a biochemical difference between humans & other mammals

Reposted from: http://edge.org/q2007/q07_6.html
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FREEMAN DYSON
Physicist, Institute of Advanced Study, Author, Disturbing the Universe

HAR1 ( Human Accelerated Region 1) As a New Tool Leading Us Toward a Deep Understanding of Human Nature

I am generally optimistic because our human heritage seems to have equipped us very well for dealing with challenges, from ice-ages and cave-bears to diseases and over-population. The whole species did cooperate to eliminate small-pox, and the women of Mexico did reduce their average family size from seven to two and a half in fifty years. Science has helped us to understand challenges and also to defeat them.

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.

I am optimistic because I see the discovery of HAR1 as a seminal event in the history of science, marking the beginning of a new understanding of human evolution and human nature. I see it as a big step toward the fulfillment of the dream described in 1929 by Desmond Bernal, one of the pioneers of molecular biology, in his little book, "The World, the Flesh and the Devil: An Enquiry into the Future of the Three Enemies of the Rational Soul". Bernal saw science as our best tool for defeating the three enemies. The World means floods and famines and climate changes. The Flesh means diseases and senile infirmities. The Devil means the dark irrational passions that lead otherwise rational beings into strife and destruction. I am optimistic because I see HAR1 as a new tool leading us toward a deep understanding of human nature and toward the ultimate defeat of our last enemy.