A recurrent idea in Steven Pinker’s essay is that group selection “adds little to what we have always called ‘history’.” I argue, on the contrary, that cultural multilevel selection (CMLS) provides a highly productive theoretical framework for the study of human history, including (and integrating over) both modeling and empirical approaches. Notable examples, developed during the last decade, include the evolution of religion (e.g., in the work of David Wilson [1] and Richard Bellah [2]), the evolution of monogamy, and my own work on the evolution of social complexity.
As an example, the demographic historian Walter Scheidel recently pointed out that Ancient Greeks and Romans were unusual, perhaps even unique among the surrounding societies, in practicing prescriptively universal monogamous marriage [3]. This “peculiar institution” then gradually spread across the globe, so that today the majority of world’s population live in countries that ban polygamy. Why this occurred is a puzzle, “since the very men who most benefit from polygynous marriage—wealthy aristocrats—are often those most influential in setting norms and shaping laws” [4]. Joseph Henrich and co-authors argue that the package of social norms that underpin modern monogamy evolved by cultural group selection. More importantly, the general CMLS framework suggests a number of specific hypotheses that Henrich et al. proceed to test in their paper. Their conclusions are not universally accepted [5], but the important point is that the application of the CMLS framework suggests new empirical directions of historical research. This has become an exciting area in social history, as indicated by a recent workshop organized at the Santa Fe Institute that brought together historians, social scientists, and evolutionary theorists.
My second example deals with the evolution of complex societies. Large-scale human societies are not simply undifferentiated ensembles of individuals. They are ‘segmentary,’ that is, their internal structure can be represented as groups nested within groups nested within groups … and so on [6]. In other words, human societies are truly multilevel entities and evolution of large-scale sociality in humans was not just one major evolutionary transition, but a whole cascade of them. In order for societies to persist without fragmenting, forces holding together groups at various levels must overcome centrifugal tendencies (and when they fail to do so, the result is a failed state). A major theoretical result in MLS is the Price equation, which specifies the conditions under which the balance shifts either toward integration, or towards disintegration [7].
Cultural traits of central interest are prosocial norms and institutions [8]. They are critical for the stability and functioning of large-scale societies, but have very significant costs at lower levels of social organization. Thus, we have a typical multilevel situation, in which traits are under divergent selective pressures acting at different levels of organization.
As I noted above, CMLS is much more than a metaphor; it yields quantitative predictions that can be (and have been) tested with historical data. The Price equation includes not only coefficients of selective pressures (working against each other at lower vs. higher levels), but also cultural variances at two (or more) levels. Incidentally, the critical importance of variances is a new insight for most social scientists, not steeped in evolutionary theory. But we can go beyond such conceptual insights to empirical applications. In particular, the Price equation suggests that large states should arise in regions where culturally very different people are in contact, and where interpolity competition – warfare – is particularly intense [9].
In a recent article, I tested this prediction for the period of human history between 500 BCE and 1500 CE, and found an excellent match between predictions and data [9]. A further development of this approach is the current collaborative project with Tom Currie, Edward Turner, and Sergey Gavrilets. We have developed an agent-based model of cultural evolution of prosocial institutions on a realistic landscape (Afroeurasia between 1500 BCE and 1500 CE). We also quantified the spatiotemporal distribution of historical large-scale societies by counting how frequently each 100 × 100 km square found itself within a large territorial polity. Our results indicate that the model predicts over 60 percent of variance in the data, a level of precision practically unheard of in historical applications.
Thus, the theoretical framework based on CMLS can not only provide new conceptual insights into the study of human history, it also guides empirical research and, most notably, yields predictions that exhibit an excellent match with data.
References
[1] Wilson, D. S. 2002. Darwin's Cathedral: Evolution, Religion, and The Nature of Society. University of Chicago Press, Chicago.
[2] Bellah, R. N. 2011. Religion in Human Evolution: From the Paleolithic to the Axial Age. Harvard University Press, Cambridge, MA.
[3] Scheidel, W. 2009. A peculiar institution? Greco-Roman monogamy in global context. History of the Family 14:280-291.
[4] Henrich, J., R. Boyd, and P. J. Richerson. 2012. The puzzle of monogamous marriage. Phil. Trans. R. Soc. B 367:657-669.
[5] Fortunato, L., and M. Archetti. 2010. Evolution of monogamous marriage by maximization of inclusive fitness. Journal of Evolutionary Biology 23:149-156.
[6] Turchin, P., and S. Gavrilets. 2009. Evolution of Complex Hierarchical Societies. Social History and Evolution 8(2):167-198.
[7] Bowles, S. 2006. Group competition, reproductive leveling and the evolution of human altruism. Science 314:1569-1572.
[8] Richerson, P., and J. Henrich. 2012. Tribal Social Instincts and the Cultural Evolution of Institutions to Solve Collective Action Problems. Cliodynamics 3: in press.
[9] Turchin, P. 2011. Warfare and the Evolution of Social Complexity: a Multilevel Selection Approach. Structure and Dynamics 4(3), Article 2:1-37.
