not all in the genes

Dominic Cummings’ 2013 essay Some Thoughts on Education and Political Priorities reveals his keen interest in the implications of intelligence research for education. His Endnote “Intelligence, IQ, genetics, and extreme abilities” (p.194) runs to 17 pages.

General Intelligence

If I’ve understood Cummings’ model of intelligence correctly, it goes like this: General Intelligence (‘g’) is a trait that’s largely genetically determined and can be measured as IQ. If we could identify the genes involved, we could spot those with high cognitive ability who are needed to find the solutions to the complex problems facing us.

There’s certainly robust evidence that cognitive ability is largely genetically determined (by multiple genes), remains stable, and is a good predictor of lifetime achievement (p.197). We do need people with high IQs to work on solutions to world problems. And children with high IQs need an appropriate education. I share Cummings’ frustration that DfE officials prioritised their notion of equality over the need to develop talent (p.64). But his model is also flawed at several levels. It includes three key components that are worth examining in more detail;

  • A hypothetical human trait – general intelligence
  • The correlation between factors within intelligence tests
  • IQ


Towards the end of the 19th century, researchers got very interested in measuring human characteristics. Some, such as height and weight, were easy to measure, but others – like ‘physiognomy’ or ‘eventuality’- were trickier because it wasn’t obvious what the features of ‘physiognomy’ or ‘eventuality’ were.


You can of course measure any human characteristic you fancy. You decide what the features of ‘adhesiveness’ or ‘ideality’ are and how to measure them, and hey presto! you’ve measured ‘adhesiveness’ or ‘ideality’. There might of course be some disagreement about the features of ‘adhesiveness’ or ‘ideality’ – or even about their very existence.

Also in the late 19th century, industrialised economies were desperate for a literate, numerate, ‘intelligent’ workforce. That requirement was one of the drivers for mass education.

In his 1904 review of measures of intellectual ability, the psychologist and statistician Charles Spearman decided intellectual ability could be measured using performance in: Classics, Common Sense, Pitch Discrimination, French, Cleverness, English, Mathematics, Pitch Discrimination among the uncultured, Music, Light Discrimination and Weight Discrimination (Spearman p.276). Essentially, he defined intelligence in terms of intellectual abilities. More recent measures such as Verbal Comprehension, Visual Spatial, Fluid Reasoning, Working Memory, and Processing Speed (Wechsler Intelligence Scale for Children – V) define intelligence in terms of cognitive abilities.


Spearman went a step further. The positive correlations between the factors in his test convinced him “that there really exists a something that we may provisionally term ‘General Sensory Discrimination’ and similarly a ‘General Intelligence’” (Spearman p.272). And the correlations between scores in cognitive ability tests have convinced others of the existence of a ‘something’ we may provisionally term ‘general intelligence’.

I haven’t been able to find out if Spearman used ‘g’ to refer to the correlation between factors, or the hypothesized ‘something’, or both. Whichever it was, critics were quick to point out that correlation doesn’t indicate causality. A positive correlation between Spearman’s factors exists, certainly. Whether ‘general intelligence’ exists other than as a folk concept is another matter.

Critics also pointed out the circularity in Spearman’s argument. Intelligence tests were assumed to measure intelligence, but because no one knew what intelligence actually was, the tests also defined intelligence – even if they varied considerably. Spearman’s measures were very different to Binet & Simon’s , and neither bears much resemblance to the WISC, or to Raven’s Progressive Matrices. As Edwin Boring put it in 1923, “intelligence is what the tests test”.


In 1912, the German psychologist William Stern developed the concept of IQ –Intelligenzquotient. IQ (initially mental age divided by chronological age, expressed as a percentage) tells you how an individual’s test score compares to the average for the population. But the criticisms of ‘intelligence’ also apply to IQ. IQ tests undoubtedly measure aspects of cognitive ability, but we don’t know whether or not they measure a genetically determined trait we may call ‘intelligence’. Or even if such a trait exists.

