Human brain still evolving
The human brain is continuing to evolve, apparently moving towards ever-greater intelligence.
In two related papers published in the journal Science, University of Chicago researchers report that two genes linked to brain size are rapidly evolving in humans.
"Our studies indicate that the trend that is the defining characteristic of human evolution-the growth of brain size and complexity-is likely still going on," says Bruce Lahn, lead researcher for both papers and an investigator at the Howard Hughes Medical Institute. "Meanwhile, our environment and the skills we need to survive in it are changing faster then we ever imagined. I would expect the human brain, which has done well by us so far, will continue to adapt to those changes."
In evolution, some individuals first acquire a genetic mutation and then, if it confers a benefit, it spreads.
"We're seeing two examples of such a spread in progress," says Lahn. "In each case, it's a spread of a new genetic variant in a gene that controls brain size. This variant is clearly favored by natural selection."
A news release describes the research in detail:
Lahn previously showed that there was accelerated evolution in humans among numerous genes, including microcephalin and abnormal spindle-like microcephaly-associated (ASPM). Both of these genes regulate brain size and therefore "were good candidates to look for signatures of selection. We indeed found such signatures when we compared humans to other species," he said. "As a natural extension of that, we asked, could it be that selection on these genes is still ongoing in humans?"
In the two Science papers, the researchers looked at variations of microcephalin and ASPM within modern humans. They found evidence that the two genes have continued to evolve. For each gene, one class of variants has arisen recently and has been spreading rapidly because it is favored by selection.
For microcephalin, the new variant class emerged about 37,000 years ago and now shows up in about 70 percent of present-day humans. For ASPM, the new variant class arose about 5,800 years ago and now shows up in approximately 30 percent of today's humans.
These time windows are extraordinarily short in evolutionary terms, indicating that the new variants were subject to very intense selection pressure that drove up their frequencies in a very brief period of time-both well after the emergence of modern humans about 200,000 years ago. Each variant emerged around the same time as the advent of "cultural" behaviors. The microcephalin variant appears along with the emergence of such traits as art and music, religious practices and sophisticated tool-making techniques, which date back to about 50,000 years ago. The ASPM variant coincides with the oldest-known civilization, Mesopotamia, which dates back to 7000 BC.
"Microcephalin," the authors wrote in one of the papers, "has continued its trend of adaptive evolution beyond the emergence of anatomically modern humans. If selection indeed acted on a brain-related phenotype, there could be several possibilities, including brain size, cognition, personality, motor control or susceptibility to neurological/psychiatric diseases."
"The next step is to find out what biological difference imparted by this genetic difference causes selection to favor that variation over the others," Lahn said.
The study was based on surveys of more than 1,000 people representing 59 ethnic populations worldwide.
For each gene, the scientists identified a large number of different copies. One class, called haplogroup D, shows two distinct characteristics. First, they are very young and therefore nearly identical. Second, despite recent emergence they have spread rapidly.
There were also geographic differences, which may spark controversy. For haplogroup D of ASPM, the researchers found a higher frequency in Europeans and surrounding populations including North Africans, Middle Easterners and South Asians. Meanwhile, they found a lower incidence in East Asians, New World Indians and sub-Saharan Africans. For microcephalin, the researchers found that haplogroup D is more abundant in populations outside of sub-Saharan Africa.
The researchers emphasize, however, that very little is known about the impact of the variants, and they may prove to have little to do with cognition or intelligence.
Furthermore, they stress that the study looked at only two genes, and that genetic variations within a population are often almost as great as the differences between groups.
SOURCE: BetterHuman
In two related papers published in the journal Science, University of Chicago researchers report that two genes linked to brain size are rapidly evolving in humans.
"Our studies indicate that the trend that is the defining characteristic of human evolution-the growth of brain size and complexity-is likely still going on," says Bruce Lahn, lead researcher for both papers and an investigator at the Howard Hughes Medical Institute. "Meanwhile, our environment and the skills we need to survive in it are changing faster then we ever imagined. I would expect the human brain, which has done well by us so far, will continue to adapt to those changes."
In evolution, some individuals first acquire a genetic mutation and then, if it confers a benefit, it spreads.
"We're seeing two examples of such a spread in progress," says Lahn. "In each case, it's a spread of a new genetic variant in a gene that controls brain size. This variant is clearly favored by natural selection."
A news release describes the research in detail:
Lahn previously showed that there was accelerated evolution in humans among numerous genes, including microcephalin and abnormal spindle-like microcephaly-associated (ASPM). Both of these genes regulate brain size and therefore "were good candidates to look for signatures of selection. We indeed found such signatures when we compared humans to other species," he said. "As a natural extension of that, we asked, could it be that selection on these genes is still ongoing in humans?"
In the two Science papers, the researchers looked at variations of microcephalin and ASPM within modern humans. They found evidence that the two genes have continued to evolve. For each gene, one class of variants has arisen recently and has been spreading rapidly because it is favored by selection.
For microcephalin, the new variant class emerged about 37,000 years ago and now shows up in about 70 percent of present-day humans. For ASPM, the new variant class arose about 5,800 years ago and now shows up in approximately 30 percent of today's humans.
These time windows are extraordinarily short in evolutionary terms, indicating that the new variants were subject to very intense selection pressure that drove up their frequencies in a very brief period of time-both well after the emergence of modern humans about 200,000 years ago. Each variant emerged around the same time as the advent of "cultural" behaviors. The microcephalin variant appears along with the emergence of such traits as art and music, religious practices and sophisticated tool-making techniques, which date back to about 50,000 years ago. The ASPM variant coincides with the oldest-known civilization, Mesopotamia, which dates back to 7000 BC.
"Microcephalin," the authors wrote in one of the papers, "has continued its trend of adaptive evolution beyond the emergence of anatomically modern humans. If selection indeed acted on a brain-related phenotype, there could be several possibilities, including brain size, cognition, personality, motor control or susceptibility to neurological/psychiatric diseases."
"The next step is to find out what biological difference imparted by this genetic difference causes selection to favor that variation over the others," Lahn said.
The study was based on surveys of more than 1,000 people representing 59 ethnic populations worldwide.
For each gene, the scientists identified a large number of different copies. One class, called haplogroup D, shows two distinct characteristics. First, they are very young and therefore nearly identical. Second, despite recent emergence they have spread rapidly.
There were also geographic differences, which may spark controversy. For haplogroup D of ASPM, the researchers found a higher frequency in Europeans and surrounding populations including North Africans, Middle Easterners and South Asians. Meanwhile, they found a lower incidence in East Asians, New World Indians and sub-Saharan Africans. For microcephalin, the researchers found that haplogroup D is more abundant in populations outside of sub-Saharan Africa.
The researchers emphasize, however, that very little is known about the impact of the variants, and they may prove to have little to do with cognition or intelligence.
Furthermore, they stress that the study looked at only two genes, and that genetic variations within a population are often almost as great as the differences between groups.
SOURCE: BetterHuman
posted by hubafract at 3:58 PM
1 Comments:
Very interesting findings. It is very important to get to the root of how the genes together orchestrate the complexities of human cognition and behaviour.
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