Disease puts pressure on the brain
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Being smart is the most expensive thing we do. Not in terms of money, but in a currency that is vital to all living things: energy. 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. The cause of this variation has been of great interest to scientists for many years. At the heart of this debate is whether these differences are due to genetics, environment or both.
Higher IQ predicts a wide range of important factors, including better grades in school, a higher level of education, better health, better job performance, higher wages, and reduced risk of obesity. So having a better understanding of variations in intelligence might yield a greater understanding of these other issues as well.
Before our work, several scientists had offered explanations for the global pattern of IQ. Nigel Barber argued that variation in IQ is due primarily to differences in education. Donald Templer and Hiroko Arikawa argued that colder climates are difficult to live in, such that evolution favors higher IQ in those areas. 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. Another study by Atheendar Venkataramani found that regions in Mexico that were the target of malaria eradication programs had higher average IQ than those that were not. 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.
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73 Comments
Add CommentThis, of course, assumes that the IQ test is entirely culturally unbiased, which only a person with a low IQ would think...
Reply | Report Abuse | Link to thisJust infectious diseases would be too simple because everyone in the United States, at one time or another, has had an infectious disease like a cold or flu. Wouldn't nutrition play a more major roll than infectious disease? There are more dumb poor people who cannot afford proper food than there are dumb rich people who can afford any kind of food they want...unless you include politicians.
Reply | Report Abuse | Link to thisHow does the author prove that it is the rate of infectious disease that formulates the average IQ, and not the average IQ that forms the rate of infectious disease? I mean, wouldn't it kind of make sense that a state with a lower average IQ would have worse health standards (and by extension, higher rates of infectious disease).
Reply | Report Abuse | Link to thisI mean, I understand that they tried to do away with as many other "reasonable" factors as they could. However, just because a state with a lower average IQ is cold, with a better education system, a good distance away from africa, but has high rate of disease does not mean that the disease is the cause of the lower average IQ, and IMO that fact is much more likely to mean that a state with a lower IQ is more likely to have lower health standards because of it.
Reply | Report Abuse | Link to thisbasically what i'm saying is that, the bubonic plague didn't cause the dark ages, but it is quite likely that the dark ages had a hand in helping the bubonic plague along.
Reply | Report Abuse | Link to thisIt would be interesting to know what margin was noted as a higher average IQ.
Reply | Report Abuse | Link to thisChances are fair to middling that this study is invalid as it may well be straining at gnats as is very common in this field of study.
One strongly suspects the underlying data and methods invalidate the whole thing as there will be no way to control for variables not mentioned in this article
I would be interested in viewing the study design, and how the extraneous variables such as education, ethnicity, parental education or IQ, as well as other outliers and modifiers were accounted for. Where can I find the complete study with design and analysis. There are many variables to be considered before one can validate this hypothesis. I do find the premise very interesting.
Reply | Report Abuse | Link to thisWe also know that trying to reduce the measure of intelligence to a single number is pretty much a joke that drastically oversimplifies the measure of human ability.
Reply | Report Abuse | Link to thisI have an IQ way,way,way up there... so I am not just kvetching in envy. I happen to know these measures of intelligence as reduced to a single figure are so imprecise as to be meaningless.
Here is the full paper, it was linked to in the article: http://rspb.royalsocietypublishing.org/content/277/1701/3801.full
Reply | Report Abuse | Link to thisFrom the (free!) text of the study:
Reply | Report Abuse | Link to this"As a measure of infectious disease levels for each nation, disability-adjusted life years lost (DALY) owing to infectious disease were used (WHO 2004b). This measure combines years of life lost and years spent disabled owing to 28 representative and important human diseases, including tetanus, malaria, tuberculosis, hepatitis, syphilis and leishmaniasis, such that one DALY equals one healthy year of life lost per 100 000 people. ... The DALY infectious-disease measure correlates strongly with other measures of human infectious disease (e.g. Thornhill et al. 2009). ...
As an independent measure of nutrient stress, DALY owing to nutritional deficiencies (WHO 2004b) were used. This calculation includes mortality and healthy years lost owing to protein-energy malnutrition, iodine deficiency, vitamin A deficiency and iron-deficiency anaemia."
If this theory is true it seems to me that a statistically significant difference should exist between the chronically ill and healthy children regarding IQ even within a small region like Massachusetts only. To my knowledge no such correlation has been established. Of course it is possible the stage of affected development is before birth.
Reply | Report Abuse | Link to thisFull disclosure I have spent my entire life using a wheelchair and have been admitted into hospitals repeatedly and I have a college degree in biological science. So I have an obvious bias. Quite frankly, I have heard this argument before "sick people aren't as smart as the rest of us." It's as tired now as it was then.
I'm willing to bet the authors would find IQ and poverty are correlated as well.
When you read the original study... it becomes plain that the researchers are mired in concepts of political correctness that dramatically skew their objectivity into the world of self-fulfilling prophecy and wishful thinking.
Reply | Report Abuse | Link to thisThe research is so dependent upon so many presumptions and assumptions that one can disregard it as anything but an amusing speculation.
I agree with you entirely Bionate.... this research is a demonstration of a nonsensical misuse of sciencey-seeming by "researchers" desperate to claim they have discovered some marvel demanding awe by others.
