Monday 6 August 2012

Pioneering studies of IQ - and the suppression of intelligence research

Tuesday, 30 September 2008

Pioneering studies of IQ by G.H. Thomson and J.F. Duff – An example of established knowledge subsequently ‘hidden in plain sight’

Bruce G. Charlton. Medical Hypotheses. 2008; 71: 625-628

Summary

Perhaps the earliest authoritative measurement of a social class gradient in IQ, with a stratification of occupations among the parents of children with different IQs, is seen in two fascinating papers published in 1923 and 1929 in the British Journal of Psychology. The authors were GH Thomson and JF Duff (both of whom were later knighted) and the papers’ main findings were confirmed by later researchers. Results of an intelligence test administered to 13419 children aged 11–12 were analyzed according to parent’s occupation. The average children’s IQ at extremes of social class among their parents included clergymen-121, teachers-116 and bankers and managers-112 at the upper end; while at the lower end there were ‘cripples and invalids’-94, cattlemen-93, hawkers and chimneysweeps-91, and the ‘insane, criminal’-88. More than 100 specific categories of parental occupations were then combined into 13 social classes, with their children’s average IQ as follows: Professional-112; Managers-110; Higher Commercial-109; Army, Navy, Police, Postmen-106; Shopkeeping-105; Engineers [ie. apprenticed craftsmen, such as mining engineers]-103; Foremen-103; Building trades-102; Metal workers, shipbuilders-101; Miscellaneous industrial workers-101; Miners and quarrymen-98; Agriculture-98; Labourers-96. A follow-up study compared an ‘intelligent’ group (IQ 136 plus) with a matched IQ 95–105 ‘control’ group. IQ testing at age 11–12 was predictive of teacher’s reports of higher levels of intelligence and health at age 16; and better performance in official examinations. The occupations of fathers, grandfathers and uncles were consistent with occupation being indicative of ‘an inherited quality’ (i.e. IQ) and there was regression from parents to grandparents and uncles among the ’intelligent’ but not among controls. Other findings included a wider variance in intelligence among boys than girls, and descriptions of the predictive value of IQ in estimating future education, examinations and health. Although the distribution, heredity and predictive value of childhood IQ measurements was once quite widely understood, for the last few decades IQ research has been regarded as morally-suspect and IQ scientists subjected to vilification, persecution and sanctions. Ignorance and misunderstanding of IQ is the norm among intellectual elites in schools, universities, the media, politics and public administration. Consequently IQ research is actively-shunned, and has near-zero influence on public policies. Since this area of science has been so comprehensively ‘disappeared’ from public consciousness as a result of socio-political pressure; it seems probable that other similarly solid and vital domains of scientific knowledge may also be ‘hidden in plain sight’.

***

Perhaps the earliest authoritative measurement of a social class gradient among the parents of children with different IQs is seen in two fascinating papers published in 1923 [1] and 1929 [2] in the British Journal of Psychology.

The authors were Godfrey H Thomson and James Fitzjames Duff – both of whom were later knighted. The research was done from Armstrong College of Durham University in the city of Newcastle upon Tyne, England – Armstrong College later became a part of King’s College which then became the independent University of Newcastle [3]. Thomson was Professor of Education in Newcastle, then later moved to the Chair of Education in Edinburgh from where he provided ‘Eleven plus’ examinations for much of Britain [4] and [5]. Duff moved to Manchester University and ultimately returned to Durham to become Warden (equivalent to Vice Chancellor – the senior administrative position in UK universities) of the collegiate Durham division of the university [3] and [6]. Duff is credited with initiating Durham’s ascent from a tiny theological and teaching college to become one of the premier UK universities [3].

As well as the intrinsic fascination of these trail-blazing researches, the two papers provoke reflection on the effect on science of changes in the national socio-political ethos. The fate of Sir Godfrey and Sir James’s papers provides an example of how once widely-accepted knowledge, generated by very senior and prestigious establishment figures, can later become generally disregarded or even denied, despite abundant scientific confirmation and elaboration by later researchers.

It seems that even in modern times, and in a liberal democratic society such as the UK where information is freely and easily accessible, scientific knowledge can apparently be ‘disappeared’ when it comes into conflict with the dominant socio-political agenda: can become, as it were, ‘hidden in plain sight’.


The social distribution of intelligence in Northumberland

The 1923 Duff and Thomson study began when an intelligence test was administered on February 24 1922, to all children aged 11 and 12 at state elementary schools in Northumberland excluding Newcastle and Tynemouth; yielding an enormous sample of 13419 children (6930 boys; 6695 girls). Further information on parental occupation was provided by teachers. The children’s IQ was then tabulated according to their parent’s (implicitly father’s) occupation.

Average IQ was 99.6, 877 children had an IQ of 120 plus and 1337 had an IQ less than 80. Boys exhibited a slightly larger apparent standard deviation than girls (no specific numbers were given by the authors), with a greater proportion of the most intelligent children being boys (IQ 130-9 - 80 boys, 49 girls; IQ above 140 – 12 boys, 4 girls) and also a greater proportion of the least intelligent being boys (IQ below 80 – 715 boys, 622 girls).

Although private schools were not sampled, and consequently there were no children with parents of the very highest social classes, nonetheless the parents social classes ranged widely from clergymen, lawyers, teachers, chemists, bankers and managers at the top; to farm labourers, brewery and mineral-water workers, ‘cripples and invalids’, cattlemen, ‘hawkers and chimneysweeps’ and the ‘insane, criminal’ at the bottom.

The average IQ (rounded to the nearest integer) of the children of some well-represented extremes of social class among the parents was clergymen-121, teachers-116 and bankers and managers-112 at the upper end; while at the lower end there were farm labourers-94; brewery workers-94; ‘cripples and invalids’-94, cattlemen-93, hawkers and chimneysweeps-91, and the ‘insane, criminal’-88. In between, by far the largest number of parents was the 5659 coal miners (average IQ of children-98).

One surprising statistic is that the children of n = 16 ‘Doctors, dentists, vets’ [i.e. veterinarians] had a reported average IQ of only 102 – the same as builders and below plumbers! My guess is that (in this particular time and place) most rural or semi-rural resident ’doctors, dentists, vets’ who sent their children to state schools were not college-educated, but had instead been trained by apprenticeship: more like craftsmen than professionals.

More than 100 specific categories of parental occupations were then combined into 13 social classes, with their children’s average IQ as follows: Professional-112; Managers-110; Higher Commercial-109; Army, Navy, Police, Postmen-106; Shopkeeping-105; Engineers [ie. apprenticed craftsmen, such as mining engineers]-103; Foremen-103; Building trades-102; Metal workers, shipbuilders-101; Miscellaneous industrial workers-101; Miners and quarrymen-98; Agriculture-98; Low grade occupations, labourers-96.

Finally the parents occupations were divided into two simple divisions of ‘brain work’ having an average IQ of 107 versus ‘hand work’ having an average of IQ 99.

Duff and Thomson also comment that although there are striking stepwise average differences in IQ by parental social class, the parental occupation according to the 13 social classes only predicted child’s IQ with a Pearson correlation of 0.28. In other words, each social class contained a range of IQs, with considerable overlapping between classes.


Following-up the children of highest intelligence

The 1929 Duff paper was a follow-up of the highest-IQ children (IQ 136 plus) which were termed the ‘intelligent’ group with an IQ 95-105 ‘control’ group matched from the same schools. Parents and teachers were asked for information, but the replies were incomplete; and data was obtained on only 64 ‘intelligent’ and 28 ‘control’ subjects.

It was found that IQ testing at age 11–12 was predictive of teacher’s reports of higher levels of intelligence and health at age 16; higher career aspirations; and also better performance in the Durham School Certificate examinations, especially the highest levels of examination results.

Occupations of fathers, grandfathers and uncles were surveyed in terms of their social class. The most striking analysis was in terms of the percentage of fathers that were at the level of skilled labourer or higher: there were 64% of fathers in the intelligent group at this level and 28% of fathers in the control group. By comparison among the intelligent group 49% of grandfathers and 52% of uncles were at this level; while in the control group 33% of grandfathers and 40% of uncles.

Duff commented that this pattern was consistent with occupation being indicative of ‘an inherited quality’ with a regression from parents to grandparents and uncles among the intelligent – but no consistent regression among the average control group when the data as a whole is analyzed. He concludes: “Intelligence is not the sole factor that determines occupation; but that it is an important factor cannot be doubted.”


Science then and now

Reading the articles after eighty years there are striking differences when compared with modern practice. Most surprisingly there is no Reference section and only five footnotes (in the earliest paper). My impression is that this paucity is partly due to embryonic nature of the field – with very little prior relevant published research; and partly due to the fact that the authors were writing for a small, familiar audience of scientific peers, who did not need to have spelled-out precisely how this piece of research fitted into the development of the subject. In those days background assumptions were often simply taken for granted, rather than referenced. The methodology was, by modern standards, skimpy – supplemented with an offer to supply extra detail to ‘anyone interested’. The general tone of these papers is therefore somewhat like a letter addressed to other members of an exclusive club.

At this early stage in the science, researchers were almost simultaneously devising methods and applying them to gather data. The social class categories used were generated specifically for this paper, and apparently on ‘commonsense’ grounds – since no detail is given about the principles underlying the classification.

Yet, for all the apparent arbitrariness and subjectivism of style (as is seems to us nowadays), and the incompleteness of the follow-up study, these two papers seem to have been both prescient and essentially correct (as judged by subsequent knowledge) and their main findings have been substantially replicated or expanded:

1. It has been confirmed that men have a wider variance in intelligence than women – with a greater proportion of both high-scorers and low-scorers [7].

2. Although Duff and Thomson’s studies did not directly measure parental IQ, the authors’ assumption was that occupations reflected IQ. Many later studies have confirmed that there is a significant social class/occupational gradient in average IQ – the size of this gradient depending upon the degree of specificity with which social class is defined e.g. [8], [9], [10] and [11].

