Research published in today’s issue of PLoS Biology builds on decades of intervening advances in evolution and genetics and take the question much further. The difference between humans and nonhuman primates in cognitive ability is explained in large part by differences in gene expression, especially during the critical periods when young brains are being formed.
Humans share many of their genes with other species, especially chimps. In fact, we share so many genes that it is hard to explain how we can be so different in terms of cognitive ability. If genes make all the difference, how can they explain the differences between chimp and human brains? And how can a mere six million years of human-chimp divergence give us enough time to accumulate enough genetic change?
The answer seems to lie in the relatively rapid evolution of differences in gene expression. In other words, while the genes themselves evolved slowly, the regulation of their expression evolved more rapidly. It’s not just the genes but their expression that’s important. It’s not just the evolution of genes but the evolution of gene expression that drives the rapid divergence between human and chimp brains.
This is especially true in the genes that control the development of the prefrontal cortex of the brain. In other words, there has been relatively rapid evolution in the genetic mechanisms that regulate genes directly responsible for the early-childhood neural development of the critically-important prefrontal cortex, which is involved in abstract thinking, planning, social intelligence, and working memory.
According to the article, “humans display a 3-5 times faster evolutionary rate in divergence in developmental patterns, compared to chimpanzees.” Most important, however, is the way this research identifies specific regulators that have evolved rapidly since human-chimp divergence. These regulators are “micro-RNAs,” some of which are specifically identified in the article, with the claim that “changes in the expression of a few key regulators may have been a major driving force behind rapid evolution of the human brain.”
According to the study’s senior author, Philipp Khaitovich, this finding suggests that "identifying the exact genetic changes that made us think and act like humans might be easier than we previously imagined." Kkaitovich was quoted in a press release issued by the journal, PLoS Biology.
The article is entitled "Micro-RNA-Driven Developmental Remodeling in the Brain Distinguishes Humans from Other Primates" and appears in the December 6 issue of PLoS Biology, where it is freely available to the public.
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