We want to know how broad a trend these two genes represent. Did we get really lucky and hit on two rare examples of such genes? Or, are they representative of many other such genes throughout the genome. I would bet, though, that we will find evidence of selection in a lot more genes.

We don't know what these new variants do. But they might confer a selective advantage by improving cognitive abilities. This needs to be confirmed.

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. If our species survives for another million years or so, I would imagine that the brain by then would show significant structural differences from the human brain of today.

The frequency of the gene increases because people who carry these genes are more fit and they have more kids. We think each gene conveys some sort of fitness advantage in brain biology. It could be an improved cognitive function or a personality trait. We're not sure. But we know whatever consequence they render is highly favored by selection.

We're envisioning what societies will want.

I think a lot of people might consider humans to be at the pinnacle of evolutionary lineage -- that we have achieved an advanced state as a species, and we have basically become the end-game. But what we found indicates that the species -- particularly when it comes to the brain, which is perhaps our most defining feature -- is still evolving.

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. 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.

They may have arisen in Europe or the Middle East and spread more readily east and west due to human migrations, as opposed to south to Africa because of geographic barriers. Or, they could have arisen in Africa, and increased in frequency once early humans migrated out of Africa.

If we look at multiple genes, the ethnic variations such as the ones we found are likely to be counterbalanced by other differences. Just because these genes are still evolving, doesn't necessarily mean they make you any smarter. We've evolved genes for selfishness, violence, cruelty û- all of which are in place because they may make survival easier.

My concern is that this is going to become justification for prejudices against certain groups.

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. If our species survives for another million years or so, I would imagine that the brain by then would show significant structural differences from the human brain of today.

In a very short period of time, this class of variants arose from a single copy to many copies. That implies that this must have happened because of positive selection.

The next step is to find out what biological difference imparted by this genetic difference causes selection to favor that variation over the others.