3. Thomson and Duff’s 1923 analysis demonstrated what later epidemiologists of the 1990s re-discovered for health and social class [12] – that socio-economic differences are not absolute or fixed in size; rather the gradient is much greater when socio-economic position is analyzed precisely than when measured imprecisely. Here there was a gradient of 33 IQ points from 121 down to 88 when 100-plus specific occupations are used; a gradient of 16 IQ points from 112 down to 96 when specific occupations are collapsed into 13 groups; and a gradient of only 8 IQ points from 107 down to 99 for the dual categories of head-work versus hand-work.

4. Childhood IQ has been confirmed to be predictive of future educational (and also occupational) attainments e.g. [13], [14], [15] and [16].

5. It has been confirmed that childhood measurements of IQ are predictive of subsequent health e.g. [9], [17] and [18].

6. IQ is confirmed to be substantially heritable, and exhibits regression to the mean consistent with the degree of heritability e.g. [13], [14] and [15].

The contemporary invisibility of IQ research
Duff and Thomson were both knighted, ending their careers as highly respected and influential figures in the UK educational establishment. The main findings of these papers from the 1920s have been amply replicated in the modern consensus on IQ [e.g. [20] and see above]. And the basic understanding of the distribution, heredity and predictive value of childhood IQ measurements which they pioneered was widely appreciated.

However, for the last few decades IQ research has generally been regarded as a morally-suspect activity and the candid discussion of IQ is taboo among the intellectual elites in schools, universities, the media, politics and public administration. IQ scientists have been – and still are – subjected to vilification, persecution and sanctions [15], [19], [21], [22] and [23]. This 80 year old knowledge is typically regarded by mainstream public discourse as surprising, shocking and controversial – or the facts may even be denied outright.

Consequently, despite its remarkable prescience and importance, this pioneering work on IQ, plus three generations of supporting scientific literature, is ignored or actively-shunned – and has near-zero influence on modern public policies.

Since this area of science has so been comprehensively ‘disappeared’ from public consciousness in the face of socio-political pressure, it seems probable that other similarly solid and vital domains of scientific knowledge may also be hidden in plain sight.


References

[1] J.F. Duff and G.H. Thomson, The social and geographical distribution of intelligence in Northumberland, Brit J Psychol 14 (1923), pp. 193–198.


[2] J.F. Duff, Children of high intelligence: a following-up enquiry, Brit J Psychol 29 (1929), pp. 413–438.


[3] E.M. Bettenson, The University of Newcastle upon Tyne: a historical introduction, 1834–1971, University of Newcastle upon Tyne, Newcastle upon Tyne, UK (1971).


[4] G.H. Thomson, Education of an Englishman, Moray House, University of Edinburgh, Edinburgh (1968).


[5] Wikipedia. Godfrey Thomson. http://en.wikipedia.org/wiki/Godfrey_Thomson; 2008 [accessed 10.07.2008].


[6] Sir James Fitzjames Duff. thePeerage.com: A genealogical survey of the peerage of Britain as well as the royal families of Europe. http://thepeerage.com/p18060.htm; 2008 [accessed 10.07.2008].


[7] L.V. Hedges and A. Nowell, Sex differences in mental test scores, variability, and numbers of high-scoring individuals, Science 269 (1995), pp. 41–45.

[8] M. Argyle, The psychology of social class, Routledge, London (1994).


[9] C.L. Hart, I.J. Deary, M.D. Taylor, P.L. MacKinnon, G. Davey Smith and L.J. Whalley et al., Scottish mental health survey 1932 linked to the Midspan Studies: a prospective investigation of childhood intelligence and future health, Public Health 117 (2003), pp. 187–195.


[10] D. Nettle, Intelligence and class mobility in the British population, Brit J Psychol 94 (2003), pp. 551–561.

[11] R. Lynn and T. Vanhanen, IQ and global inequality, Washington Summit, Augusta, Georgia, USA (2006).


[12] G.D. Smith, M.J. Shipley and G. Rose, Magnitude and causes of socioeconomic differentials in mortality: further evidence from the Whitehall Study, J Epidemiol Commun Health 44 (1990), pp. 265–270.

[13] L.M. Terman and L.H. Oden, The gifted child grows up: Volume 4 (Twenty five years follow up of a superior group), Stanford University Press, Stanford, CA, USA (1959).


[14] A.R. Jensen, The g factor Praeger: the science of mental ability, Westport, CT, USA (1998) p. 15.


[15] R.J. Herrnstein and C. Murray, The bell curve, Forbes, New York (1994).


[16] G. Park, D. Lubinski and C.P. Benbow, Contrasting intellectual patterns predict creativity in the arts and sciences, Psychol Sci 18 (2007), pp. 948–952.

[17] G.D. Batty, I.J. Deary and G.S. Gottfredson, Premorbid (early life) IQ and later mortality risk: systematic review, Annals Epidemiol 17 (2007), pp. 278–288.

[18] L.S. Gottfredson, Intelligence: is it the epidemiologists elusive ‘fundamental cause’ of social class inequalities in health?, J Personality Social Psychol 86 (2004), pp. 174–199.


[19] H.J. Eysenck, Rebel with a cause: autobiography of Hans Eysenck, W.H. Allen, London (1990).


[20] U. Neisser et al., Intelligence: knowns and unknowns, Amer Psychol 51 (1996), pp. 77–101.

[21] I.J. Deary, Intelligence: a very short introduction, Oxford University Press, Oxford (2001).


[22] L.S. Gottfredson, Applying double-standards to ‘divisive’ ideas, Perspect Psychol Sci 2 (2007), pp. 216–220.


[23] J. Malloy, James Watson tells the inconvenient truth: faces the consequences, Med Hypotheses 70 (2008), pp. 1081–1091.
 
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Do elite US colleges choose personality over IQ?

Wednesday, 27 May 2009

Sex ratios in the most-selective elite US undergraduate colleges and universities are consistent with the hypothesis that modern educational systems increasingly select for conscientious personality compared with intelligence

Medical Hypotheses. 2009; 73: 127-129

Bruce G. Charlton, , Editor-in-Chief, Medical Hypotheses

Professor of Theoretical Medicine University of Buckingham, UK


Summary

The main predictors of examination results and educational achievement in modern societies are intelligence (IQ – or general factor ‘g’ intelligence) and the personality trait termed ‘Conscientiousness’ (C). I have previously argued that increased use of continuous assessment (e.g. course work rather than timed and supervised examinations) and increased duration of the educational process implies that modern educational systems have become increasingly selective for the personality trait of Conscientiousness and consequently less selective for IQ. I have tested this prediction (in a preliminary fashion) by looking at the sex ratios in the most selective elite US universities. My two main assumptions are: (1) that a greater proportion of individuals with very high intelligence are men than women, and (2) that women are more conscientious than men. To estimate the proportion of men and women expected at highly-selective schools, I performed demonstration calculations based on three plausible estimates of male and female IQ averages and standard deviations. The expected percentage of men at elite undergraduate colleges (selecting students with IQ above 130 – i.e. in the top 2% of the population) were 66%, 61% and 74%. When these estimates were compared with the sex ratios at 33 elite colleges and universities, only two technical institutes had more than 60% men. Elite US colleges and universities therefore seem to be selecting primarily on the basis of something other than IQ – probably conscientiousness. There is a ‘missing population’ of very high IQ men who are not being admitted to the most selective and prestigious undergraduate schools, probably because their high school educational qualifications and evaluations are too low. This analysis is therefore consistent with the hypothesis that modern educational systems tend to select more strongly for Conscientiousness than for IQ. The implication is that modern undergraduates at the most-selective US schools are not primarily an intelligence elite, as commonly assumed, but instead an elite for Conscientious personality.

***

IQ and C predict educational attainment

Evidence from a range of studies suggests that the main determinants of examination results and educational achievement in modern societies are intelligence (IQ – or general factor ‘g’ intelligence) and the personality trait variously described as ‘Conscientiousness’, self-discipline, perseverance or something similar (see Ref. [1] for review). IQ is (roughly speaking) that cognitive ability which enables people to think abstractly and learn quickly; Conscientiousness (broadly synonymous with perseverance or self-discipline) is the personality trait that enables people to work hard for long periods at dull tasks, to think before acting and to take a long term view.

I have previously argued that a combination of the increased use of continuous assessment (e.g. course work rather than timed and supervised examinations) and the increased duration of the educational process implies that modern educational systems have become increasingly selective for Conscientiousness (C) [1]. My argument is that, because C is not closely correlated with intelligence, then demand for increasing levels of C will inevitably lead to reduced selectivity for intelligence. Ever-higher levels of C will usually only be attainable by progressively relaxing standards for IQ.

If this reasoning is correct, it would be predicted that the most highly-educated and most educationally-selected people would be characterized more by their extremely-high Conscientiousness than by their extremely-high intelligence. More precisely, there would be a trend for educational selectivity to increase average ranking for C more than the average ranking for IQ.

Sex ratios at the most-selective US colleges and universities

I have tested this prediction (in a preliminary fashion) by looking at the sex ratios in the most selective elite US universities. My two main assumptions are: (1) that a greater proportion of individuals with very high intelligence are men than women, and (2) that women are more Conscientious than men.

Most IQ studies find a greater proportion of men than women among very high IQ adults. For example, the US national 2008 SAT results show a higher proportion of men than women scoring in the highest band for the most g-loaded sections (Critical Reading and Mathematics) [2]. This male domination of the highest scorers in IQ testing is consistent with IQ surveys going back over many decades [3] and studies of creative and intellectual genius [4] and [5]. I will therefore assume a higher proportion of men than women at levels of very high IQ. In contrast, current evidence suggests that Conscientiousness, especially the academically-relevant sub-trait of self-discipline, is higher in women than men [1] and [6].

