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How do human brains differ from those of other primates?

  • Published23 Jul 2014
  • Reviewed23 Jul 2014
  • Author Todd M. Preuss
  • Source BrainFacts/SfN

Humans possess cognitive abilities very different from other creatures, thanks to a number of unusual features of our brains. 

For starters, our brains weigh an average of three pounds, which is enormous for an animal of our body size. By comparison, chimpanzees, our closest living relatives, have brains that are one-third the size of our own, although they are very similar to us in body size. Most of this brain-size difference reflects the evolutionary expansion of the association cortex, a group of regions that supports such sophisticated cognitive functions as language, self-awareness, and problem solving.

The size of the human association cortex is only part of what makes this region unusual in humans. In addition to having more neurons in the association cortex, brain imaging studies comparing the brains of humans to other primates show humans have a greater number of fibers connecting the brain regions involved in such human-specialized functions as language, tool making, reasoning, and social cognition. Understanding the evolution of these connections in the human brain is a major focus of my laboratory.

As humans evolved, studies show that changes occurred in their patterns of gene expression in the brain, impacting everything from brain metabolism to the ability of cells to establish new connections with other cells. Such differences in gene activity are believed to have contributed to greater levels of neuronal activity and plasticity across much of the lifespan, and may have influenced our susceptibility to neurodegenerative diseases (such as Alzheimer's disease) and to neuropsychiatric diseases (such as autism and schizophrenia). Compared to other mammals, humans appear to be unusually, and perhaps uniquely, vulnerable to these diseases.

Fu X, Giavalisco P, Liu X, Catchpole G, Fu N, et al. Rapid metabolic evolution in human prefrontal cortex. Proceedings of the National Academy of Sciences of the United States of America. 108(15): 6181–6186 (2001). 

Geschwind DH, Rakic P. Cortical evolution: judge the brain by its cover. Neuron. 80(3): 633–647 (2013).

Konopka G, Friedrich T, Davis-Turak J, Winden K, Oldham MC, et al. Human-specific transcriptional networks in the brain. Neuron. 75:601–617 (2012).  

Preuss TM. The human brain: rewired and running hot. Annals of the New York Academy of Sciences. 1225 Supplement 1(S1): E182–E191 (2011).

Rilling JK, Stout D. Evolution of the neural bases of higher cognitive function in humans. The Cognitive Neurosciences V. Cambridge, 2014.

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