Biological metaphors and methods in historical linguistics (2): Words and genes

As was mentioned in the introduction to this series of blogposts, both species and languages are often presented in a tree model. In biology, trees of each individual gene are created in order to account for horizontal transmission and other processes in which the history of a gene differs from the general history of its genome. From the sum of these trees, the species trees are then derived, a method called gene tree reconciliation (Nakhleh 2013). In linguistics on the other hand, phylogenetic trees normally are built on cognate sets of related words, from which the most likely tree of the languages is calculated. A closer equivalent however would be to describe the history of each individual word or word form, including regular sound change, irregular changes to its form, semantic changes, borrowings, and processes of word formation, and to derive the language tree based on the sum of the word histories (Gray, Greenhill, and Ross 2007, 15). Unlike its biological equivalent, this is normally done manually.

While anthropological, including linguistic, data behaves more like phenotype data than like genotype data in biology (Morrison 2014), the mechanisms themselves seem much more directly comparable between genes and language data since phenotypes would add an unnecessary layer of complexity, being expressions of genes, while genes are what is replicated from one generation to the next.

Similarly, Stevick, while maintaining the general equation between species and languages, suggests that it would be better to compare actual utterances with individual organisms (Stevick 1963, 161) or their genomes, since language is replicated through its use in communication. In this model, gene replication with mutation corresponds to communication (i.e. word exchange) with innovation (Pagel 2009, 406, 408).

One obvious difference is that in genetic, i.e. sexual, reproduction, the whole genome is recombined, whereas in each instance of communication, only part of the mental lexicon is typically affected, an exception being systemic changes like the change of one set of phonemes to another set. These systemic changes are another difference: in the genome, most genes are fairly independent, but a change to one word in the lexicon can easily reflect a wide-reaching change to many parts of the lexicon as in regular sound change.

Besides these systemic changes, words in the lexicon can also influence each other and cause sporadic changes called analogy, which is typically based on the meanings of the words. This is comparable to linked loci in the genome, even if the underlying mechanisms are ­­— of course — entirely different (Nakhleh 2013, 720, 726). From this, one can conclude that word-meaning-pairs (what Gévaudan 2007 refers to as “lexikalische Einheit”, i.e., ‘lexical unit’, on page 28), and not word forms on their own, correspond to individual genes coupled either with their function or with their position in the genome.

While individuals and not whole species reproduce, evolutionary biology normally treats the samples taken from individuals as representing the species as a whole. Similarly, linguists normally talk about language stages being derived from previous language stages spoken at least a generation before, more typically several centuries:  they do not put much focus on how language usage changes during the course of the life of a person beyond the language acquisition phase (but see e.g. Labov 1981 as an influential exception).

To go even a level deeper, some scholars compare the amino acids that make up a gene with the phonemes that make up a given word (Hruschka et al. 2015, 1), but while this may seem to make sense in the context of the other metaphors mentioned, I have not yet found a way to apply this equation in our research. More interesting in this regard is that the distribution of morphemes in a given language can be modeled in a similar manner as the distribution of protein domains within genomes (Keller and Schultz 2014).

At times, whole sequences of genes have been likened to words. This is a methodologically valid comparison,  as in both disciplines, sequences of genes on the one hand and sequences of sound strings denoting the same concept on the other hand can be aligned in order to gain insights into the likelihood that a given gene or word is orthologous or cognate with another (Koonin 2005, 217f; List et al. 2016, 6), even if it otherwise does not fit well into the metaphors employed here. An important difference in that regard is also that while gene sequences consist of the same four nucleotides, words of different languages more typically make use of different sets of phonemes. For example click sounds famously can be found in some languages of southern Africa, but are almost missing in most other parts of the world (Trask 2007, 12).

Overall, one can conclude that despite some similarities, the research objects of linguists and biology are obviously very different and it therefore should depend on the fruitfulness of the research method whether adopting a given metaphor makes sense or not. Nevertheless, thinking about these metaphors can support finding potential methods to adopt, also by pointing out which approaches one takes for granted in one’s own field but which might be handled differently in another.

References

Gévaudan, Paul. 2007. Typologie des lexikalischen Wandels: Bedeutungswandel, Wortbildung und Entlehnung am Beispiel der romanischen Sprachen. Stauffenburg-Linguistik ; 45. Tübingen: Stauffenburg.

Gray, Russell D., Simon J. Greenhill, and Malcolm D. Ross. 2007. “The Pleasures and Perils of Darwinzing Culture (with Phylogenies).” Biological Theory 2 (4): 360–75.

Hruschka, D. J., S. Branford, E. D. Smith, J. Wilkins, A. Meade, M. Pagel, and T. Bhattacharya. 2015. “Detecting Regular Sound Changes in Linguistics as Events of Concerted Evolution.” Current Biology 25 (1): 1–9.

Keller, Daniela Barbara, and Jörg Schultz. 2014. “Word Formation Is Aware of Morpheme Family Size.” PLoS ONE.

Koonin, Eugene V. 2005. “Orthologs, Paralogs, and Evolutionary Genomics.” Annual Review of Genetics 39: 309–38. https://doi.org/10.1146/annurev.genet.39.073003.114725.

Labov, William. 1981. “Resolving the Neogrammarian Controversy.” Language 57(2): 267–308. JSTOR: 413692.

List, Johann-Mattis, Jananan Sylvestre Pathmanathan, Philippe Lopez, and Eric Bapteste. 2016. “Unity and Disunity in Evolutionary Sciences: Process-Based Analogies Open Common Research Avenues for Biology and Linguistics.” Biology Direct 11 (39): 1–17.

Morrison, David A. 2014. “Are Phylogenetic Patterns the Same in Anthropology and Biology?” bioRxiv. https://doi.org/10.1101/006486.

Nakhleh, Luay. 2013. “Computational Approaches to Species Phylogeny Inference and Gene Tree Reconciliation.” Trends in Ecology and Evolution 28 (12): 719–28.

Pagel, Mark. 2009. “Human Language as a Culturally Transmitted Replicator.” Nature Reviews. Genetics 10: 405–15.

Stevick, Robert D. 1963. “The Biological Model and Historical Linguistics.” Language 39 (2): 159–69. https://www.jstor.org/stable/411199.

Trask, Robert L. 2007. Language and Linguistics: The Key Concepts. Abingdon: Routledge.


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