Keys to Human Brain Evolution


Scientists Discover Some Keys to Human Brain Evolution

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Researchers have uncovered some possible explanations for what distinguished human brain evolution from that of their primate cousins.

The questions surrounding why and how the human brain has evolved over the past six million years as compared to other primates in the evolutionary timeline have been central in the discussions of human origins research for many years. When and how did this happen? Some possible clues may have emerged as a result of new research by an international team of scientists in China and Germany, suggesting that changes in the activity levels of certain genes of the human brain during brain development may have been the cause, and that these changes were controlled by key regulatory molecules called microRNAs.  

As reported in the open-access journal PLoS Biology, the researchers analyzed brain genetic activity in humans, chimpanzees and macaques across their lifetimes, beginning with newborns. They targeted two key brain regions: the cerebellum, which controls movement, and the prefrontal cortex, which plays a major role in cognitive behavior, such as abstract thought, innovation and social interaction. What they found was that the human gene activity displayed a markedly different pattern during individual life-time human brain development from that of chimpanzee and macaque primate counterparts. Moreover, the distinquishing patterns were most pronounced in the prefrontal cortex, where, for example, genes showing the human-specific changes were four times as numerous as those showing the chimpanzee-specific changes. Many of the genes showing the human-specific patterns were identified as having neural functions, suggesting a connection to cognitive development. 

Looking deeper into the reasons why this occurred, the researchers discovered that key regulatory molecules called microRNA showed even more changes in the human prefrontal cortex. Each of these regulators targets hundreds of regular genes, changing or regulating their functions and activities. This could explain how hundreds of human-specific genes changed their activity patterns at the same time or in a coordinated fashion. It also suggests that human cognitive ability evolution may have been the result of a few mutations in key developmental microRNAs. According to Philipp Khaitovich, the lead author of the study, "identifying the exact genetic changes that made us think and act like humans might be easier than we previously imagined". 

What is more, the researchers suggest that identification of the mutations that caused these developmental gene changes could open up the door to a better understanding of the differences between Neanderthal and modern human cognitive abilities, leading to possible implications about the nature and result of modern human and Neanderthal interaction during late Pleistocene times.

The detailed report of the study can be found in PLoS Biology as: Somel M, Liu X, Tang L, Yan Z, Hu H, et al. (2011) MicroRNA-Driven Developmental Remodeling in the Brain Distinguishes Humans from Other Primates. PLoS Biol 9(12): e1001214. doi:10.1371/journal.pbio.1001214