This post summarises the arguments in the fourth chapter of my new book, Making Kids Cleverer. The rest of the chapter summaries can be found here.

A central consideration to the project of making kids cleverer is where intelligence comes from; is it in our genes or is it a product of our environments? The answer is, both. In a very obvious sense no one is ‘born clever’. Babies would universally perform poorly on IQ tests, but some may have a greater potential for intelligence than others. The mistake is to believe that our genes represent our fate. The science of behavioural genetics is probabilistic not deterministic. That said, common sense and the evidence of experience tells us that some people really are cleverer than others. Even though there is no end of academic quarrelling about exactly what intelligence might be and what IQ tests measure, we naturally find ourselves thinking of some people as bright and others as not. 

Heritability is not an intuitive concept and a fair part of the chapter is spent discussing how it works. Our genes indicate, at best, a statistical probability of how clever we might end up being, but these probabilities change markedly depending on our environment. So what sort of environmental factors might matter? I review the correlations with socio-economic status as well as considering various other inputs such as parenting and school.

I also review some of the research around group differences including sex and race. This was one of the hardest sections to get right because it’s also impossible to mention race without someone calling you a racist. I make it clear that the scientific consensus is that race, as applied to human beings, is a biologically meaningless term and that if race is biologically meaningless, it must follow that race has no causal effect on genetic differences in IQ. But just because race is biologically meaningless, it doesn’t follow that the term has no cultural, political or economic meaning. This tells us that difference in the IQ of racial groups must be product of their cultural, political and economic circumstances. Or in other words, if some racial groups score less well them than others, this is due to unfair environmental conditions. 

And because I just know some fat head somewhere will find themselves incapable of avoiding terms like eugenics, I say this:

The belief that human beings can be selectively bred in the hunt for good genes is now rightly and roundly condemned, and the eugenics label utterly abhorred as both monstrous and intellectually incoherent. Gregor Mendel’s research into pea plants led to the discovery of particulate inheritance and recessive genes, which makes a nonsense of the idea that undesirable characteristics could be weeded out through selective breeding. There is simply no way to spot people who carry but don’t express a gene; attempting to do so would lead inexorably to inbreeding, resulting in more, not fewer, heterozygous conditions. Just in case anything here seems ambiguous, let me be absolutely clear: eugenic attempts to raise intelligence are not only morally repugnant, they are also deeply stupid. [emphasis added]

Equally contentious is the well-established finding that parenting has little to no effect on adult IQ. If two adopted children are brought up in the same home they will be no more similar in personality than two adopted children raised in completely different homes. Similarly, a pair of identical twins reared in the same home are not much more alike than twins reared in separate homes. As everyone knows, identical twins share 100% of their genetic material, but despite this there are often observable differences in their behaviour and personalities. What accounts for these differences is referred to as ‘the environment’. Behaviour geneticists have identified two broad categories of environmental effects: shared and non-shared. Shared environmental effects are those that siblings have in common and, by definition, these cannot account for the differences between identical twins because, if they are raised in the same family, they share them. Therefore, all differences must be non-shared in origin.

To say this comes as unwelcome news to many parents is something of an understatement. I’m not going to rehash the research here, but if you’re interested you can sift through the summary in the book. But, on a more positive note, this means we have to think about what non-shared environmental effects might be out there. One powerful contender is the role of peer groups. Although Robert Plomin in his recent book, Blueprint, has made the claim that peer effects are gene effects by proxy (our DNA determines what peers we select) this can only be true to an extent. I contend that peer effects – whatever their cause – exert a powerful influence over all sorts of aspects of children’s personalities, including their IQ. 

Finally, I explain why some of the attempts to manipulate the environment of less advantaged children has failed to have a long-term effect on their intelligence by comparing IQ to health. Efforts to make people healthier only tend to persist fort as long as they’re making healthy choices. The effects of dit and exercise wear off relatively quickly and the same is almost certainly true of efforts to ‘artificially’ increase children’s intelligence. Instead we should focus our efforts on strategies that are more likely to last by seeking to change children’s cognitive habits over the longer term.