On this basis alone, without any calculations, and if we assume equal proportions of men and women in the US population, no important differences in sex applications to college and a sex-blind policy of selectivity; it would be expected that there was a greater proportion of men than women at highly-selective elite colleges, and that the more selective the colleges the greater would be the expected proportion of men. By contrast, if there was an equal or greater-proportion of women at elite colleges then this would be consistent with C being more rigorously selected-for than IQ.

Predicted proportion of men at elite schools – on the basis of IQ
To make this exercise more precise, it is helpful to estimate the proportion of men and women which would be expected at highly-selective schools.

I have focused on predictions related to IQ because much more is known about IQ than C, and C cannot yet be quantified as precisely as IQ. An IQ of 130 is used as a plausible threshold for selectivity at elite universities: this is approximately two standard deviations above the average IQ and includes the top 2% of the population.

However, the magnitude of the expected sex differential is relevant, since if the expected sex differential was small it could easily be swamped by statistical noise, or by other relevant variables. The magnitude of the predicted sex differential depends on the assumptions of male and female IQ average differences and distributions.

There are three mainstream explanations of why there are more men than women among the population of very high IQ people.

1. Men have a higher average IQ than women, but the same variance. For instance, Lynn suggests that men have an average IQ about 4–5 points higher than women with the sexes having the same standard deviation (conventionally 15 IQ points) [7].

2. Men and women have a near-identical average IQ, but men have a greater variance in IQ than women (higher standard deviation). For instance Hedges and Nowell present Project Talent data that suggest men and women have the same IQ, but men have a standard deviation around 10% greater than women [8].

3. Men have both a higher average IQ and larger standard deviation of IQ than women. For instance, Hans Eysenck accepted Lynn’s estimate of about 4 IQ points difference in average IQ and also assumed that women had a standard deviation of 14 compared with the male standard deviation of 15 [4].

We can use these ball-park estimates as the basis for calculating approximate expected sex ratios at elite US undergraduate schools.

Therefore on the basis of IQ considered alone (Table 1), it would be expected to find a considerably greater proportion of men than women at elite undergraduate colleges. The prediction is that the most selective institutions would admit at least 60% men (and probably a higher proportion).

Table 1.

Demonstration calculations of the effect of plausible male versus female IQ averages and standard deviations on the proportion of men and women at elite colleges with threshold IQ of 130 for a US population with average mean IQ 100 (SD 15). Key: SD = standard deviation; M = men; W = women; av. = average.

Assumption Mean IQ (SD) Percentage IQ > 130 Predicted % men at elite college

M higher av. IQ than W: M 102 (15) 3.1% c. 66% W 98 (15) 1.6%

M > SD than W: M 100 (15.75) 2.8% c. 61% W 100 (14.25) 1.8%

Men higher av. IQ: M 102 (15) 3.1% c. 74% & >SD than W W 98 (14) 1.1%





So, any sex ratio less than this would imply that other qualities than IQ are actually determining selection; or alternatively that one or more of the assumptions are incorrect – for example there might be sexually differential patterns of application or selection.

Using the About.com: College Admissions web pages (http://collegeapps.about.com/ – up to March 2009) I generated a list of sex ratios (the percentage of men) at three categories of elite US colleges and universities: (1) Ivy League plus several comparably-selective private research universities; (2) The top 10 public universities; (3) The top 10 liberal arts colleges.

From Table 2 it is clear that almost all these 33 elite US undergraduate schools select approximately equal proportions of men and women with only two technical universities (Caltech and Georgia Tech) having a male sex ratio greater than 60%. If the assumptions hold, then the implication is that elite colleges seem to be selecting mainly on the basis of something other than IQ – probably Conscientiousness.


--------------------------------------------------------------------------------


Table 2.

Sex ratios at undergraduate level – percentage of men. Colleges with more than 60% men are marked with an asterisk.

Ivy League and similar private research universities

Brown 48%
Columbia 51%
Cornell 51%
Dartmouth 50%
Harvard 47%
Pennsylvania 49%
Princeton 53%
Yale 51%
Stanford 52%
Duke 51%
Chicago 50%
MIT 56%
*Caltech 71%


Top 10 public universities

Berkeley 46%
*Georgia Tech 71%
UCLA 45%
UCSD 48%
U Michigan 50%
UNC Chapel Hill 41%
Urbana Champaign 53%
U Virginia 45%
William and Mary 46%


Top 10 liberal arts colleges: (NB: Wellesley is essentially a women’s college)

Amherst 50%
Carleton 47%
Claremont–McKenna 54%
Grinnell 46%
Haverford 46%
Middlebury 48%
Pomona 51%
Reed 45%
Swarthmore 48%
Wellesley 2%
Williams 49%





It seems that there is a ‘missing population’ of very high IQ men who are not getting admitted to the most selective and prestigious undergraduate schools. The likely reason is that their high school educational qualifications and evaluations are too low, since these men probably lack the very high levels of C required to negotiate modern educational systems and achieve the very highest level of success (in the top 2% of attainment). These men with very high IQ but only moderate C are presumably attending a wide spectrum of less-selective and lower-ranked undergraduate schools, or (less plausibly) dropping-out of the educational system altogether.

A further factor may be that colleges are also selecting on the basis of high sociability, which can be measured as the personality trait of Agreeableness [1]. Agreeableness is higher in women. High Agreeableness would not be expected to lead to better educational performance, but instead would be likely to enhance an applicant’s resume with a record of participation in societies, charities and sports together with general friendliness and club-ability – these factors may well be counted in favour of a student and would also tend differentially to favour the admission of women.

My hypothesis [1] that Conscientiousness (and perhaps Agreeableness) count for more than IQ at the level of elite college admissions receives some support from this data set, and could be tested further by longitudinal studies which measured IQ and personality during childhood (rankings of IQ and personality tend to be stable throughout life), and followed-up students through the school and college examination and selection process to observe the interaction between these variables.

The implication is that modern undergraduates at the most selective US universities are not so much an elite for intelligence, as is commonly assumed, but more of an elite in terms of traits such as perseverance and self-discipline.

Acknowledgement

My thanks to Richard Lynn for his help and advice in preparing this editorial.

References

[1] B.G. Charlton, Why are modern scientists so dull? How science selects for perseverance and sociability at the expense of intelligence and creativity, Med Hypotheses 72 (2009), pp. 237–243.


[2] College Board SAT, 2008 College Bound Seniors. ; [accessed 19.03.09].


[3] B.G. Charlton, Pioneering studies of IQ by G.H. Thomson and J.F. Duff – an example of established knowledge subsequently ‘hidden in plain sight’, Med Hypotheses 71 (2008), pp. 625–628.


[4] H.J. Eysenck, Genius: the natural history of creativity, Cambridge University Press, Cambridge, UK (1995).


[5] C. Murray, Human accomplishment. The pursuit of excellence in the arts and sciences 800 BC to 1950, HarperCollins, New York (2003).


[6] A.L. Duckworth and M.E.P. Seligman, Self-discipline gives girls the edge, J Educ Psychol 98 (2006), pp. 198–208.


[7] R. Lynn and P. Irwing, Sex differences on the progressive matrices: a meta analysis, Intelligence 32 (2004), pp. 481–498.


[8] L.V. Hedges and A. Nowell, Sex differences in mental test scores, variability, and numbers of high-scoring individuals, Science 269 (1995), pp. 41–45.
 
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Replacing education with psychometrics

Saturday, 11 July 2009

Bruce G Charlton

Replacing education with psychometrics: How learning about IQ almost-completely changed my mind about education.

Medical Hypotheses. 2009; 73: 273-277

***

Summary

I myself am a prime example of the way in which ignorance of IQ leads to a distorted understanding of education (and many other matters). I have been writing on the subject of education – especially higher education, science and medical education – for about 20 years, but now believe that many of my earlier ideas were wrong for the simple reason that I did not know about IQ. Since discovering the basic facts about IQ, several of my convictions have undergone a U-turn. Just how radically my ideas were changed has been brought home by two recent books: Real Education by Charles Murray and Spent by Geoffrey Miller. Since IQ and personality are substantially hereditary and rankings (although not absolute levels) are highly stable throughout a persons adult life, this implies that differential educational attainment within a society is mostly determined by heredity and therefore not by differences in educational experience. This implies that education is about selection more than enhancement, and educational qualifications mainly serve to ‘signal’ or quantify a person’s hereditary attributes. So education mostly functions as an extremely slow, inefficient and imprecise form of psychometric testing. It would therefore be easy to construct a modern educational system that was both more efficient and more effective than the current one. I now advocate a substantial reduction in the average amount of formal education and the proportion of the population attending higher education institutions. At the age of about sixteen each person could leave school with a set of knowledge-based examination results demonstrating their level of competence in a core knowledge curriculum; and with usefully precise and valid psychometric measurements of their general intelligence and personality (especially their age ranked degree of Conscientiousness). However, such change would result in a massive down-sizing of the educational system and this is a key underlying reason why IQ has become a taboo subject. Miller suggests that academics at the most expensive, elite, intelligence-screening universities tend to be sceptical of psychometric testing; precisely because they do not want to be undercut by cheaper, faster, more-reliable IQ and personality evaluations.

***

Introduction

It was only in early 2007 that I began properly to engage, for the first time in my professional career, with the literature on IQ. Surprisingly, this engagement had been stimulated by a book of economic history. And learning the basic facts about IQ rapidly changed my views on many things, none more so than education.

Just how radically my ideas about education were changed by learning about IQ has been brought home by two recent books: Real Education By Charles Murray [1] and Spent by Geoffrey Miller [2]. In line with analyses of Murray and Miller, I would now repudiate many of my previous opinions on the subject, and advocate a substantial reduction in the average amount of formal education and the proportion of the population attending higher education. In general, I now believe that many years of formal education can and should be substantially (but not entirely!) replaced with ‘psychometric’ measures of intelligence and personality as a basis for evaluating career potential.