Advocates for general intelligence haven’t take the criticisms lying down. Cummings quotes Robert Plomin’s dismissal of the circularity criticism: “…laypeople often read in the popular press that the assessment of intelligence is circular – intelligence is what intelligence tests assess. On the contrary, g is one of the most reliable and valid measures in the behavioral domain” (p.195).

It’s worth noting that Plomin uses g and intelligence interchangeably, even though intelligence is a hypothesized trait and he refers to g as a measure. There’s no doubt that g is reliable and valid when measuring some cognitive abilities. Whether those abilities represent a genetically determined trait we may term ‘intelligence’ is another matter – which Plomin goes on to admit: “It is less clear what g is and whether g is due to a single general process, such as executive function or speed of information processing, or whether it represents a concatenation of more specific cognitive processes…” It’s also worth noting that Plomin attributes the circularity argument to laypeople and the popular press, rather than to generations of doubting academic critics.

The implicit assumptions made by those emphasizing the importance of g and IQ, are important because they can have unwanted and unintended outcomes. One is that correlations between factors might hold true at population level, but not always at the individual level. Deidre Lovecky, who runs a resource centre in Providence Rhode Island for gifted children with learning difficulties, reports in her book Different Minds having to pick ‘n’ mix sub-tests from different assessment instruments because individual children were scoring at ceiling on some sub-tests and at floor on others. How intelligent are those children? Their IQ scores wouldn’t tell us.

Also, hunting for hypothetical snarks can waste a huge amount of time and resource. It’s taken over a century for us not to be able to find out what ‘g’ is. Given the number of genes involved ,you’d think by now people would have abandoned the search for a single causal factor. It’s a similar story for chronic fatigue syndrome (‘neurasthenia’ – 1869) and autism (‘autistic disturbances of affective contact’ – 1943); both perfectly respectable descriptive labels, but costly red herrings for researchers looking for a single cause.

Characteristics, traits, states, and behaviours

What convinces Cummings that intelligence, g and IQ are ‘somethings’ that really exist is evidence from behavioural genetics. Scientists working in this field have established beyond reasonable doubt that most of the variance in human intelligence, however you measure it, is accounted for by genetic factors. That shouldn’t be surprising. Intelligence is almost invariably defined in terms of cognitive ability, and cognitive ability emerges from characteristics such as visual and auditory discrimination, reaction time, and working memory capacity, all biological mechanisms largely determined by genes.

But not all human characteristics are the same kind of thing. Some characteristics such as height and weight are clearly physical and are easily measured. For obvious reasons genes account for most of the variance in physical characteristics.

The term trait applies to physical characteristics but also to stable dispositional characteristics. Disposition refers to people’s behavioural tendencies – how introvert or extravert they are, what they like and dislike, do and don’t do etc. The evidence from behavioural genetics suggests that genes also account for most of the variance in stable traits.

States are also dispositional characteristics, but they’re temporary and usually emerge in response to environmental factors. So Joan might be extravert and prone to angry outbursts, and Felicity might be introverted and timid, but both of them are likely to become anxious if fire breaks out in the office they share. Their reactions to the fire are largely genetically determined, but are triggered by an environmental event.

Behaviours are things people do. They are undoubtedly influenced by genetic makeup, but occur primarily in response to environmental factors, because that’s the main function of behaviour. Joan might try to extinguish the fire and Felicity might take the nearest exit, but both behaviours would be in response to specific circumstances. If we were pre-programmed automatons, the human race wouldn’t have lasted very long.

In support of his genes-determine-intelligence argument Cummings cites Stephen Hsu, a physicist turned behavioural geneticist, who claims that much of the nature/nurture debate has been settled. Hsu’s right in respect of the genetic influence on traits. But that still leaves plenty of room for the environmental influence on states and behaviours. That has significant implications for Cummings’ model of education.

Genes, intelligence and education

The principal components of Cummings’ model of education are genes, intellectual ability, effective teaching, and exam results. But in real life many other factors impact on educational outcomes. Take Ryan, Joan’s nephew, for example.

