Phylogeny and the history of language and culture

Increasingly, work is being done using the methods of phylogenetic systematics to uncover cultural and linguistic evolution. A leading lab on this work is Russell Gray’s lab at the University of Auckland in New Zealand. He and his collaborators have looked at the evolution of language, particularly Pacific languages, and other cultural trends (like canoe decoration) in evolutionary terms.

Now they have published a paper in Science (Bouckaert et al. 2012), “Mapping the Origins and Expansion of the Indo-European Language Family”. The media of course published this under headlines like “English language originated in Turkey”, thereby demonstrating that journalists understand no evolutionary thinking as well as they understand no economics. Basically by using word forms of many extant and extinct Indoeuropean (IE) languages, and a Bayesian analysis, they established that IE originated in Anatolia, or the central regions of modern Turkey. 

This is not unlikely, for certain values of “began”. They locate the origination event around 9500 years ago, which is not long after agriculture began more or less in the same region. Previous hypotheses were that IE began around 5000 years ago in the central Asian steppes, along with the domestication of horses and the invention of the stirrup.

However, how good is this thesis? The BBC article with the silly headline is actually pretty well sourced and written. They quote Prof. Petri Kallio from the University of Helsinki as saying that “Unlike archaeological radiocarbon dating based on the fixed rate of decay of the carbon-14 isotope, there is simply no fixed rate of decay of basic vocabulary, which would allow us to date ancestral proto-languages.” He remains skeptical.

This is a matter of methodology and epistemology, and it goes to the very foundation of phylogenetic method itself. At best a sample of an organism or artefact from within C14 radioisotopic dating ranges only shows that an instance of that type was around at that time and place. It does not show whether it was the earliest or latest; it merely sets up a single anchor point that all hypotheses must account for.

Likewise, a document or monument with written language shows only that a language type was there at a time. And since writing per se did not arise until around 3500 years ago, even that cannot help. All we know are where recorded languages are or were found. They are anchor points, but not fixed ones. These anchors can and do move.

And Kallio is right: there are no fixed decay rates, or molecular clocks. In fact there aren’t such things in biology either. Molecular rates of change are not universal or constant, and inferences based upon them are at best hypotheses based hypotheses. Phylogeny is a tool, but what does it show?

In my last post I noted that phylogenetic reconstructions show only relatedness. What they do not show, without some extensive ancillary assumptions, is how that relatedness arose. The increasing awareness of lateral transfer and hybridisation between taxonomic lineages indicates that there can be some complex histories even if the taxonomic relationships are treelike. NB: to head off the most common error about this, lateral transfer does not undercut the treelike structure either of evolution or phylogenetic diagrams. It makes them harder to detect, but a certain admixture can be accommodated in a standard tree classification. Of course, if the rate of lateral transfer approaches equality, then you no longer have separate taxa, and so that would count as a single lineage that temporarily separated like populations either side of a geographic barrier that are brought back into contact.

In the case of sociocultural evolution, such lateral transfer is often assumed to be rife. This is thought by some to undercut the importance of phylogenetic method in cultural contexts. I want to argue that it doesn’t, but that the inferences from phylogeny are not so obviously historical as some seem to think.

First of all if some lateral transfer is possible in biological contexts between “good species” (the term used by biologists when they know it’s a species but it doesn’t follow some set of strictures they think species must), then some must be permissible in sociocultural contexts to. A loan word in French from English doesn’t make English and French the same language, no matter what the Academie Française might think. In biology it is the entire shared developmental system, including the genome, that makes a species a species. In culture a tradition has more than just a few elemental objects; it has a functional structure, and in language a grammar.

So phylogenetics can apply nicely in contexts where traditions (or species) are well behaved. If they are relatively stable (i.e., not so transitory that they cannot be tracked), and distinct (i.e., the rate of lateral transfer is not so high they aren’t recognisable traditions any more), then you can do a phylogenetic analysis of them. It’s not so surprising really. Willi Hennig, whose Phylogenetic Systematics (1966) set up modern phylogenetics, took some of his ideas out of the discipline of stemmatics, or tracking manuscripts by differences in transcription (Platnick and Cameron 1977, Atkinson and Gray 2005)

However, there are limitations when using this to reconstruct history. For a start, suppose you have two manuscripts that differ. You cannot reconstruct the last version they share historically. Suppose you have three, and two agree mostly. Can you reconstruct the last version from that? Well the two copies that agree might be from a large copy centre, but the one that disagrees might be from a minor monastery that actually had better copying procedures and a more original version, and so on. These issues are well known to historians and biblical scholars, for example.

Now consider the argument put forward by Bouckaert et al. They look at the frequencies of cognate words and conclude from their analysis that IE began in a particular location at a particular time. Such reconstructions rely on assumptions, like a relatively constant rate of diffusion in all directions. What if the language was blocked by a cohesive language and culture in one direction? What if one population into which it diffused was more conservatively structured? What if a small military power managed to spread through large territories? Each of those shifts the “weight” of the diffusion pattern and means we might think something other than the conclusion that Anatolia was the centre of origin. There are many contingencies and possibilities allowed just by a phylogeny, in culture and language as in biology.

I am not denying the conclusions reached here. I think it likely (the use of Bayesian analysis here is significant) that Anatolia was indeed a centre of many cultural novelties. We certainly think that agriculture arose near or around there. But it doesn’t follow that because Anatolia is novel in one respect (farming) it is novel in another (language). We should avoid confirmation bias in science.

In more general terms, what counts as evidence in any historical and evolutionary process? Can we say that passerine birds first evolved in Austronesia? Can we say that writing began once and was diffused or whether there were many independent inventions? Where did the Etruscans come from? Can we make any origin claims at all? We certainly would like to. The trouble is that information gets lost over time, and the best we can do is anchor events based on actual data. All process hypotheses based on these anchoring events are at best consistent with the data, not proven or even necessarily made more likely by them (to avoid confirmation bias and affirming the consequent style inferences when unwarranted).

It may sound like I am being contrarian here. I am not. This is the standard view in palaeontology (see for example Smith 1994), for example. History is hard to find, and we never have much confidence in our extensions beyond the data. It might be that we can reasonably think IE arose in Anatolia; knowing that is a lot harder.

References

Atkinson, Quentin D., and Russell D. Gray. 2005. Curious Parallels and Curious Connections—Phylogenetic Thinking in Biology and Historical Linguistics. Systematic Biology 54 (4):513-526.

Bouckaert, Remco, Philippe Lemey, Michael Dunn, Simon J. Greenhill, Alexander V. Alekseyenko, Alexei J. Drummond, Russell D. Gray, Marc A. Suchard, and Quentin D. Atkinson. 2012. Mapping the Origins and Expansion of the Indo-European Language Family. Science 337 (6097):957-960.

Hennig, Willi. 1966. Phylogenetic systematics. Translated by D. D. Davis and R. Zangerl. Urbana: University of Illinois Press.

Platnick, Norman I., and H. Don Cameron. 1977. Cladistic Methods in Textual, Linguistic, and Phylogenetic Analysis. Systematic Biology 26 (4):380-385.

Smith, Andrew B. 1994. Systematics and the fossil record: documenting evolutionary patterns. Oxford, OX; Cambridge, Mass., USA: Blackwell Science.