New questions about old heritability estimates

Abstract

This note summarizes the main results of three recent studies on the heritability of mental traits: (1) The inferences Jinks and Fulker (1970) derived from Shields’s (1962) twin data are invalid since the assumptions of the genetic model are consistently violated by these data. A purely environmental model fits them better by a factor of 2. (2) Holzinger’s heritability coefficient (h2) is invalid since his derivations imply that dizygotic twins share no genes. (3) In contrast, Nichols’s (1965) heritability coefficient (HR) follows from a strictly additive genetic model. (4) However, the needed assumptions are consistently violated by Osborne’s (1980) personality data, which produce an excessive number of inadmissible HRs. A purely environmental model fits these data better by a factor of 14. Jointly, these results suggest that heritability estimates of mental traits in the literature should be viewed with caution. © 1989, The Psychonomic Society, Inc.. All rights reserved.