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September 01, 2003

IQ and Populations

The other day I came across this table of National IQs for all the countries in the world.  (Drawn from Richard Lynn's and Tatu Vanhanen's "Intelligence and the Wealth and Poverty of Nations", via Gweilo, via razib.)  This is fascinating information, particularly when combined with population growth rates.

For the purposes of this discussion, let's stipulate that someone's IQ is just something you can measure, which may or may not have some correlation to anything else you can measure.  Whether it has anything to do with intelligence or any particular cognitive ability will not be addressed.

The U.S. Census Bureau has a terrific website called the International Data Base (IDB).  This includes a facility to create a table of National populations for any year between 1950 and 2050.  Let's assume that countries are (first-order) self-breeding and that measured IQ was/will be stable in each country during the 100 year period.  Combining all these data yields the following graph:

world IQ over time

The dark blue line is the average IQ of the world.  I've also plotted the population growth of the five most populous countries, India, China, the U.S., Indonesia, and Nigeria; the average IQ of each of these countries is in parenthesis.  (Nigeria is currently ninth, with Brazil (87), Pakistan (81), Russia (96), and Bangladesh (81) intervening, but by 2050 it will be fifth.)  As you can see, in a 100 year period the world's average IQ will have dropped from 92 to 86, a change of 6%.  That is pretty darn significant.  And all because of differential population growth.

I extrapolated the population growth of each country another 50 years to the year 2100 (lightly shaded region of graph).  At that time the world's average IQ will have dropped below 84.  Within this time period of 150 years, extremely short by any evolutionary standard, an incredibly significant change in this key metric will have occurred.  And there is no sign of the trend bottoming out, because the growth rate of countries with lower IQs exceeds the growth rate of countries with higher IQs.  The most populous country today is China, which has a high IQ (100), but its growth is actually projected to be negative because of their "one child" policy.  After about 2030 India will be the most populous country, and it has relatively low IQ (81).  At current growth rates by 2100 Nigeria will be the third most populous country, and it has a low IQ (67).

If you're interested in playing with these numbers yourself, here's the Excel spreadsheet with all these data.  If you publish further analysis or commentary, I would appreciate it if you'd link back to this page.

There were two assumptions we made up front, and I'd like to revisit them.  First, we assumed countries are self-breeding.  With modern vehicles and opportunities for travel this is becoming less and less true, but for the bulk of the world's population it is definitely a safe assumption.  The two largest countries, China and India, are both relatively undeveloped and by-and-large people do not travel in or out of them.  The third largest country, the U.S., is the only possible exception to this assumption, because so many people immigrate into the U.S. (in 1990 8% of the U.S. population was foreign-born).

The second assumption is more interesting; we assumed measured IQ was/will be stable in each country.  The Flynn Effect predicts this is false, and that measured IQ will increase over time.  (Historical data provide significant evidence for this.)  Many explanations have been offered for this effect, including steady improvement in testing procedures, and there is some evidence that in recent years the Flynn Effect has diminished.  If the overall world IQ changes due to differential birth rates among populations with different IQs (that is, separate countries), then it seems plausible that a country's IQ could change due to differential birth rates within its sub-populations as well.  In most countries and under most circumstances the birth rate of poorer and less educated people is significantly higher than the birth rate among wealthier and more educated people.  (China is the primary exception; due to their "one child" policies the birth rate within all sub-populations is essentially the same.)  Given the positive correlation between measured IQ and wealth, and between measured IQ and education, these differential birth rates would suggest that individual countries' IQs would decrease as populations expand.  If true, this would obviously accelerate the overall decrease in world IQ over time.

There are other factors at work.  For example, AIDS is presently the most common cause of death in Nigeria, which is one of the most populous and fastest growing countries.  Wealthier and more educated people are less likely to become infected by AIDS, because of awareness of the known transmission mechanisms and available protections, and also more likely to survive infection, because of availability of treatment (at least to the point of having and raising healthy children).  Because of this the effective birth rate among wealthier and more educated people in Nigeria is probably higher than poorer, less educated people.  There is a substantial correlation between wealth, education, and measured IQ.  Thus the AIDS epidemic may have the effect of raising the average IQ of Nigerians.

