Reaction times – a reliable marker of general intelligence – have declined steadily since the Victorian era from about 183 milliseconds to 250ms in men, and from 187ms to 277ms in women.
The slowing of our reflexes points to a decrease in general intelligence equivalent to 1.23 IQ points per decade since the 1880s or about 14 IQ points overall, researchers said.
Actual IQ scores from different decades cannot be directly compared because people today enjoy better teaching, health and nutrition which would help improve their results, the scientists explained.
But the reaction times signify that the genetic component of general intelligence – which leads to the type of creativity and invention typical of the Victorian era – has been dwindling over the past century.
Dr Michael Woodley, who led the study published in the Intelligence journal this month, identified the trend by comparing reaction times from trials conducted by Victorian scientists against those carried out in recent decades.
Some attribute this decline to dysgenics, which I’m skeptical of.
Although reaction time is positively correlated with IQ (around .25-.4), modern IQ tests don’t test for it, so even though it’s correlated, it’s not necessarily a measure of intelligence. The Victorian era was the period of Queen Victoria’s reign, from 20 June 1837 until her death on 22 January 1901. This precedes IQ testing, which did not become commonplace until WW1, by at least a generation, so it’s hard to make much of an inference about IQ. The original study is pay walled, so perhaps it explains how the Victorians were able to measure reaction times within a fraction of a second without the use of modern technology.
As discussed earlier, dysgenics can come from one of two forms: from the introduction of a low-IQ population that lowers the population mean such as due to immigration, or due to the prorogation of deleterious genes that lower mean IQ at the individual level. The former can explain a 14-point mean IQ decline over the past 110 years for the United Kingdom population, as a whole, due to immigration. However, given that permanent, fixed mutations to the human genome occur over much longer periods over thousands of years, such a sudden and rapid decline of the IQ of white Europeans due purely to genetics factors, seems implausible. This seems especially implausible given that IQ is polygenic, so it would probably require many mutations for IQ to fall so much. Not only that, but extrapolating a 14-point IQ decline over 100 years, implies that humans 10,000 years ago must have had super-human levels of intelligence, which is nonsense.