Friday, 23 October 2015

PSY 3002 - Evolutionary Psychology and Medicine - Notes on the evolution of higher intelligence and the decline of intelligence

The following are excerpts from a draft of The Genius Famine by Ed Dutton and Bruce G Charlton, currently 'in the press' with University of Buckingham Press

The evolution of higher intelligence


Geoffrey Miller’s emphasis on intelligence (he emphasizes particularly ‘creative’ intelligence) providing a ‘fitness measure’ which one person can evaluate in another; and his noting that relative IQ provides a quantitative correlate of deleterious mutations - is worth pausing over and amplifying.


This implies that high IQ serves as a kind-of guarantee and advertisement of ‘good genes’ – and this is why high intelligence is regarded as attractive, and therefore why men and women of higher intelligence tend to pair-up in marriage in much the same way that good-looking men and women tend to pair-up (this system of like pairing with like is termed assortative mating).  


We have already noted that intelligence correlates with fast reaction times. This strongly implies that ‘intelligence’ is simply the function of a brain that is working well, just as strength is the function of muscle that is working well. The human body has evolved to work optimally well in a particular environment and the same is true of the human brain. Detailed historical research by British economist Gregory Clark has shown that until the Industrial Revolution a form of natural selection was operating in Western societies. Those who were not physically strong, who did not have strong immune systems, who were of low intelligence and unable to work steadily for long hours would usually either die as children or be unable to raise children of their own; and would thus be unable to pass on their deleterious genes.[1]


In other words, until about 1800 only the minority of people with (on average) the ‘best genes’ (i.e. the lowest mutation load) would be able to survive and reproduce; and among the great majority of the population only a very small proportion of their offspring (averaging much less than two, probably less than one, per woman) would survive to a healthy adulthood, reproduce and raise children of their own. In this context, which was for almost all of human history until about two hundred years ago; both new and inherited deleterious mutations were filtered-out, or purged, from the population every generation by this very harsh form of natural selection.


In much the same way, the number of surviving offspring was predicted by socioeconomic status – and especially by intelligence – in pre-Industrial Europe. Clarke shows that in seventeenth century England, for example, the richer 50% of those who left wills had 40% higher completed fertility (children of their own, still alive when they passed away) than did the poorer 50%. In essence, the English intellectual middle classes (e.g. senior clerks, merchants, lawyers, churchmen, physicians etc.) seem to have been the most successful at reproducing for several hundred years – providing the majority of viable children with each generation so that over many generations their descendants (inheriting their ancestors high intelligence) expanded as a proportion to become almost all of the English population.


Those with the lowest levels of deleterious mutations would, for that reason, have high intelligence and a high functioning immune system. As such, they would attain or maintain high socioeconomic status, and, in a context of limited medicine, their offspring would be more likely survive. In addition, genes for intelligence would permit them to become wealthier, meaning they could better protect themselves, and their offspring, from disease, poor living conditions and accidents, and they could afford to have large numbers of children (ensuring at least some survived), without risking starvation. These two related processes would ensure that the children of the richer survived better.



The message seems to be that in pre-industrial Europe (before about 1800-1850) natural selection on humans operated mostly via mortality rates – especially child mortality rates. An average of more than half of children would die before adulthood, but this consisted of near total mortality rates among the children of the poor, and ill, and of low intelligence or ‘feckless’ personality; whereas among the skilled middle classes (clerks, merchants, lawyers, doctors etc.) the mortality rates were lower and fertility (number of births) was high. Therefore in each generation most of the children came from the most intelligent group in the population, and over several generations almost all the population would have been children of the most intelligent (also conscientious, and relatively peaceful) sector of the population.


(This is why anyone English who has ever traced their family tree will find that by the sixteenth century – when records begin – their ancestors are, at the very least, wealthy though non-aristocratic farmers (‘yeomen’ or richer ‘husbandmen’).[2] And this is why every English person alive is descended from King Edward III - 1312-1377.).[3]  


Clarke argues that this harsh natural selection resulted in an increase of average intelligence with every generation, and ultimately culminated in the intellectual and social breakthroughs of the Industrial Revolution. It meant that there was a percentage of the society whose intelligence was so high that the necessary breakthroughs could be made and that the society as a whole was sufficiently intelligent such that it could maintain and even develop these breakthroughs. Furthermore, the workforce developed a personality type which was pre-adapted (by preceding Medieval natural selection, operating over several hundred years) to the needs of large scale industry and complex social organization.