The human race has been in existence for approximately 150,000 years, during which time natural selection has incrementally increased human intelligence and cognitive ability.  It is not possible to give IQ tests to humans from 100,000 years ago - at least not yet :) - so we can only surmise that there would have been a corresponding increase in measured IQ as well.  Only recently - within the last 10,000 years or so - has this trend been halted, primarily by organized agriculture which enabled a small group of humans to provide food for a larger group.  It now appears that very recently - within the last 100 years or so - this trend has been reversed.  I call this Unnatural Selection, since it appears that societal rather than evolutionary effects are at work.  The consequences of this overall decrease in world IQ have yet to be quantified, but they are bound to be significant.

More ruminations on this to follow, please stay tuned...


Posted by ole at 12:03 AM

I do so like to believe in Physis: that tendency for natural selection to improve upon itself. It's the closest thing to God I have.

Yet I hardly believe mankind is so special as to warrant an exception, so I look forward to your ruminations. I think the cud will prove indigestible, but I'd still like to see some defense for your many premises.

Love that yellow line, BTW. Good day for it, too.

Posted by: jim at September 1, 2003 02:45 AM

Firstly, regarding the Flynn effect, people who like to discuss the IQ, do not explain enough that IQ is a relative measure at a single given time... and as the Flynn effect has shown, IQ improves by huge quantities over generations... you should be careful to be as clear as possible when talking about such issues (i don't believe you are particularly clear in this post)

secondly, IQ of 81 implies borderline retarded... are you saying that most of the people in India are borderline retarded??

I suggest you read this article http://www.mugu.com/cgi-bin/Upstream/Issues/bell-curve/sowell.html which discusses some cultural issues around IQ scores and also describes how the (new immigrant) Jews in the U.S. had a lower than national average IQ in the 1920s, but in a couple of generations were far higher than national average... there are obviously some cultural things related to IQ test performance (for example, certain cultures may not be into abstract thinking, as shown by new immigrants whose descendants through familiarity with the culture do better)... also, it has something to do with nutrition, which is bound to improve... people who talk about IQ should be careful not to (apparently) fudge these issues...

Posted by: turkey time gobble gobble at September 1, 2003 06:05 AM

Jensen has shown somewhere (I'm still looking for the reference) that the Flynn Effect does not change g. All the F.E. seems to change is the non-g loaded aspects of IQ.

Also what are the demographics of the future population? Current subSaharan IQ's are partially explained by the low average age in those countries, and wouldn't that apply to the future Nigeria?

Posted by: Dick Thompson at September 1, 2003 09:50 AM

Thanks for the commentary!

Some points:
-- The Flynn Effect is real and important. Please follow the links in my post for more information and discussion. There remains widespread disagreement about the cause(s) of the effect, but not about its existence.
-- The IQ numbers are not mine. Lynn and Vanhanen developed these numbers carefully, please follow the link to their article for information about the origins of their data.
-- Average IQ doesn't say anything about any particular person, particularly in populations with millions of people. You have the cannonical bell shaped distribution.
-- I found it amazing that India's average was 81. My contact with people from India must be with the right edge of the curve.
-- There are not "obviously" cultural things related to IQ test performance. Over the past thirty years pyschometricians have refined IQ tests carefully to elminate cultural bias. People invoke tend to postulate cultural bias when they disagree with test results.
-- The impact of nutrition on IQ is limited. Studies designed to measure this (e.g. identical twins raised in different environments) fail to show much correlation.
-- After the age of five IQ is pretty invariant for any particular individual, regardless of their environment. I would not expect the low average age of sub-Saharan countries to be a significant factor in their average IQ.


Posted by: Ole Eichhorn at September 1, 2003 10:53 AM

The impact of nutrition on IQ is limited. Studies designed to measure this (e.g. identical twins raised in different environments) fail to show much correlation.

sandra scarr asserted in Born that way that there is likely a "threshold effect" in that there needs to be a minimum level of nutrition, etc. i think this explains the big different between american black IQs (85) and the average of the west african ones (70). to my knowledge the 85 result goes back about a century, and i can't imagine selection bias would have been that strong, and they are only about 20% white....

