Multilevel Selection Theory and Major Evolutionary Transitions: Implications for Psychological Science

The concept of a group as comparable to a single organism has had a long and turbulent history. Currently, methodological individualism dominates in many areas of psychology and evolution, but natural selection is now known to operate at multiple levels of the biological hierarchy. When between-group selection dominates within-group selection, a major evolutionary transition occurs and the group becomes a new, higher-level organism. It is likely that human evolution represents a major transition, and this has wide-ranging implications for the psychological study of group behavior, cognition, and culture. KEYWORDS—group selection; human evolution; multilevel selection theory; group psychology; culture The concept of a social group as a single organism has a long history in scientific and intellectual thought. According to Daniel Wegner (1986, p. 185), Social commentators once found it very useful to analyze the behavior of groups by the same expedient used in analyzing the behavior of individuals. The group, like the person, was assumed to be sentient, to have a form of mental activity that guides action. Rousseau and Hegel were the early architects of this form of analysis, and it became so widely used in the 19th and early 20th centuries that almost every early social theorist we now recognize as a contributor to modern social psychology held a similar view. Nevertheless, during the second half of the 20th century this view of society was eclipsed by a more reductionistic and individualistic view. Donald Campbell (1994, p. 23) wrote: ‘‘Methodological individualism dominates our neighboring fields of economics, much of sociology, and all of psychology’s excursions into organizational theory. This is the dogma that all human social group processes are to be explained by laws of individual behavior.’’ Developments in evolutionary biology seemed to affirm the individualistic turn in psychology. Darwin wrote about how groups can potentially, but not invariably, evolve into adaptive units (Richards, 1987). Unfortunately, many of his followers assumed that natural selection operates on individuals, groups, species, and ecosystems, as though there were no need to distinguish among levels of the biological hierarchy. These ideas were criticized in the 1960s, and a two-part consensus emerged (Williams 1966). First, higher-level entities such as social groups can evolve into adaptive units, but only by a process of higher-level selection. For example, an altruistic behavior that benefits others at the expense of the self is selectively disadvantageous within groups. However, if there are many groups in the total population that vary in the frequency of altruists, the most altruistic groups will differentially contribute to the total gene pool. Between-group selection favors altruism and can counteract within-group selection if it is sufficiently strong, causing the altruistic trait to evolve in the total population. This way of conceptualizing evolution is called multilevel selection (MLS) theory (Sober & Wilson, 1998). Even though group-level adaptations can evolve in theory, the second part of the consensus concluded that they seldom do so in the real world, because group-level selection is almost invariably weaker than individual-level selection. This conclusion was so widely accepted that group selection became a pariah concept, taught primarily as an example of how not to think. The theoretical justification for individualism in psychology seemed secure. Nevertheless, much has happened in evolutionary biology during the last half century (Wilson & Wilson, 2007). The first part of the 1960s consensus remains valid: Adaptations at any given level of the biological hierarchy require a process of Address correspondence to David Sloan Wilson, Department of Biology, Binghamton University, Binghamton, New York, 13902-6000; e-mail: [email protected]. CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE 6 Volume 17—Number 1 Copyright r 2008 Association for Psychological Science natural selection at that level and tend to be undermined by lower levels of selection. The second part of the consensus has proven to be erroneous: Higher-level selection can be a significant evolutionary force, one that sometimes even dominates lower-level selection, causing the higher-level unit to become an organism in every sense of the word. Ironically, given group selection’s previous pariah status, it is now the concept of groups as organisms that stands on a firm scientific foundation. Moreover, it is likely that human evolution represents such an evolutionary transition, and this has profound implications for psychology and all other human-related subjects.