This week in Science, three papers report that the product of the gene PRDM9 is an important determinant of where recombination occurs in the genome during meiosis. Though this may sound like something of an esoteric discovery, it's actually pretty remarkable, and brings together a number of lines of research in evolutionary genetics. How so?

A bit of background.

A few somewhat related facts:

1. A major goal in the study of speciation is the identification of the genes that underlie reproductive barriers between species. In 2008, the first such gene in mammals was found--in a cross between two subspecies of mouse where the male offspring are sterile (note that this follows Haldane's rule), a introduction of the "right" version of a single gene was sufficient to restore fertility. This gene? PRDM9, which encodes a histone methyltranferase expressed in the mouse germline. This gene has evolved rapidly across animals, especially in the part of the protein that binds DNA. This suggests it is binding a sequence that is changing particularly rapidly over evolutionary time.

2. The positions in the genome at which recombination during meiosis are not scattered randomly, but rather cluster together in what are called "recombination hotspots". Enriched within these hotspots in humans is a particular sequence motif, presumably an important binding site for whatever factor is controlling recombination. As this fact was becoming clear, a group compared the positions of these recombination hotspots between humans and chimpanzees. The result? The positions of these hotspots are remarkably different between these species. In fact, the positions of recombination hotspots in humans and chimpanzees are nearly non-overlapping, a fairly impressive fact given that the genomes themselves are 99.X% identical.

3. But perhaps #2 isn't all that surprising. If there are two alleles at a hotspot, one of which is "hot" and the other of which is "cold" (ie. doesn't initiate recombination), the mechanism of recombination results in gene conversion of the "hot" allele to the "cold" allele (for details, see here). This should result in the relatively rapid loss over evolutionary time of recombination hotspots, which in turn results in what has been called "the hotspot conversion paradox"--if hotspots should trend over time to be more "cold", how is it that they exist? One plausible resolution of this paradox--a sequence or gene that doesn't contain a hotspot itself might control the positioning of recombination elsewhere in the genome.

4. Indeed, such genes exist. In mice, two groups last year identified regions of the genome (though they didn't at the time narrow it down to a gene) controlling the usage of individual hotspots. Importantly, one such region was located distantly to the hotspot, indicating an important regulator of recombination positioning. In humans, a group last year showed that these is extensive variability between humans in how often previously identified hotspots are used, and that this variation is heritable.

PRDM9 brings all of these observations together

These three papers all report that item #1 and items #2-4 above are all related. What do they show?

1. Two groups followed up on the observation in #4 above that there was a particular region in mouse controlling hotspot usage, and identified the relevant gene as PRDM9. One group went further, testing whether variation in this gene also influenced hotspot usage in humans. Remarkably, it did, showing that variation in PRDM9 in both mice and humans leads to variation in hotspot usage. This variation changes the binding specificity of the gene, leading to changed hotspots and a resolution of the "hotspot conversion paradox" mentioned in #3 above.

2. Another group took a different route to a similar conclusion. They followed up the sequence motif mentioned in #2 above as being enriched in recombination hotspots in humans. The "hotspot paradox" predicts that, if this motif is "hot", it should be in the process of being removed from the human genome. Similarly, if it's not "hot" in chimpanzees, it should not be in the process of being removed from the chimp genome. Indeed, this motif has been preferentially lost along the human lineage as compared to the chimp lineage. They then asked, what is binding this motif? They had two criteria--a protein with a predicted binding site similar to their motif, and lack of conservation of this protein between humans and chimpanzees. Only one gene fit these criteria--PRDM9. Thus, the rapid evolution of PRDM9 is responsible for the puzzling observation that recombination hotspots are entirely unconserved between humans and chimps.

A brief conclusion

I'll reiterate that this is a pretty remarkable discovery, opening up the possibility of a direct link between the evolution of recombination and speciation. Is the effect of PRDM9 on recombination responsible for the conformation to Haldane's rule in the mouse cross described in #1? Or is there some additional effect of this gene? Is the evolution of PRDM9 sufficient to describe the evolution of recombination hotspots in all animals? One can imagine a whole host of additional questions. Certainly, this is a story to be continued.

Labels: Evolution, Genetics

Here. Or embedded:



We talk about The Faith Instinct.

Labels: Religion

As a New Year's gift, here is a free copy of an entry I put up on my data blog (details on that here). It's a quantitative look at the history of race and culture in America, together with qualitative examples that illustrate the story that the numbers tell. Enjoy.