Reply | Report Abuse | Link to thisWe can be certain without even reading their biography that the researchers are the product of a sheltered suburban lifestyle with parents probably of the white-collar bureaucrat class.
If they were from North America we could be fairly certain of it simply by reading their work.
As they seem to be are from Great Britain, we can be reasonably certain they are members of the analogous class in that country.
The amount of pseudo-scientific claptrap to be seen out of "social scientists" is amazing in its lack of scientific validity and in its pretentiousness.
Were these same individuals to confine their efforts to writing speculative essays and novels dealing with the same issues we might credit them a value to humanity.
As they feel the need to clothe their novelistic speculations in a phony veneer of scientific rigamarole... and to so horribly misuse tools that are beyond their understanding... we are forced to condemn them as a pain in society's collective neck.
I agree with you entirely Bionate.... this research is a demonstration of a nonsensical misuse of sciencey-seeming tools by "researchers" apparently desperate to claim they have discovered some marvel demanding awe by others.
Reply | Report Abuse | Link to thisWe can be fairly certain without even reading their biography that the researchers are the product of a sheltered suburban lifestyle with parents probably of the white-collar bureaucrat class.
If they were from North America we could be fairly certain of it simply by reading their work.
As they seem to be from Great Britain, we can be reasonably certain they are members of the analogous class in that country.
The amount of pseudo-scientific claptrap to be seen out of "social scientists" is amazing in its lack of scientific validity and in its pretentiousness.
Were these same individuals to confine their efforts to writing speculative essays and novels dealing with the same issues we might credit them a value to humanity.
As they feel the need to clothe their novelistic speculations in a phony veneer of scientific rigamarole... and to so horribly misuse tools that are beyond their understanding... we are forced to condemn them as a pain in society's collective neck.
Who is to say a person with a higher IQ is smarter than a person with a lower IQ? If you placed a person with high IQ in the roughest neighborhood how do you think they'll do in that environment? How about a person with a low IQ in a physics class? Both wouldn't do very well because they are out of their element. Both are smart and we need to do away with IQ.
Reply | Report Abuse | Link to thisE_caroline, your points are very well made. I, too, have a "high" IQ, but I'd be the stupidest member of a group of native sub-Saharan Africans. Why does no one ever thing that it could be the TEST that's wrong?
Reply | Report Abuse | Link to thisI meant "think", not "thing". I really can spell, I just can't type.
Reply | Report Abuse | Link to thisWhen you read the source article... you can tell the authors are white liberals with asthma.
Reply | Report Abuse | Link to thisOr perhaps people of color with asthma.
They conveniently disregard politically incorrect research they quote that supposedly demonstrates darker skin equals a lower IQ.
They go out of their way to discuss how autoimmune diseases, like asthma, are associated with a higher IQ.
The authors extrapolate extrapolation upon assumption upon presumption upon insubstantial analysis as support for their speculations.
The lack the imagination or the space or the imagination or the intellectual honesty to discuss dozens of other equally vaporous speculations that could as easily be supported as their own ideas.
Which is to say... their ideas are not especially convincing considering the fact that dozens of other speculative explanations would account for their observations as well.
Even the whole concept of intelligence as measured by IQ tests over a huge variety of cultures by a huge variety of researchers over a huge span of time... puts the lie to most every bit of statistical analysis they tried to do.
The data upon which they worked their magic simply is not uniform enough to be valid for use in the manner in which the researchers used it.
We can be pretty certain of the class of and the ailments that exist in these researchers... as it is implicit in the text of their report.
Did I make a mistake? Is "Scientific" American a subsidiary of People Magazine?
Reply | Report Abuse | Link to thisThis article, and the original study prove that "scientists" are just a dumb as the next guy, to paraphrase Richard Feynman (a real scientist).
This seems to be a well executed statistical survey, but as with all such studies correlation does not prove causation.
Reply | Report Abuse | Link to thisQuickly, IQ test scores have been known to be generally lower in equatorial regions, where the risk of infectious diseases have been known to be generally higher. It should not be surprising then, that there is a statistical correlation between the incidence of infectious disease and IQ test scores. This would be the case even if there was no causal relation between them whatsoever.
Without having studied the research, I suspect the researches cannot prove that infectious disease causes low IQ test scores any more than they can disprove that low intelligence increases one's risk of being infected by disease.
It's also worth noting that infectious diseases are generally more capable of flourishing in warmer regions than colder - just like humans, plants and other forms of life.
An argument could even be made that more intelligent humans migrated to colder climes to reduce their exposure to infectious diseases.
That having all been said, it's quite possible that, especially childhood, infectious diseases may very likely affect physiological brain development, eventually producing lower IQ test scores.
Another factor not mentioned here that can affect physiological brain development is nutrition: it would be interesting to see a study of geographical distribution childhood nutrition, population growth and IQ test scores.
I suggest that conditions that affect physiological brain development are most likely all contributing factors in producing variations in IQ test scores.
Personally, I've experienced the unnoticeable long term physiological effects of chemo induced anemia on intellectual abilities, detected only when prescribed omega-3 for an unrelated condition. Omega-3 is thought to repair damage to the insulating myelin sheaths enveloping the dendrites connecting neurons. I can attest to a very sudden and significant restoration of abilities I had unwittingly lost for many months. As a result I'm highly sensitized to the idea that malnutrition, no matter what its cause, directly affects brain performance and, in children especially, brain development.
