December 16, 2007

The Economist on the Cochran, Harpending, Moyzis, Hawks, Wang paper

An excerpt from "Darwin's Children" in The Economist:

Dr Moyzis's paper suggests ... that Homo sapiens is continuing to undergo local evolution. He and his colleagues reckon they can both estimate the rate of evolution and identify many of the evolving genes, by using a trick with the clumsy name of linkage disequilibrium.

Genes are linked together in cell nuclei on structures called chromosomes. These come in pairs, one from each parent. However, when sperm and egg cells are formed, the maternal and paternal chromosomes swap bits of DNA to create a new mixture. The pieces of DNA swapped are complementary—that is, they contain the same types of gene. But they may contain different versions of the genes in question, and these different versions can have different biological effects.

Over the generations this process of swapping mixes the genes up thoroughly, and an equilibrium emerges. If a new mutation appears, however, it will take quite a while for that thorough mixing to happen. This means recent mutations can be spotted because they are still linked to the same neighbouring bits of DNA as they were when they first appeared. Moreover, the size of these neighbouring blocks gives an indication of how long ago the mutation in question emerged; long blocks suggest a recent mutation because the mixing process has not had time to break them up.

All this has been known for decades, but it is only recently that enough human DNA sequences have become available for the technique to be used to compare people from different parts of the world. And this is what Dr Moyzis and his colleagues have now done.

What they have found is that about 1,800 protein-coding genes, some 7% of the total known, show signs of having been subject to recent natural selection. By recent, they mean within the past 80,000 years. Moreover, as the chart shows, the rate of change has speeded up over the course of that period. (The sudden fall-off at the end is caused because the linkage-disequilibrium method cannot easily detect very recent mutations, rather than by a sudden reduction in the rate of evolution.) The researchers put this acceleration down to two things. First, the human population has expanded rapidly during that period, which increases the size of the gene pool in which mutations can occur. Second, the environment in which people find themselves has also changed rapidly, creating new contexts in which those mutations might have beneficial effects.

That environmental change itself has two causes. The past 80,000 years is the period in which humanity has spread out of Africa to the rest of the world, and each new place brings its own challenges. It has also been a period of enormous cultural change, and that, too, creates evolutionary pressures. In acknowledgment of these diverse circumstances, the researchers looked in detail at the DNA of four groups of people from around the planet: Yoruba from Africa, Han Chinese and Japanese from Asia, and Europeans.

Various themes emerged. An important one was protection from disease, suspected to be a consequence of the increased risk of infection that living in settlements brings. In this context, for example, various mutations of a gene called G6PD that are thought to offer protection from malaria sprang up independently in different places.

A second theme is response to changes in diet caused by the domestication of plants and animals. One example of this is variation in LCT, a gene involved in the metabolism of lactose, a sugar found in milk. All human babies can metabolise lactose, but only some adults can manage the trick. That fact, and the gene involved, have been known for some time. But Dr Moyzis's team have worked out the details of the evolution of LCT. They suspect that it was responsible for the sudden spread of the Indo-European group of humanity about 4,000 years ago, and also for the more recent spread of the Tutsis in Africa, whose ancestors independently evolved a tolerant version of the gene.

The pressures behind other changes are less obvious. In the past 2,000-3,000 years, for example, Europeans have undergone changes in the gene for a protein that moves potassium ions in and out of nerve cells and taste buds. There have also been European changes in genes linked to cancer and Alzheimer's disease. Chinese, Japanese and Europeans, meanwhile, have all seen changes in a serotonin transporter. Serotonin is one of the brain's messenger molecules, and is particularly involved in establishing mood.

The finding that may cause most controversy, however, is that in the Asian groups there has been strong selection for one variant of a gene that, in a different form, is responsible for Gaucher's disease. A few years ago two of the paper's other authors, Gregory Cochran and Henry Harpending, suggested that the Gaucher's form of the gene might be connected with the higher than average intelligence notable among Ashkenazi Jews. The unstated inference is that something similar might be true in Asians, too.

The Ashkenazim paper caused quite a stir at the time. It was merely a hypothesis, but it did suggest a programme of research that could be conducted to test the hypothesis. So far, no one—daring or foolish—has tried. Eventually, however, such questions will have to be faced. The paper Dr Moyzis and his colleagues have just published is a ranging shot, but the amount of recent human evolution it has exposed is surprising. Others will no doubt follow, and the genetic meaning of the term “race”, if it has one, will be exposed for all to see.


My published articles are archived at iSteve.com -- Steve Sailer

16 comments:

the Narrator... said...

"So far, no one—daring or foolish—has tried. Eventually, however, such questions will have to be faced. The paper Dr Moyzis and his colleagues have just published is a ranging shot, but the amount of recent human evolution it has exposed is surprising. Others will no doubt follow, and the genetic meaning of the term “race”, if it has one, will be exposed for all to see."