Posted by: razib at September 1, 2003 12:13 PM

This area is way out of my league. Anyway, my child was designated "gifted" (higher than 98th percentile) a few years back and at that time I read up on specifics of nutrition re IQ scores and learned that children that eat at least one serving of veggies and one serving of fruit daily as well as take a multi-vitamin score 8% higher on average when taking IQ tests. Is that bunk? I don't even remember where I got that info it was a good while back. I'm just curious because I was led to believe that is established as fact.

Posted by: Katy at September 1, 2003 01:23 PM

hm...they might be less lethargic. but i doubt that veggies = more brains, after all, creatine is found in meat....

Posted by: razib at September 1, 2003 01:30 PM

and as the Flynn effect has shown, IQ improves by huge quantities over generations... you should be careful to be as clear as possible when talking about such issues

TTGG (please don't admit you actually saw Gigli ;)),

a) Flynn himself doesn't think these represent actual IQ gains. While the Flynn Effect needs to be considered, its interpretation is a grab-bag at this point. Sowell's appeal to 'there's just too much we don't know', IMO, is at the expense of a lot of stuff we DO know. And that's unfortunate.

b)'retarded' means different things to different populations. American blacks who score in the white retarded range have much higher degrees of social functioning. Also, I think IQ is not measured as accurately in third world samples than it is in industrial nations. But i don't think the information is totally worthless.

c)jews always scored high, and terman, spearman, goddard, etc. all knew this from the start. i think anecdotes that state otherwise are a form of revisionism. Ashkenazi have a clear historical reputation.


I think its either bunk or its a correlation/causation thing. As people with higher iqs are more likely to care about stuff like health and nutrition. razib makes a point with the threshold.

Posted by: Jason Malloy at September 1, 2003 03:23 PM

by "threshold" i mean that all things being equal there isn't a linear relationship between nutrition & IQ (IQ = nutrition*k). this might be true in other ways as well-visual & intellectual environment, etc. not my area, but i rushton et al. haven't given me a reasonable explanation for the 15 point IQ difference between west africa & american blacks.

Posted by: razib at September 1, 2003 05:44 PM

I just took an IQ test by "Emode" which seems to be quite error free and unbiased. I scored a total of 113in all 4 categories,i.e. mathematical, visual-spatial, linguistic nd logical. I got most questions right in linguistic are wich stated I was highly intelligent and have the natural fluency of a writer. Where do I range or average with that score.

Posted by: Phyllis Turner at September 4, 2003 02:07 PM

"at that time I read up on specifics of nutrition re IQ scores and learned that children that eat at least one serving of veggies and one serving of fruit daily as well as take a multi-vitamin score 8% higher on average when taking IQ tests. Is that bunk?"

The only thing I could find regarding veggies and vitamins boosting IQ is this:

"...it has been found that many childre, although given what appears to be a perfectly adequate diet, eat too many sweets and 'junk foods' and too little fruit's and vegetables. Their intake of vitamins and minerals is low, although not sufficiently so to attract medical attention. When given vitamin and mineral supplentation, however, their IQ increases markedly. Studies have taken large groups of apparently well-fed children and dived them into control groups, which are given placebo pills, and treatment groups , which are given proper supplementation. The treatment group achieves a four point IQ advantage over the placebo group on average...it helps only those who do suffer from a deficiency. ...For such children, an average increase of 10 or 11 IQ points has been recorded.

These were well fed children by ordinary standards; an even better effect would be expected if supplementation were given to children suffering serious dietary deficiencies"

(EYSENCK,Hans; Test Your IQ, Penguin Books, c. 1994)

Posted by: the alpha male at September 4, 2003 03:29 PM

It's unreasonable to assume that Nigeria's current rate of population growth will continue and reach 350 million.

Posted by: Lola at September 5, 2003 06:23 AM

I find that all standardized tests are flowing over with biased questions.
They either fail to reflect the different cultural backrounds in communtication, and cognition, or fail to represent the multiple intelligences.
What IQ test would you recommend? I have taken emode and received 129?
Is this score fairly average?

Posted by: amber at October 14, 2003 12:42 PM