The r/K theory of human individual differences

Differential Use of Reproductive Strategies by Human Groups?

J.P. Rushton has presented a series of articles proposing that different racial groups, having evolved under different environmental conditions, have been differentially selected, resulting in genetic differences in their reproductive behavior, intelligence, and “social rule-following.” Rushton's model is discussed with respect to two controversial points: criticisms of the nature of the data and analyses, and alternative explanations of the data. I concur with Rushton in the belief that different human groups utilize different strategies, but find the differential use of species-wide, environmentally contingent tactics a more parsimonious explanation than genetic differences.

The Cognitive Differentiation-Integration Effort Hypothesis: A Synthesis between the Fitness Indicator and Life History Models of Human Intelligence

This article presents a potential synthesis between the fitness indicator and life history models of human intelligence through consideration of the phenomena of ability differentiation and integration. The cognitive differentiation-integration effort hypothesis proposes that these effects result from a life history tradeoff between cognitive integration effort, a mating effort component associated with strengthening the positive manifold amongst abilities; and cognitive differentiation effort, a somatic effort component associated with the cultivation of specific abilities. This represents one of two largely independent sources of genetic variance in intelligence; the other is mediated by general fitness and mutation load and is associated with individual differences in levels of ‘genetic g‘. These two sources (along with a common source of environmental variance) combine to give rise to a variety of cognitive phenotypes characterized by different combinations of high or low levels of ‘genetic g‘ and cognitive specialism or generalism. Fundamental to this model is the assumption that measures of life history speed ( K) and g are essentially independent, which is demonstrated via meta-analysis of 10 studies reporting correlations between the variables (ρ = .023, ns, n = 2056). The implications of the model are discussed in an evolutionary, ecological, and developmental context. Seven key predictions are made in the discussion which if tested could provide definitive evidence for the hypothesis.