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If the radical theory that (genetic) intelligence has been declining by the equivalent of 1.16 IQ points per decade is correct, scientists should hurry up and try to figure out how to clone the Victorians while they still have enough intelligence to do so, because at the rate genetic IQ is dropping, we may need Victorians to run our society before utter collapse. If this theory is correct, in just the last 125 years, we’ve set human evolution back at least 10,000 years and have done incredible genetic damage to our species.

And yet since the 19th century, intelligence as measured by IQ tests has increased at least 30 points, causing the difficulty of IQ tests to constantly have to be increased to keep the average score from rising above 100. This is known as the Flynn effect.

Earlier this summer I though I had the Flynn effect all figured out. Of course it wasn’t me who figured it out, it was scholar Richard Lynn who decades ago noted that the rise in IQ scores had been paralleled by a rise in height (and brain size) so obviously nutrition was causing both. The average Victorian man had an IQ below 70 (by modern standards) and a height around 5’5.8″. The average young white man today has an IQ around 100 and a height of 5’10.4″. So IQ has increased by about two standard deviations, and height has increased by a comparable amount (1.78 standard deviations). It seemed the nutrition theory explained everything quite nicely and I never quite understood why IQ experts kept violating Occam’s razor by searching for alternative explanations for the Flynn effect, when Lynn brilliantly explained it so long ago. And whenever the Flynn effect appeared bigger than nutrition could explain, Lynn noted that the increase in 20th century schooling probably spuriously added an additional 8 or so IQ points to modern test scores.

The problem is that this new theory that genetic intelligence declined by one standard deviation since the Victorian era means that we no longer have to only explain why moderns are scoring two standard deviations above Victorians on psychometric tests, we also have to explain why they’re not scoring one standard deviation lower. In other words we have a three standard deviation IQ difference to explain and nutrition (as measured by height) has only increased by 1.78 standard deviations.

But then I had an epiphany. If dysgenics has caused our genetic IQ to drop by one standard deviation, then why not our genetic height? Well, genetic intelligence has declined because in the absence of natural selection (survival of the fittest), low IQ people have more children than high IQ people because they have trouble controlling their sex drives, planning ahead and using birth control. There’s no similar reason to expect short people to have more children (and in fact the research shows that while short women have more kids, short men have less, so it’s a wash).

But dysgenic fertility is only half the proposed explanation for the one standard deviation drop in genetic IQ. The other half was explained by increased mutation load, and there’s reason to think height might be just as depressed by mutation load as IQ is. So just as mutations caused half the one standard deviation decline in genetic IQ, they likely depressed genetic height by half a standard deviation.

So I think if scientists were able to clone the Victorians, we would not only find that they score about 115 on IQ tests if reared in modern society (as opposed to the sub-70 IQ’s they would have obtained in the 19th century), but we would also find that Victorian men would be taller than white men today and clock in at 5’11.7″ (2.3 standard deviations higher than the 5’5.8″ height they had in their own era). In other words, when you control for genetic decline, we see nutrition has probably actually increased by 2.3 standard deviations, almost enough to explain the three standard deviation IQ difference we would expect between Victorians raised in our time compared to their time.

How can the remaining 0.7 standard deviation be explained? Probably by the rise in schooling, media, parental socio-economic status and other cultural factors that artificially prop up IQ scores without actually increasing intelligence.