In this article I use my own experience as a case study of the potentially-disruptive influence of psychometric knowledge, and discuss further the reasons why basic IQ facts have been so effectively concealed, confused and denied by mainstream elite intellectual opinion in the UK and USA.

The importance of IQ

I have been writing on the subject of education for about 20 years (especially on higher education, science and medical education), but I now believe that much of what I wrote was wrong for the simple reason that I did not know about IQ. Personality traits are important in a similar way to IQ, however personality measurement is currently less reliable and valid than IQ testing, and less-well quantified.

In the early 2000s I argued that modern formal education should be directed primarily at inculcating the ability to think abstractly and systematically [3] and that therefore the structure and not the specific content of education was critical (although ‘science’ – broadly defined – was likely to be the best basis for this type of education [4]). I suggested that higher education should be regarded as a non-vocational process, in which most degrees are modular, and modules were optional and multi-disciplinary, so that each student would assemble their own degree program in a minimally-constrained, ‘pick and mix’ fashion [5]. I also contended that since abstract systemizing cognition was so essential to modernizing societies, a major aim of social reform should be to include as many people as possible in formal education for as long as possible [6].

All of these views I would now regard as mistaken – and the reason is mostly my new understanding of IQ [7], [8], [9] and [10]. Miller concisely explains the basic facts about IQ:

“General intelligence (a.k.a. IQ, general cognitive ability, the g factor) is a way of quantifying intelligence’s variability among people. It is the best-established, most predictive, most heritable mental trait ever discovered in psychology. Whether measured with formal IQ tests or assessed through informal conversations and observations, intelligence predicts objective performance and learning ability across all important life-domains that show reliable individual differences” [2].

The crux of my new understanding is that IQ, and to a lesser but important extent personality traits, are highly predictive of educational attainment. This is a very old finding, and scientifically uncontroversial – but the implications have still not been acknowledged.

Since IQ is very substantially inherited with a true heritability of about 80% [7], [8], [9] and [10] and personality too has about a 50% heritability [11] and [12]; and since both IQ and personality rankings are highly stable throughout a persons adult life [13] (it is, for example, very difficult for educational interventions to have any significant and lasting effect on underlying IQ [1]) – then this implies that differential educational attainment within societies is mostly determined by heredity and therefore not by differences in educational experience.

(The other big factor which influences attainment is of course the large element of chance – which affects individuals unpredictably. However, chance is not completely random, in the sense that many outcomes such as accidental injuries and a range of illnesses are also correlated with IQ and personality [14]).

When full account has been taken of IQ and personality (and the measured effects of IQ and personality have been increased to take account of the inevitable imprecision of IQ measurements and the even greater difficulties of determining personality), and when the presumed effects of chance have also been subtracted – then there is not much variation of outcomes left-over within which educational differences could have an effect. Of course there will be some systemic effect of educational differences, but the effect is likely to be very much smaller than generally assumed, and even the direction of the education effect may be hard to detect when other more powerful factors are operative [1].

I found the fact that differences in educational attainment within a society are mostly due to heredity to be a stunning conclusion, which effectively demolished most of what I believed about education. My understanding of what education was doing was radically reshaped, and my beliefs about the justifiable duration and proper focus of the system of formal education were transformed. I began to realize that the educational system in modern societies was operating under false pretences. It seems that current educational systems are barely ‘fit for purpose’ and (lacking a proper understanding of IQ) are in many instances progressively getting worse rather than better.

In sum, education is more about selection than enhancement, and educational qualifications mostly serve to ‘signal’ or quantify a person’s hereditary attributes [15] – especially IQ and personality. Differential educational experience does not seem to have much of a systemic effect on people’s ability to think or work.

To put it another way – education mostly functions as an extremely slow, inefficient and imprecise form of psychometric testing. And because this fact is poorly understood, those aspects of modern education which are not psychometric are consequently neglected and misdirected.

Policy implications of psychometrics

If psychometric measures of IQ and personality were available, then it would be easy to construct a modern educational system that was both more efficient and more effective than the current one. However, such change would result in a massive down-sizing of the educational system – with substantial and permanent loss of jobs and status for educational professionals of all types including teachers, professors, administrators and managers.

According to Geoffrey Miller’s analysis [2], this impact on educational professionals is likely to be a key underlying reason why IQ has become a taboo subject, and why the basic facts of IQ have been so effectively obfuscated. Miller notes that it is the ultra-elite, most-selective and heavily research-oriented universities which are the focus of IQ resistance. At the same time more functionally-orientated institutions, such as the United States military, have for many decades quietly been using IQ as a tool to assist with selection and training allocations [16].

“Is it an accident that researchers at the most expensive, elite, IQ-screening universities tend to be most sceptical of IQ tests? I think not. Universities offer a costly, slow, unreliable intelligence-indicating product that competes directly with cheap, fast, more-reliable IQ tests. (…) Harvard and Yale sell nicely printed sheets of paper called degrees that cost about $160,000 (…). To obtain the degree, one must demonstrate a decent level of Conscientiousness, emotional stability, and openness in one’s coursework, but above all, one must have the intelligence to get admitted, based on SAT scores and high school grades. Thus the Harvard degree is basically an IQ guarantee”.

“Elite universities do not want to be undercut by competitors. They do not want their expensive IQ-warranties to suffer competition from cheap, fast IQ tests which would commodify the intelligence-display market and drive down costs. Therefore, elite universities have a hypocritical, love-hate relationship with intelligence tests”.

The vulnerability of the elite institutions to IQ knowledge is because most of the assumed advantages of an expensive elite education can be ascribed to their historic ability to select the top stratum of IQ (and also the most desirable personality types): given the stability and predictive power of these traits the elite students are therefore pre-determined to be (on average) highly successful.

Consequently the most elite institutions and their graduates have in the past few decades, both via academic publications and in the mass media, thoroughly obscured the basic and validated facts about IQ. We now have a situation where the high predictive powers of IQ and personality and the stable and hereditary nature of these traits are routinely concealed, confused or (in extremis) explicitly denied by some of the most prestigious and best-educated members of modern society [17].


Four mistaken beliefs resulting from my lack of IQ knowledge

I will summarize under four heading my main pre-IQ errors regarding education.

Mistaken belief number 1: Modern formal education should be directed primarily at inculcating the ability to think abstractly and systematically [3].

Revision: Modern formal education should be directed primarily at inculcating specific knowledge content.

Abstract systematic thinking is exceptionally important in modern societies. And I used to believe that that abstract systematic thinking was mostly a product of formal education – indeed I regarded this as the main function of formal education [3]. But I now recognize that abstract systematic thinking is pretty close to a definition of IQ; and that strongly IQ related (or heavily ‘g-loaded’) educational outcomes – such as differentials in reading comprehension and mathematical ability – are very difficult/impossible to improve in a real and sustained fashion by educational interventions [1].

In other words, a person’s level of ability to think abstractly and systematically is mostly a biological given – and not a consequence of formal education. The implication is that formal education should not be focusing on trying to do what it cannot do – i.e. enhance IQ. Instead, formal education should focus on educational goals where is can make a difference: i.e. the teaching of specific knowledge [1].

Mistaken belief number 2: Structure not content of formal education is crucial [5].

Revision: Content not structure of education is crucial.

I used to think that it did not matter what subject was studied in formal education, so long as the method of education was one which nurtured abstract systematic thinking [3]. I believed that how we learned was more important than what we learned, because I believed that abstract systematic thinking was a result of formal education – and this cognitive ability was more important than any particular body of information which had been memorized.

This line of reasoning meant that I favoured ‘pick and mix’, wide choice and multi-disciplinary curricula as a method of improving motivation by allowing students to study what most interested them, and giving students practice in learning new material and applying systematic thinking in many knowledge domains [5].

The reason that I believed all this has been summarized by Geoffrey Miller:

“The highly selective credential with little relevant content [such as an elite college degree in any subject] often trumps the less-selective credential with very relevant content. Nor are such preferences irrational. General intelligence is such a powerful predictor of job performance that a content-free IQ guarantee can be much more valuable to an employer or graduate school than a set of rote-learned content with no IQ guarantee” [2].

Since IQ is such a powerful influence on educational (and other) outcomes [18], the value of specific educational content is therefore only apparent when IQ has been controlled-for. Since IQ is routinely ignored or denied, the value of educational content is not apparent in outcomes which are sensitive to differences in general intelligence.

Murray argues that variations in the structure and methods of education are not able significantly to influence those educational outcomes which are ‘g-loaded’ such as reading comprehension or mathematic reasoning [1]. Numerous attempts to raise real long-term intelligence (rather than merely raising specific test scores) have failed [19]. However, the subject matter being studied will (obviously!) make a big difference to what gets learned. Once we set aside the delusional goal of enhancing IQ by educational reform, then the subject matter – or curriculum – becomes a more important focus than educational structure and methods.

Charles Murray therefore endorses the approach to ‘Cultural Literacy’ or a core knowledge curriculum pioneered by Ed Hirsch (www.coreknowledge.org). This educational philosophy focuses on constructing a comprehensive curriculum of the factual material that people should know, or ‘need to know’. Over the past couple of decades some detailed and well-validated programmes of study have been developed for the USA, and these can be purchased by educational institutions and also home-schooling parents.

It is claimed that such a core knowledge curriculum should enable the student to become a citizen participating at the highest possible social level, and that a shared education in core knowledge should hold society together with a stronger ‘cultural glue’. If such benefits are real, then school, especially between the ages of about 6 and 14, is the best place to follow such a program; since, although the core curriculum involves more than mere memorization, nonetheless memorization is an important element – and young children can memorize information much more easily and lastingly than adults [1].

Understanding IQ has therefore provoked me into a U-turn on the matter of curricula. I now believe that what we learn in formal education is more important than how we learn, because what we learn can have a lasting effect on what we know; while how we learn does not, after all, teach us how to think.

