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February 21, 2008



Thanks very much for taking the time and trouble to link to these studies.

As a general remark, I would suggest that none of this data contradicts the hypothesis that IQ is a major determinant of SES and income in modernizing societies and that IQ is substantially inherited.

For example, it is a very well described property of IQ that IQ measures in early childhood are much less accurate than later in life. Probably this has to do with noise due to varied rates of development. Also, it is clear that IQ works much better for group prediction than individual prediction - and the bigger the group the better it works. And so on. The PNAS study requires more consideration, and I will need to study it further before commenting.

What these studies tend to do is *develop* the hereditary IQ hypothesis - which, like all scientific theories is continually evolving.

Pointing out the flaws and inconsistencies in a major theory is valuable and important, but it does not challenge the theory as a whole unless there is an alternative stronger theory which better explains the whole body of information. After all, the failure to account for all of variance in a multiple regression analysis is not really a limitation of a theory - but can simply be a rsult of imprecise measurement.

All the time it seems that genetic influences are more and more important than we thought. (Just this week a paper was published in Am J of Genetics which (I think) suggests that genetic effects in twin studies may be greater than previously measured, due to mutations occuring later n life.)

For example, the proponents of Intelligent Design spend a lot of time pointing out the flaws or incompleteness of current theory of Natural Selection. Sometimes their criticisms are valid, at present. But then the theory of natural selection is changing and has changed enormously since Darwin - there are major modifications every decade or so.

The crucial question is whether Intelligent Design is a better theory than Natural Selection, and of course it isn't.

Getting back to IQ. The hereditary theory of IQ as articulated by people such as Ian Deary of Linda Gottfredson is a far more powerful, validated and explanatory theory than the shifting and loosely-defined jumble of post-hoc rationalizations which constitute the rival 'environmental' theory.

People who don't want to believe in IQ can, and do, continue indefinately picking holes in the evidence, finding real or imagined inconsistencies, generating ever more post hoc environmental explanations etc. But this is no different in its strategy from creationist science - after all, nobody can ever be _compelled_ by the evidence to believe anything that they are absolutely determined not to believe.

But the evidence in relation to IQ is very strong indeed, and there is really no rival theory of any stature at all, so by ordinary standards of science practice the thing to do is to go ahead and apply the theory and test it out in practice (meanwhile keeping an eye open on what happens to monitor outcomes and make sure that they are turning out in line with predictions).

So - I would say, please regard the data you link to, plus other good science such as some of James Flynn's, not as being in any sense a refutation of the hereditarian IQ hypotheses, but a deepening and enriching of the hypothesis - just as Genetics and Sexual Selection are a deepening and enrichment of Natural Selection (although genetics was inititally - around 1900 - believed to be a refutation of Darwin, just as the Flynn effect of increasing IQ over time in 20th century modernizing societies was initially thought to be a refutation of hereditarian IQ theory.)

I find it worrying that so many people among the intellectual elites have invested so much moral capital in denying hereditary IQ. I can understand why this might be - but something has to give way. Lets hope it is the politics which gives way rather than the science.

Fabian Tassano

You raise the issue of what is 'fair'. No doubt there are many ways in which life isn't, e.g. it often happens that the better man/woman doesn't get the job.

One question which should always be explored in such discussions (but normally isn't) is why any individual would have an incentive to create a fairer system for other people. Politicians, educationalists and so forth may wish us to believe that their desire for social engineering is motivated by a love of 'fairness', but why should we believe them? If the 'market' (i.e. no intervention) produces unfairness because people are selfish and even at times malevolent, why should we think interventionists are any better? Aren't they far more likely to be merely pursuing their own agendas? E.g. revenge, power, or doing down potential rivals for themselves or their children?

Too often, the negative aspects of the 'free' outcome are tendentiously compared with some ideal in a way that totally leaves out the facts of human psychology.


Thanks for the link :). I have now written a follow-up post at Question That.

