Gene-aided man got a head start over chimps
JAMES RANDERSON
The most crucial genetic region that makes us human identified Scientists sorted the interesting changes from the less influential ones
SCIENTISTS HAVE identified perhaps the most crucial genetic region that makes us human. By comparing human DNA with that of chimpanzees and other animals they have found the region of the genome subjected to the strongest natural selection since we shared a common ancestor with chimps.
The 108-letter stretch of DNA contains two genes that appear to control brain development. The researchers speculate that the blistering pace of evolution indicates that they may have been crucial in the rapid increase in brain size and complexity that occurred in the human lineage. "It's evolving incredibly rapidly," said Katherine Pollard at the University of California in Davis. Most of the 15m or so differences between the chimp genome and our own are random, inconsequential changes that make no difference to our appearance or abilities.
To sort the interesting changes from the less influential ones, she looked further down the evolutionary tree to find regions of DNA that really are useful.
She and her colleagues looked for bits of the genome that are nearly identical in the mouse, rat and chimpanzee. These shared a common ancestor around 80m years ago, so the scientists reasoned that any DNA region that had not changed much in this time must be crucial for survival.
They then trawled these conserved regions for instances where the human equivalent had changed a lot. Top of the list is a 108-letter sequence called HAR1 (Human Accelerated Region 1), which contains two genes. This region differs by just two changes between chimps and chickens, which shared a common ancestor around 310m years ago. But since humans and chimps split five million years ago there have been 18 changes.
Tremendous pressure
"There has been tremendous pressure for millions of years to keep the sequence as it was. Then something happened in our lineage," said Pierre Vanderhaueghen at the Free University of Brussels.
He was able to get clues by adding colour labelled chemicals that would stick to the RNA product produced by the genes to slices of brain tissue from human foetuses. His results showed that one of the genes is expressed strongly in the developing neocortex during weeks seven to nine of pregnancy. —
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