IMO, the physiological effects of parasitic infections and malnutrition are a likely cause of statistical correlations between national and regional environmental conditions and IQ test scores.
would there be any correlation between fish eaters and antelope eaters?
Reply | Report Abuse | Link to thisOkay, firstly - I feel like this article is ignorant. Secondly - One of the best Neuroscience Research Laboratories is in Africa. Every culture is different and we all excel cognitively on different plains as a distinct collaborative culture. Infectious Disease alone cannot be the one thing to blame for low IQ. There are not enough studies done to prove this as accurate. The article only mentions one study. Also there are tons of variables. There seems to be some indirect force or alterior motif behind this hypothesis. I am not a very big fan of the writing of this article. It is less than articulate.
Reply | Report Abuse | Link to this"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"
Reply | Report Abuse | Link to thisI've got a problem with how you've described you covariates in this analysis. Did you only look at national wealth? Is this really a good measure of an individual citizen's economic situation? For example, let's compare a nation like the US, where both national wealth and income inequality are extremely high, to a country like Norway, where national wealth is high and income inequality is low. If we compare the actual health and nutrition of individuals in these two societies, we will find that Norwegians are on average healthier than Americans, despite the fact that American national per capita wealth is greater. The reason most likely has to do with the fact that nearly half of the American population lives close to the poverty line, whereas most Norwegians live relatively affluent lives (just there's no "mega-rich" Norwegians).
In this example, if the average Norwegian individual has better access to health care, better living conditions and better nutrition resources, it is likely that the average IQ in Norway will be higher than that in the US. And yet, again, the national wealth of the US would still be higher.
The problem here becomes that if you have failed to account for the wealth of individual citizens, predictors of overall health (which strongly correlate with wealth) such as nutrition and disease will have an inflated unique predictiveness associated with IQ.
This seems to be important, as it is my understanding that SES is one of the best and most consistent predictors of IQ available. And given that SES correlates well with overall health, availability of health care and proper nutrition, and undoubtedly high levels of infectious disease correlate negatively with health, then I would expect a strong correlation between SES and infectious disease.
So I have to ask, does the unique predictiveness of "infectious disease" with respect to IQ decrease significantly if you account for socio-economic status, nutrition and non-infectious disease?
Jt, they accounted for temperature. I suppose one could argue they also accounted for SES, in the sense of education.
Reply | Report Abuse | Link to thisNonetheless, it just strikes me as a little problematic that infectious disease presumably has a strong negative correlation with overall health. How exactly do you extract these factors from one another? People who are not healthy or who have poor nutrition are undoubtedly at a higher risk for both infection and for problems during brain development.
From the article:
Reply | Report Abuse | Link to this"Nutritional stress correlated with average national IQ (r = −0.72), but this relationship was not significant when the effects of infectious disease were removed. This supports the suggested link between intelligence and nutrition.
...
In a multiple linear regression, average national IQ (LVE and WEAM) was predicted using infectious disease, average winter high temperature, distance from sub-Saharan Africa, AVED and GDP
"
Given that nutrition correlated -.72 with IQ and infectious disease correlated -.76 with IQ, and the correlation between nutrition and IQ was not significant when accounting for infectious disease, this implies that infectious disease would similarly only account for a very small amount of unique variance in IQ when accounting for nutrition. So if you had included nutrition in your multiple regression, I kind of wonder if infectious disease would still be a significant predictor.
And I realize that the entire hypothesis is predicated upon this idea that infectious disease is an "energetic stressor". But the problem here is that you cannot know if infectious disease is actually having any impact on IQ, or if its just a covariate of the real causes... factors which we were already well aware of.
Well anyways, it's an interesting hypothesis.
This is the study of Geography. A misconception about Geographers is that we memorize places, or regions, and mankinds living areas. We are so misunderstood in the scope of our study. It does not surprise me that IQ is higher in specific locals. Geography is the study of man interacting within his environment and the relationship between the two effecting each other. The future will concern microclimates, economic zones, and food producing regions.
Reply | Report Abuse | Link to thisWe must begin to understand this relationship before it is too late.
Wait. This is not a controlled experiment, it is an observational study. To move from saying infectious disease is a predictor to saying it is a cause is an anathema to statisticians, good science, and common sense. One of the posters got this. It is probably as likely that in areas with higher iq, infectious disease might be better controlled, even indirectly. or there may be common variables.
Reply | Report Abuse | Link to thisIt is difficult to believe that SCIAM editors would allow this conclusion. After all, larger fires are not the result of more firemen answering the call. No matter how many variables are controlled for.
I performed my own international study and concluded that IQ is enhanced by sun block. After controlling for all other factors, those who use sun block have a statistically significant increase in IQ over those that don't. I just received a $6 Million grant to analyze the compounds in sun block. The effect didn't hold for those living in areas with little sun or extreme cold -- they had higher IQ's despite not using sun block. The effect was extremely pronounced in tropical areas where local native populations didn't use sun block while those vacationing at the resorts did.
Reply | Report Abuse | Link to thisCorrelation is one thing, causation another. For example, it could be that areas with poor disease control also have poor prenatal care and nutrition, which has been shown to have a significant effect on development.
