"we show that the observed Flynn effect, its turning point, and subsequent decline can all be fully recovered from within-family variation. The analysis controls for all factors shared by siblings and finds no evidence for prominent causal hypotheses of the decline implicating genes and environmental factors that vary between, but not within, families."
"Stupid people have more kids" is exactly such a prominent causal hypothesis.
"Stupid people have more kids" is exactly such a prominent causal hypothesis.