Throughout human history, there have been many instances where two populations came into contact – especially in the past few thousand years because of large-scale migrations as a consequence of conquests, colonialization, and, more recently, globalization. During these encounters, not only did populations exchange genetic material, but also cultural elements.
When populations interact, they may borrow technologies, beliefs, practices, and also, crucially, aspects of language. With this, sounds, words or grammatical patterns can be exchanged from one language to the other. For example, English borrowed "sausage" from French after the Norman conquests, while French later borrowed "sandwich" from English.
However, studying these linguistic exchanges can be challenging due to the limited historical records of human contacts, especially on a global scale. As a result, our understanding of how languages evolved over time through such interactions remains incomplete. To address this gap, researchers are now turning to genetics, which keeps the record of ancestral contacts. In this new study, a research group from the University of Zurich is using for the first time genetic evidence of historical mixing between populations to investigate the effects of contact on language, and to uncover the systemic patterns of language change.
Using genetics to solve linguistic questions
"By using genetic data as a proxy for past human contact, we were able to get around the problem of missing historical records and we could detect over 125 comparable instances of contact across the globe," says Anna Graff, lead author of the study and linguist at the University of Zurich.
The multidisciplinary research team combined genetic data from over 4,700 individuals across 558 populations with two major linguistic databases that catalogue grammatical, phonological, and lexical features in thousands of languages. They found that in instances of genetic contact, there was an increased probability of linguistic sharing in unrelated languages of 4-9%. "This opens up new ways of understanding how languages evolve through human interaction," the researcher adds.
"What surprised us most is that no matter where in the world populations come into contact, their languages become more similar to remarkably consistent extents," says Chiara Barbieri, senior author and population geneticist at the University of Cagliari. "Genetic contact can involve populations from different continents, for example in recent colonial situations, or populations from the same continent, for example during ancient Neolithic migrations. Our results show that languages are similarly affected by contact, regardless of its geographic and social scale, showing consistent links between population history and language change."
A closer look into language dynamics and society
However, while the rates are similar, the specific features behind them differ strongly. While some elements like word order or consonant sounds are easier to transfer – more so than other features of grammar or sound – the research team did not find consistent borrowability principles. "This challenges long-standing assumptions about what makes a linguistic feature more or less borrowable," explains Balthasar Bickel, senior author and Director of the NCCR Evolving Language. "It suggests that the social dynamics of contact like power imbalances, prestige and group identity easily override any constraints previously thought to be at play when people learn a new language and start to borrow from it."
In some cases, the team even found the opposite of borrowing: features becoming less similar after contact. This phenomenon occurs when groups emphasize linguistic differences to assert distinct identities. "While contact usually makes languages converge, sometimes it makes them diversify," says Graff. "Our results suggest that both convergence and divergence are part of the global story of language evolution."
The findings shed new light on how we understand the history of the world's languages – and what might lie ahead. Contact between populations has long been linked to language loss, but this study shows that it can also erode deeper layers of linguistic diversity. In our increasingly globalized world and in the face of the climate crisis, land use expansions and demographic displacements may further intensify these processes, fragmenting the linguistic record of the human past.