Reply | Report Abuse | Link to thisLess we get all wrapped around an unnecessary axle, it is not crucially important what IQ tests actually measure. We'd like to think it has something to do with intelligence, but regardless, it measures some cognitive ability and it is reasonably repeatable when given to the same individual multiple times and it has some predicability. If the report were measuring eyeball diameter as opposed to "intelligence", we wouldn't be having much of a quarrel about how well the measuring algorithm actually measures precisely the right diameter feature. (did the algorithm favor green eyes?) We'd give the author the benefit of the doubt and say that his study correlated whatever he measured with some set of external parameters. Similarly, this study correlates IQ, whatever that really means, with a number of external parameters.
Reply | Report Abuse | Link to thisExperience tells most of us that "intelligence" is a complex, manifold property and that IQ testing measures no more and no less than how well a person does answering a set of specially selected questions. Its only significance is that it has been correlated to a number of other more meaningful events like academic success.
Beyond any defects in the whole concept of "IQ" (as mentioned by many commentators here) is the very fundamental part of the scientific method that many "non-hard" scientists just seem to constantly ignore: correlation does not imply causation.
Reply | Report Abuse | Link to thisThis study would be a great deal more useful had it been made three or four centuries ago, when populations everywhere and of every kind suffered with poor nutrition and widespread infectious disease. I much doubt the picture they want to draw from this now.
Reply | Report Abuse | Link to thisThen 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?
Reply | Report Abuse | Link to thisWhat 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).
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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.
The authors of this study should be ashamed of themselves. Stephen Jay Gould would be proud.
"Massachusetts, New Hampshire, and Vermont are at the high end, for example; California, Louisiana, and Mississippi are near the low end."
Reply | Report Abuse | Link to thisYou could have predicted that from socio-economic variability alone. You may as well blame the difference on exposure to sunshine.
Simple answer of this question is Higher I.Q. depend on circumstances.Alta modern American kid have more higher I.Q. than kid rare in most backward Andaman Ia-land.I.Q mania is developed mainly by so called psychologist Hans Eysenck. He was racist,He spread racist idea that white are extra intelligent people and black are backward.I agree people who have higher I.Q. they are more smart but higher I.Q. means not Genus.This is well known fact Newton ,Einstein had low I.Q. but they were Genus.I did not handled phone up to age of 20 but my grandchildren are handling mobile at the age of 8 they are more smart than me.We must not give importance to I.Q.mania too much.
Reply | Report Abuse | Link to thisIt would actually make a lot more sense that people with lower IQs would have a more difficult time keeping healthy, especially from contracting dangerous diseases. Low IQ people may not make the association between certain sexual activities and AIDS, for example, or they may have irrational and unscientific folk beliefs about prevention or cures. High IQ subjects may have better health because they understand what it takes to attain it. This guy is probably on to something but he has cause and effect confused.
Reply | Report Abuse | Link to thisSo the correct conclusion we can draw from this is that we should act to suppress the the IQ of people because increasing the IQ will mean destruction of environment and making the life tougher to live.
Reply | Report Abuse | Link to this<i>Eppig: "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."</i>
Reply | Report Abuse | Link to thisThe problem with this analysis is that race/ethnicity is a huge confounder -- blacks and Hispanics have lower mean IQs than whites and are concentrated in "high disease" states. Why didn't Eppig test if the results hold within each race/ethnicity? If you look at the NAEP scores (which Eppig et al. use as an IQ proxy) you will notice that the racial/ethnic test score gaps are highly similar in "high disease" and "low disease" states, suggesting that Eppig's finding is largely if not entirely artefactual.
I think the negative comments and (frequently ill informed) criticisms of this article says more about the posters and the great deal of discomfort we have with the idea of IQ and its variance across and within populations than it does about the quality of the science or its conclusions.
Reply | Report Abuse | Link to thisIn particular those individuals speculating about the validity of it based on their own individual experience are way off the mark. Anecdotes, however interesting, don't defeat statistics.
The study is reasonable, it uses valid statistics, it acknowledges it measures a high correlate and offers a plausible hypothesis that might deilver a causal explanation. That's what good science does.
It doesn't make comments about intrinsic worth of people or groups with higher or lower IQ.
Without getting into meaningless debate about what IQ tests actually measure and how cross-culturally valid they might be there is general acceptance that there IS such a thing as intelligence and that individuals possess different levels of it. IQ is a reasonable measure of this as long as you understand the limitations of testing in a given context.
The fuss here is similar to the misrepresentative fuss over "The Bell Curve".
If there are measureable differences in average IQ between groups it is useful to know. It is even better to know why.
Generally the variances within a population group (however comprised) are far greater than the variances across population groups so such knowledge means we can say NOTHING about individual representaives of a given group but can make meaningful statements about populations.
If the hypothesis being put forward here for the differences in IQ is valid (and it is certainly plausible) then I would have thought this should be greeted positively since it may give us a means to intervene to improve the IQ of those in less fortunate situations. This can only be a positive since, whatever you think about IQ as a measure, the science is well established that consistently higher results on IQ tests correlate with increased life success and well being.
I look forward to more work being done in this ara
"Generally the variances within a population group (however comprised) are far greater than the variances across population groups so such knowledge means we can say NOTHING about individual representaives of a given group but can make meaningful statements about populations."
