Why Offspring in Nonhuman Families Differ:

摘要

Offspring within families, both human and nonhuman, often differ. The obvious question is: Why? Work on psychological differences on children within human families has focused primarily on differences in the nonshared environment of contemporary siblings, though the precise location of this nonshared environment is still the subject of much debate. Here I explore the range of explanations for within-brood diversity from the perspective of nonhuman families, particularly birds that share certain key features with human families. I examine the role of social rank in creating a nonshared environment within the family, and present data from a model system (an altricial bird) to illustrate how different the effective environments experienced by offspring sitting side-by-side in the same confined physical space, tended by the same parents, and experiencing similar ecological variability, can be. These broodmates can effectively live in different worlds. I then briefly explore other sources of diversity among offspring in nonhuman families, including within brood genetic differences and non-genetic maternal (parental) effects that often covary with birth / hatching rank. Given the ubiquity and far-reaching consequences of maternal effects in nonhuman families, and some human data suggestive of similar patterns, it would seem worthwhile to explore the potential role of maternal effects in creating phenotypic diversity in psychological traits among children in human families.