My post a few days ago about multiracial humans elicated many comments, and not all of them were flip or for amusement. There are some serious issues, like synergistic and antagonistic epistasis, which I would like to explore in the future. But, I think there are two primary "take home" points:
1) Aside from cases of problematic populations with recessive diseases (frankly, I think Ashkenazi Jews fall under this) the fitness benefit of outbreeding does not stand out so much as to be of great comment in the grand scheme of how you fix upon your one and only. I don't even think it really is a big issue socially in a genetic sense (as even mild levels of inbreeding can be).
2) On the other hand, the expected variance of the outcome might be greater than you would otherwise get in a homogenous population (if all your marbles are black, your expected outcomes are all black, but if you throw marbles of indeterminate color there is going to be wide range of outcomes whose probabilities are conditional upon the sample proportions).
By the latter point, I mean that greater underlying genetic variation within admixed populations (ergo, the potential in individuals) results in a more fully explored range of phenotypes (more novel combinations), this implies that more and less "fit" adaptive territory maybe explored by this population. There are lots of qualifications here, as "fitness" is contextual. One could make a case that the strategy you, dear reader, should follow as an individual should be premised upon your risk vs. yield outcome. If you are a "high quality" individual, perhaps let the die fly in the hopes of spawning the Ãbermensch. On the other hand, if you aren't exactly a catch, perhaps it is best to play it safe and minimize the risk of plumbing the deepest depths of the fitness landscape. The fair Eurasian lady pictured above has had the longest lasting Neutrogena contract yet.* Could it be that her hybrid vigor has imparted upon her skin a youthful pallor unmatched in either Europeans or East Asians? Who the hell knows? But science is all about unanswered questions.
* As the citation is Wikipedia I make no guarantee that the link will corroborate my claim!
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Is it a coincidence that you posted a photo of Kristin Kreuk, who starred in the tv movie version of Ursula LeGuin's Earthsea stories and just so happens to live in the same general vicinity as me? I don't think so. BTW, I saw her in a bar last year and she's just as beautiful in person. And who knows? If I happen to have children with my East Asian girlfriend, they might just look a little bit like Ms Kreuk!
If I happen to have children with my East Asian girlfriend, they might just look a little bit like Ms Kreuk!
d00d, don't sound too excited about this. that would be your daughter, and there are other posts that discuss the genetic issues with this....
I wasn't excited about my daughter being hot, just mentioning another coincidence. As for genetic issues, what exactly are you referring to? :-/
I speculated somewhere that high pathogen-load areas would select for more interracial mixing -- think of Brazil. Before the Euros & their African slaves came over, there was no large-scale, high-density civilization in Brazil. Within a short period of time, this tropical, bug-friendly environment undergoes a rapid shift in density, not to mention all the European & African bugs the colonists & slaves brought with them as house-warming gifts.
This is the kind of rapid environmental change that Henry & Greg just wrote about in their paper distinguishing "adapted genes" (lactose tolerance) vs "adapted genotypes" (hetereo state of the sickle-cell gene). They argue the latter is the first-response, sloppy solution that natural selection hits on when the pressure is great. But this could happen even more quickly if individuals were free to choose to explore much more of the diversity landscape themselves -- a possibility only when previously kept-apart populations suddenly live next to each other.
In F1, this may increase only variance, not mean/median, as you say. But if the long-term prospects of an allele's survival depend on it residing in a genome whose diversity exceeds some high threshold in order to evade the novel plague, then there would be proportionally more interracial children above this threshold compared to pure-breds. It would also have the ugly side-effect of proportionally more unfit, but in a sloppy knee-jerk response to plagues, it seems that all that matters is what proportion exceeds the right-tail threshold.
An objection would be that this is only one trait, and that other traits may have optimal fitness at the median value, where proportionally more pure-breds would be compared to mixed folks, and who knows how the dust will settle when all traits are considered? But rapid change in pathogen pressures appear to cause the exploration of diversity to drop everything else it's doing and do something to fight off the bugs now.