Previously I looked at how much attention elite whites have given to blacks since the 1870s by measuring the percent of all Harvard Crimson articles that contained the word "negro." That word stopped being used in any context after 1970, which doesn't allow us to see what's happened since then. Also, it is emotionally neutral, so while it tells us how much blacks were on the radar screen of whites, it doesn't suggest what emotions colored their conversations about race.

When tensions flare, people will start using more charged words more frequently. The obvious counterpart to "negro" in this context is "nigger." It could be used by racists hurling slurs, non-racists who are quoting or decrying the slur, by tribalist blacks trying to open old wounds to recruit new members, by blacks trying to "re-claim" the term, by those debating whether or not the term should be used in any context, and so on. Basically, when racial tension is relatively low, these arguments don't come up as often, so the word won't appear as often.

I've searched the NYT back to 1852 and plotted how prevalent "nigger" was in a given year, though smoothing the data out using 5-year moving averages (click to enlarge):


We see high values leading up and throughout the Civil War, a comparatively lower level during Reconstruction, followed by two peaks that mark "the nadir of American race relations." It doesn't change much going through the 1920s, even though this is the period of the Great Migration of blacks from the South to the West and Northeast. It falls and stays pretty low during the worst part of the Great Depression, WWII, and the first 10 years after the war. This was a period of increasing racial consciousness and integration, and the prevalence of "negro" in the Crimson was increasing during this time as well. That means that there was a greater conversation taking place, but that it wasn't nasty in tone.

However, starting in the late 1950s it moves sharply upward, reaching a peak in 1971. This is the period of the Civil Rights movement, which on an objective level was merely continuing the previous trend of greater integration and dialogue. Yet just as we'd guess from what we've studied, the subjective quality of this phase of integration was much more acrimonious. Things start to calm down throughout the '70s and mid-'80s, which our study of history wouldn't lead us to suspect, but which a casual look at popular culture would support. Not only is this a period where pop music by blacks had little of a racial angle -- that was also true of most of the R&B music of most of the '60s -- but was explicitly about putting aside differences and moving on. This is most clearly shown in the disco music scene and its re-birth a few years later during the early '80s dance and pop music scene, when Rick James, Prince, and above all Michael Jackson tried to steer the culture onto a post-racial course.

But then the late '80s usher in a resurgence of identity politics based on race, sex, and sexual orientation ("political correctness," colloquially). The peak year here is technically 1995, but that is only because of the unusual weight given to the O.J. Simpson trial and Mark Fuhrman that year. Ignoring that, the real peak year of the racial tension was 1993 according to this measure. By the late '90s, the level has started to plummet, and the 2000s have been -- or should I say were -- relatively free of racial tension, a point I've made for awhile but that bears repeating since it's not commonly discussed.

Many people mention Obama's election, but that was pretty late in the stage. Think back to Hurricane Katrina and Kanye West trying but failing to foment another round of L.A. riots, or Al Sharpton trying but failing to turn the Jena Six into a civil rights cause celebre, or the mainstream media trying but failing to turn the Duke lacross hoax into a fact that would show how evil white people still are. We shouldn't be distracted by minor exceptions like right-thinking people casting out James Watson because that was an entirely elite and academic affair. It didn't set the entire country on fire. The same is true for the minor exception of Larry Summers being driven out of Harvard, which happened during a remarkably feminism-free time.

Indeed, it's hard to recognize the good times when they're happening -- unless they're fantastically good -- because losses loom larger than gains in our minds. Clearly racial tensions continue to go through cycles, no matter how much objective progress is made in improving the status of blacks relative to whites. Thus, we cannot expect further objective improvements to prevent another wave of racial tension.

Aside from the long mid-20th C hiatus, there are apparently 25 year distances between peaks, which is about one human generation. If the near future is like most of the past, we predict another peak around 2018, a prediction I've made before using similar reasoning about the length of time separating the general social hysterias that we've had -- although in those cases, just going back to perhaps the 1920s or 1900s, not all the way back to the 1850s. Still, right now we're in a fairly calm phase and we should enjoy it while it lasts. If you feel the urge to keep quiet on any sort of racial issues, you should err on the side of being more vocal for right now, since the mob isn't predicted to come out for another 5 years or so, and the peak not until 10 years from now. As a rough guide to which way the racial wind is blowing, simply ask yourself, "Does it feel like it did after Rodney King and the L.A. riots, or after the O.J. verdict?" If not, things aren't that bad.

