In a previous post about the Flynn Effect, I discussed evidence showing that in Britain the average performance on the Raven IQ test had improved by an equivalent of about 30 IQ points over the 20th century, a figure that implies that the average Victorian, by today’s standard had a mean IQ of only 70! In an attempt to explain this, I suggested that the IQ’s of the average Victorian may have been artificially depressed by low education levels, however James Flynn did an analysis showing that only 5% of the Raven Flynn Effect can be explained by education. Add to that the fact that the Raven was designed to be culture fair, and thus not influenced by schooling, and I think we can virtually exclude education as even a partial explanation.
When studying the Flynn Effect, it’s best to focus on culture fair tests. You wouldn’t use tests that require defining words or describing similarities if you were comparing Bushmen to the British, you would use culture reduced tests. Similarly, the 21st century British experience a very different culture from Victorians, so they too can only be compared on culture reduced tests.
But if the Raven is culture fair, how do I explain why a population as capable as the Victorians scored so low? According to Richard Lynn, past generations had low IQ’s (and low brain size and low height) because they suffered from sub-optimum nutrition (especially before birth). However nutrition does not affect all parts of intelligence equally. Lynn cited data on identical twins showing that twin born better nourished typically had a non-verbal IQ 5.3 to 7.1 points higher, but a verbal IQ only 0 to 0.4 points higher. In other words, prenatal nutrition affects non-verbal IQ 31 times more than verbal IQ. In my opinion, this happens because humans evolved to live in groups, so the verbal IQ needed to speak, read, write, and exploit generations of cultural knowledge was more important than visuo-spatial abilities, so given the metabolic expense of the brain, when nutrients are scarce, evolution tends to preserve verbal-cultural abilities by sacrificing non-verbal acumen. Only when living standards skyrocket and nutrients become abundant do visuo-spatial abilities rapidly resurface, and you get a lot of kids who can slaughter their parents at video games and Rubik cubes.
We don’t know what the verbal IQ’s of Victorians were because unlike tests like the Raven, verbal IQ tests (with the possible exception of Digit Span on which they would have likely done as well as us) are far too culturally biased to meaningfully compare across generations. However if malnutrition stunted their non-verbal IQ’s by 30 points, we can divide this number by 31 to see that their verbal IQ’s were stunted by about 1 point. So even though Victorians had non-verbal IQ’s around 70, they had verbal IQ’s of 99 and thus were just as culturally sophisticated as we are.
What was their overall IQ? It depends how you calculate the composite score but probably more than one standard deviation below our mean, just as their brain size and height was more than one standard deviation below the modern mean. However because of their preserved verbal IQ’s, they were far more culturally advanced than a modern people with an overall IQ in the 80s. The Victorians had the intellectual skills the culture values (literacy, numeracy), so if we could meet them, we might regard them as brain damaged or learning disabled, rather than globally unintelligent.
So the lesson is, even though the Raven IQ test is an excellent measure of overall intelligence in well nourished populations, it dramatically underestimates the cultural functioning of people whose brains have been stunted by sub-optimum nutrition. Still, it’s often the only culture reduced test for third world populations who speak little English. In such cases, it should be a supplemented by a culture fair measure of verbal IQ like Backwards Digit Span, which for the poorly nourished, better measures genotypic ability.