Mistaken belief number 3: A major aim of social reform should be to include as many people as possible in formal education for as long as possible. Ever-more people should get ever-more education for the foreseeable future [6].

Revision: The system of formal education is hugely over-expanded and should be substantially reduced (to considerably less than half its current size). The average person should receive fewer years of formal education, fewer people should attend higher education institutions and do fewer bachelor’s degrees, and those in higher education should – on average – complete the process in fewer years.

The proportion of school leavers entering higher education in the UK has at least trebled over the past three decades, from around 15% to more than 45%. The rationale behind this vast expansion was based on the observation of higher all-round performance among college graduates – better performance in jobs, and also a wide range of other good outcomes including improved health and happiness [6].

However, it turns out that almost all of this differential in behaviours can be explained in terms of selection for (mostly hereditary) intelligence, rather than these improvements being something added to individuals by their educational experience. The main extra information provided by the successful completion of prolonged educational programs (i.e. extra in addition to signalling IQ) is that educational certification provides a broadly-reliable signal of a highly-Conscientious personality.

Miller has neatly described this trait: “Conscientiousness is the Big Five personality trait that includes such characteristics as integrity, reliability, predictability, consistency, and punctuality. It predicts respect for social norms and responsibilities, and the likelihood of fulfilling promises and contracts. A century ago, people would have called it character, principle, honor, or moral fiber. (…) Conscientiousness is lower on average in juveniles, and it matures slowly with age” [2].

Other attributes of a highly-Conscientious personality are self-discipline, perseverance and long-termism [20].

But a person’s degree of Conscientiousness is not a product of their educational experience; rather it is a mostly-inherited psychological attribute which develops throughout life, the relative (or differential) possession of which is stable throughout life [13]. In other words, Conscientiousness is (mostly) an innate ability in a similar sense to intelligence – and similarly difficult to influence by educational means.

It turns out that modern formal education is mainly signalling [15], or providing indirect evidence about, a person’s IQ and personality abilities which they have mostly inherited [1] and [2]. This means that imposing an ever-increasing number of years of formal education for an ever-increasing proportion of the population is ever-increasingly inefficient – and is wasting years of people’s lives, wasting vast amounts of money on the education provision, and imposing huge economic and social ‘opportunity costs’ by forcing people to remain in formal education when their time would often be better spent doing something else (for example something economically-productive or something more personally-fulfilling).

Mistaken belief number 4: Higher education should be regarded as a general, non-vocational process, in which most degrees are modular and multi-disciplinary; and where specialization or vocational preparation should be a relatively brief and ‘last-minute’ training at the end of a long process of education [3], [5] and [6].

Revision: The period of general education should not extend much beyond about 16 (the approximate age of IQ maturity), and this general education should be focused on the basic skills of literacy and numeracy together with a core knowledge curriculum.

At the age of about 16 each person could potentially leave school with a set of knowledge-based examination results demonstrating their level of competence in a core knowledge curriculum; and with usefully precise and valid psychometric measurements of their general intelligence and personality (especially their age ranked degree of Conscientiousness). The combination of psychometric measures of IQ and Conscientiousness would serve the same kind of function as educational evaluations do at present, providing a basis for employment selection or valid predictions to guide the allocation of access to further levels of formal education.

Beyond this I believe that most education should be ‘functional’ or vocational, in the sense of being a relatively-focused training in the knowledge and skills required to do something specific. This functional post-sixteen formal higher education could vary in duration from weeks or months (for semi-skilled jobs) to several years (for access to the starting level of the most highly skilled and knowledge-intensive professions such as architecture, engineering, medicine or law).

But when IQ and personality measurements are available, then the majority of ‘white collar’ jobs – jobs such as management, administration, or school teaching (up to the age of about 16) – would no longer require a college degree. Instead specific knowledge-based training would be provided ‘on the job’, presumably by the traditional mixture of a formally-structured curriculum for imparting the core knowledge and systematic elements with apprenticeship and individual instruction in order to impart specialized skills.

Murray also suggests that much specialist educational certification for careers could in principle be better done by rigorous public examinations such as those for accountancy, than by the medium of minimum-duration college degrees [1].

Measuring personality

The main unsolved problem for this psychometric approach is the evaluation of personality. Most of the current evidence for the predictive and explanatory power of personality comes from self-rating questionnaires, and clearly these would not be suitable for educational and job evaluations since it is facile to learn the responses which would lead to a high rating for Conscientiousness.

Rather than being simply asserted in a questionnaire, a Conscientious, persevering, self-disciplined personality requires to be demonstrated in actual practice. The modern educational system has, inadvertently, evolved in the direction of requiring higher levels of Conscientiousness [20]. The main factor in this evolution has been the progressive lengthening of the educational process (in the UK the modal average age for leaving formal education has increased from 16 to about 21 in the space of 30 years), but educational evaluations have also become less IQ-orientated (less g-loaded) and more dependent upon the ability of students frequently and punctually to complete neat and regular course work assignments [20] and [21].

However, the modern educational system is not explicitly aware that it is measuring Conscientiousness – the changes have been an accidental by-product of other trends, and there was not a deliberate attempt to enhance Conscientiousness-selectivity as a matter of policy. Because the educational system is blind to the consequences of its own actions, there are counter-pressures to make course work easier and more-interesting and to offer more choices – when in fact it would be a more efficient and accurate measure of Conscientiousness to have students complete compulsory, dull and irrelevant tasks which required a great deal of toil and effort!

However, it may be socially-preferable to have students prove their Conscientiousness in the realm of economic employment rather than by setting them pointless and grinding work in a formal educational context. There are plenty of dull and demanding but necessary jobs, the successful and sufficiently-prolonged accomplishment of which could serve as a valid and accurate reliable signal of Conscientiousness. So it would be more useful for people to prove their level of Conscientiousness in the arena of paid work, than by having this measurement task done by formal educational institutions.

An alternative suggestion for evaluating Conscientiousness comes from Geoffrey Miller, who advocates using broad surveys of opinion from families, peers, employers or any reliable and informed person who is in prolonged social contact with the subject [2].

Conclusions

I have previously written about the extraordinary way in which knowledge of IQ in particular, and psychometrics in general, is ‘hidden in plain sight’ in modern culture [17]. The basic facts about IQ are accessible, abundant and convincing for those who take the trouble to look; but modern mainstream intellectual culture has for around half a decade ‘immunized’ most educated people against looking-at or learning about IQ by multiple forms of misinformation and denigration [22] and [23].

The recent books of Murray and Miller marshal more strongly than before the evidence that one major reason for its taboo status is that IQ knowledge has extremely damaging implications for the vast and expanding system of formal education which employs many intellectuals directly, and which provides almost all other intellectuals with the credentials upon which their status and employability depend. Miller’s phrase is worth repeating: “they do not want their expensive IQ-warranties to suffer competition from cheap, fast IQ tests which would commodify the intelligence-display market and drive down costs” [2].

Murray argues that a properly-demanding 4 year, general and core knowledge-based, ‘liberal arts’ degree would be valuable as a pre-specialization education for the high IQ intellectual elite [1]. Perhaps because I am a product of the (now disappeared) traditional English system of early educational specialization, I am unconvinced about the systematic benefits of general education at a college level. I suspect that the most efficient pattern of higher education would be to specialize at age 16 (or earlier for the highest IQ individuals) on completion of the standard core knowledge program; and that liberal arts should mainly be seen as an avocation (done for reasons of personal fulfilment) rather than a vocation (done as a job).

In other words, a liberal arts education beyond core knowledge could, and perhaps should, be optional and provided by the market, rather than being included in the educational ‘system’. For example, in the UK such an education is universally available without any residential requirement at a reasonable price and high quality via the Open University (www3.open.ac.uk/about).

But in a system where objective IQ and personality evaluations were available as signals of aptitude, it could be left to ‘the market’ to decide whether the possession of a rigorous 4 year general liberal arts degree opened more doors; or attracted any extra premium of status, salary or conditions compared with a specialized, early vocational degree such as medicine, law, architecture, engineering, or one of the sciences. (There would presumably also be some specialist arts and humanities degrees, mainly vocationally-orientated towards training high-level school and college teachers – as was the traditional English practice until about 40 years ago [3].)

In summary, modern societies are currently vastly over-provided with formal education, and this education has the wrong emphasis. In particular, the job of sorting people by their general aptitude could be done more accurately, cheaply and quickly by using psychometrics to measure IQ and Conscientiousness. This would free-up time and energy for early training in key skills such as reading, writing and mathematics; and to focus on a core knowledge curriculum.

However, for reasons related to self-interest, the intellectual class do not want people to know the basic facts about IQ; and since the intellectual class provide the information upon which the rest of society depends for their understanding – consequently most people do not know the basic facts about IQ. And lacking knowledge of IQ, people are not able to understand the education system and what it actually does.

I can point to myself as a prime example of the way in which ignorance of IQ leads to a distorted understanding of education. Before I knew about the basic facts of IQ, I had articulated what seemed to be a rational and coherent set of beliefs about education. But since discovering the facts about IQ several of my convictions have undergone what amounts to a U-turn.

Acknowledgements

“A Farewell to Alms: a brief economic history of the world” by Gregory Clark (Princeton University Press: Princeton, NJ, USA, 2007) was the book of economic history which first stimulated my (belated) engagement with the scientific literature of intelligence and personality. The web pages of Steve Sailer have since provided both an invaluable introduction and also a higher education in the subject (e.g. www.isteve.com/Articles_IQ.htm).

References

[1] C. Murray, Real education: four simple truths for bringing America’s schools back to reality, Crown Forum, New York (2008).

[2] G. Miller, Spent: sex, evolution and consumer behaviour, Viking, New York (2009).

