Thursday, 7 February 2013

Causes of the 'dysgenic' trend in intelligence: The double-whammy IQ-reducing effect of a lower proportion of IQ-enhancing genes plus an accumulation of IQ-damaging deleterious mutations


It seems very probable that general intelligence (or 'genotypic IQ') has declined by more than one standard deviation since late Victorian times, and presumably even more since about 1800 when the Industrial Revolution began to become obvious and these changes probably began.

But what was the cause?


Using reaction time data, the decline in genotypic IQ is of-the-order of 1.5 IQ points per decade - that is about 15 points in a century - or one standard deviation.

(This rough estimate of the size and rate of decline in 'g' has been replicated by a more sophisticated and completely different - as-yet unpublished - analysis of reaction time trends that I have seen.)

In other words, the average Englishman from about 1900 would be in roughly the top 15 percent of the population in 2000 - and the difference would be even larger if we went back further towards 1800.


These numbers are not intended to be precise - indeed real precision (in the sense of exact accuracy) is not available in IQ studies for many reasons to do with the difficulties of truly random and sufficiently large population sampling; and the fact the IQ points are not on a 'ratio scale' but are derived from putting a population sample into rank order on the basis of (usually) one-off testing.

But anyway, I think that a decline of 1.5 IQ points per decade is probably too fast to be due purely to the effect on gene frequencies of differential fertility between people of different intelligence levels.

No doubt the measured decline is substantially to do with the fact that higher intelligence is correlated with lower fertility; but within this, I think there must be at least two explanations operating at the same time.


Differential fertility would lead to a decline in intelligence - let's say - by a reduction in the proportion of high IQ genes in the population.

This happens mostly because since the Industrial Revolution almost-all children that are born will survive; so reproductive success becomes almost-purely a matter of fertility; and the most intelligent sectors of the population are the least fertile, and less fertile with each generation; until eventually (i.e. for the past several decades) the most intelligent people are sub-fertile, below two offspring per woman - so that the genes which make them most intelligent will decline with each generation - first declining as a proportion of the gene pool, and then declining in absolute prevalence. 


My suggestion is that the additional mechanism of decline in intelligence is the opposite of the above: an increase in the proportion of low IQ genes in the population.


There is, I suggest, a difference between high IQ and low IQ genes.

High IQ genes have (presumably) been selected for in the past because they increased intelligence, and thereby (under ancestral - especially medieval - conditions) increased reproductive success.


But low IQ genes are spontaneously occurring deleterious mutations. These were not 'selected for'; rather it was a matter that selection failed to eliminate them.

In technical terms, the mechanism for low IQ genes is mutation-selection balance.


The idea is that before the Industrial Revolution, individuals with a higher mutational load had lower-than-average reproductive success due to very high (near total) childhood mortality rates among those of lowest intelligence.

But after the Industrial Revolution got going, and mortality rates declined for the least intelligent so that even the poorest families usually raised several-to-many children, then there was a double-whammy dysgenic effect: a reduced proportion of high IQ genes with each generation (due to progressively lowering fertility among the higher IQ) and also an increasing accumulation of IQ-damaging deleterious mutations with each generation.

So that (roughly speaking) since the Industrial Revolution, individuals with the greatest mutational load (IQ-harmful genes) have been initially been above-replacement fertile (having on average more than 2 surviving children per woman, for the first time in history perhaps), and also differentially more fertile than those with the least mutational load.


So that compared with 150 years ago there are a lower proportion (and a lowering absolute amount) of IQ-enhancing genes in the gene pool of England, plus a higher proportion and accumulation of deleterious IQ-damaging mutations.


And this double-whammy effect is, I think, why the general intelligence has declined so rapidly and so much in England over the past couple of centuries. 