Ryan lives with his mum, a single parent. She cares for her father, disabled following a work accident, and her mother who has complex health problems. They live in a former industrial town, currently in economic decline. Ryan’s parents’ relationship broke down due to the financial and time pressures on the family.

Ryan has average intellectual ability, but episodes of glue ear when he was younger left him with a slight speech and language delay. He struggled with maths and reading and was often reprimanded for not following instructions. He loved physical activities, but the regulatory education framework required Ryan, as a child who was ‘falling behind’, to do less practical activity and more arithmetic and phonics.

Ryan soon began to disengage with school. He was referred for speech and language therapy and to the educational psychologist, but both had lengthy waiting lists. By his teens, Ryan had a low reading age, was making slow progress academically, and skipped school whenever he could. His mum couldn’t find paid work to fit around caring for her parents, and was on medication for anxiety and depression.

Genes undoubtedly account for some challenges faced by Ryan and his family; his family’s health, his intellectual ability, and quite likely his glue ear. But environment plays a significant role in the shape of income, diet, viral infections, and national economic, social, and education policy. So do life events (so commonplace their importance is often overlooked); where the family happens to live, grandfather’s accident, parents’ break-up, which school is closest to home.

Then there are specific behaviours on the part of Ryan, his parents, grandparents, teachers – and government ministers. Specific behaviours are often framed as a ‘choice’, but that choice is often highly constrained by circumstances.

Choose your metrics

Cummings measures the effectiveness of the education system by exam results (although he questions the quality of the exams). Exam results are positively correlated with IQ, and IQ is largely genetically determined. So his choice of metric means Cummings places a disproportionate emphasis on influence of genes on educational outcomes.

Of course there’s nothing wrong with IQ or exam results as metrics. If you want to find someone with good cognitive abilities, a modern intelligence test can identify them. If you want candidates with a mathematical ability of at least GCSE level, check out GCSE maths results.

But the choice of a single metric for something as complex as an education system shows an inadequate understanding of complex systems. And begs the question of what education is about. If quality of life in local communities were the key metric, the education system would look very different. By bizarre coincidence, the gene pool of large populations produces people with a wide range of abilities and aptitudes, just what those populations need in order to thrive. That wide range of abilities and aptitudes should be cultivated. Cummings’ choice of metric means the exam-results tail wagging the quality-of-life dog.

Accommodating a wide range of abilities and aptitudes doesn’t equate to having ‘low expectations’ for those with less than stellar exam results. There’s no virtue in people doing jobs they don’t enjoy and aren’t good at, and careers aren’t set in stone. An academic high flyer might become a superb potter, and a former train driver might get a PhD. If the education system doesn’t offer such opportunities, it’s to the detriment of all us.

Cummings would no doubt argue that his claims about education are evidence-based; he cites evidence for pedagogical approaches that improve exam results. But his starting point is an assumption that what the world needs is academic high flyers with high IQs and ‘extreme abilities’. He looks right past those with other abilities and aptitudes essential for communities to keep functioning. And those, who through no fault of their own, can make only a very limited contribution to their communities, but like all of us have a right to a decent quality of life.

Cummings first chooses his metric and then chooses supporting evidence, but only the evidence in support of it. Ironically history is littered with examples of academic high flyers with high IQs and ‘extreme abilities’ causing chaos for the rest of us. Cummings’ use of evidence is the subject of the next post.


Spearman, C.  (1904).  ‘General Intelligence’ objectively determined and measured.  The American Journal of Psychology, 15, 201-292.


Image from People’s Cyclopedia of Universal Knowledge (1883) via Wikipedia



Toby and the social constructionists: intelligence, race & gender

Toby Young, journalist and co-founder of the West London Free School, and appointed to the brand new Office for Students (OfS), recently delivered the 2017 Constance Holden* Memorial Address. His title was “Liberal Creationism”. The text of the lecture has been published as an opinion paper in the Elsevier Journal Intelligence. Neither Toby nor the topic of intelligence are strangers to controversy, so I was curious about to what he had to say.

the fate of intelligence researchers

For the first couple of pages I was nodding along in agreement. Toby opens with a robust defence of intelligence researchers who have faced serious consequences for suggesting that biological factors contribute to intelligence – careers ending abruptly, ignominy, and worse. His description of their opponents as a ‘neo-Marxist intersectionality cult’, ‘Social Justice Warriors’, ‘Liberal Creationists’ and ‘anti-hereditarians’ had a ring of truth about it.