[3] B.G. Charlton and P. Andras, Auditing as a tool of public policy – the misuse of quality assurance techniques in the UK university expansion, Eur Polit Sci 2 (2002), pp. 24–35.

[4] B.G. Charlton, Science as a general education: conceptual science should constitute the compulsory core of multi-disciplinary undergraduate degrees, Med Hypotheses 66 (2006), pp. 451–453.

[5] Charlton BG, Andras P. The educational function and implications for teaching of multi-disciplinary modular (MDM) undergraduate degrees. OxCHEPS Occasional Paper No. 12; 2003. http://oxcheps.new.ox.ac.uk

[6] B.G. Charlton and P. Andras, Universities and social progress in modernizing societies: how educational expansion has replaced socialism as an instrument of political reform, CQ (Crit Quart) 47 (2005), pp. 30–39.

[7] N.J. Mackintosh, IQ and human intelligence, Oxford University Press, Oxford (1998).

[8] A.R. Jensen, The g factor: the science of mental ability, Praeger, Westport, CT, USA (1988).

[9] U. Neisser et al., Intelligence: knowns and unknowns, Am Psychol 51 (1996), pp. 77–101.

[10] I.J. Deary, Intelligence: a very short introduction, Oxford University Press, Oxford (2001).

[11] J.R. Harris, The nurture assumption: why children turn out the way they do, Bloomsbury, London (1998).

[12] D. Nettle, Personality: what makes you the way you are, Oxford University Press (2007).

[13] P.T. Costa and R.R. McCrae, Stability and change in personality from adolescence through adulthood. In: C.F. Halverson Jr., G.A. Kohnstamm and R.P. Martin, Editors, The developing structure of temperament and personality from infancy to adulthood, Lawrence Erlbaum Associates, Hillsdale, NJ, USA (1994), pp. 139–150.

[14] G.D. Batty, I.J. Deary and L.S. Gottfredson, Pre-morbid (early life) IQ and later mortality risk: systematic review, Ann Epidemiol 17 (2007), pp. 278–288.

[15] Caplan B. Mixed signals: Why Becker, Cowen, and Kling should reconsider the signaling model of education. . Accessed 06.04.09.


[16] R.J. Herrnstein and C. Murray, The bell curve: intelligence and class structure in American life, Forbes, New York (1994).

[17] B.G. Charlton, Pioneering studies of IQ by G.H. Thomson and J.F. Duff – an example of established knowledge subsequently ‘hidden in plain sight’, Med Hypotheses 71 (2008), pp. 625–628.

[18] L.S. Gottfredson, Implications of cognitive differences for schooling within diverse societies. In: C.L. Frisby and C.R. Reynolds, Editors, Comprehensive handbook of multicultural school psychology, Wiley, New York (2005), pp. 517–554.

[19] Spitz HH. The raising of intelligence: a selected history of attempts to raise retarded intelligence. Hillsdale, NJ, USA: Erlbaum; 1986.

[20] B.G. Charlton, Why are modern scientists so dull? How science selects for perseverance and sociability at the expense of intelligence and creativity, Med Hypotheses 72 (2009), pp. 237–243.

[21] Charlton BG. Sex ratios in the most-selective elite undergraduate US colleges and universities are consistent with the hypothesis that modern educational systems increasingly select for conscientious personality compared with intelligence. Med Hypotheses; in press, doi:10.1016/j.mehy.2009.03.016.

[22] A. Wooldridge, Measuring the mind: education and psychology in England, c.1860–c.1990, Cambridge University Press, Cambridge, UK (1994).

[23] L.S. Gottfredson, Logical fallacies used to dismiss the evidence on intelligence testing. In: R. Phelps, Editor, Correcting fallacies about educational and psychological testing, American Psychological Association, Washington, DC (2009), pp. 11–65.
 
*

Reliable but dumb, or smart but slapdash?

Monday, 31 August 2009

Bruce G Charlton

Why it is ‘better’ to be reliable but dumb than smart but slapdash: Are intelligence (IQ) and Conscientiousness best regarded as gifts or virtues?

Medical Hypotheses. 2009; Volume 73: 465-467

Editorial

Summary

The psychological attributes of intelligence and personality are usually seen as being quite distinct in nature: higher intelligence being regarded a ‘gift’ (bestowed mostly by heredity); while personality or ‘character’ is morally evaluated by others, on the assumption that it is mostly a consequence of choice? So a teacher is more likely to praise a child for their highly Conscientious personality (high ‘C’) – an ability to take the long view, work hard with self-discipline and persevere in the face of difficulty – than for possessing high IQ. Even in science, where high intelligence is greatly valued, it is seen as being more virtuous to be a reliable and steady worker. Yet it is probable that both IQ and personality traits (such as high-C) are about-equally inherited ‘gifts’ (heritability of both likely to be in excess of 0.5). Rankings of both IQ and C are generally stable throughout life (although absolute levels of both will typically increase throughout the lifespan, with IQ peaking in late-teens and C probably peaking in middle age). Furthermore, high IQ is not just an ability to be used only as required; higher IQ also carries various behavioural predispositions – as reflected in the positive correlation with the personality trait of Openness to Experience; and characteristically ‘left-wing’ or ‘enlightened’ socio-political values among high IQ individuals. However, IQ is ‘effortless’ while high-C emerges mainly in tough situations where exceptional effort is required. So we probably tend to regard personality in moral terms because this fits with a social system that provides incentives for virtuous behaviour (including Conscientiousness). In conclusion, high IQ should probably more often be regarded in morally evaluative terms because it is associated with behavioural predispositions; while C should probably be interpreted with more emphasis on its being a gift or natural ability. In particular, people with high levels of C are very lucky in modern societies, since they are usually well-rewarded for this aptitude. This includes science, where it seems that C has been selected-for more rigorously than IQ. Indeed, those ‘gifted’ with high Conscientiousness are in some ways even luckier than the very intelligent – because there are more jobs for reliable and hard-working people (even if they are relatively ‘dumb’) than for smart people with undependable personalities.

***

Moral evaluations of intelligence and personality

The psychological attributes of intelligence and personality are usually seen as being quite distinct in nature: higher intelligence being regarded as a morally-neutral aptitude which is a lucky ‘gift’; while personality or ‘character’ is morally evaluated by others, on the assumption that it is mostly a consequence of choices. So a teacher is much more likely repeatedly to praise a child for exceptional self-discipline and hard work than for being of high intelligence. In other words, virtue is seen as an aspect of character/personality rather than intelligence.

General intelligence (aka. ‘g factor’ intelligence, or ‘intelligence quotient’ or IQ) [1], [2], [3] and [4] and the ‘Big Five’ personality trait of Conscientiousness [5], [6] and [7] are the two main measurable psychological factors, higher levels of which are predictive of better educational and job performance [8] and [9]. IQ is the aptitude that enables a person to think abstractly and logically, to solve a wide range of novel problems, and to learn rapidly.

The personality trait of Conscientiousness (‘C’) incorporates features such as perseverance, self-discipline, meticulousness, and long-termism. In a nutshell, Conscientiousness is the capacity to work hard at a task over the long-term despite finding the task uninteresting and despite receiving no immediate reward.

The usual conceptualization sees IQ as a gift and C as a virtue; i.e. intelligence as an ability available to be used when necessary and personality traits such as Conscientiousness as a moral disposition to make better or worse behavioural choices. The mainstream idea would be that people are not responsible for the level of their intelligence but are responsible for their behaviour. So apparently it makes sense to praise Conscientiousness as virtuous but not similarly to praise IQ.

However, I will argue that – while there are indeed practical reasons to praise good behaviour – in reality IQ has morally-relevant elements, while high-C (and other valued personality traits) should also be regarded as a gift. So, both intelligence and personality can be regarded either as gifts or as virtues, according to context.

Intelligence is regarded as a gift

Most people regard intelligence as a ‘gift’ – and highly intelligent children have sometimes been termed gifted. This interpretation is accurate, in the sense that the main known determinant of general intelligence is heredity: people inherit intelligence from their parents [1], [2], [3] and [4]. While bad experiences (such as starvation and disease in the womb or during infancy) can pull intelligence downwards, it is at present difficult or impossible significantly to raise a person’s real, underlying, long-term predictive general intelligence by any kind of environmental intervention[10]. (It may, however, be possible to raise IQ scores by practicing IQ tests and other focused interventions; but this does not cash-out into significant and prolonged general benefits in terms of education and employment).

IQ is calculated by testing groups of people at different ages, and (usually) putting their scores into rank order and organizing rankings onto a normal distribution curve with a mean average IQ of 100 and a standard deviation of 15. Using this type of calculation, intelligence scores/rankings are relatively stable throughout life – so that a child of 8 with high IQ will usually grow to become an adult with similarly high IQ, and vice versa [1], [2], [3] and [4].

Because intelligence is a gift which is substantially hereditary and stable throughout life, on the whole it is regarded as a result of ‘luck’ and something for which people should be grateful; and not, therefore, as a virtue deserving of moral approbation or praise. Indeed, people with high intelligence may be given less help than they need, and may be held to a higher standard of behaviour, precisely because they are regarded as lucky.

Higher intelligence is socially valued more highly than lower intelligence, probably because people with a higher IQ are on average more useful economically [11] (having higher economic productivity, on average); nonetheless the most intelligent people are not usually regarded as intrinsically virtuous nor especially morally praiseworthy. And although it is true that people of low intelligence may attract hurtful and insulting descriptors such as dumb, dull, slow or stupid; nonetheless, a person with these attributes is not regarded as intrinsically wicked.

Personality traits are morally evaluated

There is a contrast between IQ and personality in respect of moral evaluations. While IQ is seen as a gift there is a spontaneous tendency to regard personality as a morally distinguishing feature – as a visible marker of a person’s underlying moral nature. It is quite normal to praise the most diligent people for their high capacity for hard work, and at the same time to regard them as merely fortunate if they are also of high intelligence.