The ending of selection for higher intelligence


This ‘eugenic’ (i.e. fitness-increasing) environment rapidly stopped in the wake of the Industrial Revolution, and soon went into reverse; with socioeconomic status becoming negatively associated with fertility, especially among women. In other words, after the Industrial Revolution the direction of natural selection turned upside-down, with higher social status, wealth and education leading to lower reproductive success.


This process – known as dysgenics (i.e. selection that is reducing fitness) – has been documented by British psychologist Richard Lynn. In addition, Lynn notes that the pattern of reproduction ceased to eliminate genes that would lead to a poor immune system or various physical impairments. Modern medicine means that genetically-damaged people can procreate leading to a dysgenic impact on health, more deleterious genes and thus a further negative impact on intelligence.[4]


Probably the most significant impact of the Industrial Revolution was in reducing child mortality rates from more than half to (eventually) just about one percent. For the first time in history, almost all the population, including the poorest classes and those with the heaviest mutation loads, were leaving behind more than two surviving children. Over a few generations, the mutational load must have accumulated – fitness must have declined – and average intelligence must have reduced due to the effects of deleterious mutations on brain development and functioning.


Since intelligence is correlated with genetic quality, this inferred population level mutation accumulation implies that average intelligence should have declined since the Industrial Revolution. 


The inferred decline in general intelligence due to both mutation accumulation plus ‘dysgenic’ patterns of fertility, can be measured using simple reaction times, which correlate with ‘g’ – and it has been found that reaction times have slowed considerably since the late 1800s when reaction times measurements were first performed. 


We will return to discuss this matter further – but so far it seems that intelligence first increased due to natural selection in the Medieval era; then has declined due to the changes in natural selection at the time of the Industrial Revolution.


So, what about personality – how was personality affected by natural selection on the European population, first in the Medieval era, then through the Industrial Revolution?


In sum, it seems that Medieval Europe was a breeding ground for high intelligence – which is one component of genius; but also a breeding ground for pro-social extraverted people of stable ‘high GFP’ personality type, high in conscientiousness, empathic; obedient, good at working regular hours and getting along with their neighbours.


However, although high intelligence is a component of genius, and although an average pro-social personality type is useful, and perhaps essential, for successful industrial societies; the high GFP/ pro-social personality is almost the opposite of that required to make a genius. And yet, late Medieval and Renaissance Europe was a veritable hotbed of genius, and it was these geniuses who enabled and triggered the Industrial Revolution.


So, how can the average population increase in pro-social personality, yet that same population generate individuals of exceptionally high intelligence who have the ‘asocial’ Endogenous personality type, some of whom made major breakthroughs and became recognized as geniuses?


Measuring the decline of intelligence


It is one thing knowing that in principle intelligence must be declining; but the problem is that IQ testing is not suitable for measuring long term trends; because an IQ questionnaire is a relative measure: it puts people into rank order by their test results – but it does not give an objective measure of intelligence levels.


In other words, IQ testing is like running races and placing people into first, second, third etc. positions, but never using a stopwatch. This makes it impossible to know, over the decades, whether people are running faster, slower or staying the same. What is needed is some kind of objective measure of intelligence: a stopwatch.


This limitation in IQ testing led to the idea by one of this book’s authors (Bruce G. Charlton) of measuring long term trends in intelligence using exactly a stopwatch measure: in other words studying the historical changes in the simple reaction time (sRT) measurement; because reaction times have been measured since the late 1800s, and provide an objective correlate of general intelligence.


Simple reaction times (sRT) typically involve something like pressing a button as rapidly as possible in response to a light coming-on, and measuring the time taken – this procedure usually takes some small fraction of a second: i.e. some few hundreds of milliseconds. Such reaction times are well known to be correlated with ‘g’ (general intelligence). While the correlation with intelligence is not large, sRTs have the great advantage of being objective and quantitative physiological measures – they are more like measuring height or blood pressure than getting people to do an IQ test (which is essentially a form of exam).


Working with Charlton, Michael A. Woodley of Menie, discovered an already-published survey of historical reaction time data that demonstrated a striking slowing of sRTs from the time of Francis Galton in the late nineteenth century until the late 20th century. This data carried the strong implication that there had been a rapid and substantial decline in intelligence over the past hundred-plus years – and opened-up a new field of research which Woodley has been actively pursuing ever since.


