22 May 2013. People were smarter during Victorian times by as much as 14 IQ points, a new analysis by three psychologists suggests. They used measures of reaction times as a marker of general intelligence and showed that it has increased steadily from about 183 milliseconds to 250ms in men, and from 187ms to 277ms in women. The earliest measurements were made by Sir Francis Galton in the 1880s, and the authors claim that imprecise measurements in the past cannot explain the trend. The slowing of reflexes corresponds to a calculated decrease in general intelligence of about 1.2 IQ points per decade since the 1880s, i.e., a total of 14 IQ points overall.
The findings are counter to the so-called Flynn effect. Thus, actual IQ scores from different decades suggest an increase in IQ with time, not a decrease. However, this is likely an artifact, as people now enjoy better teaching, health and nutrition. Such effects would not impact the simple reaction times that the researchers studied as a possible indicator of the genetic component of general intelligence.
The researchers then speculate that intelligence has been declining due to a “reverse” natural selection, as the most intelligent people now have fewer children on average than in previous decades, while there are higher survival rates among people with less favourable genes. This conclusion is clearly inspired by Professor Arthur Jensen’s work (see ‘Only one chance’, page 108). But are they not jumping to conclusions?
In a previous study of the increased reaction times over time, Irwin Silverman suggested that slower reflexes today could be due to effects of toxic chemicals, aka brain drainers. In the new article, the three psychologists reject this possibility by referring to Muriel Lezak’s handbook on Neuropsychological Assessment from 1983 (the most recent edition is from 2004). Much research during recent decades has documented that both reaction time and IQ are negatively affected by neurotoxic chemicals. Thus, it seems that Silverman’s conclusion is still viable.
However, before we accept industrial chemicals as the cause of the reported poorer reflexes and possible IQ declines, we need to consider the history of exposures. While there were no modern pesticides around in the 1880s, there certainly was lead, arsenic, some solvents and other brain drainers. Poisoning cases were frequently described, although we cannot know how common they were. And perhaps the adults that Francis Galton examined in the 1880s were born at a time where these brain poisons were fairly rare. It is hard to say, but the historical data on reaction times are certainly worrisome.