Harry H

Replying to Fabian's point about why should any individual want to create a fairer system, it could be argued that UK comprehensive schools are proof of the fact they don't. The big winners in the world of large messy comps are kids who receive plenty of help and encouragement at home. So the children of people like teachers and education officials come out on top, and there is little incentive to change things and give more breaks to the other kids.


Harry: I reckon when it comes to Fabian's views on state schooling you are preaching to the converted!

My view is that "large messy comps" don't do anyone any favours. Some - e.g. (as you say) the pupils who have the most supportive home life, and probably also those who come out top of the heap socially - might come through relatively unscathed.
Overall, though, I suspect that modern secondary schooling is detrimental to the majority of young people.

Scott Hughes

I think education is the main way class is passed on. Poor kids go to the worst schools, and rich kids go to the best. Then rich gets can afford the best colleges, and poor kids often do not even get to go to college.


"I find it worrying that so many people among the intellectual elites have invested so much moral capital in denying hereditary IQ." They clearly are not in an intellectual elite, if by "intellectual" one means people who apply their reasoning power to their concerns: 'power elite' might be nearer the mark. As for "moral capital", my guess is that they say that they deny much about IQ but many, I'd guess, behave in a way that's inconsistent with those professed beliefs. If my guess is right, then 'political capital' might be a better description. For what it's worth, I offer an argument that let me stop one bien-pensant spluttering in her tracks. "Do you", I asked, "accept that some stupid parents have bright children?" "Of course." "The genetic lottery can explain that" I said "but your environmental belief can't." To her credit, after she stopped spluttering she demanded to know why no-one had ever put that argument to her before. I replied that if she mainly talked to dim lefties, what could she expect?

Dan | thesamovar

BGC: "Pointing out the flaws and inconsistencies in a major theory is valuable and important, but it does not challenge the theory as a whole unless there is an alternative stronger theory which better explains the whole body of information."

On the whole, I tend to agree with this Lakatosian definition of falsifiability, but I think there's an exception to be made in the case where the theory doesn't appear to do much better at prediction than no theory at all (remembering that finding correlations is not the same as finding causal relationships).


Your story kind of misses the point though, which is not whether some people are born with a greater tendency to being smart than others, but the extent to which this tendency is translated into actual smartness depending on circumstances, and the heritability of this tendency.

David Crookes

Chris says: "... which suggests that the big difference in racial educational attainment in the US has environmental, not heritable, causes."

This reads too strongly to me. The paper itself discusses how the question is open:

" In order for genetic differences across races to explain the observed patterns in the
data, one needs a more complicated model than our model 2; one in which intelligence
has multiple dimensions (e.g. lower and higher order thinking), only some of which differ
across races and only some of which are present early in life. In this more complicated
model, if only lower order thinking is relevant at age one, and there are no racial
differences in lower order thinking, one can explain both absence of racial test score gaps
at age one and a high observed correlation between child and parent test scores at that
age. Later in life, higher order thinking emerges. If racial gaps exist in higher order
thinking and parent-child correlations are similar for higher order and lower order
thinking, then one can account for Blacks falling behind and child-parent correlations in
test scores remaining relatively constant with age."

We see low order intelligence in brain damaged/disabled people and failure of higher order intelligence behaviour, such as language. If there are genetic diseases that impact different functional areas of intelligence, then this strengthens the possibility that their model is incorrect.

Leah Whitcher

I can assure you teachers in bog standard schools do NOT give the brightest children the most attention. As the bright ones are self learners and are able to grasp new concets pretty quickly they are often left to get on with it while your attention is taken up with those with zero or very poor literacy skills. I speak as a teacher!


«I think education is the main way class is passed on. Poor kids go to the worst schools, and rich kids go to the best. Then rich gets can afford the best colleges, and poor kids often do not even get to go to college.»

Sort of. I think that is not quite right, but almost. The education system is the mechanism by which *middle class* is passed on. Where the middle class (those in the 5-to-20% income/wealth bracket) are essentially a class of clerics (scribes), and thus ensure their children inherit their role as clerics and thus their class indirectly through a heavily biased education system.

