Tuesday, May 27, 2014

"In this statistical sense, races are real"

Lots of interesting stuff re-told in "A Troublesome Inheritance" by Nicholas Wade and reviewed by H Allen Orr in the NY Review of Books. 

Response to Malik: Thanks for the comments. We are not experts but there are many big-shots around who do have lot to say on this matter. Again it is a pity that the old BP box is lying at the bottom of the sea where no one can find it.

The important question (for us)- is there any new knowledge? A large part of the "analysis" seems to us to be self-serving back-calculation, look at why Middle East or South Asia is struggling and put up a theory to fit the evidence. And often the evidence cited is not that clear-cut at all.

The other side (the establishment) is also of not much help, the only message we hear is that race related issues must be handled with care. We agree, but this will not stop people from speculating about the truth...so it is perhaps better that we thrash out the ideas in the open market-place (any firm judgement is unlikely to come though).
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Why did these genomic differences among peoples appear? There are two main possibilities. The first is that the differences are meaningless. The frequencies of genetic variants can start out the same across several populations and then slowly diverge from one another even when the variants have no effect on Darwinian fitness—defined, roughly, by how many surviving offspring individuals produce. Geneticists call this “neutral evolution.”

The second possibility is that the changes in our genomes were driven by natural selection. According to this hypothesis, the frequencies of genetic variants can diverge among populations because some variants increased the fitness of their carriers, perhaps by increasing their chances of survival in a harsh environment encountered on the particular continent on which they lived. 

The study of genomes provides new ways to find evidence of natural selection.

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Wade also thinks that “evolutionary differences between societies on the various continents may underlie major and otherwise imperfectly explained turning points in history such as the rise of the West and the decline of the Islamic world and China.” 

Here, and especially in his treatment of why the industrial revolution flourished in England, his book leans heavily on Gregory Clark’s A Farewell to Alms (2007). Across these historical turning points, the details differ but the story remains the same: certain peoples were predisposed genetically to behaviors and thus institutions that paved the way for their success, whether, say, economic (the West) or intellectual (the Jews). Other peoples, alas, had other genes.

Wade, now a freelance writer and reporter, is best known for his work as a journalist at The New York Times. He has also written several popular books on biology. The most recent—Before the Dawn (2006) and The Faith Instinct (2009)—focused on evolution in human beings, including the evolution of religion. In A Troublesome Inheritance, Wade maintains this focus on human evolution, though he turns to a far more controversial topic, human races. 

His goal, he says, is “to demystify the genetic basis of race and to ask what recent human evolution reveals about history and the nature of human societies.” He concludes not only that human races are real but that they probably differ genetically in surprising ways.

Wade’s main claim is that human races likely differ in social behavior for genetic reasons as a result of recent evolution. These slight differences in behavior may, in turn, explain why different sorts of social institutions appear among different peoples:
Institutions are not just sets of arbitrary rules. Rather, they grow out of instinctual social behaviors, such as the propensity to trust others, to follow rules and punish those who don’t, to engage in reciprocity and trade, or to take up arms against neighboring groups. Because these behaviors vary slightly from one society to the next as the result of evolutionary pressures, so too may the institutions that depend on them.
Evolutionary biology might therefore have something to say about why some peoples live in modern states and others in tribal societies, and why some nations are wealthy while others remain mired in poverty.

A Troublesome Inheritance cleaves neatly into two parts. The first is a review of what recent studies of the genome reveal about our evolution, including the emergence of racial differences. The second part considers the part that genetic differences among races may play in behavior and in the social institutions embraced by various races. These two parts fare very differently.

As people dispersed about the planet, they ultimately settled into the five great “continental races”: Africans (sub-Sahara), East Asians, Caucasians (Europe, the Indian subcontinent, and the Middle East), Australians, and Native Americans. Some of these groups are younger than others (America was peopled only in the last 15,000 years), but this division provides, Wade says, a reasonably realistic portrait of how human genetic diversity is partitioned geographically. Because of their geographic isolation from one another, these groups of human beings necessarily evolved mostly independently over the last tens of thousands of years. During this period of independent evolution, much of what we think of as characteristically human arose, including agriculture and settlement in permanent villages.

So what has study of the human genome over the last decade revealed? Wade’s chief conclusion here is that human evolution has been “recent, copious and regional.” The facts are fairly straightforward. The continental races of human beings differ somewhat from one other at the level of DNA sequence. As Wade emphasizes, these differences are “slight and subtle” but they can nonetheless be detected by geneticists who now have access to many genome sequences from around the planet.

