Is Hybrid Vigor IQ Warm And Fuzzy?

The July 2007 Psychological Review has Michael Mingroni reviewing an interesting theory he published in Intelligence in 2004, that IQ has increased mainly because of more interracial and cross-cultural mating:

IQ test scores have risen steadily across the industrialized world ever since such tests were first widely administered, a phenomenon known as the Flynn effect. Although the effect was documented more than 2 decades ago, there is currently no generally agreed-on explanation for it. The author argues that the phenomenon heterosis represents the most likely cause. Heterosis, often referred to as hybrid vigor, is a genetic effect that results from matings between members of genetically distinct subpopulations, such as has been occurring in human populations through the breakup of small, relatively isolated communities owing to urbanization and greater population mobility.

Regardless of whether Mingroni’s theory is true, I find it striking that it seems less politically correct than it could be. 

The first response you often hear to genetic explanations of IQ, or even the very idea of IQ, is that such ideas encourage racists, such as Nazis.  But Mingroni’s hybrid vigor theory seems tailor-made to oppose racist and other xenophobic mating policies; instead of killing off "lower" races or preventing interracial mating, Mingroni’s theory suggests one wants to encourage diverse mating and preserve other races as sources of genetic diversity. 

The currently political correct environmental explanations of IQ, in contrast, are quite compatible with racist and other xenophobic mating policies.  That is, one can nearly as easily oppose contact and mating with outsiders for fear of contamination from outsiders’ cultural and other environmental influences, as from outsiders’ genes.  Such arguments were offered in the recent immigration debate, for example.  So why are environmental IQ theories so praised for opposing racism, relative to hybrid vigor?   

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  • Well, all of this seems to be separate from what theory actually best models apparent reality, a concern that I think should have primacy.

    Second, kudos to you for writing about IQ, heredity, and human subpopulations. I don’t think such an interesting topic should be ceded to cranks and kooks, just because of various heckler vetos polluting the discourse.

    I think environmental explanations for IQ difference are framed as less “racist” (also less classist) because elites prefer a merit-based explanation for their eliteness and privilege, rather than a biological endowment explanation. Also, I think there is a deliberate blind-spot regarding regression to the mean- two very smart people don’t like to think that no matter how good a cultural environment they provide for their kids, their kids will probably be significantly less intelligent than them. So I think the application to race and racism is a bit subordinated to the subversiveness to ideas and justifications of class and parent-offspring relations.

  • josh

    I always thought hybrid vigour was the resultant population after natural selection had a chance to affect the allele frequency in the new conjoined gene pools. Shouldn’t mixing from different subpopulations lead to a higher level of both very high and very low IQ people. Are high alleles coding for high IQs even more likely to be passed down at this point?

    The answer to your question might be that endorsing the hybrid-vigour hypothesis means recognizing that differences in subpopulations may account for much of the current inequalities between races. Even if the obvious policy recommendation is to be be less discriminatory, people would be pretty unwilling to concede this. Sort of the whole, “arguments are like soldiers” thing people are always saying on this sight. One of the arguments proponents of slavery, segregation, and/or holocausts put forth is that there are different ability levels and behavioral tendencies between races. People who are against these things start by opposing that premise.

    • BayStreet

      I’m not sure why endorsing the hybrid-vigor hypothesis is at all related to “recognizing that differences in sub-populations may account for much of the current inequalities between races”.

      Hybrid vigor may be accounted for by the same principle which leads to increased risk of birth defects among children of two close relatives.

      Many genetic “defects” – from aesthetic actually result in physical or intellectual problems only (ranging from dry, disgusting ear wax and facial asymmetry to sickle cell disease and deadly Tay Sachs disease) if the child has received copies of the same non-functioning gene(s) from each of her parents.

      People from different regional populations (i.e., “races”) have the same overall frequency of non-functioning genes (hence no “superiority” of one vs. the other). However, the chances of precisely the same genetic mutation arising independently in two people whose parents are completely unrelated and coming from populations that separated 50000 years ago (e.g., Swedish and Zulu) is quite low. The chances of a maladaptive (unattractive / unhealthy) feature having persisted in both of those populations is particularly low because its transmission would occur only by chance, and because it would actually reduce its bearers’ chances of having offspring,

      In contrast, individuals whose parents come from the same regional population or “race” (e.g., two Sicilians or to Ashkenazis) are likely to share more and more recent common ancestors. It is thus more likely that they will have some of the same genes (relatively rare in the world as a whole), because they might have inherited them from the same individual.

