There are now several convincing papers that show a dysgenic effect in Western countries, but when I say big dysgenic effect what I mean are the estimates given by Woodley of Menie. He claims that in great Britain over the last hundred years average IQ has dropped by more than 10 points, that is 1 point per decade.
There are several reasons why I find these estimates unrealistic. One reason is that for such a big dysgenic effect presumably limited to western countries, the IQ gaps we see today are remarkably similar to Galton’s estimates 160 years ago.
Another reason to be skeptical is that we actually live in the golden age of mathematics. It seems unrealistic that after a drop of more than 10 points we would still have the geniuses to solve century old problems like the Poincare conjecture or Fermat’s last theorem.
I would also assume that some of the normal IQ tests used in the Wechsler test, would show a negative Flynn effect over the last decades. In actual fact the Flynn effect of the different subtests ranges from 0.07 to 1.59 standard deviations for the second five decades of the last century in the US. If the effect of environmental improvements can range from 0 to „a lot“, it seems a priori unlikely that the subtests with the weakest Flynn effect more or less exactly cancels a large dysgenic effect.
Woodley’s shtick is to find different traits that correlate with IQ and show that some sample many decades ago scored better than the average person does today. Unfortunately, this amounts to cherry picking and the long time between the studies makes sampling problems impossible to rule out.
Myopia for example correlates with IQ and has become much more prevalent in the last century. The correlation is even due to an overlap of genetic factors. Does the increasing prevalence of myopia prove a eugenic effect? Hardly. The true dysgenic effect is probably 2 to 5 times weaker as estimated via polygenic scores for the population of Iceland.