The intelligence researchers’ findings have generally supported the idea that human nature is in part biologically determined.  Historically this idea is tainted by its association with eugenics, and it’s that association, Toby suggests, that’s at the root of the opposition to the research. He claims the ‘anti-hereditarians’ are wrong to think of the biological aspects of intelligence as “inextricably bound up with these toxic political movements and fundamentally incompatible with liberal values” (p.3).  I think he’s right.

human nature and individual differences

After a brief tour of some anthropological controversies to demonstrate that all human beings have some psychological traits in common, Young moves on to “what divides us” beginning with individual differences. This is the point where I felt his argument weakened considerably.

Young says “when a progressive liberal listens to a behavioural geneticist talk about the biological basis of IQ and the positive correlation between IQ and socio-economic status, what they think they are hearing is a Social Darwinist argument in favour of the current distribution of wealth and power” (p.3). He argues that at the heart of the opposition to claims about the biological basis of human nature, whether IQ, gender or race, is social constructionism, which holds the view that “anyone who believes that human differences are rooted even in part in biology rather than socially constructed is the enemy” (p.2). What Young appears to have failed to realize is that whatever the contribution of biology and however wrong the social constructionists’ reasoning, ‘intelligence’ (IQ), ‘race’ and ‘gender’ are nonetheless constructs.

intelligence, race and gender as constructs

There’s no doubt that biological factors contribute to what we call intelligence, race and gender. Some congenital medical conditions result in low intelligence, people with ancestry in different parts of the world have different physical and physiological characteristics, women are anatomically different to men, and so on.

The concepts ‘intelligence’, ‘race’ and ‘gender’ entail biological characteristics (ability to carry our particular tasks, physical features, anatomical differences), but that doesn’t mean ‘intelligence’, ‘race’ or ‘gender’ map directly on to discrete biological entities.  Although the biological characteristics are real things in the natural world, it doesn’t follow that the concepts ‘intelligence’, ‘race’ and ‘gender’ must be real things in the natural world. As Gilbert Ryle would have pointed out, intelligence, race and gender are different kinds of things to the brains, skin colour and sexual characteristics we associate with them.

The biological characteristics mean we can operationalize those constructs in biological terms for research purposes. A researcher could decide that, for the purposes of their study, intelligence consists of the ability to perform particular tasks, measured using a particular test. A particular racial grouping could be operationalized in terms of particular physical characteristics. Gender, likewise.

It doesn’t follow that intelligence, race or gender have a biological existence independent of the concept of intelligence, race or gender. In marked contrast to brains, skin or genitals.

I think Toby is right that some more vociferous opponents to the claims about intelligence have framed the debate entirely in terms of social constructs and in doing so have completely discounted biological factors. But that’s not true of all who have questioned the claims about intelligence, race or gender.

The existence of brains, skin or genitals are rarely disputed.  They are physical entities and there’s general agreement about their characteristics. But intelligence, race and gender have been the subject of controversy more or less since they came into being because they are constructs. The question looming over all of them is ‘what do you mean by….?’

what do you mean by…?

As the psychologist Edwin Boring pointed out way back in the 1920s, intelligence is what[ever] intelligence tests measure.   Somebody, somewhere makes a decision about what a particular intelligence test measures. Intelligence tests undoubtedly measure something. Whether it’s intelligence or not depends on what you think intelligence is.

Race is controversial because the characteristics that are supposed to be typical of different racial groups are, because of the way genetic expression works, on a multi-dimensional continuum.  Even if the features considered to characterise a particular racial group are very clearly defined, it’s often difficult to decide whether or not an individual belongs to that group.

