Behavioral genetics and evolutionary psychology: Unified perspective on personality research

Human Biology, Apr 1998 by Segal, Nancy L, MacDonald, Kevin B

Heritable Individual Differences and Reproductive Success. Reproductive success is of considerable theoretical interest within an evolutionary framework. Mealey and Segal (1993) integrated behavioral genetic and evolutionary approaches in a life history analysis of reproduction-related behaviors and reproductive success. Responses to selected items from a life history interview and the Briggs Life History Questionnaire were examined for MZ twin pairs raised apart and were compared between males and females. Some reproduction-related behaviors were associated in a proximal sense with heritable personality and health-related factors, although this relationship did not translate into predictable differences in number of offspring. Reproduction behaviors of males showed greater variability than those of females because of both genetic and environmental factors.

Maternal Preference. Mann (1992) studied preterm twins as a "natural experiment" for understanding differences in parental response as a function of infant health. It was of interest to determine whether mothers showed preference for the relatively healthier infant, as would be anticipated by evolutionary reasoning. Specifically, investment in healthier offspring would help to ensure reproductive success. Interestingly, maternal response patterns were associated with infant health at 8 months of age, with healthier twins being favored. The twin sample, however, was quite small (N = 7 pairs) and zygosity diagnosis was neither performed nor considered in the analyses. This was unfortunate, given that differences in mothers' behaviors toward relatively healthy or unhealthy DZ cotwins may have been confounded with genetic differences between them.

Infant Social Behavior. Plomin and Rowe (1979) failed to find significant MZ-DZ twin differences in infant social behaviors directed toward the mother but found heritable variation underlying social response to a stranger. Reasoning from the research of Bowlby (1969), Plomin and Rowe suggested that the evolutionary underpinnings of attachment were not intrinsic to the motherchild bond but rather to pressure toward wariness of novelty.

New Research Study 1: Birth Order and Personality. Following an extensive review of the psychological literature by Ernst and Angst (1983), it has been generally accepted that birth order does not significantly affect personality development. Recent provocative analyses by Sulloway (1995, 1996), undertaken with an evolutionary perspective in mind, promise to force serious rethinking of this interesting area. It was anticipated that birth order differences would be real and would fall into predictable classes. Furthermore, a series of specific predictions was developed with reference to the dimensions of the FFM. For example, first-borns enjoy favored status with parents, given their greater reproductive value, relative to younger siblings. They are expected to attempt to maintain this status and so be attentive to their parents' desires. In contrast, given their lesser identification with parental authority, younger siblings may be more open to new experiences and may use this tendency to divert resources from older siblings. Examination of scientists' support for or rejection of evolutionary theory supports this view, with laterborns showing greater acceptance of a novel perspective. In this context birth order may be conceptualized as a nonshared environmental factor affecting differential parental investment in siblings.