Why are some languages in the same family tree so far away from one another?

It often makes sense that languages from the same family tree stay close to one another geographically. Slavic languages are tightly bound to Eastern (and parts of Central) Europe; Romance languages are mostly clustered around southern Europe and France, and even Niger-Congo languages, the largest language family tree in Africa, are glued together across a considerable portion of the continent.

But just like grammar, there are always interesting exceptions. The main languages of Finland and Hungary (namely, Finnish and Hungarian) are both Uralic, despite being tucked away in different corners of Europe. The linguistic relationship of this pair is based on shared ancestral roots rather than physical proximity. The Uralic languages originated from a common proto-language, Proto-Uralic, spoken thousands of years ago (estimates range from 6,000–10,000 years ago) in a region near the Ural Mountains in modern-day Russia. Over time, as speakers migrated and settled in different regions, the language family split into distinct branches.

And even though Finnish and Hungarian come from the same family, their similarities are mostly based on a structural and phonetic rather than a semantic level. Unlike some sister languages in the same language family, this pair is not mutually intelligible, likely due to the separate evolution over the years.

In addition to migration and history, it perhaps isn't surprising that empires and colonisation also play a role in how geographically distant languages can come from the same family. Romanian, spoken in Romania and Moldova in Eastern Europe, seems to also be miles away from siblings in the Romance family (Catalan, Spanish, Italian, French, and Portuguese). Although a language with some Slavic influence, Romania is still a Romance language (something that one can perhaps guess from its name). This traces back millennia–when the Roman Empire conquered the region of Dacia (modern-day Romania) in 106 CE under Emperor Trajan, Vulgar Latin (the colloquial form of Latin spoken by soldiers, settlers, and merchants in the Roman Empire) evolved as an important language in the area. Even after the Romans left, Romania continued to use that language for years and years into its future.

The geographical scope of family trees shows the complexity of how languages relate to each other, and how nothing about languages is truly static. If members of the same human family can move away from each other over time, surely languages under the same historical umbrella can do the same too.