Why Is Average IQ Higher in Some Places?

Christopher Eppig, Scientific American, September 6, 2011

{snip} One study found that newborn humans spend close to 90 percent of their calories on building and running their brains. (Even as adults, our brains consume as much as a quarter of our energy.) If, during childhood, when the brain is being built, some unexpected energy cost comes along, the brain will suffer. Infectious disease is a factor that may rob large amounts of energy away from a developing brain. This was our hypothesis, anyway, when my colleagues, Corey Fincher and Randy Thornhill, and I published a paper on the global diversity of human intelligence.

A great deal of research has shown that average IQ varies around the world, both across nations and within them. {snip} At the heart of this debate is whether these differences are due to genetics, environment or both.

{snip}

{snip} Satoshi Kanazawa suggested that evolution favors higher IQ in areas that are farther from the evolutionary origin of humans: sub-Saharan Africa. Evolution, the hypothesis goes, equipped us to survive in our ancestral home without thinking about it too hard. As we migrated away, though, the environment became more challenging, requiring the evolution of higher intelligence to survive.

We tested all these ideas. In our 2010 study, we not only found a very strong relationship between levels of infectious disease and IQ, but controlling for the effects of education, national wealth, temperature, and distance from sub-Saharan Africa, infectious disease emerged as the best predictor of the bunch. A recent study by Christopher Hassall and Thomas Sherratt repeated our analysis using more sophisticated statistical methods, and concluded that infectious disease may be the only really important predictor of average national IQ.

Support for this hypothesis comes not only from cross-national studies, but from studies of individuals. There have been many studies, for example, showing that children infected with intestinal worms have lower IQ later in life. {snip} In practical terms, however, this means that human intelligence is mutable. If differences in IQ across the world are largely due to exposure to infectious disease during childhood, then reducing exposure to disease should increase IQ.

Despite the strength of our findings, our study was not without its limitations. We did our best to control for the effects of education. But what we really needed was to repeat our analysis across regions within a single nation, preferably one with standardized, compulsory education. The nation we chose was the United States. Average IQ varies in the states. (Massachusetts, New Hampshire, and Vermont are at the high end, for example; California, Louisiana, and Mississippi are near the low end.) Again, infectious disease was an excellent predictor of average state IQ. The states with the five lowest average IQ all have higher levels of infectious disease than the states with the five highest average IQ, and the relationship was good across all of the states in between.

So far, the evidence suggests that infectious disease is a primary cause of the global variation in human intelligence. {snip}

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  • Mike H.

    Then why do adopted asian children in the Netherlands retain their higher average IQ when raised by native dutchmen, and black children retain their lower average IQ when raised by rich white parents?

    What a load of nonsense. Let’s take a moment to look at the racial statistics of the six states listed, shall we? The numbers are from the 2010 census unless indicated otherwise.

    New Hampshire: 92.3% Non-Hispanic White, 2.2% Asian, 1.1% Black.

    Massachusetts: Non-Hispanic White – 75.6%, Asian 5.3%, Black – 6.6%.

    Vermont: 97.95% White(as of 2005).

    California: 40.1% Non-Hispanic White

    Louisiana: Roughly 60% Non-Hispanic White, over 37% Black(as of 2005).

    Mississippi: Roughly 62.5% Non-Hispanic White, over 33% Black.

    I don’t know about the rest of you, but I’m seeing an IQ related pattern here as well – and it has nothing to do with infectious diseases.

  • Nick

    So blacks with low IQs in North America, for instance, are exposed to the same supposedly IQ sapping infectious diseases that low IQ blacks are subjected to in Africa? And at a corresponding incidence to explain the correspondingly low IQs. Seems like a specious assumption to me. Did the researchers look at a group of blacks who were subject to infectious diseases as children, and a group of blacks that weren’t subject to infectious diseases as children, and verify a difference in IQ level? That would seem to be pretty easy way to isolate (or at least rule out) the real independent variable here. Seems like it wasn’t done. Not a super convincing study, though I did follow this link from the SciAm article to a study by Templer and Arikawa (http://goo.gl/mQBhK) supporting assumptions about cold climate and IQ.