      When the two more related people (i.e., the homoracial couple), with some of the same defective genes contribute those genes to a biological child, it is likely that the child will receive two copies of some of the defectives gene, and thus have disgusting, waxy ears, a slightly lopsided face etc., which make her less physically- attractive.

      You may ask why the same thing wouldn’t happen with very attractive or healthy features (such that mixed-race individuals would also be less likely to be exceptionally good-looking). There are two reasons for this.

      First, the prevalence of healthy and attractive (i.e., adaptive) traits is not dependent on chance. It is favored by natural selection. As noted above, maladaptive (sexually unattractive or unhealthy) genetic traits are less-likely to be passed on to the next generation. In contrast, a person who manifests genetic traits that are sexually desirable, or which cause him to live longer, is likely to produce more offspring. His genes are thus likely to become more and more prevalent in the population. The most healthy and attractive traits are thus the ones most-likely to persist in more than one human population, and thus be shared by both members of a heteroracial couple.

      The second (though perhaps related) reason why we would expect mixed-race individuals to be more attractive is that humans tend to find people with statistically-average features the most attractive (this has proven to be independent of the effect of symmetry and facial smoothing produced by composite imaging). Many traits that are not autosomal recessive (e.g., oval vs square face, face length, face width) are polygenetic, and move along a sliding scale based on the aggregate effect of multiple genes. To the extent that particular sub-populations manifest more extreme characteristics (e.g., longer or shorter faces, noses etc.), a child of parents from two different sub-populations is likely to have a characteristics that are more moderate, and thus, studies show, more attractive.

      • greg s

        interesting to find this comment as I’m documenting the on my extended family’s genealogy

        I was born in the US and my wife in Peru – but both are of Sicilian descent

        We learned that we both carried the gene for sickle cell during a genetic counseling session during my wife’s pregnancy

        I’ve also learned that in addition to the fact that we’re both of spanish and sicilian descent

        We both have croatian ancestors and our great-grandparents come from areas of Sicily that were heavily norman and sephardic

        As a result, it’s interesting to for me to think that across multiple generations there can be these extreme levels of gene recombination like ours – a small counter-current running against diversity

        if this is the case, the genes we have passed on to my son may be as close as this pair of DNA have been in over 500 to 1000 years and I suspect could go back even further

        I’m considering DNA analysis just to see what it tells me regarding the origin of my collective family

    • CuriousForge

      Another explanation may be that parents of mixed-race children are more likely to be intelligent.

      This is for two reasons:

      First, a recent study has shown that persons who are liberal, and who don’t subscribe to any particular religion, are more intelligent on average. (–are-liberals-and-atheists-smarter) It is axiomatic that persons who are liberal and persons who are athiests are less set on marrying or otherwise socialiize someone from exactly the same ethnocultural background. A Norwegian-Canadian leftie isn’t going to listen to her Lutheran parents from Tromso when they disapprove of her marrying or sleeping with the child of Muslim-American parents from some small village in Iran.

      Second, a person (e.g., an Indo-canadian) who is attractive and intelligent is less-likely to have to depend on traditional match-making systems to find a mate. She’s likely to get hit-on by some hot Russian guy in college, rather than remaining single and having to crawl to her parents and ask them to arrange a marriage with some 7th cousin in the Punjab.

  • Phil

    Perhaps the allure of the environmental explanations is that it allows for the possibility that we can *do something about it*. Maybe it just takes better nutrition, better food standards, better schools, better government programs, and the gap between groups disappears. It’s more compatible with activism, and public displays of concern. The “solution” is also generally in line with policies that activists favor anyway.

    The environmental explanation also allows for someone to blame. If group X has a lower IQ, it’s because of racist policies that and exploitation that kept its children from growing up in a proper environment. “Group X shows lower IQ because of what we did to them” is more palatable than “Group X shows lower IQ because God and genetics made them that way.”

  • Hmm…

    “less politically correct”
    Political Correctness is such a sloppy term. Perhaps you could rephrase that so it doesn’t mean 10 different things to 10 different people.

    “environmental explanations of IQ”
    A good diet, prenatal care, and intellectual stimulation of toddlers is compatible with xenophobic mating policies?

