An evolutionary theory of the family.

Abstract

An evolutionary framework for viewing the formation, the stability, the organizational structure, and the social dynamics of biological families is developed. This framework is based upon three conceptual pillars: ecological constraints theory, inclusive fitness theory, and reproductive skew theory. I offer a set of 15 predictions pertaining to living within family groups. The logic of each is discussed, and empirical evidence from family-living vertebrates is summarized. I argue that knowledge of four basic parameters, (i) genetic relatedness, (ii) social dominance, (iii) the benefits of group living, and (iv) the probable success of independent reproduction, can explain many aspects of family life in birds and mammals. I suggest that this evolutionary perspective will provide insights into understanding human family systems as well.Two decades ago, in the introduction to his treatise, Sociobiology: The New Synthesis, E. 0. Wilson (1) stated that ". . . sociology and the other social sciences ... are the last branches of biology waiting to be included in the Modern Synthesis." He was referring to the untapped potential of darwinian thinking to provide a conceptual framework for better understanding many aspects of human behavior. In the intervening years, a small but growing number of evolutionary anthropologists and psychologists has begun making inroads into "darwinizing" the social sciences. But their progress has been slow and has often been met with resistance.Two often-cited reasons for such resistance are (i) a belief that the tremendous plasticity that exists in the expression of social behaviors renders applicability of biological (genetic) principles unlikely and (ii) the view that culture, rather than genes, is of overriding importance in mediating such behaviors in our own species. The first seemingly contradicts the idea of a heritable basis for social behaviors (an assumption of sociobiology), while the second argues that, even if present, heritable aspects of social behavior will be of minor importance. Both criticisms can be easily dispelled. The condition-dependent expression of many social behaviors in no way precludes them from genetic influence. The work of researchers such as Maynard-Smith (2) and Parker (3) has clarified the relationship between conditionality and the evolution of behavior. Indeed, the last decade has seen a marked shift toward viewing organisms as "decision makers," selected to accurately assess the consequences of different behavioral options available to them and to express those behavioral variants that maximize their fitnesses (e.g., refs. 4 and 5). Depending upon social circumstances, the optimal choice of behaviors may vary. But, providing that heritable variation exists in the assessment algorithms underlying the choices, natural selection can fine-tune the decision rules and thereby bring them into the realm of darwinian predictability.The second criticism pertains to the use of evolutionary models to predict the social behaviors of higher primates, partic...

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