Cooperation, Competition, and Altruism in Human Twinships: A Sociobiological Approach

Abstract

The comparative study of social relationships within monozygotic (MZ) and dizygotic (DZ) twin pairs affords a novel and informative approach to understanding how relative genetic relatedness may affect social-interactional outcomes and processes. Some old questions, such as whether MZ twins are more cooperative than DZ twins, acquire fresh meaning in light of social-genetic and sociobiological theorizing. Consider, for example, the two quotations cited above: These statements are generally reflective of the social-interactional tendencies observed between identical and fraternal twins (Frank & Cohen, 1980; Koch, 1966). Psychoanalytically oriented psychologists would most likely offer explanations based on parental attitude, physical similarity, and cultural expectations: “Physical similarity, mutual satisfactions, and reactions of others induce [identical] twins to see themselves as intimately connected and undifferentiated parts of [an] inseparable unit” (Siemon, 1980). A sociobiological view additionally acknowledges the relative genetic commonality in the two types of twins as contributing to their average differences in affiliation. It might be argued that the genetic identity of MZ twins may underlie hypothesized “recognition mechanisms” that could “trigger a series of emotions whose net effect is tribal unity” (Freedman, 1979).