As for gender… The ‘social constructionists’ so disparage by Young make an important distinction between someone’s sex (reproductive anatomy and secondary sexual characteristics) and their gender – their social role based on their sex. The distinction is a helpful one, but two terms are often, unhelpfully, used interchangeably.

A further complication is that biology, also unhelpfully, doesn’t adhere to a neat binary male/female distribution of physical sexual characteristics. One estimate§ puts the frequency of intersex characteristics as high as 1.7% of the population.

The difficulty in determining what constitutes intelligence, race or gender calls into question the validity of all correlations found between intelligence and any demographic group. That’s because someone has to decide what constitutes intelligence and what constitutes the demographic group; the validity of intelligence as a construct has been questioned ever since Spearman came up with the idea of g.

you say this, I say that

Young’s argument appears to be essentially this: Science shows that shared human characteristics and individual differences are to large extent biologically determined.  And that anti-hereditarian opposition to that finding originates in the ‘fanatical egalitarianism’ of the hard left (p.6). According to Young, the egalitarianism the hard left want can be brought about by a totalitarian dictatorship.

Interestingly, in his opening comments Young dismisses the fanatical egalitarianism embraced by the far-right (also enforced via a totalitarian dictatorship), as ‘toxic baggage’ that could be discarded. And complains “It’s not much fun to be branded a ‘Nazi’ or ‘white supremacist’ on Twitter or anywhere else” (p.1).

Totalitarian regimes of the hard left, far-right and various other political and religious persuasions, inflicted catastrophic damage on huge numbers of people during the 20th century and look set to continue doing so in the 21st. To justify their actions, some regimes used the idea that characteristics are inherited. Others have used ideology. None have taken much notice of what science has to say.

Toby has taken note of the science but has managed to fundamentally misunderstand both it and social constructionism. He’s lumped together anyone else who’s misunderstood the science, objected to spurious scientific claims, been upset by unwise off-the-cuff remarks, with left-wing ideologues.   And has used his misunderstanding to launch an attack on the hard left who he equates with Stalinists.

His argument is essentially constructed in opposition to the narrative of people he disagrees with, whether they are a ‘neo-Marxist intersectionality cult’, ‘Social Justice Warriors’, ‘Liberal Creationists’, ‘anti-hereditarians’ or vote Democrat (p.7).

If the social constructionists think intelligence, race and gender are social constructs, Young doesn’t consider the possibility they might actually be no more than social constructs, despite scientists arguing over their construct validity for decades. If sceptics get upset about scientists making questionable claims, Young assumes the scientists must be right. If any group he disagrees with marginalises the role of biological factors in individual differences, Young marginalises the role of environmental factors. If all the parties Young disagrees with fight like ferrets in a sack about the differences between their views, Young lumps them all together as if they form a homogeneous group.

That doesn’t tell us that Young is wrong and the social constructionists/neo-Marxist intersectionalists/Social Justice Warriors/Liberal Creationists/anti-hereditarians are right. What it does tell us is that misunderstandings of science can be used to justify anything.


*Constance Holden wrote for the news section of Science for 40 years.

§Blackless et al (2000). How sexually dimorphic are we?

educating the evolved mind: education

The previous two posts have been about David Geary’s concepts of primary and secondary knowledge and abilities; evolved minds and intelligence.  This post is about how Geary applies his model to education in Educating the Evolved Mind.

There’s something of a mismatch between the cognitive and educational components of Geary’s model.  The cognitive component is a range of biologically determined functions that have evolved over several millennia.  The educational component is a culturally determined education system cobbled together in a somewhat piecemeal and haphazard fashion over the past century or so.

The education system Geary refers to is typical of the schooling systems in developed industrialised nations, and according to his model, focuses on providing students with biologically secondary knowledge and abilities. Geary points out that many students prefer to focus on biologically primary knowledge and abilities such as sports and hanging out with their mates (p.52).   He recognises they might not see the point of what they are expected to learn and might need its importance explained to them in terms of social value (p.56). He suggests ‘low achieving’ students especially might need explicit, teacher driven instruction (p.43).

