Is language a replicator?
In a recent review Mark Pagel argues that language is a culturally transmitted replicator (Pagel, 2009).
Pagel starts by offering a useful update on phylogenetic methods and then uses a comparison between genetics and language phylogenetic trees to reveal similarities between cultural and biological evolution. He argues that borrowing and corruption, which could in principle be very important in the case of languages and make phylogenetic reconstruction difficult if not impossible, are, in fact, very limited. Pagel notes: "If languages are not the ‘closed shop’ to outside influences that we have come to expect of eukaryotic organisms with sequestered germ lines, the strength of descent with modification in language trees shows that the cultural processes of language teaching and learning that transmit language from one generation to the next can have a surprisingly high fidelity and can show resistance to outside effects." To put it briefly, phylogenetic trees show, or so it is claimed, that languages are faithfully reproduced from one generation to the next.
Figure 1: The phylogenetic tree of Indo-European languages, based on the Swadesh list of 200 words.
In fact, in a previous study Pagel has shown that Indo-European word evolution can be very slow, as slow as some genes' evolution (with half lives of up to 70 000 years) and that their rate of change is negatively correlated with their frequency (Pagel, 2007). A similar result was also obtained by Lieberman and coll. in the case of English verb regularisation: the more frequent the verb, the less likely it is to be regularised (Lieberman, 2007).
Pagel concludes: "For geneticists, or for anyone interested in molecular evolution, the parallels between linguistic and genetic evolution should be striking, and all the more so because language is a cultural rather than a physical replicator, without built-in error correction mechanisms and potentially subject to far greater effects of borrowing and other influences that could corrupt its signal. Like genomes, the languages we observe today are the survivors of a long process of being tried out and tested by their speakers. Like genomes, we can speculate that we have retained those languages that adapted best to our minds, and this may be the most obvious reason why we find them easy to learn and use."
The review from Pagel is well worth reading in detail and he clearly makes a strong case for phylogenetic reconstruction of language origins as a powerful tool to investigate human cultural history. Yet, if I understand him correctly, Pagel tries to make another argument: that human languages are cultural replicators, and on this particular point, the paper fails to address several important issues. In fact, in my view, the studies reviewed clearly demonstrate the interest of phylogenetic methods in language studies but they do not reveal anything more than a loose analogy between genes and languages. Let me highlight some crucial questions not addressed in the review:
1) Pagel is quite unclear on what he means by 'language replicators': it could be the language itself, like 'French', as seems to be suggested by the title, the idiolect of individuals, like my whole set of linguistic French items, or it could be unit of languages, like the word 'two'. It would have been nice to have disambiguated this in the paper. Still, I think Pagel means the last possibility because languages, as abstract units, cannot be transmitted from one generation to the next and idiolect cannot be faithfully transmitted (each idiolect, in each individual, is very specific). But if we focus on linguistic items as cultural replicators, this brings in another problem.
2) The studies reviewed in the article focus almost exclusively on a list of 200 terms (the Swadesh list), chosen because they are very remarkable. Here are the first 10 terms of the Swadesh list : I, You, He, We, You (plural), They, This, That, Here, There. What the studies shows is that among this very limited set of terms, the more frequent the terms, the more stable they are, the easier the phylogenetic reconstruction. But the conclusion drawn from this paper, that linguistic items are cultural replicators, is at best restricted to this set of terms. When Pagel insists on the fact that borrowing and corruption in a language are not so present, therefore that linguistic items are replicators, this is true of only the most remarkable 200 terms studied. There is no reason to believe that other linguistic items behave like replicators.
3) In fact, Pagel argues, implicitly, that linguistic items are cultural replicators because they are very stable. He implicitly assumes that stability is achieved only through replication, that there is no other possibility. In the beginning of the paper Pagel precises "I will not discuss the tricky and very large literatures on language origins or how we acquire it, whether our language skills are innate, or possible genetic influences on language abilities." therefore excluding from the analysis any learning mechanism. Yet, if I am not mistaken, replicators exist only in virtue of the presence of a replicating mechanism, which causes the stability of replicators, and not the reverse. Replicators in biology, genes as they are, are not defined in virtue of their stability but by the fact that they are replicated. Dark skin in the south of France and paler skin in the north are an enduring feature of French population linked to meteorology, not the presence of replicators. To argue that language are replicators, it is necessary to show that there is a learning mechanism analogous to the replication in biology AND that this mechanism is faithful enough to cause stability.
4) Finally, we have good reasons to be sceptical about the existence of a learning mechanism similar to genetic replication in the case of language learning. For instance, in a recent paper, Florencia Reali and Thomas L. Griffiths have experimentally addressed the question of the regularization of linguistic structure across several episodes of learning (Reali 2009). In their experiment, participants spontaneously tend to transform word-meaning relationship in a particular direction, producing a rapid convergence of language structure in few generations. If children transform, or regularize, the linguistic input they receive when learning a language, this process differ markedly from biological replication and produce an evolutionary dynamic very different from the biological one (see Kirby 2007 and Viciana 2009 in this blog).
To conclude, Pagel beautifully illustrates the importance of phylogenetic reconstruction to study human history. Bringing in the field of human sciences methodologies developed in biology can prove to be very useful and stimulating. However, I fail to see in Pagel's paper how more conceptual analogies, such as the use of replicators, can be used to stimulate understanding in the field of cultural evolution.
Pagel, M. (2009). Human language as a culturally transmitted replicator. Nat Rev Genet, 10(6), 405-415.
Pagel, M., Atkinson, Q. D., & Meade, A. (2007). Frequency of word-use predicts rates of lexical evolution throughout Indo-European history. Nature, 449(7163), 717-720.
Lieberman, E., Michel, J.-B., Jackson, J., Tang, T., & Nowak, M. A. (2007). Quantifying the evolutionary dynamics of language. Nature, 449(7163), 713-716.
Reali, F., & Griffiths, T. L. (2009). The evolution of frequency distributions: Relating regularization to inductive biases through iterated learning. Cognition, 111(3), 317-328.
Kirby, S., Dowman, M., & Griffiths, T. L. (2007). Innateness and culture in the evolution of language. Proceedings of the National Academy of Sciences, 104(12), 5241-5245.
Viciana, H. (2009). Cultural Attraction among birds, Institut of Cognition and Culture.