Language evolution is traditionally described in terms of family trees with ancestral languages splitting into descendent languages. However, it has long been recognized that language evolution also entails horizontal components, most commonly through lexical borrowing. For example, the English language was heavily influenced by Old Norse and Old French; eight per cent of its basic vocabulary is borrowed. Borrowing is a distinctly non-tree-like process—akin to horizontal gene transfer in genome evolution—that cannot be recovered by phylogenetic trees. Here, we infer the frequency of hidden borrowing among 2346 cognates (etymologically related words) of basic vocabulary distributed across 84 Indo-European languages. The dataset includes 124 (5%) known borrowings. Applying the uniformitarian principle to inventory dynamics in past and present basic vocabularies, we find that 1373 (61%) of the cognates have been affected by borrowing during their history. Our approach correctly identified 117 (94%) known borrowings. Reconstructed phylogenetic networks that capture both vertical and horizontal components of evolutionary history reveal that, on average, eight per cent of the words of basic vocabulary in each Indo-European language were involved in borrowing during evolution. Basic vocabulary is often assumed to be relatively resistant to borrowing. Our results indicate that the impact of borrowing is far more widespread than previously thought.

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.

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The idea that language history is best visualized by a branching tree has been controversially discussed in the linguistic world and many alternative theories have been proposed. The reluctance of many scholars to accept the tree as the natural metaphor for language history was due to conflicting signals in linguistic data: many resemblances would simply not point to a unique tree. Despite these observations, the majority of automatic approaches applied to language data has been based on the tree model, while network approaches have rarely been applied. Due to the specific sociolinguistic situation in China, where very divergent varieties have been developing under the roof of a common culture and writing system, the history of the Chinese dialects is complex and intertwined. They are therefore a good test case for methods which no longer take the family tree as their primary model. Here we use a network approach to study the lexical history of 40 Chinese dialects. In contrast to previous approaches, our method is character-based and captures both vertical and horizontal aspects of language history. According to our results, the majority of characters in our data (about 54%) cannot be readily explained with the help of a given tree model. The borrowing events inferred by our method do not only reflect general uncertainties of Chinese dialect classification, they also reveal the strong influence of the standard language on Chinese dialect history.

Das genaue Zusammenspiel von Transitivität in einem begrifflich-semantischen Sinne und rein formal-syntaktischer Transitivität ist hinsichtlich seiner Abhängigkeit von der typologischen Struktur der betreffenden Sprache bislang noch nicht hinreichend untersucht worden. Da semantische Transitivität in vielerlei Abstufungen auftritt, während auf morpho-syntaktischer Ebene diskontinuierliche Übergänge vorliegen, ist hierbei jeweils für einzelne Sprachen zu klären, bis zu welchem Grad an semantischer Transitivität eine Überführung in syntaktisch transitive Strukturen möglich ist. Speziell für das Französische ist außerdem zu berücksichtigen, daß die zum Ausdruck syntaktischer Transitivität verwendete SVO-Struktur in vielfacher Hinsicht diskursfunktional genutzt wird, wodurch die Beziehungen zwischen den verschiedenen sprachlichen Ebenen verkompliziert werden. Nur unter Berücksichtigung dieser Faktoren scheint eine adäquate Interpretation verschiedener Entwicklungen im Zusammenhang mit dem Französi-schen möglich.