Resolving the IQ paradox: Heterosis as a cause of the Flynn effect and other trends.

Abstract

IQ test scores have risen steadily across the industrialized world ever since such tests were first widely administered, a phenomenon known as the Flynn effect. Although the effect was documented more than 2 decades ago, there is currently no generally agreed-on explanation for it. The author argues that the phenomenon heterosis represents the most likely cause. Heterosis, often referred to as hybrid vigor, is a genetic effect that results from matings between members of genetically distinct subpopulations, such as has been occurring in human populations through the breakup of small, relatively isolated communities owing to urbanization and greater population mobility. In Part 1 of the article, empirical findings are listed that are consistent with a heterosis hypothesis but render other hypotheses either implausible or very difficult to test. In Part 2, a formal model of the process of heterosis is presented. The goal of the modeling is to develop a quantitatively rigorous method for estimating the potential contribution of heterosis in the Flynn effect, as well as trends observed in other heritable traits and conditions.

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

“…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.…”

Mixed-Ethnicity Face Shape and Attractiveness in Humans

“…For example, in non-human animals, cross-bred dairy cows gain weight faster and produce more milk (Cundiff et al 1974) and cross-bred dogs are more successful in guide dog training (Ennik et al 2006). In humans, heterosis has been suggested to be linked to factors such as early growth (Penrose 1955;Wolanski et al 1970) and some authors have suggested that increase in IQ may be linked to heterosis (Mingroni 2007). Such arguments might suggest that mixed-ethnicity faces may be attractive because such individuals have different appearing faces (eg healthier, more symmetric, etc) because individuals with a diverse set of genes are able to develop or maintain attractive traits.…”

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]).…”