You’d think, if cognitive functions have been biologically determined through thousands of years of evolution, that it would make sense to adapt the education system to the cognitive functions, rather then the other way round. But Geary doesn’t appear to question the structure of the current US education system at all; he accepts it as a given. I suggest that in the light of how human cognition works, it might be worth taking a step back and re-thinking the education system itself in the light of the following principles:

1.communities need access to expertise

Human beings have been ‘successful’, in evolutionary terms, mainly due to our use of language. Language means it isn’t necessary for each of us to learn everything for ourselves from scratch; we can pass on information to each other verbally. Reading and writing allow knowledge to be transmitted across time and space. The more knowledge we have as individuals and communities, the better our chances of survival and a decent quality of life.

But, although it’s desirable for everyone to be proficient reader and writer and to have an excellent grasp of collective human knowledge, that’s not necessary in order for each of us to have a decent quality of life. What each community needs is a critical mass of people with good knowledge and skills.

Also, human knowledge is now so vast that no one can be an expert on everything; what’s important is that everyone has access to the expertise they need, when and where they need it.  For centuries, communities have facilitated access to expertise by educating and training experts (from carpenters and builders to doctors and lawyers) who can then share their expertise with their communities. and training is not just for school

Prior to the development of mass education systems, most children’s and young people’s education and training would have been integrated into the communities in which they lived. They would understand where their new knowledge and skills fitted into the grand scheme of things and how it would benefit them, their families and others. But schools in mass education systems aren’t integrated into communities. The education system has become its own specialism. Children and young people are withdrawn from their community for many hours to be taught whatever knowledge and skills the education system thinks fit. The idea that good exam results will lead to good jobs is expected to provide sufficient motivation for students to work hard at mastering the school curriculum.  Geary recognises that it doesn’t.

For most of the millennia during which cognitive functions have been developing, children and young people have been actively involved in producing food or making goods, and their education and training was directly related to those tasks. Now it isn’t.  I’m not advocating a return to child labour; what I am advocating is ensuring that what children and young people learn in school is directly and explicitly related to life outside school.

Here’s an example: A highlight of the Chemistry O level course I took many years ago was a visit to the nearby Avon (make-up) factory. Not only did we each get a bag of free samples, but in the course of an afternoon the relevance of all that rote learning of industrial applications, all that dry information about emulsions, fat-soluble dyes, anti-fungal additives etc. suddenly came into sharp focus. In addition, the factory was a major local employer and the Avon distribution network was very familiar to us, so the whole end-to-end process made sense.

What’s commonly referred to as ‘academic’ education – fundamental knowledge about how the world works – is vital for our survival and wellbeing as a species. But knowledge about how the world works is also immensely practical. We need to get children and young people out, into the community, to see how their communities apply knowledge about how the world works, and why it’s important. The increasing emphasis in education in the developed world on paper-and-pencil tests, examination results and college attendance is moving the education system in the opposite direction, away from the practical importance of extensive, robust knowledge to our everyday lives.  And Geary appears to go along with that.

3.(not) evaluating the evidence

Broadly speaking, Geary’s model has obvious uses for teachers.   There’s considerable supporting evidence for a two-phase model of cognition ranging from Fodor’s specialised, stable/general, unstable distinction, to the System 1/System 2 model Daniel Kahnemann describes in Thinking, Fast and Slow. Whether the difference between Geary’s biologically primary and secondary knowledge and abilities is as clear-cut as he claims, is a different matter.

It’s also well established that in order to successfully acquire the knowledge usually taught in schools, children need the specific abilities that are measured by intelligence tests; that’s why the tests were invented in the first place. And there’s considerable supporting evidence for the reliability and predictive validity of intelligence tests. They clearly have useful applications in schools. But it doesn’t follow that what we call intelligence or g (never mind gF or gC) is anything other than a construct created by the intelligence test.