Reply | Report Abuse | Link to thisThat's not true. We can and do make probabilistic assessments of individuals based on their group membership if we do not have more precise information about them. It would be irrational to not do so.
Actually I would disagree with you although it may come done to semantics about what you mean by "probabilistic assessment"
Reply | Report Abuse | Link to thisAnd it is a common miconsception.
Here is what I mean when I said you can say nothing.
Let us consider a hypothetical individual who has a certain IQ. Whatever that IQ might be it is what it is. If you were to guess at it based on your knowledge of the distribution of the IQ within the population of which this group was a member you would have a certain probabibility of being "correct".
But - it wouldn't actually be the probability you might think based on the population distribution.
Why not?
Because you have no way of determining whether or not that individual has been truly "randomly sampled" from the population.
Unless you can control for this factor you can't really say anything meaningful about the individual - only about a truly randomly selected "set" from the overall population.
So, with due respect, your appeal to "being rational" falls over
I disagree. If you have no information about the individual apart from his or her group membership, it's reasonable to assume that he or she is average rather than exceptional.
Reply | Report Abuse | Link to thisWell, we'll have to agree to disagree.
Reply | Report Abuse | Link to thisBut with due respect it's not reasonable to assume anything when you have literally no knowledge or control of the factors that led to the encounter.
Statistically what you are saying is actually invalid.
In any event it's not really germane to my comments about the article
You are one point of data. Perhaps you are an outlier.
Reply | Report Abuse | Link to thisIf you're looking at populations, what matters is whether a cause increases the likelihood of an effect. It doesn't matter if it guarantees it.
Also, if your illness was not one that took resources away from your brain during critical phases of its development, it is not relevant to this discussion.
IQ is affected by the level of difficulty of birth, the longer labour is prolonged the more brain damage of the baby. Poorer areas and countries are likely to have worse facilities for child birth.
Reply | Report Abuse | Link to thisHumans are products of evolution...part of being humsn is our physical brain. Political correctness stifles this simple fact.
Reply | Report Abuse | Link to thisThe average IQ of those in Sub Saharan Africa is just scrapes the mid 70's. Yes, human intelligence is 'mutable' but this is within potential inrtelligence capacity. Some genetic groups are well below those of others in intelligence. A fact that can't be glossed over by political correct mumbo jumbo.
"If the hypothesis being put forward here for the differences in IQ is valid (and it is certainly plausible) then I would have thought this should be greeted positively since it may give us a means to intervene to improve the IQ of those in less fortunate situations."
Reply | Report Abuse | Link to thisYes, if the hypothesis is valid. I personally don't believe that it offers nearly as much explanatory power as its authors do. Given a cursory review of the article, it is clear that it doesn't really discuss the possibility that infectious disease is only associated with IQ due to its association with other factors such as individual wealth* and nutrition. Having said this, I certainly agree that this study offers something to consider, although I don't know what actual impact it will have on future research. We already know that childhood dieases can affect brain development, and we also already know ways to reduce the IQ gap between groups, such as improving health and nutrition or educational opportunities. From this perspective, it seems a little premature to be touting the importance of this finding. Now, I don't blame the authors, that's what authors are supposed do--market their research. But I still have to disagree with the proposition that differences in exposure infectious disease are likely to significantly impact intelligence.
For those who still believe that "racial" differences in IQ are explained due to groups differences in intelligence, I really don't see what there is to argue about. Read up on the Flynn Effect. Or at least take a second look at your arguments. I have yet to hear a single argument put forth in support of this claim which couldn't just as easily be explained by differences wealth, social class or education.
*It's hard to know whether "national wealth" or per capita GDP was a good substitute for a more specific measure of individual wealth.
After experiencing the tenor of the commentary here, I am sorry I subscribed to Sci American. It's just as ridiculous as every other site's commentary.
Reply | Report Abuse | Link to thisMark, assigning a prior probability that an individual has an IQ in some narrow range based on group membership is no less reasonable than assuming that, say, you will more likely be mugged by a gang of young men than a gang of young women.
Reply | Report Abuse | Link to this"For those who still believe that "racial" differences in IQ are explained due to groups differences in intelligence, I really don't see what there is to argue about. Read up on the Flynn Effect. Or at least take a second look at your arguments."
I think it is you who should read up on the Flynn effect. The Flynn effect is qualitatively different from racial IQ gaps (particularly the black-white gap in America). Research shows that the gains in IQ due to the Flynn effect do not represent real gains in ability, at least not to a large extent. Therefore, if you give the same IQ test to old and young people, the lower scores of the old do not necessarily imply that they have less intellectual ability, i.e. the test is biased against them. In contrast, racial gaps between contemporary groups in America represent unbiased estimates of actual gaps in ability.
"I have yet to hear a single argument put forth in support of this claim which couldn't just as easily be explained by differences wealth, social class or education."
No serious researcher, no matter how anti-hereditarian, claims that the black-white gap is due to differences in wealth, social class, or education. The b-w gap is reduced by only about a third (from 15 points to 10 points) if you control for such socioeconomic factors. Moreover, the children of poor, uneducated whites have similar if not higher IQs than the children of well-to-do black professionals.
