Tuesday, April 10, 2007

Freeman Dyson, one of my favorite scientists to read, at TCS Daily:
I am especially optimistic just now because of a seminal discovery that was made recently by comparing genomes of different species. David Haussler and his colleagues at UC Santa Cruz discovered a small patch of DNA which they call HAR1, short for Human Accelerated Region 1. This patch appears to be strictly conserved in the genomes of mouse, rat, chicken and chimpanzee, which means that it must have been performing an essential function that was unchanged for about three hundred million years from the last common ancestor of birds and mammals until today.

But the same patch appears grossly modified with eighteen mutations in the human genome, which means that it must have changed its function in the last six million years from the common ancestor of chimps and humans to modern humans. Somehow, that little patch of DNA expresses an essential difference between humans and other mammals. We know two other significant facts about HAR1. First, it does not code for a protein but codes for RNA. Second, the RNA for which it codes is active in the cortex of the human embryonic brain during the second trimester of pregnancy. It is likely that the rapid evolution of HAR1 has something to do with the rapid evolution of the human brain during the last six million years.

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