In addition, the fact that there is evidence that supports Geary’s claims doesn’t mean all his claims are true. There might also be considerable contradictory evidence; in the case of Geary’s two-phase model the evidence suggests the divide isn’t as clear-cut as he suggests, and the reification of intelligence has been widely critiqued. Geary mentions the existence of ‘vigorous debate’ but doesn’t go into details and doesn’t evaluate the evidence by actually weighing up the pros and cons.

Geary’s unquestioning acceptance of the concepts of modularity, intelligence and education systems in the developed world, increases the likelihood that teachers will follow suit and simply accept Geary’s model as a given. I’ve seen the concepts of biologically primary and secondary knowledge and abilities, crystallised intelligence (gC) and fluid intelligence (gF), and the idea that students with low gF who struggle with biologically secondary knowledge just need explicit direct instruction, all asserted as if they must be true – presumably because an academic has claimed they are and cited evidence in support.

This absence of evaluation of the evidence is especially disconcerting in anyone who emphasises the importance of teachers becoming research-savvy and developing evidence-based practice, or who posits models like Geary’s in opposition to the status quo. The absence of evaluation is also at odds with the oft cited requirement for students to acquire robust, extensive knowledge about a subject before they can understand, apply, analyse, evaluate or use it creatively. That requirement applies only to school children, it seems.


Fodor, J (1983).  The modularity of mind.  MIT Press.

Geary, D (2007).  Educating the evolved mind: Conceptual foundations for an evolutionary educational psychology, in Educating the evolved mind: Conceptual foundations for an evolutionary educational psychology, JS Carlson & JR Levin (Eds). Information Age Publishing.

Kahneman, D (2012).  Thinking, fast and slow.   Penguin.

evolved minds and education: intelligence

The second vigorously debated area that Geary refers to in Educating the Evolved Mind is intelligence. In the early 1900s statistician Charles Spearman developed a technique called factor analysis. When he applied it to measures of a range of cognitive abilities he found a strong correlation between them, and concluded that there must be some underlying common factor that he called general intelligence (g). General intelligence was later subdivided into crystallised intelligence (gC) resulting from experience, and fluid intelligence (gF) representing a ‘biologically-based ability to acquire skills and knowledge’ (p.25). The correlation has been replicated many times and is reliable –  at the population level, at least.  What’s also reliable is the finding that intelligence, as Robert Plomin puts it “is one of the best predictors of important life outcomes such as education, occupation, mental and physical health and illness, and mortality”.

The first practical assessment of intelligence was developed by French psychologist Alfred Binet, commissioned by his government to devise a way of identifying the additional needs of children in need of remedial education. Binet first published his methods in 1903, the year before Spearman’s famous paper on intelligence. The Binet-Simon scale (Theodore Simon was Binet’s assistant) was introduced to the US and translated into English by Henry H Goddard. Goddard had a special interest in ‘feeble-mindedness’ and used a version of Binet’s scale for a controversial screening test for would-be immigrants. The Binet-Simon scale was standardised for American children by Lewis Terman at Stanford University and published in 1916 as the Stanford-Binet test. Later, the concept of intelligence quotient (IQ – mental age divided by chronological age and multiplied by 100) was introduced, and the rest, as they say, is history.

what’s the correlation?

Binet’s original scale was used to identify specific cognitive difficulties in order to provide specific remedial education. Although it has been superseded by tests such as the Wechsler Intelligence Scale for Children (WISC), what all intelligence tests have in common is that they contain a number of sub-tests that test different abilities. The 1905 Stanford-Binet scale had 30 sub-tests and the WISC-IV has 15. Although the scores in sub-tests tend to be strongly correlated, Early Years teachers, Educational Psychologists and special education practitioners will be familiar with the child with the ‘spiky profile’ who has high scores on some sub-tests but low ones on others. Their overall IQ might be average, but that can mask considerable variation in cognitive sub-skills. Deidre Lovecky, who runs a resource centre in Providence Rhode Island for gifted children with learning difficulties, reports in her book Different Minds having to essentially pick ‘n’ mix sub-tests from different assessment instruments because children were scoring at ceiling on some sub-tests and at floor on others. In short, Spearman’s correlation might be true at the population level, but it doesn’t hold for some individuals. And education systems have to educate individuals.

is it valid?

