Heterosis doesn't cause the Flynn effect: A critical examination of Mingroni (2007).

Abstract

Mingroni (2007) proposed that heterosis or hybrid vigor may be the principal driver of the Flynn effect--the tendency for IQ scores to increase at a rate of approximately 3 points per decade. This model was presented as a resolution to the IQ paradox--the observation that IQ scores have been increasing despite their high adult heritability--on the basis that substantial changes in IQ can only be accounted for by changes in underlying genetic factors. It is here argued that this model is predicated upon a misconception of the Flynn effect, which is most pronounced on the least g-loaded components of cognitive ability tests and is uncorrelated with genetic effects such as inbreeding depression scores (which are correlated with the g loadings of tests). Evidence supportive of the recently proposed life history model of the Flynn effect is presented. In the discussion, other theoretical objections to the heterosis model are also considered. On this basis, it is concluded that the Flynn effect is strongly entwined with developmental status and that heterosis cannot be its principal cause.

Can GE-Covariance Originating in Phenotype to Environment Transmission Account for the Flynn Effect?

“…Increases in migration are certainly compatible with the interpretation of Ph->E transmission as active GE-cov. While increases in genetic means seem plausible, the actual effect size is unlikely to be large [45]. We note that genetic mean increases pose no problem in principle, as they readily can be added to the model [38].…”

“…It has been hypothesized that genetic mean increases due to outbreeding (hybrid vigor) is an important contributor to the Flynn effect [44,45]. We consider it plausible that outbreeding has resulted in increases in genetic means.…”

Heterosis: Many Genes, Many Mechanisms—End the Search for an Undiscovered Unifying Theory

“…However, many interspecific hybrids suffer from reduced longevity and reductions in fertility. Heterosis in humans has been proposed, sometimes controversially, to affect multiple phenotypes including attractiveness [1], IQ [2,3], and height [4][5][6]. In agricultural settings, there are numerous examples in which heterosis has been harnessed to create more productive and more uniform products including livestock [7][8][9][10][11] and crop plants (reviewed in [12][13][14][15][16][17][18][19]).…”

Future Efforts in Flynn Effect Research: Balancing Reductionism with Holism

“…A good example of avoiding the IQ paradox can be seen in a recent critique of Mingroni [10] by Woodley [13]. Although he at least addresses the paradox, there is a complete lack of understanding that the problem is one of magnitude, not profile.…”

“…In the interest of full disclosure, however, I have argued for more than a decade that the most plausible cause of the Flynn effect is the genetic factor heterosis [10,12], (however, see [13]). For the record, I still believe heterosis is the only factor capable of explaining all relevant findings, including the consistently high heritability of IQ, the lack of shared family environmental effects, the so-called "twin paradox," the occurrence of trends in many other traits and conditions, the steady pace of the changes, the appearance of several of the trends in very young children, the limited impact of intervention efforts, the lack of lasting effects due to environmental insults, evolutionary implications, the magnitude of the changes, and other findings.…”