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A detailed scan of the human genome has revealed a small snippet of DNA that has undergone accelerated evolution in humans.
The precise role of the DNA section is unclear, but it is part of a gene that becomes activated during a critical stage of brain development in humans. The genetic code fragment is also found in other animals, but has remained largely unchanged for several million years.
The researchers say the finding, detailed in the Aug. 17 issue of the journal Nature, could help explain why the brains of humans are nearly three times larger than those of chimpanzees, our closest living relative.
Evolution fast track
The researchers compared the genomes of humans, chimpanzees, mice and rats and identified sections of DNA that have remained largely unchanged over the 80 million years or so since we all shared a common ancestor.
The search was then refined to look for the snippets of DNA that have changed markedly since the 6 million years or so since the ancestors of humans and chimps split.
"Some DNA regions have hardly changed at all over many millions of years in most species," said study team member Katherine Pollard, who is now at the University of California, Davis. "My twist was to look for a subset of these genes that have changed just in humans."
Pollard found 49 regions in the human genome that showed signs of rapid evolution. The majority of these so-called "human accelerated regions," or HARs, were located near genes that help regulate the function of other genes. Furthermore, 12 of the HARs were located near genes involved in brain development.
Topping off the list was HAR1, a section of DNA made up of 118 bases, or "letters." A computational analysis of HAR1 showed that is essentially the same in all mammals except humans.
In the time since humans and chimps split about 6 million years ago, HAR1 has racked up 18 base substitutions when only one or none would be expected by chance.
For comparison, the HAR1 region of chickens and chimps only differ by two substitutions, even though more than 310 million years have passed since they shared a common ancestor.
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The precise role of the DNA section is unclear, but it is part of a gene that becomes activated during a critical stage of brain development in humans. The genetic code fragment is also found in other animals, but has remained largely unchanged for several million years.
The researchers say the finding, detailed in the Aug. 17 issue of the journal Nature, could help explain why the brains of humans are nearly three times larger than those of chimpanzees, our closest living relative.
Evolution fast track
The researchers compared the genomes of humans, chimpanzees, mice and rats and identified sections of DNA that have remained largely unchanged over the 80 million years or so since we all shared a common ancestor.
The search was then refined to look for the snippets of DNA that have changed markedly since the 6 million years or so since the ancestors of humans and chimps split.
"Some DNA regions have hardly changed at all over many millions of years in most species," said study team member Katherine Pollard, who is now at the University of California, Davis. "My twist was to look for a subset of these genes that have changed just in humans."
Pollard found 49 regions in the human genome that showed signs of rapid evolution. The majority of these so-called "human accelerated regions," or HARs, were located near genes that help regulate the function of other genes. Furthermore, 12 of the HARs were located near genes involved in brain development.
Topping off the list was HAR1, a section of DNA made up of 118 bases, or "letters." A computational analysis of HAR1 showed that is essentially the same in all mammals except humans.
In the time since humans and chimps split about 6 million years ago, HAR1 has racked up 18 base substitutions when only one or none would be expected by chance.
For comparison, the HAR1 region of chickens and chimps only differ by two substitutions, even though more than 310 million years have passed since they shared a common ancestor.
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