Thursday 14 March 2013

The harshness of selection for higher intelligence: mostly a matter of the lethality of low IQ


Many people who pride themselves on being tough-minded acknowledge the reality of differences in human intelligence, and have speculated on the evolutionary causes.

Such speculations are usually framed in terms of the reproductive advantages of high intelligence; yet the actual historical reality was probably more a matter of the lethality of low intelligence.


The best worked-out example of differential intelligence is probably Cochran, Hardy and Harpending's theory of Ashkenazim high intelligence

In a positive sense, this was a matter of those with highest intelligence having the highest reproductive success due to the economic benefits of working as money lenders and the like.

But, on a second look, what they are mostly saying is that the selection pressure of medieval central Europe was such that Jews who were of low intelligence (and unable to do the job of money lender) were eliminated.


It is quite likely the same story wherever high intelligence was selected: the low intelligence people mostly died early from lethal accidents in societies too complex for them to understand

Or they died as unintelligent infants because their unintelligent mothers were unable to rear them in complex societies:

Or, in more general terms, they died of starvation and disease because they were unable to make the transition between low-tech nomadic hunter-gatherer lifeways and the more complex and elaborately-tooled high latitude H-G or later agricultural societies.


So, it is probable that high intelligence was mostly a consequence of natural selection culling those who were of lowest intelligence by accidents, diseases and starvation.


This apparently implies that the substantial decline of intelligence since the industrial revolution

is most likely (as a first hypothesis) due to to lower mortality rates among the least intelligent, resulting in cessation of the medieval societies 'culling' of lowest IQ persons.


If so, then this presents a much harsher view of matters than generally acknowledged.

It is reasonable to suppose, on current evidence, that the only sure and certain way that general intelligence could have been maintained at pre-1800 levels, was by humans having continued to live under the kind of high mortality rate selection pressure which killed off many or most of those with the lowest intelligence.

When society became less harsh, and mortality rates of the unintelligent declined from their near-total levels of medieval society, a substantial decline in general intelligence was inevitable.

It is plausible further to suppose that one consequence of this decline from pre-1800 levels of 'g' will inevitably be the decline of that post-industrial revolution civilization; since innovation will slow, stop, then go into reverse. 


So medieval selection against low intelligence led to industrialization, which relaxed seleection against low intelligence, which relaxation will destroy industrialization.

If so, then modernity was a self-limiting 'blip' in world history; and we should anticipate a return either to the kind of harsh selection for higher intelligence; or else to go back to the simple hunter-gatherer organization; when average intelligence was lower than in agricultural societies, and (what we would think of as) very low general intelligence was not a overall disadvantage to reproductive success.



Bruce B. said...

Low intelligence didn’t have to be lethal. Stupid people couldn’t support a family so they didn’t marry. They had their hands full just subsisting.

Adam G. said...

Plausible, but there have to be other factors involved, because there are significant disparities in IQ between different agricultural areas.

Thomas said...

Are you suggesting that God wanted us to become less intelligent?

Bruce Charlton said...

@Thomas - No, I am not.

Dan said...

"Low intelligence didn’t have to be lethal. Stupid people couldn’t support a family so they didn’t marry. They had their hands full just subsisting."


If you have good cultural norms, things can be quite harmonious.

In Europe for centuries, a man could not marry if he couldn't provide, and if he didn't marry he wasn't making babies, for the most part.

Matt Parrott said...

Being unintelligent is more dangerous in more extreme habitats than in more mild habitats, yet human intelligence was more acutely selected for in these safe and mild regions.

Human intelligence is a product of male territorial aggression, having been selected for most acutely in the regions which were categorically the most populous and, therefore, the safest.

Furthermore, this hypothesis suggests that all the animal kingdom would be selected for increased intelligence levels. If intelligence were a generically useful environmental adaptation, a stroll through the forest would be like a stroll through a Disney film of talking animals prancing and chattering about.

Dan said...

Differential mortality by IQ is alive and well, so to speak.

Drawbacks said...

You don't mention Ron Unz's recent article on the evolution of high Chinese intelligence, although the timing may not be coincidence.

Bruce Charlton said...

@Drawbacks, Thanks for getting me to read the Unz article.

(I had heard of it, but I tend to discount what people say about Unz because he funds so many of them!)

It was an excellent essay, and indeed I suspect I shall never forget his depiction of Chinese society.

The Chinese national character, and the nature of their abilities, are exactly what would be expected from hundreds of years of harsh selection in the kind of society described - the character of a successful farmer.

And this contrasts quite easily with the kind of character and abilities which would be expected from the European conditions of selection - the character of a successful clerk/ craftsman.

And this, in turn, explains why creative genius is essentially a European phenomenon. I had tended to explain it in terms of the duration of selection - that the Chinese had been under selection for high intelligence and conscientiousness for longer and were further down the path.

But I now perceive that there was a large difference in the most adaptive personality type between China and Europe (a difference among the most intelligent, I mean) which could also be a major selection factor.

In China it seems that low C was rapidly punished by death from starvation - in Europe the class/ caste system provided a cushion (and the high rate of death from disease rather than starvation made European life easier for survivors).

George said...

It is interesting how intelligence is best nurtured in a harsh environment. Similarly the body is most healthy in some degree of physical stress.

This certainly contrasts our modern aproach - equality of material comforts for all wihout struggle. If we think what hat literally means materially we have death! this corresponds directly to Fr. Rose's observations on how modern intellectuality leads to nowhere but Nihilism and destruction of all higher aspirations.