  • Douglas Knight

    Robin Hanson,
    You sound like you are comparing an explicit model which predicts that it’s PC to something else which says it isn’t. What is that other thing? some implicit model, a gut reaction? or its actual reception?

  • Stuart Armstrong

    So why are environmental IQ theories so praised for opposing racism…
    Similar question: why are differences in human capacities seen as supporting the free market, while similarities are seen as supporting more socialistic policies? One can easily reverse the arguments in both cases.

    As for your own question, I feel it’s a counter-coallition. For some historical reason, the racists and the genetic IQers were generally on the same size. A counter-coallition formed with opposite ideas, and maintains itself today, even after the crumbling of the racist coallition.

    I had a model I put together some time ago using markov chains to model how people shared their opinions with each other. Under relatively mild conditions, opinions would soon group into opposing camps, due to mutual reinforcement. If you believed X, you were more likely to believe Y; more importantly, you were more likely to have friends who believed X and Y. The fun thing was that there were no connections at all between X and Y! Ideas just get linked, even if they seem contradictory. Think opinions on tax rates versus military spending, abortion versus capital punishement…

    So why are environmental IQ theories so praised for opposing racism, relative to hybrid vigor?
    The answer to your full question is much easier, I think: few people have ever hear of hybrid vigour theories in humans.

  • That is, one can nearly as easily oppose contact and mating with outsiders for fear of contamination from outsiders’ cultural and other environmental influences, as from outsiders’ genes. Such arguments were offered in the recent immigration debate, for example. So why are environmental IQ theories so praised for opposing racism, relative to hybrid vigor?

    Because the people doing the praising don’t believe in culture, or don’t believe in its significance? Shouldn’t the positive connotations of “multiculturalism” be evidence of that? If you don’t think that a culture espousing human rights, property rights, and intellectual freedom is better than one that doesn’t, a critique of cultural contamination would be as incoherent as a critique of, say, left-handedness.

  • michael vassar

    Hopefully: Great points.

    Stuart: I think that your explanation is clearly the main thing going on here.

    Robin: Scientifically, hybrid vigor is a non-starter for the Flynn effect. The Flynn effect is much too big to be compatible with plausible past levels of inbreeding, and much too linear.

  • Adrian Tschoegl


    1) This part of your sentence in your penultimate paragraph “…one wants to encourage diverse mating and preserve other races as sources of genetic diversity”, seems internally contradictory.

    2) That aside, the heterosis hypothesis would suggest that we should identify strongly endogamous groups such as the Amish (where, by-the-way, endogamy may be starting to result in an increase in genetic disorders), to determine if in such groups IQ has been stable over the period of the covered by the Flynn effect. A practical problem might be finding past tests. For instance, one couldn’t use the results on Armed Forces tests as the Amish are pacifists and were excused from the draft.

    3) I suspect that anti-racists may have embraced environmental explanations for IQ because they feared that if IQ was heritable rather than environmental, undoing apparently race-correlated differences in achievement would be impossible, and such differences would provide a basis for anti-miscegenation laws.

    Michael Vassar:

    I am inclined to your critique, but if we recall that the period from about 1830 to about 1930 was one of relativley open borders and mass migration, particularly to countries that are now developed and where possibly most of the IQ testing underlying the Flynn effect has taken place, perhaps there is a basis for the heterosis effect.

  • On a slightly tangential note, I wonder why people still associate genetic IQ theories with immutability. Yes, we can’t directly do much about that component now, but we have every reason to believe we’ll have the relevant germline engineering and/or other capabilities in, say, 50 years.

  • Dog of Justice, not to belittle your point, but it’s obvious, and doesn’t even require fancy technology like germline engineering. Selective breeding would do the trick, and quickly. The reason you haven’t seen it mentioned much is because the whole discourse is performative, rather than genuinely inquisitive, it seems to me. Read this also as a disagreement with Adrian’s explanation point #3.

  • Adrian Tschoegl

    Hopefully Anonymous:

    Could you expand on your third sentence? I don’t quite follow your point, and am ready to be convinced otherwise on mine.

  • Dog of Justice, not to belittle your point, but it’s obvious, and doesn’t even require fancy technology like germline engineering. Selective breeding would do the trick, and quickly.

    Um, it seems pretty obvious to me that selective breeding is prohibitively costly. Yes, it’s easy to imagine how such a system would work, but I cannot imagine how we get from our current society to one willing to implement such a policy, and that’s probably a good thing.