Looking at absolute levels may be somewhat inaccurate -- maybe all that counts is where the upswings and downswings are. So I've also plotted the year-over-year percent change in how prevalent "nigger" is, though this time using 10-year moving averages to smooth the data out because yearly flucuations up or down are even more volatile than the underlying signal. In this graph, positive values mean the trend was moving upward, negative values mean it was moving downward, and values close to 0 mean it was staying fairly steady:


Again we see sustained positive growth during the Civil War, the two bookends of the nadir of race relations, although we now see a small amount of growth during the Harlem Renaissance era. The Civil Rights period jumps out the most. Here, the growth begins in the mid-1940s, but remember that it was at its lowest absolute levels then, so even the modest increases that began then show up as large percent increases. The PC era of the late '80s through the mid '90s also clearly shows up. There are several periods of relative stasis, but I see three periods of decisively moving against a nasty and bitter tone in our racial conversations: Reconstruction after the Civil War (admittedly not very long or very deep), the late '30s through WWII, and the "these are the good times" / Prince / Michael Jackson era of the mid-late '70s through the mid '80s, which is the most pronounced of all.

That trend also showed up television, when black-oriented sitcoms were incredibly popular. During the 1974-'75 season, 3 of the top 10 TV shows were Good Times, Sanford and Son, and The Jeffersons. The last of those that were national hits, at least as far as I recall, were The Cosby Show, A Different World, Family Matters, The Fresh Prince of Bel-Air, and In Living Color, which were most popular in the late '80s and early '90s. Diff'rent Strokes spans this period perfectly in theme and in time, featuring an integrated cast (and not in the form of a "token black guy") and lasting from 1978 to 1986. The PC movement and its aftermath pretty much killed off the widely appealing black sitcom, although after a quick search, I see that Disney had a top-rated show called That's So Raven in the middle of the tension-free 2000s. But it's hard to think of black-focused shows from the mid-'90s through the early 2000s that were as popular as Good Times or The Cosby Show.

(In the top picture, the comparison between Jennifer Beals and Halle Berry shows that a black-white biracial babe actress who came of age during the late '70s and early '80s took a white husband twice, while her counterpart who became famous in the early '90s went instead for black men.)

But enough about TV. The point is simply that the academic material we're taught in school usually doesn't take into account what's popular on the radio or TV -- the people's culture only counts if they wrote songs about walking the picket line, showed that women too can be mechanics, or that we shall overcome. Historians, and people generally, are biased to see things as bad and getting worse, so they rarely notice when things were pretty good. But some aspects of popular culture can shed light on what was really going on because its producers are not academics with an axe to grind but entrepreneurs who need to know their audience and stay in touch with the times.

Labels: culture, data, History, Pop Culture, race

Slate reviews the scholarly literature. Explaining the mechanics of the over-representation of engineers at the higher echelons of transnational terrorism is a guessing game, but the empirical reality seems relatively robust. Though I suspect that sociological and economic factors are necessary (see the linked paper in the article), I think the ultimate precondition has to be the psychology and training of engineers, who are geared toward analysis of a problem and devising a solution. The most ingenious/ridiculous models of Young Earth Creationism seem to spring from the minds of fundamentalist engineers, who must resolve their Biblical literalist premises with the world as it is. One can foresee how the same sort of mentality would be much more explosive in the Islamic world, where the fundamentalist premises lead to a set of inferences (e.g., Islam's manifest superiority over the West) which seems at variance with the state of the world. The engineer resolves this contradction by devising "solutions."

Labels: Terrorism

Earlier this year, John Tierney reviewed several studies on how delaying gratification makes us feel better in the short term by preventing guilt but makes us feel more miserable in the long term by causing regret over missed opportunities. I added my two cents here, just to note that this sounds like part of the Greg Clark story about recent genetic change in the commercial races that adapted them to the emerging mercantile societies they found themselves in. What I had in mind was the delaying of vice -- investing a dollar today rather than splurging, moderating the amount of drink or sweets you enjoy, and so on.

But now Tierney has another review of related studies which show that we delay gratification even for what should be guilt-free pleasures like redeeming a gift card, using frequent flier miles, and visiting the landmarks in your local area. And don't we all have enjoyable books and DVDs we've been putting off? After indulging in these cases, there is no potential bankruptcy, no hangover, and no tooth decay -- so why do we indiscriminately lump them in with genuine vices and put off indulging in them? Obviously this tendency too is a feature of agrarian or industrial groups -- hunter-gatherers would never leave gift cards lying around in their drawers.