NOTE: The focus upon accumulation of deleterious genetic mutations due to relaxation of the selection effect of childhood and early adult disease and mortality (which had previously served as a sieve of strongly fitness-reducing mutations) was something I got from Narrow Roads of Gene Land: evolution of sex, Volume Two of WD Hamilton's collected papers. One aspect is that such relaxation of selection is probably unprecedented in human history - indeed, it is possible that recent post-Industrial Revolution conditions may have generated a positive selection in favour of deleterious mutations (amplifying their frequency, at least up to the point when they become fatal or induce sterility). At any rate, the quantitative effect of this process of accumulating deleterious mutations in a population is only imprecisely measurable (I believe); whereas the quantitative effect of differential fertility on differential IQ is pretty well understood, and fairly precise measurements of the effect size are possible. 



Daybreaker said...

Mass immigration makes it a triple whammy.

MC said...

Just so I understand your position in the article, you believe that genotypic IQ has gone down by a standard deviation even while phenotypic IQ has gone up? Is that due to education? Or do you believe that the Flynn Effect is a fiction?

Bruce Charlton said...

@MC - If you follow the link/s you'll see this specifically discussed.

In short, the Lynn/ Flynn effect is real - IQ scores have risen through the 20th century (although this seems to have stopped in recent years). Probably for more than one reason - some are 'phenotypic' and to do with nutrition and reduced infectious diseases, others are 'artifacts' to do with 'inflation' of test scores from various factors - familiarity, teaching to the test etc.

But IQ scores are generated by performance on direct or indirect tests of cognitive performance - they can be used to put subjects into rank order for general intelligence, but they are not a measure of general intelligence in the way that reaction times are.

You can improve your performance on a test, or a type of test, but you cannot learn to have shorter reaction times - it is a property of nervous system performance.

It has been known for a century that general intelligence was highly heritable, and also that the most intelligent were the least fertile (especially among women) - so it was always known that underlying (genotypic) intelligence must be declining, and that as long as this continued eventually this would overcome any phenotypic effects.

What was needed was a measure of 'g' that was free from that artefacts of pen and paper testing - reactino times is such a measure, and fortunately there are reaction time measures going back to the late 1800s.

My personal view is that psychometricians have often been incapable of understanding (because they lack medical and biological knowledge) while public intellectuals have *deliberately* misunderstood and misinterpreted the Lynn/ Flynn effect (even down to the level of ignoring Lynn's priority in describing it!) - it is not really a strange or surprising observation, and should never have been seen as a refutation of the fact of declining general intelligence in the past couple of hundred years.

Daybreaker said...

Isn't this about the genetic decline of whites and not "intelligence" as such? You do say "in the West" but mostly you talk as though "the West" was the world.

Bruce Charlton said...

@D - Well, I am talking about the English, and before the era of mass immigration - my *presumption* is that much the same applies where there are sufficiently similar populations subject to similar trends in birth and death rates - Scotland and Wales, Western Europe, Scandinavia and the Anglosphere, probably Japan... But in fact much the same trends likely apply to many undeveloped countries over more recent decades as well.

Dan said...

Bruce --

It's hard to believe things could be as dysgenic as you suggest.

(1) Mortality in relation to IQ and education is not trivial; it is substantial. Just look at a chart like this. Being dumb/uneducated knocks off 10-14 years of your life, after accounting for race.

(sorry for the leftist link)

Presumably the clock starts ticking at about age 22 or something before which the question of whether someone has a degree is not applicable. Thus a gap of about 12 years develops in a 50 year span. That is huge.

(2) That large mortality gap is just looking at adults. It doesn't even include infant, child and teenage mortality, which would have occurred before someone can complete their education. The mortality gap may thus be greater still.

(3) When we look at the relationship of fertility / IQ it looks substantially dysgenic, but studies almost always looks at women. Female hypergamy is substantially at play. For men, earnings and education and IQ do not seem to have a negative effect on fertility and may even have a positive effect.

(4) Yes, educated women have fewer children, but education is not intelligence. The fertility gap is mitigated by the fact that education is only partly correlated with IQ.

(5) The hereditary relationship of IQ is substantially less than 100%. There is reversion both down to and up to the mean.