Yet it is probable that both IQ and personality traits (such as the ability to work hard) are almost-equally hereditary ‘gifts’. The heritability of IQ is generally quoted as between 0.5 and 0.8 (probably at the higher end) [1], [2], [3] and [4] and the heritability of personality is quoted as being around 0.5 [5], [6] and [7]. However, the estimate of personality heritability is certainly an underestimate due to the sub-optimal conceptualization of personality traits, and especially to the lesser precision of current personality measurement methods compared with IQ tests [4]. To the extent that these things can be observed in everyday experience, both IQ and personality are probably about-equally inherited; and the high IQ and extra-hard-working person should about-equally thank their genes rather than congratulate themselves.

Furthermore, rankings of personality, like IQ, are generally stable throughout life; so that a highly Conscientious child will probably grow into a highly Conscientious adult and vice versa (whatever their familial, educational and socially experiences may be). However, it is also important to recognize that average personality traits change through the lifespan – e.g. Conscientiousness levels increase through early adult life, while Extraversion declines [12]. The high-C personality type which enables people to work hard, be self-disciplined and pursue long-term goals is therefore, in this sense, no more ‘virtuous’ than the high IQ ability quickly to do complex verbal, mathematic and symbolic puzzles.

But Conscientiousness is often regarded as highly moral behaviour, and an exceptionally-reliable individual will probably be regarded as virtuous even when they are of low IQ. However, in contrast, a person who is low in C is likely to be feckless, distractible, slapdash, and focused on short-term rewards – even when they are very intelligent. These behaviours are regarded as moral deficiencies; and the coexistence of high IQ in some ways makes it worse, because it is often felt that clever people ‘should know better’. Of course, low-C traits are negatively evaluated probably for the obvious reason that they are not very useful socially – indeed a person of very low Conscientiousness is likely to be a poor student and troublesome employee under most circumstances.

Aside, it should be noted that low-C may also be associated with some positively-evaluated attributes; especially creativity (insofar as highly creative people tend to have very high IQ and moderately high ‘Psychoticism’ which trait includes moderately-low Conscientiousness [13]). I have previously suggested that selecting for very high-C will therefore – as an unintended side effect – tend to reduce the average level of creativity; and that this may have happened in science over the past several decades [14].

Furthermore, it has been argued that in the hunter gatherer societies of our ancestors it would probably have been advantageous for most people to have lower levels of C than seem to be optimal nowadays; in the sense that it was more important for hunter gatherers to react spontaneously and quickly to immediate stimuli; and less important for them to plan far ahead, or to be able to persevere in the unrewarding and often repetitive tasks that characterize much of formal education or agricultural and industrial employment [7].

But in modern societies, it is certainly an advantage (on average) to have higher levels of C.

Moral evaluation of personality

The evidence therefore suggests that it is likely that although the two psychological attributes of IQ and C are not highly-correlated (see Ref. [13] for review); the ability to work hard and with self-discipline and the ability of general intelligence are about-equally inherited, about-equally stable throughout life, and about-equally difficult to change either by self-determination or by the social interventions of other people. It seems that we as individuals are pretty much ‘stuck with’ the intelligence and the personalities with which we were born; and it is strange that exceptional IQ should be regarded as a gift while exceptional C is regarded as being the praiseworthy result of resolution and effort.

It might be argued that personality traits are associated with moral behaviours in a way that IQ is not. Certainly personality traits do have moral aspects. Three of the Big Five – Conscientiousness, Agreeableness and Neuroticism – have one extreme which would generally be immoral [6] and [7]. For example, it would generally be regarded as ‘bad behaviour’ to be low in Agreeableness since this would include selfishness, uncooperativeness, emotional coldness, unfriendliness, unhelpfulness. Likewise it may be regarded as socially-undesirable to be high in Neuroticism since this would include proneness to mood swings, irritability and anger.

But the reason that humans apparently spontaneously regard personality in moral terms is presumably because humans respond to incentives. Society would probably wish to encourage pro-social behaviour by praising it, on the basis that even though personality rankings cannot be much changed by whole-population interventions, at the individual level behaviour can be shaped by incentives – by rewards and punishments.

Furthermore, high-C behaviour takes more effort than low-C behaviour. Although the ability to work hard on topics that are uninteresting is mostly hereditary, and therefore a gift, hard work is still hard work, and it is still easier not to work hard! Slapdash, distractible behaviour is undemanding, takes less effort. So, unless there is system of incentives which encourages hard work, then the default position is to work less hard, or not to work at all.

However, when the same incentives are applied to the whole of a group of people varying in C; it is unreasonable and may be cruel to expect that the Conscientiousness gap between high and low individuals to disappear. Although all students might work harder, at least while the incentives were being applied, the gap between high-C and low-C students would remain, and the size of this gap might increase. Certainly, this is what has been found with IQ, when attempting to close various IQ-testing ‘gaps’. And, insofar as C is like IQ (heritable and stable), the possible size of improvement due to interventions is likely to be modest or negligible [2]. The accumulated experience of trying to improve general intelligence (in developed nations) is that it is difficult or impossible to produce sustained long-term improvements in intelligence, especially when the improvements are tested by independent outcomes such performance in employment. Improvements are often superficial results of specific training which only enhance specific types of test performance or evaluations done while under the influence of structured motivational systems [10].

Conclusion

Personality clearly has a moral dimension, but something similar could also be said of intelligence in the indirect sense that higher intelligence is associated with reduced levels of a range of social pathologies including crime and family breakdown [15].

Furthermore intelligence is associated with several aspects of personality and behaviour. There is a positive association between IQ and the Big Five trait of Openness to Experience – which means that more-intelligent people are more likely to seek novelty, enjoy artistic experiences, and be imaginative [7]. Furthermore, intelligence is associated positively with atheism and also with what have been termed ‘enlightened’ values such as left-wing or ‘liberal’ and anti-traditional/anti-conservative views [16]. So that IQ is associated with several morally-evaluated socio-political views which could be judged as virtuous, adaptive, mistaken or even damaging – according to one’s socio-political and religious perspective.

I do not, however, wish to press the similarity of personality and intelligence too hard since these attributes may have a somewhat distinct evolutionary rationale, and selectional basis [17]. My main point is that, although we regard intelligence and personality as different kinds of psychological attributes, in fact they are similar in several important ways.

Nonetheless, in sum, it seems that our traditional interpretations of intelligence and personality require modification. IQ is not just an ability which can be used as required; instead higher IQ is also a predisposition which on average includes a bias towards some types of behaviours and away from others. And high conscientiousness – such as the ability to take the long view, work hard and persevere in the face of difficulty – should probably be interpreted with more emphasis on its being a gift in much the same sense as high intelligence – despite the fact that IQ is ‘effortless’ while high-C emerges mainly in tough situations where exceptional diligence is required.

People with high levels of IQ are mostly very lucky, as is widely recognized; but people with high-C are very lucky too, because they are usually well-rewarded for this aptitude in modern society; and indeed rewarded in science too, where it seems that self-discipline is now selected-for more rigorously than IQ [14].

Indeed, in some ways those ‘gifted’ with high-C are even luckier than very intelligent people, because there are always going to be more jobs for reliable and hard-working people (even if they are relatively ‘dumb’) than jobs which are suitable for smart people who are undependable, short-termist and slapdash.

References

[1] U. Neisser et al., Intelligence: knowns and unknowns, Am Psychol 51 (1996), pp. 77–101.

[2] A.R. Jensen, The g factor: the science of mental ability, Praeger, Westport, CT, USA (1988).

[3] N.J. Mackintosh, IQ and human intelligence, Oxford University Press, Oxford (1998).

[4] I.J. Deary, Intelligence: a very short introduction, Oxford University Press, Oxford (2001).

[5] J.R. Harris, The nurture assumption: why children turn out the way they do, Bloomsbury, London (1998).

[6] G. Matthews, I.J. Deary and M.C. Whiteman, Personality traits, Cambridge University Press, Cambridge, UK (2003).

[7] D. Nettle, Personality: what makes you the way you are, Oxford University Press, Oxford, UK (2007).

[8] M.R. Barrick and M.K. Mount, The big five personality dimensions and job performance: a meta analysis, Pers Psychol 44 (1991), pp. 1–26.

[9] A.L. Duckworth and M.E.P. Seligman, Self-discipline outdoes IQ in predicting academic performance of adolescents, Psychol Sci 12 (2005), pp. 939–944.

[10] H.H. Spitz, The raising of intelligence: a selected history of attempts to raise retarded intelligence, Erlbaum, Hillsdale, NJ, USA (1986).

[11] L.S. Gottfredson, Implications of cognitive differences for schooling within diverse societies. In: C.L. Frisby and C.R. Reynolds, Editors, Comprehensive handbook of multicultural school psychology, Wiley, New York (2005), pp. 517–554.

[12] P.T. Costa and R.R. McCrae, Stability and change in personality from adolescence through adulthood. In: C.F. Halverson Jr, G.A. Kohnstamm and R.P. Martin, Editors, The developing structure of temperament and personality from infancy to adulthood, Lawrence Erlbaum Associates, Hillsdale, NJ, USA (1994), pp. 139–150.

[13] H.J. Eysenck, Genius: the natural history of creativity, Cambridge University Press, Cambridge, UK (1995).

[14] B.G. Charlton, Why are modern scientists so dull? How science selects for perseverance and sociability at the expense of intelligence and creativity, Med Hypotheses 72 (2009), pp. 237–243.

[15] R.J. Herrnstein and C. Murray, The bell curve: intelligence and class structure in American life, Forbes, New York (1994).

[16] I.J. Deary, C.D. Batty and C.R. Gale, Bright children become enlightened adults, Psychol Sci 19 (2008), pp. 1–6.

[17] L. Penke, J.J. Denissen and G.F. Miller, The evolutionary genetics of personality, Eur J Personality 21 (2007), pp. 549–587.
 