The tone there is comical. Its a,"soon they'll know that we know that they know that we know" kind of thing.

With each passing story like this though, you get the sense that there is a shuffle amongst the media and academia in regards to how to "present" the information once it is undeniable.

And that is the thing to look out for; not the information, but the spin...

SKT said...

Don't confuse mutations with evolution. Most mutations are bad. We might be seeing more people in the population with a broader degree of mutations because modern technology (esp. medicine) is allowing them to survive and leave offspring. That is to be expected.

I think evolution is becoming convergent for people across the world. Evolution is driven by the environment, and people are now adapting the environment to suit their needs. People live in comfortable, climate controlled homes, and eat three square meals a day purchased from a store. That's a big change from a thousand years ago, when a Scandinavian viking might have been hunting wild boars vs. someone in the African bush gathering berries vs. Japanese villagers fishing, etc. to survive. Very different lifestyles back then, very similar lifestyles today.

Born Again Democrat said...

The best popular summary so far I would say.

RobertHume said...

Speaking of Asians' IQ. In Gladwell's recent New Yorker interview of Flynn he seems to say that Flynn thinks that the reported high IQ for Asians is an artifact of comparing IQ scores on tests with different calibration.

This seems like a very difficult question requiring expert analysis. Does anyone have an expert opinion? Has anyone read Flynn in detail on this subject?

Dutch Boy said...

This phenomenon is nothing new in history. The Finns and Hungarians ceased being and looking like Central Asians and became European in appearance in a matter of hundreds of years. Likewise the wolf became the dog once placed in a human environment. This cannot be accounted for by mutation alone. What we need is a new Lamarckism that recognizes the interplay of environment on genetic selection via epigenetic phenomena.

tommy said...

This phenomenon is nothing new in history. The Finns and Hungarians ceased being and looking like Central Asians and became European in appearance in a matter of hundreds of years.

Only a small percentage of the ancestors of modern Finns and Hungarians were Central Asian.

Tim said...

This fits nicely with Gregory Clark's book, A Farewell to Alms. Clark is an economic historian, and he argues that European society created significant selection pressure. Rich parents had many more surviving children than poor parents, so the culteral and genetic advantages of the rich survived and prospered.

slocombe said...

"Likewise the wolf became the dog once placed in a human environment."

A commonly believed fallacy. Dogs evolved from wild dogs, not wolves.

gcochran said...

skt, dutchboy, slocombe:

Wrong.

tommy said...

You have to love how they spin things:

Human evolution has speeded up over the past 80,000 years. That raises awkward questions about the concept of “race”

Actually, it raises awkward questions for race denialists.

This demonstrates that pygmyism is not a result of early malnutrition, as another hypothesis has it.

I've always presumed pygmyism was a rather severe adaptation to dense jungle environments. African elephants dwelling in the deep jungles also tend to be quite a bit smaller than their cousins roaming the grasslands. The incredibly agile pygmies would have been fierce competitors for non-pygmy hunter-gatherers in the same environment.

Anonymous said...

I wonder what effect modern medicine such as anti-biotics, insulin, and other wonderdrugs will have on future evolution. It should seem clear that many more people who would never have made it to the next gene pool are now kept alive and breeding, sometimes with others that have the same afliction. I guess we will find out.

Martin said...

I would be willing to bet money that every single person who works for The Economist in a reportorial or editorial capacity believes in evolution - good little Darwinists all. So why is it that people who believe that people have evolved by means of natural selection are so surprised when told that evolution through natural selection continues to this day? Who did they think would have interrupted it? God?

Rest assured though that as soon as the conventional wisdom about human racial differences changes, the Economist will leap right on board, and will sneeringly deride all those who say it does not matter, just as they today would deride those who say it does.

Fatuous and false erudition, delivered with a wink and a mocking sneer, is the Economist's chief product.

egoldstein said...

Could you elaborate on your reply to skt, Greg? Why won't gene flow and our increasingly similar lifestyles and environments halt the genetic divergence of the races? When Harpending said the races "are" becoming less alike, I thought he was just speaking carelessly, but it sounds like you have another idea.

sabanaoeste said...

A commonly believed fallacy. Dogs evolved from wild dogs, not wolves.

There are still some bones of contention involved in the question of domestic dog origins.

Dutch Boy said...

Since the Finns speak a Finno-Ugric dialect (as do the Hungarians) it is likely that most of their ancestors did also (i.e., they were of Central Asian descent). The other dialects of this family are found thousands of miles from Europe.

tommy said...

Since the Finns speak a Finno-Ugric dialect (as do the Hungarians) it is likely that most of their ancestors did also (i.e., they were of Central Asian descent).

Nonsense. By the same logic, it could be argued that since the majority of Irish people speak the Germanic language of English, this must mean the majority of Irish ancestry is Germanic (or even that most Irishmen are actually English).