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.

Tuesday, September 20, 2016

Network of who marries whom, by profession

This blog is supposed to be about phylogenetic networks, not social networks. However, this post is a blatant exception.

Earlier this year, Adam Pearce and Dorothy Gambrell released this interesting web page:
This chart shows who marries CEOs, doctors, chefs and janitors
It is an interactive interface to a database of who marries whom. It is well known that people in certain professions tend to marry others with a given profession, and this database quantifies this pattern. The data are from the United States Census Bureau’s 2014 American Community Survey, which covers 3.5 million households. However, much of the dataset clearly also applies to many countries in the "western world".

The infographic is a matrix of professions organized left to right by more male-dominated to more female-dominated (as determined from the data in the database). If you move the mouse-pointer over any profession (or use the search box) then lines link the most common professions that the focus profession tends to marry, with line thickness indicating quantity. The pink and blue color gradients indicate the sexes of the two spouses.

You could try well-known marriage links like those for veterinarians (who tend to marry other veterinarians) and nurses (who tend to marry medical doctors), but more interesting ones for readers of this blog might be: biologists, mathematicians and statisticians (shown in the image above), computer programmers, or information professionals.

However, if you want to get really confused, try looking at "waitresses", "cooks" and "chefs", which seem to offer intransitive relationships.

Tuesday, September 13, 2016

An old network of the Shepherd and Herdsman's dogs

I have previously noted that the first known phylogenetic network concerned dog breeds, in 1755 (The first phylogenetic network) — a network is needed because many dog breeds are hybrids between other breeds. I have also noted the inappropriate recent tendency to use phylogenetic trees for these breeds, instead (Why do we still use trees for the dog genealogy?). I have also provided a sampling of known phylogenetic networks from the early 20th century (Phylogenetic networks 1900-1990). This post combines all of these themes.

Max Emil Friedrich von Stephanitz was a cavalry captain (rittmeister), but his enduring legacy was as a dog breeder and historian of German dog breeds. His best known book is (available here):
Der Deutsche Schäferhund in Wort und Bild (1921) Ant. Kämpfe, Jena.
This was translated into English as:
The German Shepherd Dog in Word and Picture (1923), translated by J. Schwabacher.
In this book von Stephanitz argued that the German Shepherd was a specific type of shepherd or herdsman's dog. Indeed, over the previous two decades he had tried to standardize the German Shepherd breed as a working dog, rather than as a show dog in the British tradition of the 19th century.

As part of his argument, he presented a stammbaum of related breeds.

The second picture shows the genealogy from the English translation.

Note that the German Shepherd is not involved in a recent reticulate history, as are all of the herdsman's breeds. This is part of von Stephanitz's argument for the importance of preserving the German Shepherd's identity.

You can read a bit more about the German Shepherd and its ancestor the Hoffwart, the farm guard dog, at König the Hovawart founder revisited: the myth of the Hoffwart.

Wednesday, September 7, 2016

Choosing wines based on their labels

In this blog, we have occasionally used networks to illustrate differences between countries in some socially determined characteristic. This is a form of exploratory data analysis. Today's example concerns which characteristics of the label are used when choosing a bottle of wine for purchase.

The data are for a 12-country survey co-ordinated by:
Steve Goodman (2009) An international comparison of retail consumer wine choice. International Journal of Wine Business Research 21: 41-49.
The data were collected using different techniques in each country — some data were collected online, others as mall intercepts, in-store surveys or various combinations. However, in each case the people were asked to rank the following 13 characteristics in order of importance for choice "the last time you bought a bottle of wine in a shop to have for dinner with friends":
  • Tasted the wine previously
  • Someone recommended it
  • I read about it
  • Origin of the wine
  • Grape variety
  • Brand name
  • Matching food
  • Medal or award
  • Information on back label
  • An attractive front label
  • Information on the shelf
  • Promotional display in store
  • Alcohol level below 13%
A total of 2,969 people were surveyed, with 154-364 per country. The data were standardized in order to make them directly comparable between countries.

For the exploratory data analysis, I first used the manhattan distance to calculate the similarity of the different countries and label characteristics, based on their choice scores. This was followed by a neighbor-net analysis to display the between-country and the between-characteristic similarities as separate phylogenetic networks.

The network for the 12 countries is shown in the first graph. Countries that are closely connected in the network are similar to each other based on the choice of label characteristics, and those that are further apart are progressively more different from each other.

Clearly, there are no strong groupings of countries, indicating that the people all do things differently. Nevertheless, there are some patterns here.

Some of the country associations are to be expected, based on the similarities of their cultures, such as the grouping of Australia, New Zealand and the USA. However, it might be expected that the other English-speaking country, the UK, would be in the same group, rather than where it is, associated with the two Asian countries, China and Taiwan. Similarly, it might be expected that France would be associated with the other mainland European countries, Austria, Germany and Italy, but this association is only weak.

The source of these patterns becomes clear when we consider which wine-label characteristics were used to make the purchase choice. These are shown in the next network where, once again, characteristics that are closely connected in the network are similar to each other based on their ranking across countries, and those that are further apart are progressively more different from each other.

The characteristics that were consistently ranked highest are at the top-right of the network, progressing down to those ranked lowest, shown at the bottom of the network. Note that the label and its detailed contents are grouped at the bottom, along with shelf and promotional information. The rumor that a "nice label" is an important component of choice is not supported by these data. As the author notes: "it does appear that in-the-store / point-of-purchase / nice-labels information might in fact be too late to influence decisions" — people more often make their choice before they get to the store.

Instead, the contents of the bottle and its origin rank high, along with previous experience (awards and recommendations); but, not unexpectedly, nothing beats personal experience with the wine. One's own prior opinion is more important than anything else.

The somewhat unexpected location of France in the network arises because the French ranked "Matching food" as their top criterion, whereas most other people chose "Tasted the wine previously". However, for Italy it was a close-run thing between these two choices, making the Italians the closest to the French.

The unexpected location of the UK in the network arises because these three were the only countries where "Grape variety" was a long way down the choice list. This might be related to the fact that the British have long been wine consumers, back in the days when grape varieties were not prominently displayed on wine labels, unlike the situation for the "new world" wine consumers, where it is often the most prominent piece of information. However, traditional lack of interest in grape varieties would also apply to the other European countries.

Interestingly, China and Taiwan also put "Matching food" a long way down their lists, as did the New Zealanders, whereas Australia, the UK and the USA put "Matches food" near the middle of their lists. Thus, only half of the countries thought that this criterion, which is traditionally considered to be important, was of much interest. Anyone who has ever tried drinking a wine whose taste does not complement the accompanying food (as I sadly have) will thus think that half the world is crazy. Perhaps these people are not drinking their wine with a meal? Philistines!