IQ: Matzo with sauce get it nearly right
The journal abstract:
The paradox of intelligence: Heritability and malleability coexist in hidden gene-environment interplay.
Sauce, Bruno; Matzel, Louis D.
Intelligence can have an extremely high heritability, but also be malleable; a paradox that has been the source of continuous controversy. Here we attempt to clarify the issue, and advance a frequently overlooked solution to the paradox: Intelligence is a trait with unusual properties that create a large reservoir of hidden gene–environment (GE) networks, allowing for the contribution of high genetic and environmental influences on individual differences in IQ. GE interplay is difficult to specify with current methods, and is underestimated in standard metrics of heritability (thus inflating estimates of “genetic” effects). We describe empirical evidence for GE interplay in intelligence, with malleability existing on top of heritability. The evidence covers cognitive gains consequent to adoption/immigration, changes in IQ’s heritability across life span and socioeconomic status, gains in IQ over time consequent to societal development (the Flynn effect), the slowdown of age-related cognitive decline, and the gains in intelligence from early education. The GE solution has novel implications for enduring problems, including our inability to identify intelligence-related genes (also known as IQ’s “missing heritability”), and the loss of initial benefits from early intervention programs (such as “Head Start”). The GE solution can be a powerful guide to future research, and may also aid policies to overcome barriers to the development of intelligence, particularly in impoverished and underprivileged populations.
The above article is in the Psych. Bulletin, a top journal in psychology which is devoted to surveying the research literature on a particular subject and attempting a theoretical integration of it. Sauce & Matzel, however, don't come up with much. Their concept of gene–environment (GE) networks is really just a rehash of the well-known finding that to maximize your final IQ you need good environmental influences on top of your genetic given.
Considering that the article is a research summary, it is however interesting how high the genetic given is rated. They say that measured IQ is 80% genetic. Around 70% is the figure that has mostly been quoted in the past and people who hate the idea of IQ have on occasions put the figure as low as 50%.
The authors are aware that an enriched (stimulating) environment from early childhood on can bump up IQ but they are also aware that the gain is not permanent once the enrichment fades out. Headstart kids, for instance, test as brighter while in the program but revert to an IQ similar to their peers when they get into normal schooling.
But what the authors conclude from that is, I think, too optimistic. They seem to think that the environmental enrichment should be kept up into much later life. What they overlook is that all environmental influences tend to fade out as maturation goes on and by about age 30 environmental influences seem to zero out entirely. Identical twins reared apart will have very similar IQs at whatever age that is measured but the greatest similarity occurs when it is measured around age 30.
So growing up is a process of your genetics coming to the fore and the advantages/disadvantages of your environment fading out. So enriching the environment throughout childhood is pissing into the wind. What you are trying to manipulate will have less and less influence as maturation goes on and it will have NO final influence.