Gene Expression

Weird lands of the tails

Yesterday’s post on the speed of Jamaican sprinters, and Genetic Future’s skepticism of a one-gene answer for their dominance. The discussion brought up some adaptive talk; I’m not against adaptation, and I think it’s entirely plausible that populations differ enough in the distribution of phenotypes that there are different genetic potentialities…but, I have some issues with the intersection of the two in this particular case. Here’s my logic….

Sprinters at the Olympic level are the best of the best. They’re not just good, they’re not just superior, they are the pushing the limits of human capabilities in a particular direction. In other words, they’re the extreme tail of a distribution. What’s that distribution? I suspect it’s approximately normal (or can be so with easy scaling, I wouldn’t be surprised if the “fast” end of the tail is very long while the median is rather low; positive skew). Let’s just go with the normal for now, because the fudge doesn’t affect my logic even if it is a fudge. How good are the Olympic level winners?

Let’s assume that they’re 0.00000083 of the plausible full sample space of male winners. I got that number by figuring that the winners are among the 10,000 fastest men out of 3,000,000,000 X 0.25. I multiplied by 0.25 because there’s obviously an age constraint, though the world’s population is generally rather youthful. So, on a distribution where the area under the curve = 1, you’re looking at 0.00000083 out of that. If the mean = 0, and standard deviation is 1 unit, then the whole area under the distribution beyond 4.79 standard deviations represents the 0.00000083 who are potential world class male sprinters.

A standard deviation is just an easy way to measure the spread or dispersion of the distribution, but let’s make this concrete. The standard deviation of IQ is 15, and the mean is 100. Mensa level IQ is 130, 2 standard deviations above the norm and in the top 2-3% of the population. An equivalent to the proportion above for world class sprinters is an IQ of 172. Chances are you’ve never met someone who has a repeatedly tested IQ of 172 (I specify repeatedly because many bright people take many IQ tests and there’s a distribution of these scores; and many smart people just offer up their highest scores as somehow representative when they should really just average all the scores). In other words, world class sprinters are almost inhuman in terms of their abilities when it comes any comparison to the typical person.

Now, let’s go back to the original distribution, where the mean = 0 and standard deviation = 1. Obviously don’t take the mean as 0 too seriously, it’s just standardized for convenience. Let’s recall that 4.79 standard deviations above the mean is the cut off for world class sprinters. What happens when we increase the mean?

at 0.01, a 1% increment in standard deviation units, 0.00000088 of the distribution is above 4.79
at 0.05, a 5% increment up in the distribution, 0.0000011 of the distribution is above 4.79
at 0.1, a 10% increment up in the distribution, 0.0000014 of the distribution is above 4.79

In other words, a 10% increase in the mean value (standard deviation units) of the distribution resulted in a 1.6 fold increase in the number of the highest level caliber sprinters. The point being that very small deviations in the initial parameters of the distribution can result in very big effects on the tails. This is often an issue when we talk about sex differences, but the distance down the tail is much greater when we’re talking about the highest level sprinters, or athletics in general. Granted, athletic performance is strongly conditioned on training and will, but there is clearly a major component of innate potentiality at the highest levels where any edge on the margins is the difference between good and great (ergo, the payoff of performance enhancing drugs in many sports).

As I said above my assumptions are certainly way off somewhere, but, I think the logic is robust in the face of major deviations in the values of the parameters. The basic idea here is that elite sports, the best of the best, are simply so far off the norm that trivial differences between populations which do not manifest within 2 or 3 standard deviations in any visible manner may do so at the far ends of the distribution.

This brings me to the issue of adaptation. A comment below is illustrative:

All of the 100m sprinters are American/Caribbeans. All are West African in heritage. Those are the fastest people in the world, on average (in these events). They were artificially selected in slavery, making them even faster than they would have been otherwise.

What exactly does this add in terms of value? We assume that slave masters weren’t playing a game of Russian Roulette with sprinting heats. One can make the general case that selection for robusticity or strength might have resulted in somewhat greater speed, but to me some of these explanatory models for why West Africans and their descendants dominate sprints and East Africans dominate longer distances, or why South Asians just suck at sports, aren’t even wrong. They’re just ad hoc band-aids thrown on top of our ignorance. We just don’t know.