  • slipping into darkness

    Why not test of IQ and drugs at same time? We can’t, because somebody at the ACLU might sue us. Where do they get the money?

    http://www.news4jax.com/news/29105590/detail.html

    ACLU Plans Lawsuit Over Welfare Drug Tests

    MIAMI — The American Civil Liberties Union of Florida plans to challenge the state’s law requiring new welfare recipients to pass a drug test.

  • olewhitelady

    Many children in Haiti have worms because they eat dirt. I would think this might be a symptom of low IQ. But, are the children low mentally because they eat dirt, or do they eat dirt because they’re low mentally?

  • sbuffalonative

    I can’t wait to see this research cited as evidence as to why we need Obamacare.

    What for (expensive) efforts to eradicate disease in urban areas, testing, and transferring ‘at risk’ children from densely populated (black) urban areas to low density areas (White suburbs).

    Of course, it’s more likely that less intelligent people lack the ability to care for themselves or take the initiatives to protect themselves.

    I work with a black woman who has asthma. She has gone to the emergency room twice to be treated for asthma attacks. She smokes. Under Obamacare, this is the kind of person you and I are going to be giving our health care money to.

  • True Blue

    What they discovered (and try so hard to avoid admitting) is that low IQ and disease go hand in hand, and that low IQ contributes to the contagion and spread of disease. QED.

    To simply destroy their argument, look at the technical and economic revolutions in Europe following the Black Plague; no signs or symptoms of a lower than average IQ there. If anything you see the opposite; a tremendous boom of innovation and growth that rose steadily into our modern Western civilization. Johannes (Gensfleisch) Gutenberg -inventor of the printing press- was born less than 50 years after Eurpoe’s population had been halved by disease.

    But (fallacies aside) at least their study gives us yet another reason to want to avoid seeing our nations flooded with third world IQ’s and their concumbent diseases.

  • neanderthalDNA

    People with lower IQ’s will, especially when reinforced by others of low IQ, be less likely to live in good sanitation, in healthy environments.

    Again, broken libtardisms completely ignore the obvious explanation…

  • Anonymous

    California IQ,along with school and college admit test scores has been dropping since 1960 due to Hispanic, especially Hispanic Indian immigration.

  • Anonymous

    “and concluded that infectious disease may be the only really important predictor of average national IQ.”

    WHAT? lol I would think that the number of huts with no indoor plumbing would also bean a good predictor!

  • William

    “So far, the evidence suggests that infectious disease is a primary cause of the global variation in human intelligence”

    This postulate is contradicted by the fact that races with low IQ’s in their ancestral homeland also manifest low IQ’s outside of their ancestral homeland when born and raised in western countries with low infection rates and immunisation programs as well as provision of good nutrition and good education.

    And of course, as any scientist knows, correlation is not causation. A basic reality SciAm seems to have unscientifically ignored.

    What a travesty of the scientific method! What utter disingeniousness!

    This magazine, “Scientific American” has long lost even the smidgin of credibillity and respect it once had, I no longer buy it for I will not support its misrepresentations. Moreover they are in the habbit of conducting ‘smear attacks’ on individuals without offereing equal or any right of reply. Witness the disgracefull, in my opinion, personal attack on Bjørn Lomborg “The Skeptical Environmentalist”

    It seems Satoshi Kanazawa is now their target.

    Nutrition, infection and neurogenisis (new brain cell growth in adults) may play their part but in each and every case the gap has remained constant when conditions are controlled for.

  • Lucas

    Anyone notice those lower IQ States also have an abundance of Obama supporters? I’m just saying.

  • sshadow

    “We tested all these ideas. In our 2010 study, we not only found a very strong relationship between levels of infectious disease and IQ, but controlling for the effects of education, national wealth, temperature, and distance from sub-Saharan Africa, infectious disease emerged as the best predictor of the bunch.”

