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category: Biology

Multilevel Selection is a Productive Theoretical Framework for Investigating Human History

Post: June 30, 2012 10:35 am
Author: Peter Turchin         Source: ETVOL Exclusive

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.


Comments

Post: June 30 2012 4:30 pm By: Steve Davis


And of course, cultural multi-level selection does not apply only to humans.
Darwin pointed out that the intellectual differences between humans and other animals were differences of degree, not of kind.

Post: June 30 2012 6:33 pm By: Lynn O'Connor


Wonderful post, and it would be so obvious if many academics hadn’t gone through decades of trashing group selection—but lets face it, the western faith in individualism forms an underpinning to this bias against group selection. I’ve worked with David Sloan Wilson, followed him for years, and our own research clearly indicates processes that involve group selection (competition between groups) as well as individual fitness (competition within groups). For two decades we’ve been studying empathy-based guilt (for example, survivor guilt broadly defined, how you feel when you see a beggar on the street or how you feel when you get a promotion while your friend gets laid off, or when you are happily married while your brother is miserable, married to an abusive wife), or a guilty-kind of worry about others due to “imaginary crimes.” Survivor guilt is associated with cooperative behavior on one level (and one of David’s students demonstrated this empirically)—that is it’s a good thing for competition between groups, but it can be associated with depression, anxiety, etc, for the individual, so it is not necessarily so adaptive in competition within the group. Recently I posted on my Psychology Today blog, “Our Empathic Nature” describing our recent research on the role of this kind of guilt in forgiveness (again, something required on the level of between group competition). You can find other empirical studies on our lab’s web site, http://www.eparg.org —Thanks for this post, I’m going to get your work.

Lynn O’Connor

Post: July 2 2012 9:11 am By: Peter Turchin


Lynn, I think you are right in pointing to the western faith in individualism as one of the reasons why multilevel selection had to struggle so much for acceptance. That’s probably why the selfish gene theory, but also rational choice theory and methodological individualism in social sciences have been such dominant paradigms. Another factor is that most people who live in western societies take cooperation for granted. They just don’t realize how fragile it is, and that the fact that we are capable of cooperating in societies of millions of individuals is one of the greatest evolutionary puzzles.

Post: July 4 2012 2:08 pm By: Helga Vierich


After weeks of debating about the applicability of group selection to human culture, especially the human bio-cultural evolutionary dance, at the Richard Dawkins’ Foundation website, I was startled to see Richard preface yet another essay from one of his supporters for “only” gene selection with the following plea:

“In the nicest possible way and with great respect, could I make two suggestions to would-be commenters, based on past experience when this topic has come up-

Please pause before offering your own common sense view. There are topics in science, of which this is one, where common sense is not a good guide. If it were, professional biologists would not have been arguing about it for five decades. There is a large back literature in which the likelihood is strong that whatever commonsense view you put forward has already been proposed and exhaustively discussed. As an analogy, common sense is notoriously misleading when we try to understand quantum mechanics. If you could do physics by common sense, we wouldn’t need physicists. To a lesser extent, something like the same thing applies here.

Please note that Homo sapiens is a very peculiar species and probably not the best testbed for the theories under discussion. That is not to say that the theories under discussion will forever be irrelevant to human affairs. But the argument at hand is sufficiently difficult that it is worth trying to understand it and solve it, at least to begin with, without the additional complications that arise with human culture. It’s not a bad idea to think about lions or ants or acorn woodpeckers as your model animal when trying to get to grips with these evolutionary theories.

Richard ”

http://richarddawkins.net/articles/646338-the-demise-of-group-selection 

I stopped coming to the site from then on. I give up.  He gets it, but he does not want to talk about it, I guess.

Post: July 14 2012 8:02 pm By: Helga Vierich


That said, I have a few quibbles with the material represented here by Peter Turchin.  One obvious one is that he has ignored the evidence from forager ethnographies which strongly suggests that monogamy is widespread among them, especially in mobile populations.  Since our evolution was dominated by this form of economic system, it seems unlikely that it was invented by the Romans.  This is underscored by the fact that humans universally “fall in love”.  They tend to form intense emotional and sexual bonds, which MAY coincide with marriage, but often occur despite such previous culturally mandated arrangements.  The sex drive is manifestly less emotionally powerful than this drive to form “pair” bonds (see http://ca.youtube.com/watch?v=OYfoGTIG7pY&feature=user). 
Secondly, and of greater import, is that “groups” (meaning more or less permanent and stable co-residential groups) are not actually typical of foragers, at least not on a local level.  Foragers form temporary camping groups (“bands”) that are fluid in membership and size.  These camps move every few weeks or months, and often change membership with each move.  there are clusters of such camps in a local region, which exchange members more often and are more closely related, but even then, different camp “clusters” tend to exchange members and personal through intermarriage and frequent back and forth visiting.  Even the whole grouping comprising people speaking a common language is not without its links of gifting networks and intermarriage.  The co=linguistic unit would be the one I would chose if asked to identify a “group” that the people themselves identify with.  In my own particular fieldwork, among hunter-gatherer people in the Kalahari, each such linguistic entity numbered between 1200 and 3000 people.  The smaller “camp cluster” between 130 and 180, and the camps between 15 and 50 (average 28).
If one is to try to apply multilevel selection to the models of human bio-cultural evolution before the neolithic “revolution”, then, it would be most appropriate to apply it to the kinds of selection pressures that might have favoured one forger “group” over another.  given that there is scant evidence of widespread violence - and almost none of warfare, in the ethnographic evidence from mobile foragers, not in the archaeological evidence, the role of cooperation and trade would seem to me to loom larger than the role of “collateral” competition featuring violence.

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Post: November 23 2013 8:20 pm By: Tim Tyler


The problem for group selection is not “history”, but kin selection.  Kin selection is widely accepted, and the best formulations of group selection makes no new predictions not also made by kin selection. Group selection’s main contribution seems to be confusion and controversy - and these are not particularly useful or novel.