Most languages with front rounded vowels are found in the more northern parts of Eurasia.
Many of the Uralic, Mongolic, and Turkic languages that contain front rounded vowels also have vowel harmony systems, such as rounding or backness harmony. The processes which bring about fronting or roundedness harmony may be important in introducing front rounded vowels into a language's inventory.
Front rounded vowels can also develop independently of vowel harmony. In French, [y] is the result of an older [u] moving forward while remaining rounded. French re-developed [u] by moving [o] upwards. For example, the familiar second-person pronoun tu, pronounced [ty], is spelled the same as its Latin source tu which had a back vowel, and the plural or polite second-person pronoun vous is pronounced with [u], but it derives from Latin vos which had a mid vowel. Some varieties of modern English are similarly fronting [u]. In cases like these the creation of front rounded vowels is independent of adjacent sounds in the word.
In other languages front rounded vowels evolved as previously back vowels became fronted by adjacent segments. For example, in German, back vowels became fronted when followed by high front vowels. The front vowels causing this change were often in inflectional or derivational endings and were then lost or changed into mid vowels. In the different Chinese languages, [y] is often derived from [ut]. The tongue must be moved forward to pronounce the [t], so the [u] can shift forward as well. If the [t] is lost then the change from [ut] to [y] is complete.
Considering the different historical scenarios which can give rise to front rounded vowels, it is notable that they are relatively concentrated in a particular geographical region. It is likely that the presence of front rounded vowels in some languages can facilitate phonetically-motivated processes in other nearby languages.
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Mandarin". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Cantonese". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Wu". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Tibetan (Standard Spoken)". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "French". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Albanian". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Turkish". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Dagur". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Khalkha". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Finnish". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Dryer, Matthew S.; Haspelmath, Martin, eds. (2013). "Hungarian". World Atlas of Language Structures Online. Max Planck Institute for Evolutionary Anthropology. /wiki/Matthew_Dryer
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson
Maddieson, Ian (2013). "Front Rounded Vowels". In Dryer, Matthew S.; Haspelmath, Martin (eds.). The World Atlas of Language Structures Online. Leipzig: Max Planck Institute for Evolutionary Anthropology. Retrieved 24 April 2022. /wiki/Ian_Maddieson