I want to emphasize how small the deviations need to be in some of these parameters for there to be a noticeable difference in potentiality at the edges. It is quite possible that these small differences in the distribution are due to genetic correlations between traits, or rather banal byproducts of morphological features. There is quite a large range in human metabolic processes, and some of these differences operate on the level of populations. It is entirely possible that these upstream phenotypic differences would be what is truly relevant when you’re talking 4 or more standard deviations from the norm on a trait. There doesn’t need to be any strong selection regime predicated on an exceptional event or period such as slavery; all there needs to be are some genetic differences between populations. When it comes to top level athletic events the range of between population differences in talents can be almost random since the independent variables are buffeted by innumerable selective forces and stochastic dynamics.

Comments

  1. #1 Ian
    August 22, 2008

    You might want to have Seed check the time setting on their server. I saw your blog just now saying 6:46 when my computer clock said 6:35. I checked with NIST (http://www.time.gov/) and my computer is within 2 seconds of official time.

    But hell, time is relative right? And who has time for relatives?!

  2. #2 Ian
    August 22, 2008

    Okay, now I read this offline, I have a serious comment. Is it possible that there’s a founder-effect in play here: that in the same way we have a “genetic Adam” and a “genetic Eve”, is it possible, somewhere back down the line, that the progenitor(s) of the American/Caribbeans had a genetic make-up which made them faster for whatever reason?

  3. #3 Josh
    August 22, 2008

    Razib once again comes in with a bad ass post. Really good stuff.

  4. #4 bgc
    August 22, 2008

    Of course running is a fairly basic human/ animal attribute – which might plausibly have been selected.

    So, in this instance there is no real reason to favor a null hypothesis of genetic drift over an adaptationist presumption – I would say both are about equally likely a priori.

    For a predator (like humans) sprinting is about catching animals (or people) which run slower than the predator (eg cheetah versus antelope), while endurance running is about catching animals which run faster than the predator (eg hyenas versus antelope) – but with which the predator can maintain sensory contact (by sight or smell).

    Some (not all) of the Kalahari Bushmen have the endurance to run down antelopes and the like, suggesting there may have been some selection for endurance running. Sprinting would (I guess) be more about surprising the prey before they could get up to speed, or escape to safety (down a burrow, into forest).

    Maybe these could be mapped onto the differences in the ecological demands of East and West Africa and the different athletic ability of East and West Africans? And also tested on other populations with contrasting ecological demands for running sustained over many generations?

    Such a hypothesis could be further elaborated and tested, I guess, if anyone thought it interesting enough (I don’t). But I don’t think it could be rejected without some further investigation.

  5. #5 razib
    August 22, 2008

    Some (not all) of the Kalahari Bushmen have the endurance to run down antelopes and the like, suggesting there may have been some selection for endurance running.

    greg cochran told me that was a exaggerated (that they normally don’t do this, but some anthropologist paid some weird dude to do it).

    But I don’t think it could be rejected without some further investigation.

    i do. west africans aren’t the only ones who live in forests (or around). also, africans haven’t really hunted much for a while now. and groups that were HG much more recently are slower, like north american natives (though the body plan of native peoples of the new world is still rather “siberian,” even tropical ones, so that much put a constraint on adaptation). i’ve attempted plotting regressions. but i gave up when i realized that south indians weren’t faster than north indians (forest vs. non-forest), that south chinese weren’t faster vs. north chinese.

  6. #6 razib
    August 22, 2008

    Is it possible that there’s a founder-effect in play here: that in the same way we have a “genetic Adam” and a “genetic Eve”, is it possible, somewhere back down the line, that the progenitor(s) of the American/Caribbeans had a genetic make-up which made them faster for whatever reason?

    sure. but you could check effective population for this. but as i note above, i don’t think that the deviations would have been very big at all, so the stochastic dynamics might not even require a major population contraction.

  7. #7 deadpost
    August 22, 2008

    What’s wrong with South Asians, that you are saying? They’d be The lot of them look more robust than the average East Asian, who are winning medals.
    I mean, look at least at American stereotypes about both, the East Asuab is usually the nerdier physique. The East Asian usually is scrawnier.

  8. #8 ronathan richardson
    August 22, 2008

    [please don't leave retarded comments benjvinc@gmail.com]

  9. #9 ziel
    August 22, 2008

    Adaptational explanations for higher foot speed based on acquiring or avoiding becoming food are suspect. Humans are so much slower than four footed mammals, the marginal speed boost possessed by West Africans couldn’t possibly help. the plodding Hyenas mentioned above run at 40mph – that’s a lot better for long-range hunting of antelope than the 15mph even the best marathoners can muster. Humans can’t even outrun a hippo, which neither hunts nor is hunted. There’s no four legged food source in Africa a human can run down nor any four-legged predator he could escape by running. It seems plausible the speed advantage is a side-effect of a more generally “athletic” physique – long legs, finer muscle tone, more muscular buttocks. But why that?

