One of Diamond’s propositions was that continent shape and orientation mattered. Those continents stretching wider from east to west have less variation in climate and it easier for people to move around and for cultures to mix and blend.

Continents spanning a long distance north to south instead presented humans with huge variations in climate and landscape: deserts, jungles, ice caps and tundra wastelands. The result: cultural difference survives along a north-south transect more than east-to-west.

Instead of continents, Laitin’s team chose modern nation-states. Indigenous language was a proxy for cultural diversity.

After computing the north-south and east-west axes of each country, they plotted the number of surviving Indigenous languages, looking for any discernible pattern.

The results confirmed Diamond’s earlier hunch. The degree of north-south orientation is positively related to the persistence of linguistic diversity. Countries such as Chile, long and thin, had higher levels of linguistic diversity than wider, flatter states, such as Russia.