Preprint, not peer reviewed, submitted for the inclusion in the anthology "Evolutionary Thinking Across Disciplines", ed. by Agathe du Crest, Martina Valkovic, Philippe Huneman & Thomas A.C. Reydon, Synthese Library, Springer. To appear in 2022. Evolutionary Aspects of Language Change Johann-Mattis List While it has been known for a long time that human languages can change in var- ious ways, it was only in the early 19th century that scholars realized that certain aspects of language change proceed in a surprisingly regular manner, allowing us to re- construct historical stages of languages which have never been documented in written sources. The findings led to the establishment of historical linguistics as a scientific discipline, devoted to the investigation of how languages change and why. Although evolutionary thinking plays a major role in historical linguistics, practitioners often have the tendency to emphasize the peculiarities of language evolution rather than the commonalities with other kinds of evolution. In part, this seems to be justified by some phenomena for which it is difficult to find counterparts in different disciplines. In part, however, this may also due to a communication problem that is characteristic for interdisciplinary research, since scholars lack a common terminology. As a result, it is difficult for linguists to explain their particular evolutionary views on language change to practitioners from other disciplines, while evolutionary terminology from disciplines such as biology is difficult to grasp for linguists. In the study, I will try to present some important evolutionary aspects of language change for which it is hard to find counterparts in other disciplines and then point to current challenges of evolutionary studies in historical linguistics which have to deal with these aspects. 1 Introduction Language change and language evolution have received much attention of late. Inspired by quanti- tative approaches from evolutionary biology, scholars have started to pay increased attention to the phylogenetic development of the world’s larger language families (Gray et al. 2009; Bouckaert et al. 2012; Bouckaert et al. 2018; Kolipakam et al. 2018; Sagart et al. 2019; Gerardi et al. 2021). Had phylogenetic reconstruction been largely ignored in qualitative research, or reduced to the subgrouping of the major branches of a language family by means of qualitative cladistic analysis, it has now become a popular research topic in historical linguistics and – despite initial skepticism – the majority of scholars now seems to accept phylogenetic studies based on Bayesian inference or maximum likelihood as a powerful set of tools that are valid for the exploration of a language family’s past. The introduction of phylogenetic methods in historical linguistics is accompanied by an increas- ing amount of discussions devoted to the nature of language evolution in comparison with other kinds of evolution. Following a long tradition of skepticism towards evolutionary explanations 1 List Evolutionary Aspects of Language Change 2021 of language change, many scholars still emphasize the peculiarity of language evolution in com- parison with biological evolution, and some scholars even find it misleading to discuss language change as an evolutionary phenomenon at all. On the other hand, there is a growing number of attempts to model the dynamics of language evolution formally and computationally. In the fol- lowing, I will try to give a short background on the history of evolutionary thinking in the field of historical linguistics from the beginning of the 19th century until today (§ 2) and then point to four aspects of language change which I consider crucial, in so far as they reflect differences in the evolutionary processes which often do not have a direct counterpart in evolutionary biology. I will then discuss three unsolved problems in historical linguistics for which no solutions have been proposed so far, also due to the fact that they are peculiar for language change. While I am not able to propose a proper solution for these problems, I conclude that future efforts in linguistics should try to concentrate on the adaptation of methods from other disciplines to linguistic needs rather than to the direct transfer. 2 Background The discipline of comparative linguistics has a long tradition of evolutionary thinking, reaching much deeper back in time than that of biology (List et al. 2016). In contrast to biologists, who had to infer that observed biological diversity was the result of a long succession of changes, linguists could observe these changes almost directly through the comparison of documents written in the same language at different times. Having almost direct access to ancestral stages of contempo- rary languages was a striking advantage of linguistics over biology which was already observed by August Schleicher (1821-1868) in 1863 (Schleicher 1863). It helped linguists not only in the development of methods for the inference of phylogenetic relationships but also allowed them to propose techniques by which the supposed pronunciation of individual words in ancestral lan- guages could be estimated. This technique, known as “linguistic reconstruction” (Fox 1995) is still the key objective of historical language comparison and linguists consider it as as much more important than the reconstruction of phylogenies. 2.1 From Words to Trees Linguists have known for a long time that languages evolve and that the languages we observe today may stem from common sources which themselves no longer exists. First speculations on the common descent and the tree- or network-like separation of languages can already be found in early studies of the 17th century and thereafter (List et al. 2016). Until the late 18th century, however, the dominant view among scholars in Europe was that all human languages were products of the mythical Confusion of Tongues which prevented the construction of the Tower of Babel (Klein 2004). First systematic investigations in which languages were compared for their genetic relatedness were carried out towards the end of the 18th century and reached first popularity with the detection of the Indo-European language family, represented specifically by Sanskrit, Ancient Greek, Latin, and Gothic (Rask 1818; Grimm 1822), which was later expanded by more languages from other branches (Slavic, Albanian, Armenian, see e.g. Hübschmann 1877), and reached its current state with the detection of Hittite (Hrozný 1915). Unlike modern phylogenetic trees, early linguistic trees were much less formal and systematic, but had the tendency to resemble true trees much more closely. As an example, consider Schle- 2 List Evolutionary Aspects of Language Change 2021 icher’s tree from 1853 (Schleicher 1853), which has the appearance of a massive oak with a big trunk. Only later, the family tree visualizations became more schematized, but the interpretation was still far away from being formalized. Figure 1: August Schleicher’s Oak Family Tree As an example for the lack of formalization, consider again a tree by Schleicher, this time from 1861 (Schleicher 1861). While this tree looks much more formalized than the earlier tree from 1853, the description of this tree in the text is interesting, since Schleicher points to branch lengths as representing the supposed time which had elapsed since separation while at the same time em- phasizing that the distance between extant languages reflected their synchronic closeness. While the German passage remains unclear in the wording, one way to read it is to assume that Schle- icher made a direct distinction between the “closeness” of languages as shown by their horizontal arrangement on a tree and the closeness as derived from the history reflected in divergence times. While it is impossible to depict the former systematically in a two-dimensional drawing, it is pos- sible that Schleicher thought of some additional closeness between languages independent of their evolutionary history and tried to mark this in his tree drawing by separating the major subgroups visually from each other in the tree and by placing languages like Albanian and Greek horizontally close to each other while at the same time assigning them a larger divergence time than given for Celtic and Italian. 3 List Evolutionary Aspects of Language Change 2021 Die ältesten teilungen des indogermanischen bis zum entstehen der grundsprachen der den sprachstamm bildenden sprachfamilien laßen sich durch folgendes schema anschaulich machen. Die länge der linien deutet die zeitdauer an, die entfernung der- selben von einander den verwantschaftsgrad. (Translation): The oldest splits of Indo-European until the development of the funda- mental languages of the language families which constitute the stem of the language [sprachstamm] can be visualized by the following schema. The length of the lines in- dicates the elapsed time, the distance of the lines from each other indicates the degree of relationship. (Schleicher 1861: 6f, my translation and emphasis) Even if my attempt to interpret the peculiarities of Schleicher’s family tree from 1861 along with his explanations turns out to be wrong: what seems important about this early phase of tree thinking in historical linguistics is that scholars did not use the tree model as a clear-cut tool for mathematical modeling. Instead they used the idea of a branching tree as a source of inspiration for the modeling of phenomena which they could observe but not yet