It must be because of how recent the change toward delaying gratification has been. Given enough time, we might evolve a specialized module for delaying gratification in vices and another module for doing so in guilt-free pleasures, which would be better than where we are now. But when our genetic response to a change is abrupt, typically we have broad-brush solutions that take care of the intended target but also leave plenty of collateral damage. Over time our solutions get smarter, but it takes awhile. Just look at how crude the responses to malaria are.

We see this domain-general taste for (or aversion of) risk in other areas. People who lead more risky lifestyles buy much less insurance than people who lead cautious lifestyles. Those who ride motorcycles without helmets would be richer and more likely to pass on their genes if they bought a lot of insurance, while those who play it safe would be richer by not buying all that superfluous insurance. Instead, daredevils are daredevils all the way -- including a contempt for insurance.

This casts doubt on how easy it is to change our behavior so that we no longer postpone our indulgence in guilt-free pleasures. Because we have a domain-general delay of gratification, it will still just feel wrong. You can also argue the logic of buying lots of insurance to the motorcyclist who rides without a helmet, but that won't change his mind because his tastes for risk is across-the-board.

Labels: Behavioral Economics, Psychology

Actually, not really. New York on Track for Fewest Homicides on Record. I assume that those who project long term fiscal problems due to a contraction in the financial sector in New York City are probably correct (assuming that the financial sector actually doesn't expand back to its pre-2009 size). But the assumption that the economic fallout would lead to 1970s levels of anomie doesn't seem to be panning out. As I indicated earlier I found suggestions of such a reversion plausible at the time because I had a rather economistic mental model of the "root causes" of crime. But that seems less plausible when you look over the arc of the past century. Another model of course is that in fact it was financial sector workers who were driving much of the crime directly by subsidizing illicit activity through their enormous incomes generated by the efficiencies of capital allocation which they drove (I'm not being serious here).

Labels: data

A lot of people (including paying readers! kidding!) are complaining about the new commenting format. I'll be euphemistic and observe that it's suboptimal. But I don't have time to work on tweaking and beautifying it now, so please be patient. Over time it'll move up the stack of my priorities, and hopefully your awesome contributions to the discussion will be facilitated by a more elegant and user-friendly commenting interface by the end of January.

Additionally, I am thinking that posting "admin" messages in this space is also suboptimal. It uses space which should be allocated to real posts about science and such. If you're in the minority of readers who actually cares enough about your blog-reading experience to gripe in the comments, I invite you to subscribe to/follow my twitter feed, I'm gonna put "admin" related stuff there from now on. You can also send messages via twitter. Email is fine as always, but if you're someone who I don't recognize, there's a non-trivial chance that you'll stay at the bottom of the task stack and I'll never get back to you. I have my twitter feed on my Google homepage, so I am more likely to see random direct messages (as I noted earlier, I get a non-trivial number of messages from PR people, so it isn't unlikely that I'm forgetting emails in the "none of the above" folder).

Labels: Admin

Understanding the precise molecular mechanisms underlying changes in animal morphology is a tricky problem--usually two species which have diverged morphologically (say, mice and humans) are now so unrelated as to make genetic study exceedingly difficult, if not impossible. For years, a group led by David Kingsley has been addressing this problem in a cleverly-chosen model--three-spined sticklebacks. Importantly for the question of morphological evolution, freshwater populations of this fish have lost many of the spines and pelvic girdle carried by the saltwater populations (there are a number of hypotheses, probably not all mutually exclusive, for why this has been under selection).

In a new paper, this group demonstrates the precise genetic alteration underlying this change in a number of freshwater populations. Perhaps surprisingly, it appears to be due to the recurrent deletion (in different freshwater populations) of an enhancer of an important developmental gene. Strikingly, creating a transgenic freshwater fish with a copy of this enhancer (which normally is missing) leads to freshwater fish with a pelvis like the saltwater fish.

In fact, this enchancer seem to fall in a "fragile" (read: repeat-laden) region of the genome, which presumably increases the rate of deletion at this site. If one imagines there are a number of genetic paths to get to the reduced pelvis size favored in freshwater environments, the probability of each path depends on the mutation rate of each genetic change. In this case, many (though not all) freshwater populations have independently taken the same path, likely due to the increased mutation rate at this fragile site.

