About Yasha's Research

Evolved, adaptive systems are generally robust.  In other words, they typically continue to function even in the face of perturbations.  That is not to say that they are infinitely malleable or that they are unaffected by changing conditions.  Indeed, they can and do collapse in the face of enough pressure.  Nevertheless, as reviewed extensively by Andreas Wagner (1), evolved biological systems tend to be highly resilient.  For instance, Wagner argues that the genetic code did not arise by chance, but rather because it is robust to replication errors.  The redundancy in the genetic code is such that the most common replication errors result in silent mutations.  The arrangement of the code means that even when replication errors lead to non-silent mutations, they most often lead to substitutions of amino acids with similar properties.  Wagner systematically extends the notion of robustness to ever higher levels of biological complexity, ending with a detailed discussion about the ways in which the developmental pathways that lead to phenotypic traits are robust to variations in the genes that make up those pathways.  My work suggests that the notion of robustness should be extended even further to include cultural systems, a subject that has largely escaped the attention of those studying cultural evolution.

Robustness is an important concept because it illustrates the ways in which evolution is constrained.  Sometimes, these constraints are imposed by the environment as in the case of stabilizing selection maintaining local maxima in the fitness landscape (2).  Other constraints are intrinsic to organisms.  Pleiotropy, for example, constrains evolution because genes may have effects on multiple characters.  A mutation that might be adaptive for one of these traits may have negative consequences for others (3-5).  Similarly, canalization works to minimize phenotypic variation in the face of changing developmental conditions or in the background of genetic variation (6-8).  Because many traits evolve more or less independently of one another, evolutionary constraints manifest at even higher levels of organization than the organism.  For instance, pentadactyl limbs are retained in organisms as diverse as humans, bats and amphibians even though these limbs are put to very different uses and despite the fact that so many other characters have diverged radically among these species.  It seems that once certain evolutionary trajectories have been launched, variation becomes limited to paths of least resistance and that novelty can only emerge in certain directions (9).  This may account for why some body plans persist for hundreds of millions of years.  Although the traditional location of most modern body plans within the Cambrian explosion has been called into question (10), none of the theoretical objections cast doubt on ancient origins and persistence of phyletic traits.

Robustness is also an essential concept for understanding evolvability, the ability of a system to respond to natural selection (11-14).  This seems counterintuitive.  After all, robustness is marked by a lack of change so it would seem to work against a system’s ability to adapt to new conditions and, indeed, it sometimes does (14).  However, a biological system that is relatively insensitive to changes in protein structure, enzyme function, metabolic flux, developmental pathways, etc., can potentially accumulate a vast store of hidden variation.  As this variation builds up, some combination of traits may prove more adaptive in the existing environment or may allow the exploration of new niches.  Evolvability and robustness, then, are closely related phenomena.

Robustness of cultural systems has received very little attention.  However, there are reasons to believe analogous processes may be at work.  Fischer, for instance, follows four waves of English immigration to the United States, each from different regions of England, and shows not only that the distinct folkways of these immigrants survived the Atlantic crossing, they spread out from their initial settlements and persist into modern times, accounting for regional differences in such diverse cultural traits as cooking habits, architectural practices, attitudes towards democracy, egalitarianism and much more (15).  In a similar vein, Nisbett and Cohen argue that regional patterns of violence committed by white males in the United States are the result of persistent differences in conceptions of honor.  Southerners are raised in a “culture of honor” that expects men to respond to personal insults swiftly and, if necessary, violently.  These practices were adaptive within the context of the Celtic herding cultures that settled the south since mobile wealth in the form of cattle is relatively easy to steal and must be actively defended.  However, these practices have persisted long after most people have given up herding as a way of life (16).  Finally, Putnam follows the progress of regional governments in Italy from their establishment in the 1970s.  Almost without exception, regional governments in northern Italy function better than those in the south by any number of objective standards.  This holds true despite the fact that all regional governments began at the same time, with nearly identical constitutions and with similar funding.  Putnam attributes these different outcomes to differences in the way that social capital is activated in these regions, patterns of behavior that can be traced back 500 years or more (17).

Clearly, the historical trajectory of a society is critical to its development and evolution.  North refers to this as path dependence and he argues that failure to take it into account can render any attempt at institutional change futile (18).  All too often social reformers expect that changing formal rules is sufficient to bring about change.  They frequently fail to realize the power of informal rules, social norms and historical patterns to resist such attempts.  Even if they do appreciate these recalcitrant forces, there is, as yet, no comprehensive theory that accounts for cultural robustness in a way that can help manage it.  However, if the same general processes that lead to robustness in biological adaptive systems have counterparts in cultural systems then there is cause to hope that cultural robustness, properly understood and managed, might lead to greater cultural evolvability.