This initial finding, which Charlton published on his blog, has since been improved, replicated and confirmed by Woodley and his colleagues[5] who have deployed other convergent methods for indirectly measuring long term intelligence changes.[6] 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, or one standard deviation, in a century. [7] (Indeed, by more recent estimates from Woodley, the decline seems to extend over the past two hundred years, and is probably about two standard deviations – or approximately 30 IQ points.) To put this in perspective, 15 points would be approximately the difference in average IQ between a low level security guard (85) and a police constable (100), or between a high school science teacher (115) and a biology professor at an elite university (130). 


In other words, in terms of intelligence, the average Englishman from about 1880-1900 would be in roughly the top 15 per cent of the population in 2000 - and the difference would be even larger if we extrapolated back further towards about 1800 when the Industrial Revolution began to initiate massive demographic changes in the British population (although this was a time before reaction time measures existed).


These numbers are not intended to be precise - indeed real precision (in the sense of exact accuracy in averages and measures of scatter around averages) is not available in IQ studies for many reasons to do with the difficulties of truly random and sufficiently large population sampling, lack of a full range of unbiased and objective data; 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.


However, the take-home message is that there has been a large and important decline in the average intelligence of Western populations over the past century and more. In every day terms; the academics of the year 2000 were the school teachers of 1900, the school teachers of the year 2000 would have been the factory workers (the average people) of 1900, the office workers and policemen of 2000 were the farm labourers of 1900, while the low level security guards and shop assistants of 2000 were probably in the workhouse, on the streets or dead in 1900.


The substantial long-termed unemployed underclass of 2000 simply didn’t exist in 1900. And even this estimate is ignoring the expansion of education since 1900, which expanded the middle class occupations and would, in itself, reduce the average intelligence of academics and teachers in 2000 compared to 1900.  



But what about the Flynn effect?


Objective measures show that intelligence has declined rapidly and substantially over the past century or two; but it is also true that the so-called ‘Flynn Effect’ has been evident.


This name refers to the fact that IQ raw scores (i.e. the results on IQ tests, the proportion of correct answers) have been rising throughout the 20th century in Western countries.[8] So, performance in IQ tests has been increasing at the same time as real, underlying general intelligence has been decreasing.


This can happen because IQ score is a relative, not an absolute, measure of intelligence – and because it is essentially the result of a timed examination involving answering questions. There are likely to be many reasons for increasing IQ scores, indeed any reason for increased exam scores might be contributory – for example improved health, cultural change, educational expansion, socialization of testing procedures, test question and format familiarity, teaching of test strategies, increased use of multiple choice formats (where guessing is encouraged), probably also increased levels of cheating – all may contribute variously to IQ test scores rising even as intelligence declined.


But even the Flynn effect has now plateaued or gone into reverse in a number of countries,[9] and the rise in scores have been shown to be occurring most on the least g-loaded parts of the tests.[10] So, general intelligence has been declining substantially and rapidly even though IQ test scores used to be increasing.


Furthermore, it seems likely that while underlying intelligence was much higher in the past, the measurable intellectual performance – for example in examination, intelligence tests, and in real life situations - of most people was severely damaged by lack of education, harsh physical conditions such as cold and damp, starvation, disease, exhaustion and endemic severe infectious disease, pain and disabilities and so on. Such factors would be expected substantially to reduce (or abolish) many aspects of intellectual performance in difficult tasks by (for example) impairing concentration and motivation.


Imagine doing an IQ test, an examination, or attempting any challenging intellectual activity such as reading a difficult book or performing calculations; while suffering with a fever or chronic pain or gnawed by hunger: imagine suffering fevers, pain, or hunger continuously for most of your life… but this was the normal situation for most of the population in earlier times. No matter what their underlying level of intelligence might be, their performance was significantly impaired for much of the time.  



High-IQ genes versus low-IQ genes


At a genetic level, intelligence may in principle reduce because of a reduction in high intelligence genes in a population and/or as an accumulation of intelligence-damaging mutations in the population.