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Citation: Chan et al. (2009) Adaptive Evolution of Pelvic Reduction in Sticklebacks by Recurrent Deletion of a Pitx1 Enhancer. Science. Published Online December 10, 2009 [DOI: 10.1126/science.1182213]

Labels: Genetics

& a happy New Year.

Ross Douthat, Into The Mystic:

But as the Pew chart suggests, there is one sense in which religion was less influential in mid-century American life than it is today, and that's the realm of personal mystical experience. Slightly more people went to church in 1962, but many fewer people went out looking for their own private encounters with the numinous. This isn’t a surprising correlation, since the traditional Christian churches tended to either discourage mystical freelancing or (in the case of Catholicism) encourage it only within the framework of monastic discipline. The churches constrained and channeled Americans' religious impulses; their declining influence let a hundred mystic flowers bloom. Christianity became less culturally powerful, but religion itself - whether you were a tongues-speaking Pentecostal, a Gaia-communing pantheist, or some combination thereof - became much more freewheeling and intense.

Whether atheists, agnostics, and secular-minded Americans should prefer this dispensation depends on which raises their hackles more: Having laws and moral norms that are heavily influenced by Christianity, or having a culture that's heavily influenced by mysticism and supernaturalism. If you favor legal abortion, no-fault divorce, and easy access to pornography, today's America is a more pleasant place to live than the America of mid-century. (Especially if, like some atheists, you find pantheism to be the most congenial form of theism.) But if you don't like having your seatmate on an airplane ask if you've been born again...if you don't like being harangued at cocktail parties about the Mayan apocalypse or the healing power of crystals...if you don't like seeing the shelves at your local bookstores filled up by authors who claim to have conversed with the Almighty...well, then you might legitimately feel nostalgia for an earlier, less mystical America.

I recently recorded a diavlog with Nicholas Wade on The Faith Instinct. In that book Nicholas outlines the change in religion from its "primitive" state to what we would term "higher religion." Higher religion is built on the foundations of primitive religion, as institutional religion becomes less powerful in the lives people in the Western world people seem to be reverting back to their cognitive "default" settings. More often when you strip away adherence to theology you do not get atheism, you get animism.

Is this good for the small set of atheists and asupernaturalists? On an interpersonal level it might add a bit more confusion to one's life, as you never know which direction someone trying to sell you on supernaturalism is going to come from. But on a societal level it probably reduces the ability of religious elites to manipulate sects as cohesive functional units toward their ends.

Labels: Religion

Just a weird random thought. In the early 20th century the Ainu of Japan were considered by many physical anthropologists a branch of the white race. This fit in nicely with the historical fantasy of the period which often featured "Lost Races," with a lost white race the best of all. By contrast, the Negrito and Melanesian populations were considered outliers of the black race. Though the idea of Ainu as white seems to have diminished, in part because those sorts of ideas aren't too popular today, and partly because hardly any Ainu remain who do not have substantial ancestry from the Japanese. On the other hand, there remain pan-Africanists and black nationalists who talk about the unity of black peoples, from India to Melanesia. To the left is a photo where I've placed an Ainu man from the 19th century next to contemporary Andaman Islanders. I think you could understand why physical anthropologists of the period classified populations as they did based on appearance.

But with all the more recent genetic studies it seems pretty clear that the Ainu and the Andaman Islanders are part of a broader swath of "easterners" who swept out of Africa (in fact, there are Y chromosomal haplogroups which the Ainu share with Andaman Islanders). Older classical markers suggested that the Ainu were an East Asian people, and the uniparental markers suggest the same thing (I don't see any more recent SNP array studies which look at the Ainu). As for the Andaman Islanders, it seems very likely that they're simply an island population of the ancient "eastern" substrate of South Asia, which has been admixed on the mainland with a "western" quasi-European element, which in many regions and castes is now dominant. The Ainu and the Andaman Islanders are probably just the remains of the physical diversity which was once much more common in eastern Eurasia than it is today. That diversity may have gone by the wayside because of the expansion of the Han and the Austronesians, but it may serve as a hint that there may be only a few basic human racial morphs which reoccur, whether by chance or adaptation.

