Open Access Kent State (OAKS)

Furthering the cause of consilience in the social sciences a model is proposed in which Eriksonian life span theory and life history theory are integrated. The model explains individual differences in the Eriksonian developmental stages as a function of the individual differences in developmental trajectories of life history theory as conceptualized by Belsky, Steinberg, and Draper (1991). Erikson's fifth stage of identity formation is used to examine the model, with the results of three studies presented to illustrate the viability of the model. Future research should examine other aspects of the model and the relationship between the developmental trajectories in life history theory and the Eriksonian stages in greater detail.

Until recently, variations in life history strategy were studied exclusively at the species level. Although this domain of study has been extended to examine systematic differences in life history strategy among various human ethnic groupings, more recent evolutionary theories of human development and related behavioral genetic work imply substantial within-group individual variation in life history strategy. We constructed a latent variable model identifying a single common factor, denoted as K, which underlies a variety of otherwise disparate life history parameters. This “K-Factor” loaded 0.36 on childhood attachment to the biological father, −0.36 on childhood attachment to any non-biological father figure, 0.38 on adult romantic partner attachment, −0.51 on mating effort, −0.58 on Machiavellianism, and −0.41 on risk propensity. The bivariate correlations of the K-factor with higher-order personality factors were statistically significant, −0.24 with “Big Neuroticism” and −0.67 with “Big Psychoticism”, and approached significance, correlating 0.12, with “Big Extraversion”. The K-factor appears to be an underappreciated individual difference variable of major importance to human development.

Multiple selective pressures maintain and increase heritable behavioral variability among individuals across both developmental and evolutionary time: (1) directional social selection favors convergent traits, promoting mutually beneficial cooperative interactions; (2) disruptive social selection favors divergent traits, providing release from within-species competition; (3) genetic diversification responds adaptively to the stochastic (random) characteristics of environmental hazards such as uncontrollable morbidity (disease) and mortality (death); (4) developmental plasticity epigenetically directs development adaptively along different alternative pathways, modifying permanent and stable behavioral dispositions to suit long-term contingencies of survival and reproduction; and (5) behavioral flexibility deploys rapid and reversible short-term adaptive behavioral responses to transient situations.

Evolutionary psychology is an important meta-theoretical paradigm for understanding universal and sex-differentiated adaptations. Despite this, it remains somewhat ignored within the mainstream study of individual differences. We outline some of the evolutionary approaches that lend to a fuller understanding of individual differences related to personality psychology. This chapter is presented in four main sections: (1) a brief summary of trait-based approaches that have been used to understand human personality, (2) an introduction to some of the evolutionary principles important to understanding behavior, (3) an explication of the function of individual differences within populations and the evolutionary mechanisms that produce such variation, and (4) a review of contemporary evolutionary models of individual differences with particular focus on personality traits.