The effects of educational training are only one case of producing two groups (before and after) separated by IQ test performance on easier and harder items. The crux of the issue is whether we know that the causes between groups are genetic if they are differentiated by a Jensen effect and that the causes are environmental if they are differentiated by an anti-Jensen effect. A Jensen effect occurs when the two groups differ more as cognitive tasks become more complex. It is shown that genes vs environment must be diagnosed on a case-by-case basis, not in terms of whether a Jensen effect is present.

Te Nijenhuis et al. (2019) cite studies that show that training on cognitive tasks produces the largest standardized gains on the easiest items and the smallest standardized gains on the most difficult items. They note that this creates an anti-Jensen effect, and use this as a trump that is supposed to show that my basketball examples are irrelevant. I use a new basketball example that is compatible with those studies. It assumes that at some point improvement on the easy skills ‘stalls’ – and all that is left is some improvement on the hard skills. Therefore, further environmental enhancement means the higher level skill gap is increased, which gives a classic Jensen effect, which shows that the presence of such does not entail genetic causality. The difference is that we really can produce virtually optimum basketball skills while for cognition, we are still well short. I also address the problem of why IQ gains over time do not show an anti-g pattern. After all, they are environmentally caused, and ‘should’ do so if an anti-g pattern and environmental causes go together.