Differential fertility would lead to a decline in intelligence by a reduction in the proportion of high IQ genes in the population. This happens from a combination of the relatively less intelligent people having on average the most children, and the most intelligent people having very low fertility. Since the most intelligent people are sub-fertile, with less than two offspring per woman, the genes which have made them the most intelligent will decline in each generation - first declining as a proportion of the gene pool, and then declining in absolute prevalence. 


For instance, when there is a woman with ultra-high intelligence who has zero children (which is the most usual outcome among ultra-intelligent women), then whatever it was about her genes which made her so intelligent is eliminated from the gene pool: this is the loss of ‘high-IQ genes’.[11]


But our suggestion of mutation accumulation is that there is an additional mechanism of an accumulation of what could be termed ‘low-IQ genes’. To be clear: these are not genes coding for low intelligence – rather they are damaged genes which pathologically reduce intelligence. So, as well as there being a decline in intelligence from the reduced proportion of ‘high-IQ’ genes, there is also an increase in the proportion of ‘low IQ genes’ in the population.


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 not, in general, a product of natural selection: rather they are spontaneously occurring deleterious mutations, which happen with every generation due to any cause of genetic damage (e.g. electromagnetic radiation, chemical damage), or errors in replication.


These mutations will, if not eliminated, accumulate generation upon generation. Therefore when they have accumulated, the low-IQ genes were not ‘selected for’; rather it was a matter of lack of selection, relaxation of natural selection. ‘Low IQ gene’ therefore usually means something like a genetic mutation that – in potentially a wide range of ways, by impairing almost any aspect of brain structure, organization or functioning - actively damages brain processing speed and efficiency, hence reducing general intelligence.


In technical terms, the selection mechanism for eliminating these spontaneously accumulating low IQ genes is mutation-selection balance. The idea is that mutations spontaneously occur and need selectively to be eliminated. In other words, by some means, those organisms which have damaging mutations must (on average) fail to reproduce - must indeed be prevented from reproducing - so they will not hand-on the mutations to the next generation, and contaminate the gene pool with mutations.


Conversely, only a small proportion of the population – i.e. those with good genes – are allowed (by the selective environment) to reproduce; and typically this minority will provide nearly all of the next generation.


Since there are new mutations each generation, as well as the possibility of some inherited from parents, the process needs to be perfect over the long term, otherwise the accumulation of damaging mutations will eventually prevent reproduction and damage survival to cause extinction. The term for such extinction is mutational meltdown – and this has been observed to occur in some lower organisms, especially when mutations are accumulating and the population is reducing. This probably happens in some inbred captive populations such as in zoos, as well as in modern human society.


The term mutation-selection balance refers to the fact that the occurrence of mutations must be balanced by the elimination of mutations: natural selection (including sexual selection – mate choice) must be powerful enough to sieve-out all the deleterious mutations. If natural selection is not strong enough to do this, then mutations will accumulate, brain function will be damaged, and intelligence will decline. 


Each spontaneous mutation has about a fifty-fifty chance of damaging brain function, because the brain depends on a very high proportion of genes to develop normally and make its structural components, its proteins, enzymes, hormones, neurotransmitters and so on. Thus the brain is a large ‘mutational target’ (as Geoffrey Miller has termed it) – and will usually show up, in a quantitative fashion, the amount of mutational damage a person has. In other words, high intelligence requires ‘Good Genes’ – where good genes means a genome low in mutations; conversely a high mutational load will cause low intelligence.


Before the Industrial Revolution, individuals with a higher mutational load, which means a higher load of low-IQ genes (and therefore lower intelligence) had lower-than-average reproductive success due to very high (indeed, probably near total) childhood mortality rates. But since the child mortality rates fell from more than half to about one percent in most of Europe, almost all babies that are born have survived to adulthood, and most of them have reproduced. Therefore, we must assume that there have by now been several generations – in England at least eight generations - of mutation accumulation. And we must also assume that this has had a significant effect in reducing intelligence.


This produces what is truly a ‘dysgenic’ effect on intelligence, since it is not evolved, not adaptive, not a new ability – but instead a lowering of intelligence due to a pathological process; a destruction of adaptive human intelligence caused by an accumulation of damage.   


And although intelligence decline is a sensitive measure of mutation accumulation – it is not the only consequence. Many other human adaptations would be destroyed by mutation accumulation – including evolved human personality types. As well as pulling down human intelligence; mutation accumulation would be expected to destroy the Endogenous personality, to impair human creativity – and would be a further nail in the coffin of genius.



