Could one gene separate humans from our primate cousins?

By comparing the results of the human genome project with the primate genome project, scientists have identified one specific type of 'micro-RNA' that may be responsible for how our brains evolved to be distinct from all other species on the planet.

RNA, or ribonucleic acid, is a kind of 'mini-DNA' — single-helix rather than the double-helix of DNA and shorter than the DNA strand — that the body uses for many of its everyday functions. Micro-RNA are strands of RNA that have developed a short group of genes in the middle of their chain that can form a loop, and this loop allows the two halves of the RNA to fold back on themselves, like a hairpin, to create a double-helix, like DNA. Rather than act like other RNA, to simply code and regulate genes, these micro-RNAs act like little project managers, organizing other RNA strands and telling them which genes to code and regulate.

In studying the over 1400 micro-RNAs in our bodies, scientists identified only 10 of those that were unique to humans. Of those 10, they found just one — called 'miR-941' — that is active in our brain cells. Further investigation showed that regions of the genomes of chimps and macaques (two of our primate cousins) were similar to the sequences of the human genome that contain miR-941, but those regions lacked the structure that allows human miR-941 to form the hairpin and thus act as a micro-RNA to manage other RNAs.

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So, based on this discovery, sometime in the Miocene Epoch (between four and eight million years ago) after humans and chimpanzees split off from the same common ancestor, a genetic variation — such as a DNA rearrangement — took place that caused human miR-941 to form the hairpin structure. After that, further variations duplicated the sequence to form multiple copies, which caused that sequence to be expressed more often than other sequences.

So, what does all this mean?

Is this the one gene that separates us from our primate cousins? Some headlines have suggested this, but the answer to that question is "No". There are many genes that separate our species. This just happens to be one unique evolutionary trait that we developed, and other primates didn't develop, that has a specific influence on our brains.

Is miR-941 responsible for us wearing clothes, living in buildings, collecting in cities, driving cars and using computers, as opposed to wandering naked around the forest, foraging for food? Sure, but only in conjunction with a lot of other factors in our genetic code, though.

The fact is, no one is sure exactly what this particular micro-RNA does yet, and it may be very difficult to figure that out until we can improve our technology and understanding of the DNA sequence. The difficulty stems from the discovery that the region of our genome that has miR-941 also contains a gene that is used in the processes that control neural function. If a genetic defect is introduced into the sequence to disable miR-941 (to see what happens without it), that defect also disables this other gene, and the result would be mental disabilities and developmental problems. However, these cannot be conclusively attributed to either gene sequence, since both are affected.

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What the researchers do believe miR-941 may have a role in are 'hedgehog-signaling pathways' — those that enable the human embryo to develop properly — and 'insulin-signaling pathways' — which help to regulate blood sugar — thus, according to the study, miR-941 "potentially has a role in the evolution of human longevity." Also, with its connection to the genes that help control neural function, this suggests it does have some impact on cognitive abilities, and taken together "the unusual features of miR-941 evolution, as well as its potential association with functions linked to human longevity and cognition, suggest roles of miR-941 in the evolution of human-specific phenotypes."