    Germline engineering is the first technology I see on the horizon that is consistent with essentially no restriction of the reproductive freedoms expected by everyone (outside of China, anyway).

  • Adrian, I’ll try to post it on my blog if I get a chance. Robin would prefer I limit myself to 2 of the most recent 10 posts in the comments of the overcomingbias blog at all times.

  • If heterosis is the explanation we should see different rates of progress in different populations depending on how open they are for foreign genes. We ought to see much bigger gains in the US than in Scandinavia, for example (and during different time periods). Given the recent reports that the Flynn effect may be slowing in Norway yet its immigration is now at a historical high, I think heterosis is unlikely to be the big explanatory factor.

    As for cost-effective and non-coercive selective breeding, “liberal eugenics” is the answer. If people are allowed to do PGD and select embryos freely there will be a selection pressure towards desirable (whatever they are) traits. If this is cheap enough (current costs are on the order of several thousands of dollars and a pretty sizeable amount of effort) and culturally acceptable it could become a major selective factor.

    I think too many people have grown up with the view that “biology is destiny”. Everything that is biological is regarded as set in stone, so anything that can be changed or modified has to be part of the nonbiological realm. This seems to be true both among the nature and nurture people, while the real messy state of affairs of multiply interacting processes lacks the simple appeal of “blank slates” and “the blood will tell”. We may be seeing a simplicity bias, where the quick and simple story has an advantage over the complex and nuanced one.

    As for the link to racism, I would also think it is mostly historical accident. Maybe if genetics was developed later than sociology the racists would have been talking about “cultures with pernicious and infective power-structures” or “human capital limiting languages”. As long as someone thinks trait X cannot be changed, is inherent in a certain population, and has a negative value it works well as an explanation for why the population should be discriminated against. Although the real cause of the claim (and why the claimant is not suggesting helping these victims) is usually the assumption that members of the population have an intrinsically low value regardless of X; X only acts as a sign or rationalisation.

  • TGGP

    To me it seems doubtful that there has been enough intermarriage relative to the past to cause the Flynn effect.

    Gene Expression has a pretty good post showing how white admixture cannot explain the higher IQs among African Americans compared to Africans (lending weight to the idea that Africans are environmentally disadvantaged).

    Alon Ziv has written a book about mixed marriages resulting in hybrid vigor. Steve Sailer (who is quoted in the book) reviews it here.

  • TGGP

    Also, it should be noted that the Nazis did not care much for IQ tests because they showed Ashkenazi jews to be the most intelligent.

  • Martin

    josh: “I always thought hybrid vigour was the resultant population after natural selection had a chance to affect the allele frequency in the new conjoined gene pools.”

    Hybrid vigor results from decreased homozygosity (essentially, your level of in-breeding) when two different populations mix.

    josh: “Shouldn’t mixing from different subpopulations lead to a higher level of both very high and very low IQ people.”

    Not if IQ (or health, or whatever) is being decreased by recessive (Mendelian-type) alleles. If all the genes affecting intelligence are quantitative, then you would first expect regression toward the mean, followed by spread of the normal distribution.

  • As for cost-effective and non-coercive selective breeding, “liberal eugenics” is the answer. If people are allowed to do PGD and select embryos freely there will be a selection pressure towards desirable (whatever they are) traits. If this is cheap enough (current costs are on the order of several thousands of dollars and a pretty sizeable amount of effort) and culturally acceptable it could become a major selective factor.

    Okay, I probably misunderstood what was meant by “selective breeding”; I had mentally categorized this sort of embryo selection as a sort of primitive form of germline engineering. Sorry about that. Yes, this form of selection is powerful enough to have a significant impact.

  • Doug S.

    There’s also been a “Flynn effect” in height. People today are not only better at IQ tests than they used to be, but they are also taller than they used to be. Would it be as interesting to read about the relative influences of culture and genetics on the radical increase in average height since, say, 1800?

  • Alcofibras Nasier

    Genetics was developed later than sociology (Mendel’s work remained deeply obscure until c.1900; ‘Genetics’ was only coined by Bateson in 1905). Not sure where that leaves Anders Sandberg’s comments though; the overall point about the bias towards simplicity is a strong one. As for the origins of the ‘biology is destiny’ nostrum, how much of that has to do with race, and how much with gender…

  • josh


    Thanks, I get it now.

