Is H2 = 0 a null hypothesis anymore?

This time I mean it: The nature-nurture debate is over

The target article is skeptical of the heritability concept while maintaining an old-fashioned point of view about it. As a descriptive statistic, it is to be expected that heritability goes up and down in different circumstances, but the relationship between heritability coefficients and the biological processes that underlie them is difficult to specify, and may be impossible in humans.

The evolutionary genetics of personality

Genetic influences on personality differences are ubiquitous, but their nature is not well understood. A theoretical framework might help, and can be provided by evolutionary genetics. We assess three evolutionary genetic mechanisms that could explain genetic variance in personality differences: selective neutrality, mutation‐selection balance, and balancing selection. Based on evolutionary genetic theory and empirical results from behaviour genetics and personality psychology, we conclude that selective neutrality is largely irrelevant, that mutation‐selection balance seems best at explaining genetic variance in intelligence, and that balancing selection by environmental heterogeneity seems best at explaining genetic variance in personality traits. We propose a general model of heritable personality differences that conceptualises intelligence as fitness components and personality traits as individual reaction norms of genotypes across environments, with different fitness consequences in different environmental niches. We also discuss the place of mental health in the model. This evolutionary genetic framework highlights the role of gene‐environment interactions in the study of personality, yields new insight into the person‐situation‐debate and the structure of personality, and has practical implications for both quantitative and molecular genetic studies of personality. Copyright © 2007 John Wiley & Sons, Ltd.

Weak Genetic Explanation 20 Years Later: Reply to Plomin et al. (2016)

Plomin, DeFries, Knopik, and Neiderhiser (2016, this issue) are correct in their assertion that many discoveries of behavior genetics have proven to be robust and replicable. I note, in contrast, that more specific assertions about the role of genetics in the development of behavior have failed to replicate. Reflecting on why more general findings replicate better than specific ones sheds light on the difficulties of studying complex human development and on the role played by genes in determining its course.

Three Laws of Behavior Genetics and What They Mean

Behavior genetics has demonstrated that genetic variance is an important component of variation for all behavioral outcomes, but variation among families is not. These results have led some critics of behavior genetics to conclude that heritability is so ubiquitous as to have few consequences for scientific understanding of development, while some behavior genetic partisans have concluded that family environment is not an important cause of developmental outcomes. Both views are incorrect. Genotype is in fact a more systematic source of variability than environment, but for reasons that are methodological rather than substantive. Development is fundamentally nonlinear, interactive, and difficult to control experimentally. Twin studies offer a useful methodological shortcut, but do not show that genes are more fundamental than environments.

Differential Susceptibility: The Genetic Moderation of Peer Pressure on Alcohol Use

Although peer pressure can influence adolescents' alcohol use, individual susceptibility to these pressures varies across individuals. The dopamine receptor D4 gene (DRD4) is a potential candidate gene that may influence adolescents' susceptibility to their peer environment due to the role dopamine plays in reward sensation during social interaction. We hypothesized that DRD4 genotype status would moderate the impact of 7th-grade antisocial peer pressure on 12th-grade lifetime alcohol use (n = 414; 58.7% female; 92.8% White). The results revealed significant main effects for antisocial peer pressure, but no main effects for DRD4 genotype on lifetime alcohol use. Adolescent DRD4 genotype moderated the association between peer pressure and lifetime alcohol use. For individuals who carried at least one copy of the DRD4 7-repeat allele (7+), antisocial peer pressure was associated with increased lifetime alcohol use. These findings indicate that genetic sensitivity to peer pressure confers increased alcohol use in late adolescence.

A phenotypic null hypothesis for the genetics of personality

We review the genetically informed literature on the genetics of personality. Over the past century, quantitative genetic studies, using identical and fraternal twins, have demonstrated that differences in human personality are substantially heritable. We focus on more contemporary questions to which that basic observation has led. We examine whether differences in the heritability of personality are replicable across different traits, samples, and studies; how the heritability of personality relates to its reliability; and how behavior genetics can be employed in studies of validity, and we discuss the stability of personality in genetic and environmental variance. The appropriate null hypothesis in behavior genetics is not that genetic or environmental influence on personality is zero. Instead, we offer a phenotypic null hypothesis, which states that genetic variance is not an independent mechanism of individual differences in personality but rather a reflection of processes that are best conceptualized at the phenotypic level.