A number of issues have been vigorously debated in relation to intelligence. One is its construct validity. There’s no doubt intelligence tests measure something – but whether that something is a single biologically determined entity is another matter. We could actually be measuring several biologically determined functions that are strongly dependent on each other. Or some biologically determined functions interacting with culturally determined ones. As the psychologist Edwin Boring famously put it way back in 1923 “intelligence is what the tests test”, ie intelligence is whatever the tests test.

is it cultural?

Another contentious issue is the cultural factors implicit in the tests.  Goddard attempted to measure the ‘intelligence’ of European immigrants using sub-tests that included items culturally specific to the USA.  Stephen Jay Gould goes into detail in his criticism of this and other aspects of intelligence research in his book The Mismeasure of Man.  (Gould himself has been widely criticised so be aware you’re venturing into a conceptual minefield.)  You could just about justify culture-specificity in tests for children who had grown up in a particular culture, on the grounds that understanding cultural features contributed to overall intelligence. But there are obvious problems with the conclusions that can be drawn about gF in the case of children whose cultural background might be different.

I’m not going to venture in to bell-curve territory because the vigorous debate in that area is due to how intelligence tests are applied, rather than the content of the tests. Suffice it to say that much of the controversy about application has arisen because of assumptions made about what intelligence tests tell us. The Wikipedia discussion of Herrnstein & Murray’s book is a good starting point if you’re interested in following this up.

multiple intelligences?

There’s little doubt that intelligence tests are valid and reliable measures of the core abilities required to successfully acquire the knowledge and skills taught in schools in the developed industrialised world; knowledge and skills that are taught in schools because they are valued in the developed industrialised world.

But as Howard Gardner points out in his (also vigorously debated) book Frames of mind: The theory of multiple intelligences, what’s considered to be intelligence in different cultures depends on what abilities are valued by different cultures. In the developed industrialised world, intelligence is what intelligence tests measure. If, on the other hand, you live on a remote Pacific Island and are reliant for your survival on your ability to catch fish and navigate across the ocean using only the sun, moon and stars for reference, you might value other abilities. What would those abilities tell you about someone’s ‘intelligence’? Many people place a high value on the ability to kick a football, sing in tune or play stringed instruments; what do those abilities tell you about ‘intelligence’?

it’s all about the constructs

If intelligence tests are a good measure of the abilities necessary for learning what’s taught in school, then fine, let’s use them for that purpose. What we shouldn’t be using them for is drawing conclusions about a speculative entity we’ve named ‘intelligence’. Or assuming, on the basis of those tests, that we can label some people more or less ‘intelligent’ than others, as Geary does e.g.

Intelligent individuals identify and apprehend bits of social and ecological information more easily and quickly than do other people” (p.26)


Individuals with high IQ scores learned the task more quickly than their less-
intelligent peers” (p.59)


What concerned me most about Geary’s discussion of intelligence wasn’t what he had to say about accuracy and speed of processing, or about the reliability and predictive validity of intelligence tests, which are pretty well supported. It was the fact that he appears to accept the concepts of g, gC and gF without question. And the ‘vigorous debate’ that’s raged for over a century is reduced to ‘details to be resolved’ (p.25) which doesn’t quite do justice to the furore over the concept, or the devastation resulting from the belief that intelligence is a ‘thing’.  Geary’s apparently unquestioning acceptance of intelligence brings me to the subject of the next post; his model of the education system.



Gardner, H (1983). Frames of Mind: The theory of multiple intelligences. Fontana (1993).

Geary, D (2007).  Educating the evolved mind: Conceptual foundations for an evolutionary educational psychology, in Educating the evolved mind: Conceptual foundations for an evolutionary educational psychology, JS Carlson & JR Levin (Eds). Information Age Publishing.

Gould, SJ (1996).  The Mismeasure of Man.  WW Norton.

Lovecky, D V (2004).  Different minds: Gifted children with AD/HD, Asperger Syndrome and other learning deficits.  Jessica Kingsley.