    Mr Eppig, did you include race in “We tested all these ideas”? If you had considered white vs unmixed black you would find a solid 30 IQ points difference. I’ve never seen a study that showed that American children with more vs less childhood infectious disease have any known IQ differences. How do you explain Dr Rushton’s finding that the highest unmixed black IQ in South Africa was 103. This was in their most elite Universities. Surely the infectious disease burden of their college bound wasn’t very much. The highest IQs of white elite University students would be 150 and above. Northern PacRim Asiatics would be similarly gifted. Now ask yourself, is it more likely that infectious disease or genetics would account for these differences. You must think that South Africa’s college bound blacks have enough of an infectious disease burden over and above American whites to account for a 50 IQ point difference in their best students. Comon Mr Eppig, your own mind is a terrible thing to waste.

  • Truth

    I have been making making a similar argument, in a different context, to Utopians for the over a decade based on something I had read. It is that children who’s parent have their children raised in drive-by-daycare are more likely to have learning disabilities because of issues related to constantly being infected by diseases carried by other children. The Utopians have always quickly stated that such reasoning was ridicules and its only purpose was to force women stay in the kitchen barefoot and pregnant. You can be sure those same Utopians will now embrace the theory the diseases can affect intelligence, but not the diseases that would be contracted in drive-by-daycare.

  • Expat68

    The more likely explanation is that low-IQ people generally don’t take care of themselves as well as smarter people do, but of course none of the multi-culti crowd will ever admit such a thing.

  • SoCal LoCal

    Of course IQ correlates with disease rate. Genetically fit persons tend to be healthier, more attractive, and smarter. Visit a trailer park for confirmation. This latest attempt to muddy the waters does not pass the laugh test.

  • Jesse

    One of the worst infectious diseases in the world is malaria, killing over a million people every year and affecting many times more, sapping the body and stunting the development of the brain if you are infected as child.

    Meaning those that have had malaria, do have a higher risk of getting lower intelligence.

    But what about those that do not suffer from this? Those that grow up in a place away from their natural habitat, like african-americans?

    And people seem to forget that malaria existed in Europe as well, and was particularly vicious during world war I, where at certain fronts it was so bad that the war stopped due to soldiers not being able to fight.

    And for that matter, more soldiers died during WWI from diseases than from from bullets, grenades and gas.

    But there is no malaria in Europe now, so everyone assumes that there never was malaria in Europe.

    Despite the fact that malaria was made extinct in Europe only quite recently, with the help of DDT.

    Although they had before that managed to keep it down by draining swamps and generally making an effort to try and stop the spread of the disease.

    Europeans are generally blamed for killing off a large part of the american natives with all the nasty diseases they brought with them.

    So Europe was a plagued with disease as anywhere else. What changed?

    Why did it change?

    Could it be that the correlation between disease and intelligence is actually reversed? That low rates of infectious diseases does not lead to higher intelligence, but that high intelligence leads to lower rates of infectious diseases?

  • Anonymous

    Intestinal parasites were common in Europe during the 19th century. The people behind this study know nothing about history.

  • Herman

    I was born in Germany in 1930. As a child, I had all the usual diseases: scarlet fever, measles, whooping-cough, intestinal worms; in 1943. I aquired hepatitis type A in a Hitler Youth summer camp; in 1944, pneumonia. During the war, the food ration was 1800 to 2000 calories per day; from 1945 to 1948, it was reduced to 1400 to 1500 calories, most of it in potatoes, bread and other carbohydrates, very little in meat, fat, milk and cheese, which are said to be most important for body and brain development during the teen years. But I can’t complain about a lack of intelligence. My IQ was never tested; that was not usual in Germany. But I was an excellent student, especially in mathematics, and later became a successful and renowned engineer, member of several DIN commissions etc. My generation suffered roughly the same diseases and the same hunger as I, but this is the generation which created the German “Wirtschaftswunder” (economic miracle)in the years after 1950. How about doing an extended study on this generation in Germany?

  • Paleface 6

    So they controlled for “national wealth.” Do they not understand that “wealth” is not something lying on the ground to be pickup and used, but is created by the nation’s inhabitants? America had and has plenty of natural resources, but no “wealth” at all until Whites came along and created it.

    This study can be (and should be) ignored. They did the study in 2010, and are writing about it in 2011. They couldn’t possibly have enough data assembled at this time to support any conclusion.

  • A. Windaus

    Have they not just controlled for race when “controlling for the effects of distance from sub-Saharan Africa”?

