Flynn-Dickens Model for IQ Gains

Take those born with genes that make them a bit taller and quicker than average. When they start school, they are likely to be a bit better at basketball. The advantage may be modest but then reciprocal causation between the talent advantage and environment kicks in. Because you are better at basketball, you are likely to enjoy it more and play it more than someone who is bit slow or short or overweight. That makes you better still. Your genetic advantage is upgrading your environment, the amount of time you play and practice, and your enhanced environment in turn upgrades your skill. You are more likely to be picked for your school team and to get professional coaching.

Thanks to genes capitalizing on the powerful multiplying effects of the feedback between talent and environment, a modest genetic advantage has turned into a huge performance advantage. Just as small genetic differences match people with very different environments, so identical genes tend to produce very similar environments—even when children are raised in separate homes.

In other words, kinship studies of basketball, no matter whether they involved people with identical genes or different genes, would underestimate the potency of environmental factors. Playing, practicing, being on a team, coaching, all of these would be credited to genes—simply because differences in them tend to accompany genetic differences between individuals. Genes might seem to account for as much as 75 percent of variance across individuals in basketball performance. If someone showed that the present generation was far more skilled at basketball than the last (as indeed they are), Jensen's math would prove that it was impossible. It would show that those aspects of environment that are not correlated with genes (which is all that environment gets credit for in kinship studies) were very feeble. So feeble that the present generation would have to be within the top one percent of the last in terms of quality of environment for basketball.

The cognitive ability differences measured by IQ tests may have the same dynamics. People whose genes send them into life with a small advantage for these abilities start with a modest performance advantage. Then genes begin to drive the powerful engine of reciprocal causation between ability and environment. You begin by being a bit better at school and are encouraged by this, while others who are a bit 'slow' get discouraged. You study more, which upgrades your cognitive performance, earn praise for your grades, start haunting the library, get into a top stream. Another child finds that sport is his or her strong suit, does the minimum, does not read for pleasure, and gets into a lower stream. Both of you may go to the same school but the environments you make for yourselves within that school will be radically different. The modest initial cognitive advantage conferred by genes becomes enormously multiplied.

If g-factor is inherited, then how do we explain the Flynn Effect? This model suggests genetic advantages translates into environmental advantage, the environment feeds back to become more challenging.