The central fact is that genetic differences among human beings who derive from different continents are statistical. Geneticists might find that a variant of a given gene is found in 79 percent of Europeans but in only, say, 58 percent of East Asians. Only rarely do all Europeans carry a genetic variant that does not appear in all East Asians. But across our vast genomes, these statistical differences add up, and geneticists have little difficulty concluding that one person’s genome looks European and another person’s looks East Asian. 

To put the conclusion more technically, the genomes of various human beings fall into several reasonably well-defined clusters when analyzed statistically, and these clusters generally correspond to continent of origin. In this statistical sense, races are real.

Natural selection can take a genetic variant that is beneficial but initially rare and drive it to much higher frequency in a population. This process leaves a signal in the genome. Because a whole stretch of DNA that surrounds the beneficial variant will rise to high frequency along with the variant, nearly everyone in the population might end up carrying the same DNA sequence in this part of the genome. Geneticists will thus see a stretch of the genome that shows unusually little genetic variation in a population.

Using this or, more often, related approaches, geneticists have obtained fairly good evidence of natural selection acting on our genomes. Indeed Wade reports that 14 percent of the human genome has experienced recent natural selection. These genomic approaches can’t tell us why natural selection acted in a particular case (was it, say, adaptation to a new parasite?), but they can tell us that these bouts of natural selection were sometimes recent and restricted to particular continents.

Wade’s survey of human population genomics is lively and generally serviceable. It is not, however, without error. He exaggerates, for example, the percentage of the human genome that shows evidence of recent natural selection. The correct figure from the study he cites is 8 percent, not 14, and even this lower figure is soft and open to some alternative explanation. And Wade generally assumes that evidence of selection reflects adaptation to the ecological environment, whereas some events might reflect the action of other evolutionary forces like sexual selection, in which individuals compete for mates, not for survival.

In the latter half of A Troublesome Inheritance, Wade ventures into far more controversial territory. His claims are, in outline, simple enough.

As human beings evolved over the last tens of thousands of years, the genetic basis of people’s behavior may have changed, just as the basis of their skin color did. Some of these changes may have resulted from Darwinian adaptation to new forms of social life. 

For example, the “Great Transition” from nomadic life to permanent settlement that began some 15,000 years ago likely produced a profoundly altered social environment: populations grew larger, people interacted with more non-kin, and society became more hierarchical.

In response to this new environment, social behaviors may have changed by natural selection. In some societies, people who were less aggressive or more trusting, for instance, might have prospered under these conditions. Indeed Wade argues that, because the rich could produce more surviving children than the poor once permanent settlements appeared, genes for whatever behaviors underlay their success could spread. “The social behaviors of the elites could thus trickle down into the rest of society” by natural selection.

Crucially, Wade says that “evolution in social behavior has necessarily proceeded independently in the five major races,” reflecting their geographic and thus genetic isolation. The net result of all of this, during settlement as well as other events in recent evolutionary history, is that the continental races might well come to differ genetically in social behavior.

Why, for instance, do Chinese immigrants to Malaysia and Thailand succeed so often compared to the Malays and Thais themselves? After all,
people are highly imitative, and if Chinese business success were purely cultural, everyone would find it easy to adopt the same methods. This is not the case because social behavior, of Chinese and others, is genetically shaped.
Wade also thinks that “evolutionary differences between societies on the various continents may underlie major and otherwise imperfectly explained turning points in history such as the rise of the West and the decline of the Islamic world and China.” 

Here, and especially in his treatment of why the industrial revolution flourished in England, his book leans heavily on Gregory Clark’s A Farewell to Alms (2007). Across these historical turning points, the details differ but the story remains the same: certain peoples were predisposed genetically to behaviors and thus institutions that paved the way for their success, whether, say, economic (the West) or intellectual (the Jews). Other peoples, alas, had other genes.

These are big claims and you’d surely expect Wade to provide some pretty impressive, if recondite, evidence for them from the new science of genomics. And here’s where things get odd. Hard evidence for Wade’s thesis is nearly nonexistent. 

Odder still, Wade concedes as much at the start of A Troublesome Inheritance:
Readers should be fully aware that in chapters 6 through 10 they are leaving the world of hard science and entering into a much more speculative arena at the interface of history, economics and human evolution.
It perhaps would have been best if this sentence had been reprinted at the top of each page in chapters 6 through 10.
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Link: http://www.nybooks.com/articles/archives/2014/jun/05/stretch-genes/
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regards