Everyone knows about the Flynn Effect, but very few about the Woodley Effect.
When Woodley was working on his paper in 2013 “Were the Victorians cleverer than us? The decline in general intelligence estimated from a meta-analysis of the slowing of simple reaction time” I wrote to Charles Murray about his findings, and in his reply he asked: “So when are we going to get a reconciliation of the Flynn Effect and the Woodley Effect?” Thus, Murray has named both the apparent environmental rise in intelligence, and the possible fall in underlying genetic intelligence.
By analogy with agriculture, we could say that the Flynn Effect is about adding fertilizer to the soil, whereas the Woodley Effect is about noting the genetic quality of the plants. In my last post I described the current situation thus: The Flynn Effect co-exists with the Woodley Effect. Since roughly 1870 the Flynn Effect has been stronger, at an apparent 3 points per decade. The Woodley effect is weaker, at very roughly 1 point per decade. Think of Flynn as the soil fertilizer effect and Woodley as the plant genetics effect. The fertilizer effect seems to be fading away in rich countries, while continuing in poor countries, though not as fast as one would desire. The genetic effect seems to show a persistent gradual fall in underlying ability.
The review is unusual, to say the least. It is rare to read so positive a judgment on a young researcher’s work, and it is extraordinary that one researcher has changed the debate about ability levels across generations, and all this in a few years since starting publishing in psychology.
The table in that review which summarizes the main findings is shown below. As you can see, the range of effects is very variable, so my rough estimate of 1 point per decade is a stab at calculating a median. It is certainly less than the Flynn Effect in the 20th Century, though it may now be part of the reason for the falling of that effect, now often referred to as a “negative Flynn effect”.
You can now see that calculating the rate of decline is somewhat difficult. Perhaps a median would be “less than 1 per decade”. The time spans vary, the measures also, though the latter variance is an advantage, in that it suggests a general underlying cause. However, the range of estimated decline is very large, from 0 to 4.8 per decade.
- Colour acuity, over 20 years (0.8 generation) 3.5 drop/decade.
- 3D rotation ability, over 37 years (1.5 generations) 4.8 drop/decade.
- Reaction times, females only, over 40 years (1.6 generations) 1.8 drop/decade.
- Working memory, over 85 years (3.4 generations) 0.16 drop/decade.
- Reaction times, over 120 years (4.8 generations) 0.57-1.21 drop/decade.
- Fluctuating asymmetry, over 160 years (6.4 generations) 0.16 drop/decade.
Either the measures are considerably different, and do not tap the same underlying loss of mental ability, or the drop is unlikely to be caused by dysgenic decrements from one generation to another. Bar massive dying out of populations, changes do not come about so fast from one generation to the next. The drops in ability are real, but the reason for the falls are less clear. Gathering more data sets would probably clarify the picture, and there is certainly cause to argue that on various real measures there have been drops in ability. Whether this is dysgenics or some other insidious cause is not yet clear to me.
Ultimately, I cannot give “Historical variability in heritable general intelligence” a higher recommendation. Not since The Bell Curve (Herrnstein &Murray, 1994) has a single work offered such immense psychometric revelations about advanced human societies and their pasts and futures.
My view is that whereas formerly the debate was only about the apparent rise in ability, discussions are now about the co-occurrence of two trends: the slowing down of the environmental gains and the apparent loss of genetic quality. In the way that James Flynn identified an environmental/cultural effect, Michael Woodley has identified a possible genetic effect, and certainly shown that on some measures we are doing less well than our ancestors.
How will they be reconciled? Time will tell, but here is a prediction. I think that the Flynn effect will fade in wealthy countries, persist with fading effect in poor countries, and that the Woodley effect will continue, though I do not know the cause of it.