Insights & Perspectives Networks of lexical borrowing and lateral gene transfer in language and genome evolution Johann-Mattis List 1) *, Shijulal Nelson-Sathi 2) , Hans Geisler 3) and William Martin 2) Like biological species, languages change over time. As noted by Darwin, there are many parallels between language evolution and biological evolution. Insights into these parallels have also undergone change in the past 150 years. Just like genes, words change over time, and language evolution can be likened to genome evolution accordingly, but what kind of evolution? There are fundamental differences between eukaryotic and prokaryotic evolution. In the former, natural variation entails the gradual accumulation of minor mutations in alleles. In the latter, lateral gene transfer is an integral mechanism of natural variation. The study of language evolution using biological methods has attracted much interest of late, most approaches focusing on language tree construction. These approaches may underestimate the important role that borrowing plays in language evolution. Network approaches that were originally designed to study lateral gene transfer may provide more realistic insights into the complexities of language evolution. Keywords: .borrowing; language evolution; lateral transfer; network approaches; prokaryotic evolution : Additional supporting information may be found in the online version of this article at the publisher’s web-site. Introduction For a long time, both biologists and linguists have been using family trees to model how species and languages evolve. But in contrast to biology – where the tree model is generally accepted to be the most realistic way to model how eukaryotic species (species with nucleated cells, such as animals and plants) evolve – linguists have always treated language trees with a certain suspicion. They have emphasized that – given the important role that horizontal transmission plays in language history – such trees can only capture vertical aspects of language evolution, while horizontal aspects (which linguists traditionally model as “waves” that spread out in circles around a center in geographic space) are ignored. In the last decade, language trees have experienced a strong revival, espe- cially in the public notion of linguistics as reflected in popular scientific literature and in articles addressed to a not exclusively linguistic readership [1]. Ear- lier linguistic work on phylogenetic reconstruction was, with a few excep- tions [2–8], qualitative in its nature. But starting about 10 years ago, computer methods originally designed to infer trees from molecular sequence data made their way into the analysis of large linguistic datasets, leading to a resurgence of language trees [9–15]. If the reconstruc- tion of trees had only played a minor role in historical linguistics up to that point, it has now become a specific field of interest, and some scholars even go so far as proclaiming tree construction as a priority for historical linguistic endeavor [16]. In traditional historical linguistics, these new approaches are met with a certain amount of reservation, since their results are often not in concor- dance with those achieved by tradition- al methods [17–20]. One important reason for such discrepancies is the relatively large number of individual DOI 10.1002/bies.201300096 1) Research Center Deutscher Sprachatlas, Philipps-University Marburg, Marburg, Germany 2) Institute of Molecular Evolution, Heinrich-Heine University D€ usseldorf, D€ usseldorf, Germany 3) Institute of Romance Languages and Literature, Heinrich-Heine University D€ usseldorf, D€ usseldorf, Germany *Corresponding author: Johann-Mattis List E-mail: mattis.list@uni-marburg.de www.bioessays-journal.com 141 Bioessays 36: 141–150, ß 2013 The Authors. BioEssays Published by WILEY Periodicals, Inc. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Think again