  • Martin

    Doug: My family is an interesting (albeit anecdotal) test case. My parents grew up in Czechoslovakia, while me and my sister grew up in the United States. My father is 5’7, and my mother is 5’2. I’m 6’1 and my sister is 5’7. We gained 5-6 inches over our parents, which demonstrates that nutrition (and probably hormones in meat) can play a big role.

    I’m willing to bet that the gains in height and intelligence are *mostly* environmental.

  • Adrian, regarding your point #3:

    The concepts “undoing apparently race-correlated differences in achievement would be impossible” and “a basis for anti-miscegenation laws” do not follow from “IQ [is] heritable rather than environmental”, but I think that’s a fairly easy point to grasp, and has been probably since the discourse on this topic began. Thus I think this whole dynamic was primarily performative. Michael Kinsely has a great expression he uses for some public political exchanges, he calls them “kabuki”. I think there’s a kabuki element to the whole discourse on IQ, heredibility, and human subpopulations, which is a damn shame because it’s a distraction from actual scientific inquiry, in my opinion.

    And I think Robin plays into it by making a belief as teams pander in the OP. Thankfully, other posters to this blog (notably Eliezer) are being more transparent, and thus more enlightening, on these dynamics. Eliezer’s posts on Belief as cheer/attire: very enlightening. Robin’s foil-seeking post regarding the “political correctness team” — enlightening primarily as an example of problematic phenomena Eliezer’s been describing.

  • Hopefully, I have no idea what you mean by “making a belief as teams pander in the OP.”

  • Anders, is simplicity bias something that has been documented as widely occurring? That phrase isn’t well known, and I doubt it’s a sufficiently strong pattern to explain the degree to which people believe “biology is destiny”.

  • A half dozen years before Mingroni, Arthur Jensen discussed how hybrid vigor has a (modest) upward effect on IQ in his 1998 magnum opus “The g Factor.” Jensen cited one study in Hawaii that found a 2 point IQ advantage for interracial marriage, but I haven’t seen much else to support this, and 2 points is down around the margin of error.

    In general, to overcome in-breeding depression, you don’t have to marry somebody from the next continent — somebody from the next valley will do fine. The big problem causing in-breeding depression is not prejudice against interracial marriage but cousin marriage, which is wildly popular in much of the world — e.g., in Iraq, about half of all married couples are first or second cousins!

  • Jim

    The Flynn effect is rather large, approximately 15 points of IQ gain in the past 50 years. That’s one standard deviation. It has been observed in every country where reliable measurements are available.

    One could postulate the racial-mixing hypothesis in the US or Europe, but the Flynn effect is equally observable in countries like Japan, where racial mixing is almost non-existant.

    Nutrition seems like a better candidate in most countries, but in the US – and especially the white population – nutrition has been at a very high level for well over sixty years. There must be some other explanation. I wish I knew.

    Isolated by race, the 2007 black US population today does better on IQ tests than the white population did two generations ago.

  • Lynn Collins, PH.D.

    I have taught highly gifted mathematics students in a magnet program for 35 years. I have had many students whose parents were from two different races: Asian(Chinese, Korean, Vietnamese, Indian) and Causian, African-American and Causian, even parents from Eastern Europe and American.
    All of these students were exceptionally intelligent, highly talented, responsible. mature, and most were far more physically attactive than the average teenagers. In most cases they had other high level talents: music, ballet, ice skating, soccer, other sports as well as leadership skills within their schools.
    Interestingly, as a teacher of the highly gifted, I had many more biracial students than most teachers. I also taught brilliant math students with Aspberger’s syndrome and some with emotional disorders and strange behaviors, but these students were never among the biracial students.
    I came to the conclusion by myself long before I heard of the concept of “hybrid vigor” , “heterosis”, or “the Flynn effect” that interracial marriage was very much an advantage for the children – at least genetically if not socially.
    Certainly this is not a scientific experiment – just an observation of a Mathematics teacher with 40 years of classroom experience…..

  • I read up on a study which stated that children of parents who speak more than one language in the household do better (not necessarily ebonics) with IQ, so does the study get into the impact that causes, and compensate for it? Likely not, since the study seems focused on a biological observation to assess the theory.

  • Cassie

    Each generation is obviously more knowledgeable than the previous due to the increase of knowledge as well as the changing of lifestyles. Also, prior to the twentieth century most people were still consumed with survival and didn’t have the resources or free time to spend reading, writing, surfing the internet, etc. like we do today.

