Assignment 3: Studying Change

LETTER

Understanding cumulative cultural evolution Joseph Henricha,1, Robert Boydb, Maxime Derexc, Michelle A. Klinec, Alex Mesoudid, Michael Muthukrishnae, Adam T. Powellf, Stephen J. Shennang, and Mark G. Thomash

In a narrow critique of two early papers in the literature on cumulative cultural evolution, Vaesen et al. (1) mis- understand the work they criticize, mischaracterize multiple lines of research, and selectively ignore much evidence. While largely recycling prior criticisms, they provide no new models, evidence, or explanations (2).

Not only do their criticisms of Henrich’s (3) and Powell et al.’s (4) modeling assumptions miss their mark (2), but Vaesen et al. (1) also ignore many other models that do not rely on these assumptions yet arrive at sim- ilar predictions. These other models variously include conformist transmission and explore these processes using nonnormal distributions, discrete traits, networks, etc. (2, 5). Of course, no one expects demographic/ population variables to be the only things that matter; cultural packages related to clothing or housing, for example, will vary with latitude for reasons unrelated to demographics, risk, or mobility.

Vaesen et al. (1) are correct that these models assume that at least some individuals can sometimes assess the relative success or payoffs of different traits or individuals, but they are incorrect in claiming that there is little evi- dence for such learning. First, they ignore a vast body of laboratory evidence showing that infants, children, and adults use cues of success, skill, or competence in learn- ing (2, 6). Second, Vaesen et al. (1) also ignore work showing that (i) Hadza and Ache foragers acquire cultural information obliquely from broad networks (7) and (ii) success biases are well documented in traditional pop- ulations (2). Finally, the studies cited by Vaesen et al. (1) do not support their claims about vertical transmission; instead, all support the two-stage learning process used by Henrich (3), Powell et al. (4), and many others. Here,

individuals initially learn from their parents, and then up- date only if they observe others who are more successful than their parents. Evidence from fisher-horticulturalists and foragers support this pattern and shows that second- stage updating from nonparents is particularly prevalent in domains with high variation in skill/success. For exam- ple, Aka foragers learn from great hunters and presti- gious shamans (2).

Vaesen et al. (1) ignore laboratory tests of these models (2). Using novel learning tasks, several exper- iments show how group size and interconnectedness influence the accumulation of skill, know-how, and complexity, and some demonstrate the “Tasmanian effect” (8). If the models are so poor, it is peculiar that they have withstood multiple experimental tests by independent researchers.

Vaesen et al. cite studies by Collard and coworkers (refs. 67, 70, 72, 73, 75, and 79 in ref. 1) that do not find a significant relationship between census population sizes and complexity. However, the theory explicitly predicts that it is the size of the population that shares information—the effective cultural population size (3)— that matters, and if there is extensive contact between local or linguistic groups, there is no reason to expect census population size to correspond to the theoreti- cally relevant population (2). Inappropriately, Collard and coworkers used highly interconnected populations, and make no effort to measure these interconnections or deal with the conceptual problems of using census estimates (refs. 67, 70, 72, 73, 75, and 79 in ref. 1). Finally, Vaesen et al. (1) ignore important findings linking population size to both linguistic complexity and innovation rates (2, 9, 10).

1 Vaesen K, Collard M, Cosgrove R, Roebroeks W (2016) Population size does not explain past changes in cultural complexity. Proc Natl Acad Sci USA 113(16):E2241–E2247.

2 Henrich J, et al. (2015) Appendix to Understanding Cumulative Cultural Evolution: A Reply to Vaesen, Collard, et al. (June 20, 2016). Available at ssrn.com/abstract=2798257. Accessed September 30, 2016.

3 Henrich J (2004) Demography and cultural evolution: Why adaptive cultural processes produced maladaptive losses in Tasmania. Am Antiq 69(2):197–214.

aDepartment of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138; bSchool of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287; cInstitute of Human Origins, Arizona State University, Tempe, AZ 85287; dHuman Biological and Cultural Evolution Group, Department of Biosciences, University of Exeter, Penryn TR10 9FE, United Kingdom; eDepartment of Psychological and Behavioural Science, London School of Economics and Political Science, London WC2A 2AE, United Kingdom; fMax Planck Institute for the Science of Human History, Jena 07743, Germany; gInstitute of Archaeology, University College London, London WC1E 6BT, United Kingdom; and hResearch Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom Author contributions: J.H. drafted the paper; and J.H., R.B., M.D., M.A.K., A.M., M.M., A.T.P., S.J.S., and M.G.T. revised the paper. The authors declare no conflict of interest. 1To whom correspondence should be addressed. Email: [email protected].

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4 Powell A, Shennan S, Thomas MG (2009) Late Pleistocene demography and the appearance of modern human behavior. Science 324(5932):1298–1301. 5 Mesoudi A (2011) Variable cultural acquisition costs constrain cumulative cultural evolution. PLoS One 6(3):e18239. 6 Henrich J (2015) The Secret of Our Success: How Learning from Others Drove Human Evolution, Domesticated Our Species, and Made Us Smart (Princeton Univ Press, Princeton).

7 Hill KR, Wood BM, Baggio J, Hurtado AM, Boyd RT (2014) Hunter-gatherer inter-band interaction rates: Implications for cumulative culture. PLoS One 9(7): e102806.

8 Derex M, Beugin M-P, Godelle B, Raymond M (2013) Experimental evidence for the influence of group size on cultural complexity. Nature 503(7476):389–391. 9 Bettencourt LMA, Lobo J, Helbing D, Kühnert C, West GB (2007) Growth, innovation, scaling, and the pace of life in cities. Proc Natl Acad Sci USA 104(17): 7301–7306.

10 Bromham L, Hua X, Fitzpatrick TG, Greenhill SJ (2015) Rate of language evolution is affected by population size. Proc Natl Acad Sci USA 112(7):2097–2102.

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