The Chicago team discovered, by comparing modern man with our ancestors of 37,000 years ago, that there are big changes in two genes linked to brain size.

They say they believe that one of the new variants emerged only 5,800 years ago, yet is present in 30% of today's humans, which is relatively short in evolutionary terms.

It seems each gene variant emerged around the same time as the advent of so called "cultural" behaviours.

One variant, the microcephalin, appeared along with the emergence of traits such as art and music, religious practices and sophisticated tool-making techniques, which date back to about 50,000 years ago.

That variant is now present in about 70% of humans alive today.

The other, called the ASPM variant, originated at a time that coincides with the spread of agriculture, settled cities and the first record of written language.

According to researcher Dr Bruce Lahn, the big question is whether the genetic evolution seen, had actually caused the cultural evolution of humans or was merely chance.

They guess that it might have something to do with the important role that these genes play in brain size, but stress that did not necessarily mean better intelligence.

Dr Lahn says that just because these genes are still evolving it does not necessarily mean they make you any smarter.

He adds that their studies indicate that the trend that is the defining characteristic of human evolution, the growth of brain size and complexity, is likely to be still ongoing.

He speculates that if our species survives for another million years or so, the brain by then might show significant structural differences from the human brain of today.

The next step say the researchers will be to figure our what biological difference imparted by the genetic differences, caused natural selection to favour that variation over others.

They say they must have conferred some evolutionary advantage, such as a desired change in cognition, personality, motor control or resilience to neurological or psychiatric diseases.

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Conditions such as trauma, spinal cord injury and stroke can destroy these travel networks as well as brain cells. Labs such as Dr. Yu's are doing stem cell transplants to re-establish roadways and get undifferentiated stem cells to repopulate such ravaged areas. He hopes the new developmental markers will help in this effort by showing what cell surface molecules should look like “ and consequently how the cells should act “ at certain points along the way.

Two of the biggest problems facing stem cell transplantation are functional recovery “ getting the cells to do the right job once they arrive at a target organ “ and controlling their proliferation so they don't start forming tumors, says Dr. Yu.

MCG Biochemist Erhard Bieberich is exploring the potential of the lipid ceramide, which helps eliminate potentially harmful cells during brain development, to halt unwanted proliferation of transplanted stem cells.

Dr. Yu hopes the new developmental markers will help with the other problem. "There are other players, but these are important factors that help the brain form. I think it's a good start. Now that we have these to use as examples, discovery of other markers should come faster."

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