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Why are women so intelligent? - Adaptiveness of maternal IQ

Tuesday, 9 February 2010

Why are women so intelligent? The effect of maternal IQ on childhood mortality may be a relevant evolutionary factor

Bruce G. Charlton

Medical Hypotheses, 2009; 74: 401-2. in the press

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Summary

Humans are an unusual species because they exhibit an economic division of labour. Most theories concerning the evolution of specifically human intelligence have focused either on economic problems or sexual selection mechanisms, both of which apply more to men than women. Yet while there is evidence for men having a slightly higher average IQ, the sexual dimorphism of intelligence is not obvious (except at unusually high and low levels). However, a more female-specific selection mechanism concerns the distinctive maternal role in child care during the offspring’s early years. It has been reported that increasing maternal intelligence is associated with reducing child mortality. This would lead to a greater level of reproductive success for intelligent women, and since intelligence is substantially heritable, this is a plausible mechanism by which natural selection might tend to increase female intelligence in humans. Any effect of maternal intelligence on improving child survival would likely be amplified by assortative mating for IQ by which people tend to marry others of similar intelligence – combining female maternal and male economic or sexual selection factors. Furthermore, since general intelligence seems to have the functional attribute of general purpose problem-solving and more rapid learning, the advantages of maternal IQ are likely to be greater as the environment for child-rearing is more different from the African hunter-gatherer society and savannah environment in which ancestral humans probably evolved. However, the effect of maternal IQ on child mortality would probably only be of major evolutionary significance in environments where childhood mortality rates were high. The modern situation is that population growth is determined mostly by birth rates; so in modern conditions, maternal intelligence may no longer have a significant effect on reproductive success; the effect of female IQ on reproductive success is often negative. Nonetheless, in the past it is plausible that the link between maternal IQ and child survival constituted a strong selection pressure acting specifically on women.

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Humans are an unusual species because they exhibit an economic division of labour [1]. And most theories concerning the evolution of specifically human intelligence have either focused on the value of abstract thinking and rapid learning in solving economic problems such as hunting, gathering, farming and defence; or on sexual selection mechanisms in producing creative intelligence to entertain the prospective mate (for review see [2]).

Both types of theory apply more to men than women, and tend to regard high intelligence in women as having been somewhat passively pulled-along by rising male intelligence due to the relative slowness of evolving sexually dimorphic traits [2]. But, while there is evidence for men having a slightly higher average IQ (perhaps about four IQ points [3]), the sexual dimorphism is not striking except at very unusually high and low levels of intelligence [4].

However, there is some evidence of a more female-specific selection mechanism which concerns the distinctive female role in child care, especially during the offspring’s early years. I have located two studies which demonstrate a statistical relationship between increased maternal intelligence and reduced child mortality [5] and [6]. These are supported by a host of indirect studies which find the same negative correlation between proxy measures of IQ such as educational attainment or duration, and measures of child health which might plausibly correlate with mortality (e.g. [7] and [8]).

So it seems likely that there would be a selection pressure tending to increase maternal intelligence since (all else being equal) increased intelligence would lead to a greater chance of offspring surviving to adulthood. This would lead to a greater level of reproductive success for intelligent women, and intelligence is substantially heritable – so this is a plausible mechanism by which natural selection might tend to increase female intelligence in humans (all else being equal).

Any effect of a mother’s intelligence on improving survival of her children is likely to be amplified by assortative mating for IQ: in other words people tend to marry others of similar intelligence [1] and [9]. This suggests that a woman of higher-than-average-intelligence (who is more likely to keep her children safe) is also likely to have a higher-than-average-intelligence husband (who is likely to be a better economic provider). A more-intelligent wife would also be able more rapidly to learn to use these extra resources from her smarter husband in improving the health and survival of their offspring.

Furthermore, since intelligence seems to have the functional attribute of a general purpose problem-solving ‘module’ [10], the advantages of maternal IQ are likely to be greater as the environment for child-rearing is more different from the African hunter-gatherer society and savannah environment in which ancestral humans probably evolved. In an ancestral society and environment, it is likely that women have been equipped (by natural selection) with the ‘maternal instincts’ necessary for successful child-rearing. But as humans have moved further ‘out of Africa’ and into evolutionarily unfamiliar climates and ecologies, and have developed novel economic systems such as agriculture and cities – then the advantages of higher maternal IQ (including attributes of better ability to solve novel problems and more rapid ability to learn from experience) may have become more important. This would fit with some evidence (also consistent with explanations for higher male IQ) for varying human general intelligence according to multi-generational ancestral experience of higher latitude, agrarian economy, distance from Africa and some other indices of evolutionary novelty [11], [12], [13] and [14]. The effect of maternal IQ on child survival may make this a special case of Gottfredson’s ‘deadly innovations’ hypothesis [15].

However, the effect of maternal IQ would probably be of major evolutionary significance only in situations where childhood mortality rates were high: presumably, the higher the childhood mortality rates, the greater would be the differential effect on survival of higher maternal intelligence. Until the industrial revolution all societies experienced high childhood mortality rates due to factors such as birth problems, starvation, disease, parental death, predation and other types of violence [12]. Then in industrializing/developing countries from about 1800, mortality rates fell more rapidly than birth rates and populations began to grow and living standards to rise. The modern situation is that population growth is determined mostly by birth rates, and child mortality rates are low enough that some of the population groups with the highest child mortality are growing rapidly due to even-higher birth rates; and populations with the lowest child mortality may be shrinking due to sub-replacement birth rates [12] and [13]. Indeed, there is a strongly inverse relationship between IQ and reproductive success in women in modern societies (e.g. [16]).

So, in modernizing societies, maternal intelligence may no longer have a significant effect on reproductive success, or the relationship may be negative – nonetheless, in the past and especially in agrarian societies rich in evolutionarily novel situations that impact on child-rearing, it is plausible that the link between maternal IQ and child survival constituted a strong selection pressure acting specifically on women (it should, however, be remembered that most newly arising traits are initially inherited by both sexes, and that it takes longer for sexually dimorphic traits to evolve – see [2] for review).

This idea of maternal influence on childhood mortality driving an increase in female intelligence might potentially be testable. For example, specifically female intelligence might be measured in relation to the quantitatively evaluated degree of environmental evolutionary-unfamiliarity among ancestors (somewhat as in Ref. [11]), or perhaps in relation to differences in the nature and intensity of child-rearing practices and specific hazards (as in the study of the Ache tribe reported in [15]). And since the reason for women’s high IQ is postulated to be different from the reason for men’s high IQ (i.e., maternal benefits versus economic benefits), then it may be possible to generate and test predictions of how these sex differences would affect the nature and application not only of abstract reasoning, but also personality and other cognitive attributes.

For instance, the degree of selection probably on maternal psychology in situations of high child mortality in evolutionarily unfamiliar situations may affect the relative level of intelligence in women compared with men, or may affect the personality traits of higher conscientiousness and agreeableness/empathizing self-reported by women (for review see [9]). The population magnitude of such sexually dimorphic personality traits may vary in ways that can be predicted according to that population’s ancestral experience of maternal natural selection. Furthermore, Cochran and Harpending’s hypotheses that Ashkenazi Jewish men were under exceptionally powerful economic selection pressure for evolving higher intelligence over the past millennium [14] might be expected to create a larger than usual men-to-women IQ differential in this group.

In summary, differences in maternal psychology (intelligence and perhaps personality) could have had importance fitness effects by their influence on child survival in situations of high childhood mortality. This idea may provide a useful framework for understanding more about the evolution of human intelligence.


References

[1] M. Ridley, The origins of virtue: human instincts and the evolution of cooperation, Viking, London (1996).

[2] G. Miller, The mating mind: how sexual choice shaped the evolution of human nature, Doubleday, London (2000).

[3] R. Lynn and P. Irwing, Sex differences on the progressive matrices: a meta analysis, Intelligence 32 (2004), pp. 481–498.

[4] H.J. Eysenck, Genius: the natural history of creativity, Cambridge University Press, Cambridge, UK (1995).

[5] P. Sandiford, J. Cassell, G. Sanchez and C. Coldham, Does intelligence account for the link between maternal literacy and child survival?, Soc Sci Med 45 (1997), pp. 1231–1239.

[6] J. Čvorović, J.P. Rushton and L. Tenjevic, Maternal IQ and child mortality in 222 Serbian Roma (Gypsy) women, Pers Indiv Differ 44 (2008), pp. 1604–1609.

[7] J.G. Cleland and J.K. van Ginneken, Maternal education and child survival in developing countries, Soc Sci Med 27 (1988), pp. 1357–1368.

[8] S. Desai and S. Alva, Maternal education and child health: is there a strong causal relationship?, Demography 35 (1998), pp. 71–81.

[9] G. Miller, Spent: sex, evolution and human behavior, Viking, Penguin (2009).

[10] S. Kanazawa, General intelligence as a domain-specific adaptation, Psychol Rev 111 (2004), pp. 512–523.

[11] S. Kanazawa, Temperature and evolutionary novelty as forces behind the evolution of general intelligence, Intelligence 36 (2008), pp. 99–108.

[12] G. Clark, A farewell to alms: a brief economic history of the world, Princeton University Press, Princeton, USA (2007).

[13] R. Lynn, The global bell curve, Washington Summit Publishers, Atlanta, GA, USA (2008).

[14] G. Cochran and H. Harpending, The ten thousand year explosion: how civilization accelerated human evolution, Basic Books, Philadelphia, PA, USA (2009).

[15] L.S. Gottfredson, Innovation, fatal accidents, and the evolution of general intelligence. In: M.J. Roberts, Editor, Integrating the mind: domain general versus domain specific processes in higher cognition, Psychology Press, Hove, New York (2007).

[16] Nettle D, Pollet TV. Natural selection on male wealth in humans. Am Nat 2008;172:658–66.
 
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