Assuming that "tolerance or desire to interracially mate" is a stable disposition with non-trivial additive genetic variance, then in 2006 you'd expect to find more interracially minded individuals in areas subject to long-standing, harsh pathogen loads, like South Asia, Iran, and Brazil, rather than Finland, Kalahari H-Gs, or Japan. The latter might be up for some limited intermixing, but the former would be more so.
Interracial mixing in Brazil is due to a severe scarcity of European women for about two hundred years. The Portuguese mated (more often raped) female Indians and Africans for a simple lack of options.
Razib & Evolgen know the evol gen better than I do -- but I just read Orr's 2005 NRG history of theories of adaptation, and one take-home message was that the effects of each consecutive change follow an exponential decay curve, so that the earliest changes are of large effect and much later changes are minor tweaks.
So that's another possibility w/ interracial mixing -- given the broader sample space, natural selection hits on these large effect alleles sooner than by other means, like waiting for a mutation to occur & spread through a +/- endogamous population. So even if it turns out that mixed kids aren't any more or less fit, it still could be that they reach their local optimum faster than more pure-bred kids, giving a temporary illusion of hot, healthy mixed kids -- the kids of the rest of the population might end up this way too, but it'll just take longer.
so that the earliest changes are of large effect and much later changes are minor tweaks.
yes, i think so.
keep the models coming, they're interesting....
I am not sure of environmental factors (such as historic discrimination) but I do not believe African Americans are more fit than more monoracial groups in America, probably the opposite...African Americans (from the studies I have seen) range from 18-24% white (primarily Anglo-Saxon and Scot) and about 1-4% Native American (but this was a very small study only focusing on African Americans in the Carolinas. NOt to mention that African Americans are also composed of several dozen subSahara African tribes primarily from Mid and South West Africa (but also a little from East African nations such as Mozambique)...African groups have more genetic distance between them than any other continental "racial" group.
Does this make them more fit? Well not as far as chronic disease go...no, but on average they still live in worse environments than white Americans.
rasfarengi,
a previous comment i made:
remember that the key is better than expected values/fitness. i don't think it has to be superior to both populations necessarily to show some hybrid effect (though better than expec. could just be dominance).
the question is this: is african american chronic disease susceptibilities (pick a disease) worse than weighted average of africans and whites? yes, there is a assumption that hybrid vigor implies superiority in relation to parental types, but, on a reductionistic scale it is important to consider greater than expected fitness.
Razib:
It is hard to tell since West African blacks (on average) live at such a low standard of living.
You would have to test west african blacks in the UK, France, and America who grew up there.
There are a lot of very mixed populations, not just Latin America but probably the most mixed population in the world are in Central Asia...from Iran to Kyrgzstan...or actually XInjiang in China.they have pretty much a bit of everyone from Eurasia in them and trace amounts of haplogroups dominent in SubSahara Africa (guessing that came from Muslim slave trade, as their are decendents of black African slaves in Western India (ver few though)...seems everyone wanted a black man working for them. :-/ (http://www.colorq.org/MeltingPot/article.aspx?d=Asia&x=Habshi)
most mixed population in the world are in Central Asia
be careful about analogizing this region to latin america. latin american is a region of recent admixture of historically discrete population clusters. central asia has always been at the crossroads, and one might argue that powerful element of clinal gradation can be discerned across eurasia. in other words, deleterious side effects due to antagonistic synergistic epistasis might eventually be masked in this population because of modifier genes which arise....
Back in 2001, I pointed out that the fact that the best golfer of all time is famously mixed in race might not be a coincidence. For a sport like golf, that calls on a variety of skills and thus isn't like 100 meter dash sprinting where West Africans dominate, having a wide variety of types of genes might increase your chance of getting the very best genes for golf. By the same logic, it would increase your chances of getting the world's worst set of genes for golf, but then nobody forces you to play golf.