Addendum: The non-Bantu populations of southern Africa look East Asian. Also, since the Reich et al. paper on Indian genetics came out I've been reading up, and now I can see how the Andaman Islanders do kind of "look Indian." More specifically, there are some subtle facial features which South Asians have which must have come down from people distantly related to the Andaman Islanders. Look at the individual on the left in the photo above.

Labels: Genetics

Most of the readers of this weblog probably have as much use for the Singularity as John Derbyshire, but for those of you who dig Overcoming Bias and Less Wrong, you might check out Transhuman Goodness. The author, Roko Mijic, is so normal he could almost pass as a civilian!

I was skimming through a book on Scandinavian migration to Utah the other day, these Scandinavians being converts to Mormonism. The author noted that while most Scandinavian Americans settled in areas where farming was relatively easy, these converts went to Utah, which is a less than optimal territory when it comes to per unit productivity. Fair enough. But it got me thinking about why Mormons are so successful: perhaps it's just a function of migration. There were lots of American sects which arose during the early 19th century. The Disciples of Christ and the Seventh Day Adventists derive from the same period of religious ferment during the Second Great Awakening. But the Mormons have been the most successful. Why?

Perhaps it was the Mormon theology, the awesomeness of Joseph Smith. Or perhaps Mormons really are the One True Faith and god is on their side. But then I remembered that the original Mormons were New Englanders, and that most of New England's population in 1800 derived from the period between 1630-1640. The 20-30,000 who left England to establish a Puritan utopia in the New World. In the colonial period, and up to the Civil War, New Englanders were the most fertile group of Americans. Those Puritans who emigrated to New England in the 17th century, and remained (many went back to England during the period of Cromwell), have been extremely successful genetically in relation to their relatives in the home country. The reason is the simple Malthusian nature of biological increase; America had more room for growth (though England's population did grow very fast in the two centuries after the Puritans left, it did not match America).

The Utah Mormons are not the only descendants of Joseph Smith's religious idea. The Community of Christ, once the Reorganized Church of Latter Day Saints, and long under the stewardship of the Smith family, remained in the Midwest while Brigham Young led the migration west. Today the Community of Christ is in many ways a small mainline Protestant denomination, having lost or never developing the uniqueness of the Utah Mormons in terms of their theology. Numerically and socially it is relatively marginal, to the point where many Americans would be surprised as its existence (splinter Mormon sects which practice polygamy get a lot more press for obvious reasons).

The Community of Christ might illustrate the dynamic of attraction and absorption which occurs to splinter sects within a mature society. Over time minorities standardize their norms with that of the majority as they become respectable. This means they lose their distinctive cohesion. By contrast, the Utah Mormons were a people apart for several generations because of the nature of geographical distance in the 19th and early 20th centuries. Only with the rise of modern communication have they been assimilating, deemphasizing (at least in public) some of the more exotic aspects of their theology which might shock mainstream Christians. But because of the long incubation period in Utah the Church of Latter Day Saints remains fundamentally separate from what most Christians refer to as the "Great Tradition" of orthodox Christianity. By analogy to biology what occurred was an instance of allopatric religious speciation. In this model the great success of Mormons rests on their human geography during their formative period.

Some world historians point out that it has been nearly 1,500 since the last great distinctive world religion arose which challenged the status quo. Sikhism and Mormonism are instances of religious speciation, but they are small potatoes compared to Islam. Additionally, both of these traditions have shown some evidence of drifting back into their parent tradition (though Sikhs resist this, Hindus often claim Sikhs as simply a Hindu sect, while some Mormons have been slowly emphasizing their shared commonalities with other Christians). Perhaps modern communication technology and mobility will prevent future religious fissions on planet Earth? Perhaps subsequent to Islam the technological and communication gaps which new religions utilized to overturn older orders simply closed? In fact, if you read the travels of Ibn Battuta you might conclude that Islam itself served as a critical catalyst in closing up all the remaining gaps and discontinuities across the Old World oikoumene!

Labels: Religion

I already posted on the new paper on African American Genetics. I noticed that Frank Sweet says:

It is interesting that the 18 percent mean of Euro DNA markers in A-As has been holding steady for about 8 years now, having replaced the prior estimate of 25 percent.

Where did the prior estimate come from? I recall seeing it as well too. Were the older markers biased towards ones which might have been shaped by recent selection? The new paper doesn't have anything definitive in regards to this (they they mention the variance in African vs. European across different regions of the genome), though certainly some genes which affect malaria seem to have been shifted away from what you'd expect.

Labels: Genetics

Cosmos and Culture.