  10. #10 razib
    August 22, 2008

    The lot of them look more robust than the average East Asian, who are winning medals.

    so? black americans are fatter than white americans, but that doesn’t mean they’re slower at the elite levels….

  11. #11 Eric J. Johnson
    August 23, 2008

    > Adaptational explanations for higher foot speed based on acquiring or avoiding becoming food are suspect. Humans are so much slower than four footed mammals [...]

    Looking beyond the quadripeds, one animal with a decidedly human-like speed is humans. Perhaps war is a more plausible selector. An open terrain might increment the relative valence in warfare of pursuit afoot, but I am not aware that such a correlation exists (I am not familiar with the West African landscape). Even if it did I imagine drift/founder would still be hard to reject.

  12. #12 diana
    August 23, 2008

    Razib,

    Veronica Campbell-Brown (the Jamaican gold medalist in 200M and something else) said, “In Jamaica we don’t have many other sports than track.” (Actually, men have cricket, which Usain Bolt excelled in as a fast bowler, but women don’t have that.)

    Mightn’t this explain the Jamaican supremacy? Unless we can prove that Jamaicans come from a specialized gene pool, I’d go with the usual genetic West African superiority – plus motivation. Being a silver medalist in Jamaica means something. Being a silver medalist in the US means bupkis.

    Lastly – everybody’s talking about natural selection here, plus a bit of slavemaster eugenics. Well, what about sexual selection? Is it possible that a guy who looks like Usain Bolt is esp. attractive to a woman who looks like Veronica Campbell Brown? I think so.

  13. #13 Ian Gould
    August 24, 2008

    “Okay, now I read this offline, I have a serious comment. Is it possible that there’s a founder-effect in play here: that in the same way we have a “genetic Adam” and a “genetic Eve”, is it possible, somewhere back down the line, that the progenitor(s) of the American/Caribbeans had a genetic make-up which made them faster for whatever reason?”

    It’s noteworthy that while Jamaica did really well in Beijing, other countries with a similar genetic make-up such as, say, Haiti, Cuba and Trinidad didn’t.

    A strong founder effect in Jamaica (i.e. a handful of genetically superior runners in the first few generations)could explain that.

    But so could the Jamaican focus on track events – or a combination of the two.

    I’d point out that there are probably nearly as many people of Afro-Caribbean descent in the US as their are in Jamaica.

    I’d also point to the quite extraordinary performance of Australia in Olympic events across all types of events.

    Last time I checked, Australia was running fifth over all in the medal count. That’s pretty amazing for a country with 1/15 the population of the US.

    Maybe it was genetic selection operating in the convict shops – or maybe its because Australia for the past twenty years has been plowing hundreds of millions of dollars in the Australian Institute of Sport and its state equivalents.

  14. #14 razib
    August 24, 2008

    Maybe it was genetic selection operating in the convict shops – or maybe its because Australia for the past twenty years has been plowing hundreds of millions of dollars in the Australian Institute of Sport and its state equivalents.

    perhaps you could consider that there is *more than one explanation* for a trend? people really enjoy knocking around strawmen, so easy. just because some interlocutors are retards doesn’t mean all are.

  15. #15 Ian Gould
    August 24, 2008

    Frankly, given your gratuitously offensive and argumentative responses, I’m surprised you have any interlocutors at all.

    I certainly won’t be wasting my time on you in future.

  16. #16 razib
    August 24, 2008

    I certainly won’t be wasting my time on you in future.

    ah, a good day indeed!

  17. #17 dre
    August 24, 2008

    The population that cares most about an activity is the population that is most successful at that activity.

    That’s the context in which I view the elite in any sport, business, or other occupation. Of course, people who have necessary resources are able to care more – elite bankers don’t usually come from impoverished nations. Neither do Formula One drivers.

    If baseball is a valuable part of Japanese and Central American culture, there will be a lot of good Japanese and Central American baseball players. If basketball is more important to young, African-American boys than it is to Irish-American boys, there will be a lot of good African-American baskeball players and not so many Irish-American ones. If table tennis is something Chinese children grow up with every day as a culturally valuable activity, there will be some excellent Chinese pingpongers.

    I am not a statistician, nor am I a geneticist, but I’d be willing to bet that the very topmost, tail-end performers are more likely to be drawn out in a culture that values an activity, while some of the potential best performers find other careers in cultures that do not value that activity, having never known their potential.