'Huh?' - what you tell your children not to say when they did not understand what you just told them - has nonetheless taken over the word. 

Linguists have determined the word is both vital and universal. Without words 'huh' they believe we would be unable to signal when we have problems with hearing or understanding what was said, and our conversations would be constantly derailed by communicative mishaps - biologists instead know that it became such because it is so simple and that humans would have come up with a different word instead.

But the European Research Council wanted to study the ubiquity of 'huh' and so linguists have. Is 'huh' even a word? Most American parents say it is not but the linguists say that it is, because although it
is much more similar across languages than words normally should be, it does differ across languages in systematic ways. However, they note that actual words are dramatically different. 'Dog' is 'inu' in Japanese and chien in French whereas 'huh' is just 'huh', a grunt in many cultures.  

 A word like huh? -- used to initiate repair when, for example, one has not clearly heard what someone just said -- is found in roughly the same form in spoken languages across the globe. Languages 1-10 are examined in detail in the study. Locations are approximate. In all languages except 1, 2, and 21 the pitch of the word is rising.
1. Cha'palaa ʔaː 2. Icelandic ha 3. Spanish e 4. Siwu ãː 5. Dutch hɜ 6. Italian ɛː 7. Russian aː 8. Lao hãː 9. Mandarin Chinese ãː 10. Murrinh-Patha aː 11. ǂĀkhoe Haiǁom hɛ 12. Chintang hã 13. Duna ɛ̃: 14. English hã 15. French ɛ̃ 16. Hungarian hm/ha 17. Kri ha: 18. Tzeltal hai 19. Yélî Dnye ɛ̃ 20. Yurakaré æ 21. Lahu hãi 22. Tai/Lue hy̌/há 23. Japanese e 24. Korean e 25. German hɛ̃ 26. Norwegian hæ 27. Herero e 28. Kikongo e 29. Tzotzil e 30. Bequia Creole ha: 31. Zapotec aj. Credit: Max Planck Institute for Psycholinguistics

Why is 'Huh?' so similar across languages? To understand this, Mark Dingemanse and colleagues at the Max Planck Institute for Psycholinguistics in Nijmegen studied the specific context in which this word occurs. In human communication, when we are somehow unable to respond appropriately, we need an escape hatch: a way to quickly signal the problem.

This signal has to be easy to produce in situations when you're literally at a loss to say something; and it has to be a questioning word to make clear that the first speaker must now speak again. Since these functional requirements are fundamentally the same across languages, they may cause spoken languages to converge on the same solution: a simple, minimal, quick-to-produce questioning syllable like English 'Huh?', Mandarin Chinese 'A?', Spanish 'E?', Lao 'A?', or Dutch 'He?'.

The basic principle is well-known from evolutionary biology: when different species live in similar conditions they can independently evolve similar traits, a phenomenon known as convergent evolution. For example, sharks and dolphins have different evolutionary origins but similar body plans, because they live in the same aquatic environment. In the same way, Dingemanse and colleagues propose that words may converge on similar forms when they occur in strongly similar conversational 'environments'. A clear effect of this conversational ecology on the specific shape of linguistic expressions has not been observed before.

Although 'Huh?' may almost seem primitive in its simplicity, a word with this function is not found in our closest evolutionary cousins. Only humans have communication systems in which complex thoughts can be expressed and communicative mishaps can be solved on the spot. Even a humble word like 'Huh?' can teach us a lot about our nature as ultrasocial animals, they say. 

Citation: Dingemanse M, Torreira F, Enfield NJ (2013) Is “Huh?” a Universal Word? Conversational Infrastructure and the Convergent Evolution of Linguistic Items. PLoS ONE 8(11): e78273. doi:10.1371/journal.pone.0078273