Isolated human groups speak more diversified languages
Languages are diverse: thousands are spoken worldwide, and they differ widely in the structures they use. Human DNA variation preserves the history of populations and individuals. Are these two dimensions of human diversity related? Does the diversity of languages correlate with the diversity of their speakers?
This question has captured the imagination of scientists and the public for over a century. A new international study led by the University of Zurich and published in PNAS suggests the answer is yes – but not in the way one might expect. Regions with low genetic diversity across speakers show languages with high diversity, and vice-versa. In other words, the more diverse our DNA, the more similarly we speak!
Contact between groups increases genetic but decreases linguistic diversity, while isolation does the opposite: decreasing genetic diversity while allowing languages to diversify. This link between speakers’ relationships and language change reveals an important driver of language evolution. © NCCR Evolving Language
At first glance, the findings seem surprising. One might expect regions with greater genetic diversity, often shaped by migration and population mixing, to also show greater diversity in language. But the study reveals the opposite.
“We were struck by how robust this inverse relationship is across the globe”, says Anna Graff, lead author of the study and linguist at the University of Zurich. “Places where people have mixed more tend to be genetically diverse, but their languages are structurally more similar. In contrast, places with long-term isolation show less genetic diversity, yet much greater diversity in how languages are structured.” Crucially, this relationship holds after adjusting for a wide range of confounding factors, including deep population history such as the timing of continental settlement.
To uncover this pattern, the researchers combined large-scale genetic and linguistic datasets, analysing how genetic variation across individuals relates to structural variation across languages within each region. Importantly, they controlled for other possible influences like geographic proximity, population density and environmental factors, allowing to isolate the role of demographic history.
The result is a clear global signal: the same forces that shape the genetics of human populations – contact, migration and isolation – also shape the diversity of language structures, but in opposite ways. “The key insight is that contact and isolation have opposite effects on genes and languages”, explains Chiara Barbieri, senior author and population geneticist at the University of Cagliari. “Contact increases genetic diversity, but it also promotes the spread of linguistic features, making languages more similar. Isolation, by contrast, limits genetic diversity while allowing languages to evolve independently.”
This dynamic helps explain why some regions of the world stand out as hotspots of linguistic diversity. Areas such as New Guinea or the Himalayas are relatively isolated genetically; at the same time their languages are hotspots of diversity. “Such hotspots give us a glimpse of what languages can do when evolving under conditions of relative isolation”, says Balthasar Bickel, senior author and Director of the NCCR Evolving Language. “They preserve a wider range of ways of organizing grammar, sound and meaning, a range that cannot be observed elsewhere because it got reduced by long histories of contact.”
Beyond documenting a striking global pattern, the study highlights a broader implication: linguistic diversity is deeply intertwined with human history. “What might initially look like a paradox turns out to be a simple and actually intuitive principle”, Graff concludes. “The same processes that keep populations apart allow languages to grow apart as well.”
