The association between g and K in a sample of 4246 Swedish twins: A behavior genetic analysis

Whereas the heritability of general intelligence (g) is very well documented, there are relatively few reports of the heritability of life history speed (K). Moreover, the correlation between g and K is of great theoretical significance. Here, we examine the heritabilities of g and K in a sample of 2123 complete Swedish twin pairs, as well as looking for evidence of common genetic variance between the two. We find a significant albeit very small correlation between relatively strong measures of g (the Wiener Matrizen Test) and K (the Mini-K; r = .03, p < .05). Controlling for attenuation by reliabilities and imperfect validity using validity generalization increased the correlation to rho = .05 (p < .05). There was no significant common additivity between g and K, however path elimination in behavior genetic structural equations modeling suggests that the small common variance is nonetheless likely to stem from shared additive genetic influences rather than from environmental influences. The implications of this are discussed. Our new estimate of the heritability of the life history in the Swedish population is a particularly significant result, as the heritability of life history speed has never before been established in non-US samples.