(6) It may be that some culling of low IQ happens in utero, due to bad genes. Some substantial proportion of pregnancies end in miscarriage, including very early on.

A lot of today's pathologies seem to reflect not low IQ but high IQ. Witness how Obama support approached 100% at places like Yale, and that is against someone smart and capable like Romney.

Witness the absurdity of the elite media, which is clearly quite bright.

Bruce Charlton said...

@Dan - Well, all that you are saying is that you can't explain the change in average intelligence using the models you have! - this doesn't mean there hasn't been such a change! I say we need to go back and look at the models of change in intelligence - especially looking at the role of accumulated deleterious mutations when natural selection is relaxed.

Mortality rates and life expectancy are almost irrelevant - the population in the endemic famine areas of Africa (e.g. Ethiopia, Mauritius) has been doubling every fifteen years or so despite the high death rates. In the modern world fertility trumps all at one end, while self-sterility trumps all at the other end.

Further examples are the Roma (gypsies) in Eastern Europe and the Aborigines in Australia (both with 'g' probably around 2SD below Europeans) which have the highest mortality rates by far in the places where they dwell, yet due to high fertility these populations are growing rapidly in absolute (and even more in relative) terms.

"A lot of today's pathologies seem to reflect not low IQ but high IQ." - I agree, I wrote about this in my clever sillies articles. But modern high IQ is a lot less than high IQ of 100 plus years ago.

And the Flynn effect means that among moderns, many of those with high IQ scores are NOT very high in g. Partly for this reason, IQ scores are much less predictive than they used to be.

Dan said...

Contra the notion that only imbeciles and the genetically defective have children in modernity, I have looked at the Forbes list, clicking on bios and counting the children.

I got an average of about 3 kids per billionaire, twice the developed world average. This is only kids they acknowledge to an interviewer and only kids they've had so far.

Billionaires obviously will tend to be much smarter, more energetic and harder working than the average bear because you have to win a lot of battles to get to the top.

Guys like Carlos Slim (6) Bernard Arnault (5), Sheldon Adelson (5) are not uncommon. Childlessness is rare among billionaires who have completed their fertility.

Billionaires are just a sliver of society, but they are an indicator. Ivory tower PhD's are separate indicator of smarts with low fertility but if billionaires are more fertile that those with a PhD in victimology that is probably not bad. The fitness of the former must be leagues better than the fitness of the latter.

Bruce Charlton said...

@Dan - "only imbeciles and the genetically defective have children in modernity,"

Come come! - nobody sensible says that! But just look at the *average* data - its been the same pattern since the 1800s, Galton noticed it, it's not subtle.

That said, the effect is much stronger in women, with highly intelligent women having an average of about 0.5 children.

I think it may turn out that female dysgenic fertility has a different (more powerful) effect than male - that may the kind of mechanism we need to consider.

Dan said...

"highly intelligent women having an average of about 0.5 children"

That would be remarkably low. Do you have a link on that?

Your main datapoint for a 1+ SD decline in G seems to be reaction time. Are there other explanations?

E.g. the average modern is chronically fatigued and very sedentary.

Civilization does some remarkable things today that it didn't do in the past: handheld supercomputing, drilling for oil sideways miles under the sea, supporting many billions in gluttony etc.

This doesn't suggest total failure of IQ.

I have a bunch of kids and I want to think they aren't completely screwed :).

Bruce Charlton said...

@Dan - I'm sorry - I can't be bothered to dig out links; it would take me hours. If you don't want to believe the implications of reaction time data, then I can't make you! Either it is true or it isn't.

Dan said...

I'm your reaction time info and it is difficult to determine how strong a case is there. The Flynn numbers suggest something different so something doesn't add up.

Is Galton's the only data point that gives such good results for the Victorians?

Some things I'd like to know...

- Was his dataset representative of the population as a whole?
- Did he average reaction times for each person or did he pick a person's best time? I can so how picking a person's best time could be seen as their 'true' reaction time.

My best reaction time is probably a std deviation better than my average.

Bruce Charlton said...