I dont wish to engage on your assertions about racial differences in IQ as it is not germane to the article.
Reply | Report Abuse | Link to thisThat they have been measured is well established but the causes are not well known and the validity is subject to question. In any event as I said the same data show (read the "Bell Curve") that variances within a racial population are larger than variances between such populations (differences in means notwithstanding)
Your understanding of statistics is quite plainly poor.
The population distribution of any parameter can only be used to make probabilitic assessments about individual data or sets of data that are randomly sampled. Full Stop. Period.
A "chance" encounter with an individual may well result from a factor which skews the sample population which you cannot control. For example - you meet a member of a group in the street for whom you know the normal distribution - but unbeknownst to you that week there is a conference of high achieving individuals from that group who happen to be meeting in the town - hence your guess will be radically wrong.
If you were to argue that from a statistically significant series of encounters (large enough to overcome any possible sample biases) then you would be right to make reasonable estimates of their intelligence with 95% confidence limits - that might stand scrutiny - but your argument about an individual is simply wrong - read more statistics to find out.
"Research shows that the gains in IQ due to the Flynn effect do not represent real gains in ability, at least not to a large extent."
Reply | Report Abuse | Link to thisI think you've hit the nail on the head with your description of the Flynn Effect, which demonstrates that differences in IQ can be produced by systematic biases in test constuction which differentially affect performance across groups. This can lead to the inflation of measured group differences, while real differences in the construct being measured are non-existant. In this sense, the Flynn Effect is an important illustration of the fallibility of measurements like the intelligence quotient.
Now, it appears that you believe this is irrelevant based upon the following statement:
"In contrast, racial gaps between contemporary groups in America represent unbiased estimates of actual gaps in ability. "
Frankly, I have a hard time accepting an unsubstantiated claim which asserts that <i>any</i> artificial measure of intelligence can be fundamentally unbiased. This seems to be an unprovable assumption, which also suffers from the fact that it is implausible.
"No serious researcher, no matter how anti-hereditarian, claims that the black-white gap is due to differences in wealth, social class, or education. The b-w gap is reduced by only about a third (from 15 points to 10 points) if you control for such socioeconomic factors. Moreover, the children of poor, uneducated whites have similar if not higher IQs than the children of well-to-do black professionals."
This is simply false. I assume you are speaking about studies conducted in the US. It is self-evident, to anyone who knows the slightest bit of American history, that blacks in America still suffer from significant racial bias. How can you say that it is possible to control for social class, when much of American society is infused with images and attitudes that suggest the social and intellectual inferiority of black Americans?
You know the real irony of this whole mess is that we started using IQ because it was supposedly a correlate of "intelligence", a highly general construct which we now understand is non-existant. And yet, now that we are aware of this flaw in our old understanding of intelligence, we continue to use IQ. The reason? Because IQ is correlated with financial success. Ironically, this is because we have designed our entire system of education to cater to individuals who perform well on IQ tests. I won't deny that IQ is a correlate of some useful abilities. But I am highly skeptical of the claim that IQ offers a truly useful measure of the sorts of abilities that we want citizens in our society to display.
Reply | Report Abuse | Link to thisYou make a good point. For instance, Japanese and Chinese score significantly higher on IQ tests than do whites, even though white scientists devised them-- Oh, wait.
Reply | Report Abuse | Link to thisYou make a good point. For instance, Japanese and Chinese score significantly higher on IQ tests than do whites, even though white scientists devised them-- Oh, wait.
Reply | Report Abuse | Link to thisWell, the National Academy of Science and APA investigated Arthur Jensen's claims that tests have equal predictive validity across ethnic groups. They found that Jensen was correct.
Reply | Report Abuse | Link to thisIIRC, Eppig's previous study showed a similar disease load for the Caribbean and South America, but South Americans had significantly higher average scores. This is consistent with the evolutionary explanation, that certain mental traits may be favoured in different cultural and geographic environments.
I think you'll find that in future, studies like this will better clarify the cause of group differences:
Reply | Report Abuse | Link to this"But the organisation is involved in even more controversial projects. It is about to embark on a search for the genetic underpinning of intelligence. Two thousand Chinese schoolchildren will have 2,000 of their protein-coding genes sampled, and the results correlated with their test scores at school. Though it will cover less than a tenth of the total number of protein-coding genes, it will be the largest-scale examination to date of the idea that differences between individuals’ intelligence scores are partly due to differences in their DNA.
Dr Yang is also candid about the possibility of the 1,000-genome project revealing systematic geographical differences in human genetics—or, to put it politically incorrectly, racial differences. The differences that have come to light so far are not in sensitive areas such as intelligence. But if his study of schoolchildren does find genes that help control intelligence, a comparison with the results of the 1,000-genome project will be only a mouse-click away."
http://www.economist.com/node/16349434?story_id=16349434
This is an excellent study. It confirms my theory (see my book "Breaking Free of Nehru" in which I've outlined how liberty predicts IQ. Greater infectious disease is ONE of the many outcomes of low levels of freedom. You could also correlate with any of the other correlates of freedom (e.g. openness to trade). In brief, FREEDOM is crucial for it impacts on our lives in an infinite variety of ways, such as health and wealth. IQ is merely one of the many outcomes.
