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.
https://community.dur.ac.uk/a.r.millard/genealogy/EdwardIIIDescent.php. 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. http://charltonteaching.blogspot.co.uk/2012/02/convincing-objective-and-direct.html
– 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.
