent of normal size and a severely underdeveloped cortical architecture that is characteristic of the human brain. The researchers found that mutations in a single gene, centrosomal NDE1, was responsible for the deformities.


An MRI of brain of patient with severe form of microcephaly compared to a control subject. A team of researchers have found that mutations in a single gene may cause large discrepancy in size of the cerebral cortex. Courtesy Yale University School of Medicine.

Reports Murat Gunel, co-author of the paper and the Nixdorff-German Professor of Neurosurgery and professor of genetics and neurobiology at Yale, "The degree of reduction in the size of the cerebral cortex and the effects on brain morphology suggest this gene plays a key role in the evolution of the human brain..........These findings demonstrate how single molecules have influenced the expansion of the human cerebral cortex in the last five million years.  We are now a little closer to understanding just how this miracle happens."

The study involved a collaboration of scientists from universities and institutions around the world,  including Yale, Harvard, Northwestern, the University of Cambridge, and others in Saudi Arabia and Turkey.

The detailed research reports for both studies is published in the April 28 online issue of Current Biology, by Cell Press.