    But in looking at actual historical documents, journal entries, music, etc, I believe our ancestors had better reasoning skills and deeper understanding and wisdom.

    One of my college professors said they had to change tests and academic programs every few years due to less capable students. Are the IQ tests updated as well?

    If so, then what is the standard of intelligence? And what are the IQ tests measuring? When I look at today’s kids, I see children who are taught knowledge and testing skills but lack deeper understanding and reasoning skills.

  • Dan

    If biracial people are attractive on average, is it possible that attractive people are more likely to breed outside of their race? If a black athlete comes together with a white cheerleader, then that could produce people like Halle Berry and Tyra Banks. I’ve seen a lot of tall, attractive white women with part-black offspring. I’m not saying it’s that way most of the time of course.

    As for the possibility that biracial people have higher IQs and more talent, could it be that parents of biracial children invest more in their kids? This article postulates that :

  • Eric

    It is hard to believe that people still talk about the “Flynn” effect.
    1) Before Flynn it was noted by others; he just put it in terms that seemed to argue against IQ from genes and more for IQ from environment.

    2) The so called effect is only on timed test that are multiple choice. Adults can teach kids to guess! So on test that are not timed that have a penalty for a wrong guess the 3 points per decade vanishes like magic!

    3) genes and epigenetics (yes environment like breast milk for some allels) explain IQ. To argue and pretend not is to be like those who saw the emporors clothes as the best!

    4) I also see hybrid vigor as good. But I also think that the genetic and epigenetic data that is being created faster and faster willl enlighten us all and help us to make more informed choices.

  • john

    The answer to the IQ question is already there. Look at a map of Earth. What countries are just barely out of the Stone age technology wise…

    Let’s see.

    Nearly all nations in Black Africa are primitive and backwards. Except for South Africa [why is that, hmmm].

    Most Arabs and North Africans are mixed race people today, they are mixed Caucasian and Black African. Their IQ is between the average IQ of a European and a African, and it shows in their nation’s development level.

    However according to this article, you would think that Arab and North African nations would be First world since the population of those nations are mixed race. However this article is obviously incorrect. Arab and North African nations are still backwards compared to Europe and North America on the development index.


    Japan, Korea and China are all either first world nations now, or are rapidly on their way to becoming first world.

    IQ tests for East Asians show that they are among the most intelligent groups of people on Earth. It shows in the development level for East Asian nations like Japan.

    Clearly IQ has a genetic basis to it. If it did not then there would be no development pattern among nation’s on a racial basis. Again look at Black Africa. The nations there are all among the same level development wise, which is not very developed at all..Then look at Europe which is developed. And North Africa is right in the middle development wise.

    For the doubters…Look at Haiti. It is a 99% Black African descended nation smack dab in the middle of the Carribean, yet it is also the poorest nation in the Western hemisphere. Its development index is on par with nations actually in Africa…Yet the only connection Haiti has to Africa is its people are racially Africans. Is that solid proof for a genetic basis for IQ ? Yea its as good as it gets for proof. That may be seen as racist, but racist or not it is the truth.

    More proof – Canada, Australia, New Zealand, USA. All white majority nations. All have development indexes on par with Europe. The exceptions are cities such as Detroit – which have a black majority population – and predictably, resembles more of a African city than it does a White European one as far as development goes.

  • Rational Bean

    Don’t want to delve too deep here since; a) I’m not addressing hybrid virgor directly and b); I can see I’m a bit out of my league intellectually, but let’s be careful about presuming that intellegence is a net plus.

    It seems that desirable traits such as strength or intellegence often come at the expense of some other desirable trait. So, much depends on the environment.

    Being brainy might not make up for the loss of some other desirable trait. In a cold environment it might be better to be big and dumb as opposed to smart and small.

    • Raston

      I agree but your last sentence is the opposite of reality. Cold climates have produced people who are big, but also smart. Scandinavian countries have one of the highest IQs on Earth and they are also one of the largest people to. Reason being, dumb people cant survive easily in a cold climate, they will either freeze to death, or starve to death.

      On the other hand, Tropical climates lend themselves to those who are small and dumb. You dont need to think about how to survive the winter there…since even in winter, its still hot in the tropics. This is probably why hunter/gatherer societies were common until the early 1900s in Africa and S.America, the native people never had a reason to advance beyond that point. A cold climate can force people to adapt and weed out the ones not intelligent enough to adapt.