Tuesday, September 27, 2016

Inheritance in cultural evolution

I recently reviewed a book anthology devoted to the application of phylogenetic methods in archaeology (see List 2016, PDF here). This book, entitled Cultural Phylogenetics: Concepts and Applications in Archaeology, edited by Larissa Mendoza Straffon (2016), assembles eight articles by scholars who discuss or illustrate the application of phylogenetic approaches in different fields of anthropology and archaeology.

The volume presents a rich collection of different approaches, covering various topics ranging from the evolution of skateboards (Prentiss et al.) to the spread of the potter's wheel (Knappett). The articles dealing with theoretical questions range from historical accounts of tree-thinking in biology and anthropology (Kressing and Krischel) to an overview of the impact of Darwinian thinking on archaeology and anthropology (Rivero). Although I missed a golden thread when reading the eight articles of the volume, it is definitely worth a read for those interested in evolutionary approaches in a broader sense, as most articles explicitly reflect differences and commonalities between biological and cultural evolution, providing concrete insights into the challenges that archaeologists face when trying to promulgate quantitative approaches.

It is clear that evolution in the general sense is much broader than merely evolution in biology, as I have often tried to illustrate in this blog when showing how phylogenetic approaches can be applied in linguistics. Provided that descent with modification holds — in a broader sense — also for cultural artifacts, it is obvious to search for fruitful analogies between biological and cultural evolution, in order to profit from methodological transfer in disciplines like anthropology and archaeology. It is also clear, however, that certain analogies between biological evolution and evolution in other fields should be considered with great care. Even in linguistics, this is clearly evident, and I have pointed to this problem in the past (see Productive and unproductive analogies...). The goal cannot be a to try to press biological methods into the anthropological template. Instead, we have to rigorously test our proposed analogies, and adapt the biological methods to our needs if necessary.

What surprised me when reading the book was that the majority of the articles did not really seem to care about the crucial differences between biological and cultural evolution, but rather tried to fit the feet and heels of cultural evolution into biology's shoes. Tree thinking dominated most of the articles (with Knappett as a notable exception), and the scholars tried hard to find a clear distinction between vertical and lateral inheritance in cultural evolution. While it is clear that this distinction is the basis for phylogenetic tree applications, where patterns that do not fit a tree are explained as instances of homoplasy or lateral transfer, it is by no means clear why one would go through all the pain to identify these patterns in cultural evolution.

Consider, as an example, the evolution of skateboards. At some point in the history of mankind (some late point!), people decided to put wheels on a board and to do artistic tricks with it. Later, other people merchandised this idea, and started to sell those boards with wheels. Later on, other companies jumped on the bandwagon and started to produce their own brands, thus instigating a fight for the "best" model for a certain kind of clientel. In all of these cases, ideas for design were clearly taken among groups of people, further modified by specific needs or trends, until the current variety of skateboards arose. But which of these ideas were transferred vertically, and which ideas were transferred laterally? Can we identify processes of "speciation" in skateboard evolution, during which new brands were born?

In biology and linguistics we have the clear-cut criteria of interfertility and intelligibility. They cause us enough problems, given that we have ring species in biology and dialect chains in linguistics, but at least they give us some idea how to classify a given exemplar as belonging to a certain group. But what is the counterpart in the evolution of skateboards? Their brand? Their shape? Their users? The analogy simply does not hold. We have neither vertical nor lateral transfer in topics such as skateboard evolution. All we have is a before and an after— a complex network in which objects were constantly recreated and modified, be it based on ideas that were inspired by other objects or people, or independently developed. It seems completely senseless to search for a distinction between vertical and lateral patterns here, as it is not even clear to what degree we are actually dealing with decent with modification.

It seems to me that the problem of inheritance needs to be addressed in cultural evolution before any further quantitative applications using tree-building methods are carried out. Given that ideas can easily be develop independently, the crucial question for studies of cultural evolution is whether similar ideas can be shown to share a common history. It is (as David mentioned in earlier in a blog post on False analogies between anthropology and biology) the general problem of homology that does not seem to be solved in most studies on cultural evolution. Here, linguistics has generally fewer problems, given that linguists have developed methods to test whether two words are homologous. In cultural evolution, however, the assessment of homology is far from being obvious.

I think that cultural evolution studies such as the ones presented in the book would generally profit from network approaches. By network approaches, I do not necessarily mean evolutionary networks (in the sense of Morrison 2011), as the problem of inheritance is difficult to solve. Instead, I am thinking of exploratory data analysis using phylogenetic networks (Morrison 2011), or some version of similarity networks (Bapteste et al. 2012). Phylogenetic network approaches are frequently used in biology, and are now also very popular in linguistics. Similarity networks are more common in biology, but we have carried out some promising studies of linguistic data (List et al. 2016). As all of these approaches are exploratory and very flexible regarding the data that is fed to them, they might offer new possibilities for exploratory studies on cultural evolution.

  • Bapteste, E., P. Lopez, F. Bouchard, F. Baquero, J. McInerney, and R. Burian (2012) Evolutionary analyses of non-genealogical bonds produced by introgressive descent. Proceedings of the National Academy of Sciences 109.45. 18266-18272.
  • Knappett, C. (2016) Resisting Innovation? Learning, Cultural Evolution and the Potter’s Wheel in the Mediterranean Bronze Age. In: Mendoza Straffon, L. (ed.) Cultural Phylogenetics: Concepts and Applications in Archaeology. Springer International Publishing: Cham and Heidelberg and New York and Dordrecht, pp. 97-111.
  • List, J.-M., P. Lopez, and E. Bapteste (2016) Using sequence similarity networks to identify partial cognates in multilingual wordlists. In: Proceedings of the Association of Computational Linguistics 2016 (Volume 2: Short Papers), pp. 599-605.
  • List, J.-M. (2016) [Review of] Cultural Phylogenetics: Concepts and Applications in Archaeology; edited by Larissa Mendoza Straffon. Systematic Biology (published online before print).
  • Morrison, D. (2011) An Introduction to Phylogenetic Networks. RJR Productions: Uppsala.
  • Prentiss, A., M. Walsh, R. Skelton, and M. Mattes (2016) Mosaic evolution in cultural frameworks: skateboard decks and projectile points. In: Mendoza Straffon, L. (ed.) Cultural Phylogenetics: Concepts and Applications in Archaeology. Springer International Publishing: Cham and Heidelberg and New York and Dordrecht, pp. 113-130.
  • Rivero, D. (2016) Darwinian archaeology and cultural phylogenetics. In: Mendoza Straffon, L. (ed.) Cultural Phylogenetics: Concepts and Applications in Archaeology. Springer International Publishing: Cham and Heidelberg and New York and Dordrecht, pp. 43-72.
  • Mendoza Straffon, L. (2016) Cultural Phylogenetics. Concepts and Applications in Archaeology. Springer International Publishing: Cham.