THE human brain may have shot ahead of its primate predecessors by shifting the activity of a suite of genes into a higher gear. A new analysis of chimp and human brains has discovered that for the small number of genes that differ between chimps and people, 90 per cent are more active in human brains.
Having identified some of these supercharged genes, Carrolee Barlow of the Salk Institute for Biological Sciences in La Jolla, California, speculates that our neurons communicate at faster speeds. 鈥淚t鈥檚 like comparing a Volkswagen and a Porsche,鈥� she says. 鈥淭hey are very similar but a Porsche engine gets the gas moving to the pistons much better.鈥�
Despite obvious differences between chimps and humans, the biological changes responsible have been elusive. Brain imaging has revealed only minor neurological differences between the two species. And evolutionary changes to gene DNA sequences may be less than 1 per cent.
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But last year, researchers announced that the gene activity in human and chimp brains had changed or evolved much more than gene activity in the rest of the body. And early this year, another group reported that the majority of these changes were due to increases in gene activity in the human brain.
The new work by Barlow鈥檚 team reveals how dramatic the trend of gene activation in the human brain is. Starting with a set of about 12,000 genes, they found 91 that differed significantly in human and chimp brains. In 83 of these cases, the human brain had higher gene activity.
In contrast, where genetic activity differed in heart and liver, human genes had decreased activity just as often as they had increased activity (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2135499100).
Ajit Varki of the University of California, San Diego, part of the team that published the evolutionary analysis of human and chimp brain genes last year, says the new results are striking. But he suspects other types of genetic change were crucial in human brain evolution. 鈥淲e know from the fossil record human evolution was a complex, multistep process,鈥� he says. 鈥淢y guess is that many different types of genetic events probably played a role.鈥