Decline of intelligence due to mutation accumulation


So, the decline of intelligence that has now been measured using reaction times and confirmed with other methods, has been too fast, and gone too far, fully to be accounted for by the mechanism of differences in fertility between most and least intelligent.


To re-emphasize; we have no doubt that this mechanism of differential fertility has had an effect in reducing intelligence over the past two hundred years, but there must be other additional explanations for so great and rapid a decline in intelligence – a decline (we argue) that has been sufficient to all-but eliminate world class geniuses from the European population, and hence the world.


Woodley and Charlton suggest that the main additional mechanism to reduce intelligence may be the generation-by-generation accumulation of deleterious genetic mutations; as a result of the near-elimination of historically high child mortality rates which used-to clear mutations from the gene pool with each generation.[12] 


But after the Industrial Revolution got going, mortality rates declined for the least intelligent along with everyone else; 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 low IQ genes (intelligence-damaging deleterious mutations) with each generation.


In sum, 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. And compared with 150-200 years ago, there is now 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, we think, why average general intelligence has declined so rapidly and so much in England over the past couple of centuries. 



[1] Clark, G. (2007). A Farewell to Alms: A Brief Economic History of the World. Princeton, NJ: Princeton University Press.
[2] See, Dutton, E. (October 2013). So were your ancestors wealthy? Family Tree.
[3] Millard, A. (2010). Probability of descending from Edward III. Durham University.
[4] Lynn, R. (2011). Dysgenics: Genetic Deterioration in Modern Populations. London: Ulster Institute for Social Research.
Charlton, B.G & Woodley, M.A. Objective and direct evidence of ‘dysgenic’ decline in genetic ‘g’ (IQ). Bruce Charlton’s Miscellany blog. posted 28 February 2012; Woodley, M. A., te Nijenhuis, J. & Murphy, R. (2013). Were the Victorians cleverer than us?: The decline in general intelligence estimated from a meta-analysis of the slowing of simple reaction time. Intelligence, 41: 843-850. See also:  Woodley, M. A.; Madison, G. & Charlton, B. (2014). Possible dysgenic trends in simple visual reaction time performance in the Scottish Twenty-07 cohort: a reanalysis of Deary and Der (2005). The Mankind Quarterly, 55: 110-124; Woodley, M. A. & Figueredo, A. J. (2013). Historical Variability in Heritable General Intelligence. Buckingham: University of Buckingham Press.
[6] For example, they have found a secular decline in vocabulary, large vocabulary being a proxy for intelligence. Woodley of Menie, M.A.; Fernandes, H.; Figueredo, A.J. & Meisenberg, G. (2015). By their words ye shall know them: Evidence of genetic selection against general intelligence and concurrent environmental enrichment in vocabulary usage since the mid-19th century. Frontiers in Psychology, 6: 361. They have also noted a decline in colour discrimination, which itself g-loaded. See, Woodley of Menie, M.A., & Fernandes, H.B.F. (2015). Well, color me stupid! Secular declines and a Jensen effect on color acuity - more evidence for the weaker variant of Spearman's other hypothesis. Personality & Individual Differences. In press.
[7] Woodley, M. A. (2014). How fragile is our intellect? Estimating losses in general intelligence due to both selection and mutation accumulation. Personality and Individual Differences, 75: 80-84.
[8] Flynn, J. R. (2012). Are We Getting Smarter? Rising IQ in the Twenty First Century. Cambridge: Cambridge University Press.
[9] See, Dutton, E. & Lynn, R. (2015). A negative Flynn Effect in France, 1999-2008/9. Intelligence, 51: 67-70.
[10] Flynn, Op. cit. 
[11] In terms of ‘IQ genes’, it has been found that the possession of a particular allele on Chromosome 6 increases IQ by around 4 points. See, Chorley, M. J., M. Seese, M. J. Owen, et al. (1998) A quantitative trait locus associated with cognitive ability in children. Psychological Science, 9: 159-166. 
[12] Hamilton, W. D. (2002). The hospitals are coming. Chapter in Narrow Roads of Gene Land - Volume 2. Oxford, UK: Oxford University Press; Woodley, M. A. (2014). How fragile is our intellect? Estimating losses in general intelligence due to both selection and mutation accumulation. Personality and Individual Differences, 75: 80-84.