All,
Just catching up, here.
Here are two articles on how and when we slowly became capable of ruling/ruining the world.
I particularly like the age estimate of the "last sweep" (i.e., between 200,000 and 500,000 years ago) mentioned in Wade's paper. On the other hand, I suppose it is unfortunate that Lahn et al. have not been able to detect Richard Klein's famous 50-40,000 year old "sweep". The only one that really counted.
Jacques Cinq-Mars
Evolution of Gene Related to Brain's Growth Is Detailed
By NICHOLAS WADE
Published: January 14, 2004 – The New York Times
A gene that helps determine the size of the human brain has been under intense Darwinian pressure in the last few million years, changing its structure 15 times since humans and chimps separated from their common ancestor, biologists have found.
The gene came to light two years ago, when a disrupted form of it was identified as the cause of microcephaly, a disease in which people are born with an abnormally small cerebral cortex.
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Dr. Bruce T. Lahn and fellow geneticists at the University of Chicago have decoded the DNA sequence of the gene in apes, monkeys and people and have identified the changes caused by the pressure exerted by natural selection. Most of the other changes in DNA units generally make no difference to the protein specified by the gene, and evolutionary forces are neutral to them.
The gene, known as the ASPM gene, has been under steady selective pressure throughout the evolution of the great apes, a group that includes orangutans, gorillas, chimpanzees and humans, Dr. Lahn and colleagues say in an article being published today in the journal Human Molecular Genetics. By contrast, the versions of the gene possessed by monkeys, dogs, cats and cows show no particular sign of being under selective pressure.
The progressive change in the architecture of the ASPM protein over the last 18 million years is correlated with a steady increase in the size of the cerebral cortex, the part of the brain responsible for higher cognitive function, during the ape and human lineage. Evolution has been particularly intense in the five million years since humans split from chimpanzees.
"There has been a sweep every 300,000 to 400,000 years, with the last sweep occurring between 200,000 and 500,000 years ago," Dr. Lahn said, referring to a genetic change so advantageous that it sweeps through a population, endowing everyone with the same improved version of a gene.
CLICK HERE for the full article.
Gene 'helped create human brain'
BBC News – Wednesday, 14 January
Scientists have identified a gene that appears to have played a key role in the development of the human brain.
They believe it is responsible for the expansion of an area of the brain called the cerebral cortex which controls abstract reasoning.
This is much bigger in humans than their closest relatives - and gives us our extraordinary brain power.
The research, by Howard Hughes Medical Institute, US, is published in the journal Human Molecular Genetics.
Lead researcher Dr Bruce Lahn said: "People have studied the evolution of the brain for a long time, but they have traditionally focused on the comparative anatomy and physiology of brain evolution.
"I would venture, however, that there really hasn't been any convincing evidence until now of any gene whose changes might have contributed to the evolution of the brain."
The Howard Hughes team focused on the particular gene, called ASPM, because mutations in its make-up are known to be linked to severe reductions in the size of the cerebral cortex in people who carry them.
They compared the make-up of the human form of the gene with that in six other primate species, each of which corresponds to a key stage in the evolutionary path of modern man.
They ranged from the chimpanzee, which is man's closest living relative, to the owl monkey, a relatively primitive creature analogous to an early stage of human evolution.
They found evidence that the make-up of the gene changed significantly between the species - and the higher up the evolutionary scale they went, the more changes they found.
The biggest difference was found between the human and chimpanzee forms of the gene - confirming that the recent phase of human evolution has been the most speedy and profound.
By contrast, when researchers looked at the make-up of the gene in more primitive animals such as cows, sheep, cats and dogs they found little evidence of significant changes between species.
This implies that the speed of change was much slower further down the evolutionary ladder.
Dr Lahn said: "The fact that we see this accelerated evolution of ASPM specifically in the primate lineage leading to humans, and not in these other mammals, makes a good case that the human lineage is special."
The next stage in the research will be pin down exactly how ASPM functions in the brain.
Research has suggested that the gene regulates the rate at which brain cells are produced in the cerebral cortex.
A bit of complementary info if you
CLICK HERE.
