Gene Surfing

The Surprising Genetic Advantage of Being on the Frontier
November 11, 2011 As people are able to dig more deeply into their own DNA, they are going to find some surprising things. They'll see that sometimes it doesn't matter how good an ancestor's genes were. What can matter more is whether or not that ancestor lived on the frontier. A new study out suggests that the genes of people on the frontier are 1.2 to 3.9 times more likely to be in today's population than the genes of the people who stayed behind. This is true whether the particular versions of their genes were better or not. Scientists have dubbed this phenomenon "gene surfing." Frontier folks' genes are surfing in on a wave of human expansion. And who said scientists weren't poetic? This is not how most people think these things should work. They think that over time, the gene versions (or alleles) best suited for a certain environment will become more common. And it usually is the case that "good" genes win out over "bad" ones. But not always. Luck can play a role too.
When Location Matters More
In the last few years, research has been pointing to the idea that being on the frontier is an advantage genetically. This new study drives the point home. Scientists looked at a group of people from Quebec. These people kept excellent ancestry records which meant that the scientists could trace in minute detail how the population expanded over time.

Sometimes where you are
matters more than the
genes you have for
genetic success.
As they tracked the people's progress across Quebec, scientists found that people on the frontier had more kids than the people who stayed behind. They also found that these kids had more kids too. It looks like women on the frontier had more children because they started having them earlier and for a longer time. Their children were also more likely to marry early and so have more children too. These extra kids meant that more of these people's genes were in the population even though the genes themselves weren't necessarily an advantage. Some people are probably shaking their heads saying, "This isn't how things are supposed to work. Genes have to have an advantage to become more common." This is true for the most part but remember that it isn't actually the gene that has the advantage, it is the person who has that gene. Usually the two are linked but not always. This becomes easier to understand once advantage is defined. A genetic advantage is one that allows people to have more kids over multiple generations. When they have more kids, their genes become more common. Almost always this is because people have a gene that leads to a helpful trait. For example, when humans moved to Europe where it was cold and dark, people who had genes for lighter skin did better. After a few generations, there were lighter Caucasians there instead of darker Africans. This is exactly the kind of thing that happened on the frontier. The difference is that the genes weren't the advantage, the situation was. The frontier people's genes were just in the right place at the right time and so were spread more widely. Of course it may be that people who go to the frontier are more adventure seeking anyway. Many studies actually suggest that this may be the case. This would mean that these other genes just hitchhiked in with the "novelty-seeking" genes. In any event, these studies point out that we didn't just get our genes from the winners in our family. Sometimes we got our genes from those who happened to be in an advantageous situation.

More Information

Ways a Trait Can Become More Common
When people think about evolution, they tend to think about it as positive traits increasing over time. Basically, living things with an advantage do better and so are more likely to pass on their genes. Over time, those "good" genes become more common.

When trees got dirty,
being light colored became a
disadvantage for these moths.
The classic example of this is peppered moths in England. Before the industrial revolution, the trees in a certain region were all light colored. And so were most of the moths. These lighter colored moths blended in better with their surroundings which meant birds had a harder time finding them. Darker moths stood out and so were quickly gobbled up. Once smokestacks started belching out smoke, things changed. Now the trees were all darker so that the lighter moths stood out. In a short time, most of the moths were dark. These kinds of examples make sense. And they are somehow comforting because the better genes for a particular environment prevail – it seems like a species improves over time. But this isn't how it always works. As the Quebec study showed, sometimes it just helps being in the right place at the right time. The most extreme example of this is something called the founder effect. If two people move to an island and found a population there, everyone is going to have a combination of those two people's genes (barring the occasional mutation). So if both had red hair, everyone on the island will have red hair too. (Click here for why this is the case for red hair and not necessarily all traits.) The red hair version of the MC1R gene will be very common here even if it is a disadvantage. This is also how certain diseases become more common in some groups. For example, Ashkenazi Jews suffer from more Tay Sachs and some Amish groups have extra fingers and toes because the founding ancestors were carriers for these diseases. Even though these traits are a disadvantage, they end up being more common that you might predict because of the founder effect.

By chance the blue bugs win out.
Another way a trait can become common is through something called genetic drift. This is where random chance leads to certain traits winning out in a population. Imagine 10 bugs, 5 green and 5 blue. By chance, the green ones are clustered mostly in the north part of a field and the blue ones in the south. Now imagine a fire sweeps across the northern part of the field, sparing the south. In a few generations, blue will become more common not because it is better, but because blue ancestors were in the right place at the right time. This is kind of what happened on an island in the Pacific called Pingelap. In 1775, a huge typhoon wiped out 90% of the people on the island. The remaining 20 survivors stayed and repopulated the island. One of the 20 was a carrier for a rare form of colorblindness where people see everything in grays. Now, 10% of the people have this form of colorblindness and 30% are carriers. All because of the typhoon that spared the carrier. And these are just some of the ways that gene versions can become common whether they are an advantage or not. Evolution is mostly survival of the fit. But sometimes it is survival of the lucky too.