Evolutionary biology and personality psychology. Toward a conception of human nature and individual differences.

Although personality psychology subsumes the study of both individual differences and species-typical characteristics, the field has not yet resolved several key concerns: (a) what are the most important species-typical characteristics; (b) what are the most important ways in which individuals differ; and (c) how can species-typical characteristics and individual differences be reconciled within a general theory of personality. Evolutionary biology provides one set of criteria for identifying these characteristics and for designating relative importance among them. Genotypic universality, automaticity, and adaptation are examined as potential criteria for identifying important species-typical characteristics. Heritability, inclusive fitness, sexual selection, and assortative mating are evaluated as criteria for designating important individual differences. Suggestions are made for resolving some of the conceptual and operational difficulties entailed by implementing these criteria. It is argued that, although substantial problems remain, evolutionary biology can provide one means for identifying relations between individual differences and species-typical characteristics. Evolutionary biology and personality psychology, broadly conceived, share several common concerns. Both fields seek to identify enduring organismic characteristics and to locate their origins and functional significance in environments. Both fields deal with past and present adaptation. And both grant a central role to individual variation, which is the focus of most personality research and the sine qua non of evolution. These shared concerns suggest intriguing potential connections. This article attempts to offer directions for an integrative effort, while identifying some of the difficulties of this endeavor. The first section of the article identifies several key issues in personality psychology, with particular attention given to the separation between approaches emphasizing species-typical tendencies and those focusing on systematic variation around those tendencies. The second section identifies themes in evolutionary biology that parallel those in personality psychology, typological and population approaches, and highlights some of the alternative aims, assumptions, methods, and limitations of each. The third section outlines three major directions for linking evolutionary biology and personality psychology. The final section attempts to identify some of the most promising programs for future research. Some Key Concerns in Personality Psychology Although disagreement exists about the defining issues in personality psychology, the following questions address one set of the field's prominent concerns: 1. What are the major enduring commonalities among people in action, motivation, and cognition? This question subsumes study of the origins of the major commonalities, their stability and change over time, their relations to each other, their functional significance, and their consequences. One major current concern is to establish criteria for considering something species typical or part of human nature. 2. What are the important enduring ways in which individuals differ in action, motivation, and cognition? This question embraces study of the origins of major individual differences, their development (stability and change) over time, the relations among them, and their consequences. A major task in personality psychology is to establish criteria for identifying the most important ways in which individuals differ (Allport, 1937; Buss & Craik, in press; Cattell, 1946; Goldberg, 1972; Wiggins, 1979). I would like to thank Leda Cosmides, Kenneth H. Craik, Stephan E. Glickman, Harrison G. Gough, Richard J. Herrnstein, Arthur R. Jensen, Douglas Kenrick, Gerald A. Mendelsohn, Daniel J. Ozer, Robert Plomin, Edward O, Wilson, and especially Carolyn Phinney for helpful comments on earlier versions of this article. Requests for reprints should be sent to David M. Buss, Department of Psychology and Social Relations, Harvard University, William James Hall, 33 Kirkland Street, Cambridge, Massachusetts 02138. 1 The term human nature is used here without reference to content and without commitment to particular units such as motivational states, cognitive processes, or classes of acts. October 1984 • American Psychologist Copyright 1984 by the American Psychological Association, Inc. Vol. 39, No. 10, 1 1 3 5 1 1 4 7 1135 3. How can the relations between the major commonalities and the major individual differences be conceptualized and understood? Subsumed by this question are the following subquestions. How do findings of individual variation limit or importantly qualify statements about the major commonalities? How do species-typical patterns constrain the manifested range of individual differences? How can theory and research on the major commonalities and individual differences be integrated to form a coherent understanding of our species? In the past five decades, a separation has developed in the field of personality psychology between theory and research. Most personality theories focus on describing human nature, on identifying, in Maddi's (1980) terms, the "core tendencies" or "core characteristics" of the species. Psychoanalytic theory, for example, posits universality of energizing force and of psychic apparatus, as well as invariance of stage sequence. Dimensions of individual difference can be derived from such theories. For example, variation can be attributed to differences in the speed of transition through the universal stages or to differences in the current level attained. But these individual differences are subsidiary to common attributes. Species-typical characteristics have usually taken precedence over individual differences in personality theories. In contrast, most current personality research focuses on individual differences: describing, explaining, and identifying covariation between the ways in which individuals differ. Indeed, many current personality psychologists define the field solely by reference to this issue: "Personality is that branch of psychology which is concerned with providing a systematic account of the ways in which individuals differ from one another" (Wiggins, 1979, pp. 395; Wiggins, Renner, Clore, & Rose, 1971). This focus seems to exclude from study the key issue of speciestypical characteristics that forms the core of most personality theories. In sum, although the prominent concerns in personality psychology involve individual differences and common human characteristics, the field has proposed few criteria for identifying the most important individual differences, the important speciestypical characteristics, and the relations between these sets of attributes (but see Cattell, 1946; Eysenck, 1967; Goldberg, 1972;Gough, 1968; Norman, 1963; Wiggins, 1979). Evolutionary biology provides one framework for investigating these issues. Typological and Population Approaches in Evolutionary Biology It is an oversimplification to speak of evolutionary biology as though it were a single, monolithic, consensually agreed upon set of ideas (Mayr, 1982). Major differences surround key issues such as the unit and level of selection (e.g., gene, individual, or group; see, e.g., Alexander, 1979; Dawkins, 1976; Williams, 1966), the amount of genetic variation within species (e.g., Wilson, 1978), and the explanatory status of evolutionary theory (e.g., Searle, 1978). At least two major themes may be identified, each with separate aims, assumptions, methods, and limitations. The first, here called "typological thinking" (adapted from Mayr, 1963), has as its aims discovering basic species-typical characteristics, discovering the adaptive significance of species traits, monitoring the genetic basis of species behavior, and predicting species-typical responses from evolutionary postulates. Applied to Homo sapiens, this set of concerns reduces to attempts to uncover the "pan-human psyche," the "traits of human nature" (Wilson, 1978, p. 34), the "human biogram" (Tiger & Fox, 1971), or the "universal human ethogram" (Fuller, 1983, p. 460). An assumption (sometimes implicit) of typological thinking is that within-species variation is relatively small, a deviation from the species archetype, and subsidiary in importance to the major topography of species traits. Among recent evolutionary approaches, sociobiology has tended to emphasize species-typical traits (as has ethology). Genetic variability within species is recognized, but does not occupy a central role in such approaches. According to Wilson (1978), "either possibility—complete cultural determination versus shared cultural and genetic determination of variability within species—is compatible with the more general sociobiological views of human nature" (p. 43). Indeed, even though genetic heterogeneity within populations is required by evolutionary models of sociobiology (Fuller, 1978, 1983), "sociobiology has tended to downgrade [within-species] differences and to stress the universal of human nature that have been shaped by similar selective forces everywhere" (Fuller, 1983, p. 470; emphasis added). Comparative phylogenetic analysis is one of the major methods of typological thinking (Wilson, 1975), Species comparisons highlight the similarities of our species with others, generating, for example, general mammalian traits (e.g., group living) or general primate traits (e.g., hierarchical social arrangement), as well as the unique features of each species. Correlating variations in ecological niches with variations in the traits of species that occupy 2 It may be more accurate to speak of "evolutionary approaches with typological (species-typical) emphasis," rather than "typological approaches." The latter is used here for expositional clarity. 3 Other methods include those of behavioral ecology and laboratory-based experiments. 1136 October 1984 • American Psychologist Table 1 A Comparison of Typological and Population Approaches Typological Population