To date, so little work has been done in this area that it will likely be many more years before any attempt can be made to develop a comprehensive theory of cultural robustness.  My work includes three ongoing projects that represent first steps that will hopefully pave the way toward a more unified theory.  The first project, “The Role of Religion in Managing the Commons,” looks at institutional practices that can be regarded as cultural adaptations that function to allow groups to sustainably manage their resources.  If perturbation of these practices leads to poorer outcomes, then that suggests a role for natural selection in maintaining adaptive social practices.  The second project, “Exploring the Semantic Space of Ritual,” looks at how frequency of repetition affects transmission of cultural practices.  This represents a first step toward understanding if cultural systems have evolved to be robust to errors in transmission in ways analogous to the mechanisms employed by biological systems to minimize the effects of errors in DNA replication, transcription and translation.  The third project, “Tight and Loose Congregations:  Why They Are Different and Why they Coexist,” explores how groups manage individual autonomy and group conformity.  Note that all three projects involve detailed examinations of the proximate mechanisms that enable groups to function as cooperative units adapted to specific environments.  This level of description is needed to understand how robust elements of a system interfere with evolvability in some cases but enable evolvability in others.


1             Wagner, A. Robustness and Evolvability in Living Systems.  (Princeton University Press, 2005).
2             Estes, S. & Arnold, S. J. Resolving the paradox of stasis: Models with stabilizing selection explain evolutionary divergence on all timescales. American Naturalist 169, 227-244 (2007).
3             Stearns, F. W. One hundred years of pleiotropy: a retrospective. Genetics 186, 767-773 (2010).
4             Wagner, G. P. et al. Pleiotropic scaling of gene effects and the 'cost of complexity'. Nature 452, 470-U479, doi:10.1038/nature06756 (2008).
5             Wang, Z., Liao, B. Y. & Zhang, J. Z. Genomic patterns of pleiotropy and the evolution of complexity. Proceedings of the National Academy of Sciences of the United States of America 107, 18034-18039, doi:10.1073/pnas.1004666107 (2010).
6             Flatt, T. The evolutionary genetics of canalization. Quarterly Review of Biology 80, 287-316 (2005).
7             Siegal, M. L. & Bergman, A. Waddington's Canalization Revisited: Developmental Stability and Evolution. Proceedings of the National Academy of Sciences of the United States of America 99, 10528-10532 (2002).
8             Stearns, S. C. Progress on canalization. Proceedings of the National Academy of Sciences of the United States of America 99, 10229-10230 (2002).
9             Futuyma, D. J. Evolutionary Constraint and Ecological Consequences. Evolution 64, 1865-1884, doi:10.1111/j.1558-5646.2010.00960.x (2010).
10           Budd, G. E. & Jensen, S. A critical reappraisal of the fossil record of the bilaterian phyla. Biol. Rev. Cambridge Philosophic. Soc. 75, 253-295 (2000).
11           Aldana, M., Balleza, E., Kauffman, S. & Resendiz, O. Robustness and evolvability in genetic regulatory networks. Journal of Theoretical Biology 245, 433–448 (2007).
12           Bloom, J. D., Labthavikul, S. T., Otey, C. R. & Arnold, F. H. Protein stability promotes evolvability. PNAS 103, 5869–5874, doi:10.1073/pnas.0510098103 (2006).
13           Bornberg-Bauer, E. & Kramer, L. Robustness versus evolvability: a paradigm revisited. HFSP Journal 4, 105–108, doi:10.2976/1.3404403 (2010).
14           Draghi, J. A., Parsons, T. L., Wagner, G. P. & Plotkin, J. B. Mutational robustness can facilitate adaptation. Nature 463, 353-355, doi:10.1038/nature08694 (2010).
15           Fischer, D. H. Albion's Seed:  Four British Folkways in America.  (Oxford University Press, 1989).
16           Nisbett, R. E. & Cohen, D. Culture of honor : the psychology of violence in the South (Westview Press, 1996).
17           Putnam, R. D., Leonardi, R. & Nanetti, R. Y. Making Democracy Work:  Civic traditions in modern Italy.  (Princeton University Press, 1993).
18           North, D. C. Institutions, Institutional Change and Economic Performance.  (Cambridge University Press, 1990).