The rich, those in the top 1%-5%, transfer their class via a direct transfer of assets and power.


Try this:


It refers to a very nice study by Charles Murray (co-author of The Bell Curve) on siblings of various IQs, and what happens to their income over time. (I have read the formal study, this is an accurate journalistic summary.)

The results are confirmed by many other longitudinal studies of IQ and class using regression analysis - but this study is really neat and particularly easy to comprehend.

The stubborn fact is that IQ is more important than class - high IQ kids born into low classes rise in wealth and status; low IQ kids born into high classes decline in class and status.

OK, IQ doesn't explain *everything* (personality will probably turn out important for example). Literally nobody says that IQ explains everything.

The problem is exactly the opposite - people (elite intellectuals) who routinely deny or minimize the importance of IQ, who propagandize to this effect, who persecute viciously (and ignorantly) those who go by the science instead of the propaganda (eg. James Watson, Arthur Jensen, Charles Murray etc etc).

As I keep saying, if you don't control for biological variables such as IQ specifically and genes in general, then you will have a completely false picture of how things work.

In particular, if the huge importance of IQ and genes are denied you will grossly over-estimate the importance of social variables such as class ('privilege') and styles of upbringing.


Oh dear, BGC, dragging in facts; is that fair?

Tim Jones

I think that there is a flaw in your reasoning in the second half of point 3. It's known that the heritable effects of IQ show themselves more in early life - higher IQ children are later developers.

It seems to me that points 2,4, and 5 do not really support your argument.

Overall, I'm not sure that advocating hatred really is a "glass half-full/half-empty" issue. It seems to me that if you're going to do that then you need to be sure of your ground.


Fabian said: "Too often, the negative aspects of the 'free' outcome are tendentiously compared with some ideal in a way that totally leaves out the facts of human psychology."



Isn't the study referred to in (1) based upon a very small sample?

Matt Munro

IQ is 40% to 80% inherited, and outcome (in the sense of turning IQ into cash and status) is the product of IQ and environment. In other words nature and nurture transact.
So stupid kids + good environment (e.g the Royal siblings) will do ok but not become rocket scientists or hedge fund managers. Conversely clever kid + good environement (grammar school boy) will do well
While clever kid + bad environemnt (bright kid at bog standard comp) might do ok,
stupid kid + bad environment (sink comp with a "challenging" intake) is doomed for a life of McJobs.
IQ is the most important biological predictor, and parental expectation (which broadly translates as "middle classness") is the biggest social predictor of outcomes.


Matt Munro
"IQ is 40% to 80% inherited"

Do the numbers actually mean something? Do you mean that 40% to 80% of the variation in IQ (amongst whom exactly?) is due to genetic factors.

Or do you actually mean that between 40 to 80 points of the average 100 IQ comes from genetic factors? (In which case I would be very surprised that it wouldn't be more, given that the IQ of a worm is normally very low). (OK I was only kidding - I know I'm cruel).

Still 40 - 80 % is a huge range, hasn't all the research that has been done narrowed it down a bit?

Matt Munro

No because teasing apart gentic and environmental factors is difficult. The 40-80 figure orginally comes from "The Bell Curve" and I would interpret it as meaning if an individual has an IQ of 100, between 40 & 80 (of that 100) is a genetic endowment, the remainder is environmental. Teasing nature/nurture apart is almost impossible on an individual basis, which is why the Bell Curve used longditidinal studies, to "follow the genes" if you like. The other problem is that IQ is a measure of overall cognitive architecture and functioning, essentially a combination of various types of memory, spatial awareness, cognitive speed, etc, as such it is likely a product of the interraction of many genes (there is no single "inteligence gene") so trying to attribute IQ neatly into nature/nurture components is like trying to attribute percentage points of a Formula 1 cars' speed between the driver and the car. It's an emergent property of the 2.

BTW worms don't have a frontal cortex, so they all have zero IQ.

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