  • deadindenver

    Here’s a thought, I.Q. test Germans & Japanese who were born near the end of WWII and years right after the war. Due to devastation wrought by the allies, disease among young children was wide spread. See if there hypothesis holds up.

  • Josey Montana

    Hmmmm…

    This makes perfect sense to me.

    Smart people kill germs.

    Dumb people don’t.

    Next problem to solve!

  • Anonymous

    I doubt the fact that Haitian children eat dirt has anything to do with IQ. It’s probably because they are starving.

  • down the bayou

    i find fault with their findings. mississippi, louisiana, and california are states with high summer temperatures. i have not seen snow in years! in tropical locations, are diseases not more vigorus? in colder locations in the north diseases might have a more difficult time, no? they failed to take the factor of climate into consideration.

  • Ben

    It is sad to see that the Scientific American confused correlation with causation. They did not establish exactly HOW disease cause lower IQ.

    This is so embarrassing.

  • WR the elder

    Scientific American is hopelessly politically correct. They’re still a good place to go for a layman’s level explanation of particle theory or plate tectonics, but on social issues it’s always the straight left wing egalitarian line.

  • Anonymous

    Vices the most notorious seem to be the portion of this unhappy [n***o] race: idleness, treachery, revenge, cruelty, impudence, stealing, lying, profanity, debauchery, nastiness and intemperance, are said to have extinguished the principles of natural law, and to have silenced the reproofs of conscience.–

    Encyclopaedia Britannica, 1798.

  • Marc B

    If you are a science worshiping liberal and Darwin devotee, it should be very apparent that IQ is influenced by evolutionary adaptation. Those living in latitudes further away from the Equator required more cunning and planning to survive the often harsh seasonal changes, so IQ increased to assist in their survival. This screws with the entire notion of egalitarianism, which is the foundation for their house of cards.

  • Doug

    It wouldn’t be surprising that

    “children infected with intestinal worms have lower IQ later in life”

    since high IQ parents are more likely to protect their children from intestinal worms. This confusion of cause and effect permeates the whole article.

  • StandardBearer

    The amazing thing is that they are acknowledging that there is “global variation in human intelligence”, and even more incredible, they aren’t blaming it on “White racism”! The tide is turning.

  • Anonymous

    I was watching some men dunk a basketball the other day. After a few minutes I dozed off. When I awoke I felt stupid. It occurred to me that watching people dunk a basketballs and actually dunking a basketballs saps large amounts of energy from one’s brain.

    I put this theory to some highly sophisticated statistical analysis and so far the evidence suggests that dunking basketballs is a primary cause of the variation in intelligence in America and elsewhere.

  • White Guy In Japan

    “It seems Satoshi Kanazawa is now their target.”

    He has been in “their” sights for awhile. I’m a big fan of evolutionary psychology and some of his work in particular. He took a lot of heat for a study that concluded that Black women were ranked as slightly less attractive than women of other races. (In a race with 4 people, someone is bound to come in last place.) People have been trying to get him fired for that study.

    Of course, he could come back to Japan where such research is not so controversial.

  • Old Raleigh Native

    Apparently the author, Christopher Eppig, had some really serious infectious diseases as a young child.

  • Anonymous

    I am not sure that state boundaries are an especially logical

    category for this topic. I’ve long been interested in the

    varied mental ability levels of the rural villages in my state–settled largely after the Homestead Act. Clearly, the abler

    settlers and the more affluent ones headed for the best soil and proximity to the rivers and streams–and soon, proximity to

    the sprouting railroads. While as far as I know there were no mental ability requirements for being granted a Homestead, there certainly were for hanging onto one and for acquiring more land. The quality of the soil tended to determine a lot about the subsequent quality of the rural villages. Up until the late 50’s or so, each village had its own high school drawing upon the surrounding farm population for a typical radius of 8-10 miles or so. The incidence of scholarship awards, and later National Merit semi-finalists, and other indicators reflected this original settlement pattern, as would the quality and extent of usage of the books in the town library or the high school library.

  • Tom UK

    Another herculean effort from the Left to put the cart before the horse.

    Genetics, including heritable intelligence is such a brilliant determining factor- it explains so many things with an absolute minimum of prior assumptions. Trouble is, reality is somewhat racist!