I don’t think IQ tests are rubbish. They are a useful tool that can help identify specific learning difficulties and do appear to measure something we can call general cognitive ability. I’m not going to do a full treatment of the ins and outs of IQ here but rather just focus on one idea that is misunderstood – the heritability of IQ.
By looking at monozygotic twins and by other means, researchers can examine which traits are primarily due to genetic factors or to environmental factors. Actually even the way I just described that is misleading – everything is a bit of both. Our genes express shape our development in the context of environment but we can still look at particular situations and see the extent to which genes or environment influence particular characteristics.
One of those characteristics is IQ and in Western developed nations the degree to which IQ is inherited has been estimated as high as 0.8 (on a scale of 0 to 1) in adult twins. Oddly the estimate is much lower when looking at children (0.45). However, some people see this as confirming all sorts of odd ideas about race or society.
So why is this a weird internet idea? Primarily because it isn’t showing what people may think it is showing. Genetics may well play a role in intelligence – indeed it must play some role because our genes affect all parts of our bodies including our brain – but what the heritability studies are looking at is the extent to which heritability accounts for the variation in IQ between people. Most of this data has been gathered in WEIRD societies, that is: Western, educated, industrialized, rich and democratic. Why does this matter? If society and our general cognitive environment have an impact on IQ then a whole set of factors will add up to a ‘rising tide that lifts all boats’ – factors such as most people having sufficient food, some access to modern medical care, free compulsory education for children, access to television, high levels of literacy or even exposure to urban environments that may help improve the cognitive skills that IQ tests focus on (but not necessarily the cognitive skills IQ tests might not focus on). As everybody in a modern urbanized wealthy Western democracy gets some exposure to these factors, a great deal of a person’s IQ may be accounted for by those factors but almost none of the VARIATION between people.
What would we see if this was the case? Well what we would expect to see is overall IQ scores improving across the board in Western societies up to some point of diminishing returns. And that is exactly what we do see.