Dr Rosalind Arden has investigated whether the concept of general intelligence, usually seen as exclusively human, can be found in apes and dogs, and finds positive results. This is interesting in its own right, and also useful in refuting the argument that “g” is just an artefact of the intelligence tests used in factor analytic studies. I will try to get her to report more about her work on dogs next week.
In the mean time, here is her note replying to the general question as to how researchers in the field see the topic of nature and nurture, and whether it is worth continuing to research it.
Nature and Nurture
The standard statistical methods in behavioural genetics (the field in which nature and nurture are empirically tested) quantify the proportion of differences among a measured population (at a specific point in time) on a given behaviour, characteristic or trait. This gives results such that differences among people are (for example) 60% genetic and 40% environmental.
What does the average reader make of this 40%? What do we mean by the ‘environment? Most people I work with seem to assume that: we don’t know exactly, but it is something to do with the world out there. That may be true, and there may be significant elements of the world out there that do contribute to such differences (such as acute infections in childhood). But we have done a woeful job of finding out just how much of this ‘environment’ could be random biological developmental noise, rather than the environment 'out there in the world'. One place to start with this question is to measure the variability of specified traits within a population of organisms that share the same genes. Work like this has been done - researchers have examined variability within such 'isogenic' populations, but their findings have not been much discussed in relation to the meaning of the 'unique environment' in human studies.
The potency of Nature is often misunderstood. Knowing that the differences in trait X between people are caused 60% by genes does not tell you that genes determine 60% of trait X in Jane or Jimmy. As others have said, a heritability estimate is not a ‘gene-o-meter’. Heritability is a population level statistic, not an individual metric. Nor is knowing the population-level estimate of genetic influence on psychological traits (such as intelligence) very informative about limits (such as Jane/Jimmy could never get A levels’ or ‘would be assured A levels’) because there are so many other determinants of getting A levels. These include aspects of the external environment – and other traits in Jane/Jimmy (such as propensity to be excited by work, having friends who encourage work, and so on).
It’s rarely useful to ‘know less’ (the alternative to knowing more); so learning more about nature and nurture is a good thing. There is great consensus among scientists who conduct empirical work in this area about the value of knowing more - which is encouraging. Pretty much everyone I know: shares the view that learning about ‘the causes of traits’ is a work in progress, has some humility about what we know, and is keen to learn more.