Reply | Report Abuse | Link to thisThere's been much grousing about "correlation is not causation" in these comments. And of course it is true: correlation says nothing, necessarily, about causation. But part of the problem here is the study authors' apparent ignorance of what is likely to be the key mechanism. They do not discuss iron-witholding -- an innate defense against infection -- and the role of iron in brain and cognitive development, including functions represented by I.Q. There's much more than can be represented in this short post, but the short version is: infections cause an effective iron deficiency by virtue of the host's effort to withhold iron from the pathogens. Serum iron plummets. This has profound implications for the developing brain, both fetally and post-natally. Iron deficiency is well-established as an influence on brain development and measured I.Q. Iron deficit has an influence on these things through the entire developmental cycle. It is quite easy to see how frequent or chronic infections -- such as occur commonly, even routinely, in poor and poorly-developed nations -- could have disastrous effects on population IQs. And that is not all. Thyroid hormones are disordered in infection and other acute conditions, and thyroid hormones are, like iron, critical for brain and cognitive development, and normal IQs. Again, a short post is not the place to discuss the vast literature on this subject. Suffice to say that the authors of the original paper seem quite unaware of these facts -- in spite of the fact that they offer the missing precise mechanistic explanation for their findings.
Reply | Report Abuse | Link to thisMark, your example of a chance meeting of a high achieving individual is not relevant. Of course I am not claiming that my probabilistic estimate applies to everybody. The estimate will have practical utility only when one must repeatedly guess people's IQs without information other than group membership. For the same reason ethnic profiling of e.g. terrorists can be useful.
Reply | Report Abuse | Link to thisHowever, knowledge of group membership can be useful also when dealing with high-IQ individuals: http://tinyurl.com/yl58hoh.
zstansfi, whether a test is biased or not is an empirical question that can be investigating using standard methods. See this paper: http://tinyurl.com/6e5otgd. They write:
"It appears therefore that the nature of the Flynn effect is qualitatively different from the nature of B–W differences in the United States. Each comparison of groups should be investigated separately. IQ gaps between cohorts do not teach us anything about IQ gaps between contemporary groups, except that each IQ gap should not be confused with real (i.e., latent) differences in intelligence. Only after a proper analysis of measurement invariance of these IQ gaps is conducted can anything be concluded concerning true differences between groups.
"Whereas implications of the Flynn effect for B–W differences appear small, the implications for
intelligence testing, in general, are large. That is, the Flynn effect implies that test norms become obsolete quite quickly."
They note that several studies have demonstrated that measurement invariance holds in comparisons of contemporary groups blacks and whites in the US, indicating that IQ tests measure the same construct in both groups. There has been a lot of research on test bias, all of it showing that bias is not the source of the black-white gap in America. In general, the finding is that IQ tests overpredict black performance in school and jobs, and are thus biased in favor of blacks and biased against whites and other groups with a higher mean ability. Arthur Jensen's "Bias in Mental Testing" (1980) is a classic and still very useful treatment of the topic.
"This is simply false. I assume you are speaking about studies conducted in the US. It is self-evident, to anyone who knows the slightest bit of American history, that blacks in America still suffer from significant racial bias."
Reply | Report Abuse | Link to thisThe reality is that affirmative action, the disparate impact doctrine, and other anti-white and anti-Asian policies favor blacks at the expense of whites. Whatever bias blacks may suffer from is insignificant compared to the benefits they get for being black.
"How can you say that it is possible to control for social class, when much of American society is infused with images and attitudes that suggest the social and intellectual inferiority of black Americans?"
You yourself claimed that the black-white IQ gap can be explained by controlling for "differences wealth, social class or education." In reality, controlling for such factors eliminates only a fraction of the gap.
You have not demonstrated that "images and attitudes" influence IQ scores. To the extent that images and attitudes suggest black intellectual inferiority, they simply reflect the reality of black intellectual inferiority. In general, American society and media tend to portray blacks in a very positive light, whereas all criticisms of blacks are easily treated as racism.
Interesting. I can only imagine how intelligent I would have been if I had not suffered all of the usual childhood infections that I did, including the measles and lots of ear infections and more. Einstein would have to make room. Seriously, anything can be proved using statistical methods for the elimination of undesired data. You may have found one factor, but why do so any scientists insist on looking for a single explanation of what is obviously a complex phenomenon. What is intelligence by the way? Sure, there are forms of talent that seem inherited (or perhaps shaped by mutation in the moment of conception) but to test for a very complex set of variables is not very intelligent. As a philosopher I have increasingly come to acknowledge the existence of a practical form of intelligence, that many scientists, and others, lack. I lack it too, incidentally.
Reply | Report Abuse | Link to thisThe more literate the culture, the higher the I.Q.s of it's members, and the higher their attention to good health practices. It's that simple on the surface, even if you overlook the real possibility that cultural effects of such behaviors are also heritable over time.
Reply | Report Abuse | Link to thisPeople get bigger, smaller, evolve different facial and other physical characteristics for many reasons associated with their regions, and brains have differing physical characteristics as well. Changes in the physical represent changes first in the strategies needed to survive in different places. You don't read books to help solve problems where there aren't any books for example, or practice good health behaviors with a non-book learned witch doctor.
I should add that here's another of the usual bits of "scientific" research that search for a what when where how and possibly why, without reversing that order of inquiry to at least test the conclusions.
Reply | Report Abuse | Link to thisLOL! Not that I disagree with you, e_caroline, but if you think the researchers are mired in political correctness... just take a look at the commenters!
Reply | Report Abuse | Link to thisYep. This study may well be confusing an effect with a cause. Higher IQ is correlated with cleanliness, better housing, and etc. It is even correlated with lower levels of obesity and drug abuse. So here we have two researchers using tortured connection to argue a silly explanation for IQ differences. What are we to believe that mentally retarded people are full of disease? That everyone has the same exact IQ attributes if not for the rate of infection. Absolute silliness.
Reply | Report Abuse | Link to thisYes, dc9loser, I.Q. is correlated with many things: infections, toxin exposures, goitrogen exposures, obesity, micronutrient deficiencies (iodine deficit ALONE can can loss of scores of I.Q. points), endocrinopathies, and a bunch else. There is nothing "tortured" or "silly" about any of this. It is simply reality -- complex reality. It so happens that brain development, and hence I.Q., is influenced by a great many things. No, everyone would not have the "same exact I.Q. if not for the rate of infection", for several reasons. Principally, that all the other influences would not be precisely the same (except in rare instances). Secondarily, that the genetic portion of influence -- if it exists -- would not be the same.
Reply | Report Abuse | Link to thisFurther, regarding this: "are we to believe that mentally retarded people are full of disease?" Presumably you mean "are we to believe that mentally retarded people suffer from more infections, which are the cause of their retardation". I don't know of any data on rates of parasitic infection in the mentally retarded. I do know however that micronutrient deficits and toxin exposures can either cause or contribute to retardation. Co-existing parasitic infestation (such as e.g. in the third world), causing further iron depletion, would very likely exacerbate these influences. This is not "absolute silliness"; it is science -- or at least as close to science as biomedical investigations can get.
PS: I wrote: "I don't know of any data on rates of parasitic infection in the mentally retarded." That is, apart from Eppig et al's work here in question! Actually, there is a good deal of work prior to Eppig et al in this area. There's clearly a relationship, very likley causal, and related to iron and possibly other micronutrient deficiencies caused or exacerbated by parasitic infestation. Anyone interested in further background might wish to consult this review:
Reply | Report Abuse | Link to thishttp://www.nmcth.edu/nmcj_articles_pdf/volume_wise/nmcj_vol9_no1/Anisha%20Jasti.pdf
Review Article
Nepal Medical College Journal 2007; 9(1):
Mental and behavioral effects of parasitic infections
Pardon, but the link I gave (review article) apparently no longer works.
Reply | Report Abuse | Link to thisHere's a link to the abstract on medline:
http://www.ncbi.nlm.nih.gov/pubmed/17593680
And the full text is available here:
http://scholar.google.com/scholar_url?hl=en&q=http://imsear.hellis.org/bitstream/123456789/46705/2/nmcj%2520vol.9_no.1_article.12.pdf&sa=X&scisig=AAGBfm1wHraEaSsDe6sGt58U16pg4HuTHw&oi=scholarr
Surely 'IQ' as an authoritative measure of human intelligence (and capability) can be taken seriously only by people who may not be highly intelligent themselves. They may or may not have high IQs.
Reply | Report Abuse | Link to thisGSC
interesting to see if there is more variation in average IQ within groups than there is between groups as this is a finding inherent to statistical studies found and seen over and over again. The area of intelligence is especially rife with this conclusion. It appears in a given study that there is a very large difference between groups, when indeed, although there doe exist a difference between the two or more groups, the difference the exists within the groups goes unreported or at least under reported, and is of vital importance and interest. Is it that we are only interested in focusing on disparities between groups of people and not concerned that greater differences already exist within the same groups, but are uninteresting because they don't stir up the social conscience or point out some injustice in the social fabric. It should be considered interesting and important enough in any large study to at least report the differences that exist within groups as well as the differences between groups, so that we might assess the relative differences, and therefore discuss these matters intelligently rather than blindly pointing out differences that exist and always will exist when we compare groups of individuals. I'm not suggesting that the between group differences aren't important and don't warrant investigation or attention, but I do believe that it's equally important to attend to the differences that already exist within the groups under investigation, and not ignore themas though they don't exist or as though there is some injustice, or inequity that only exists between social groups, and aren't found within these same groups.
Reply | Report Abuse | Link to this"So far, the evidence suggests that infectious disease is a primary cause of the global variation in human intelligence."
Reply | Report Abuse | Link to thisHow does he know it is that way around? Maybe low IQ countries and states have higher rates of infectious disease because they are poorly run due to low IQs. Or maybe high rates of disease and low IQ are both caused by something else, such as poverty.
There are certain rude facts of life that we must concede, to wit: "All men are equal, just some are more equal than others."
Reply | Report Abuse | Link to thisIsn't that a bit of post hoc ergo propter hoc thinking? Discussions about evolution etc... I would argue it is more about development - perhaps higher IQ clusters developed better in society and economy, but I would argue that as areas developed higher socio-economic levels, they were allowed to develop broader, higher intellectual pursuits. Thus, the Anglo-Saxon sphere exceeds Africa, while Asia excels in areas where there was more Anglo influence (Singapore, Hong Kong)....
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