Final answer:
The formation of different languages from a single ancestral language is termed cladogenesis, part of a complex process that has resulted in the vast number of languages and dialects in existence today, including creoles, revived languages, and regional dialects.
Step-by-step explanation:
The development of different languages from a single ancestral language is known as cladogenesis. Just as a single ancestral species of bird may give rise to multiple species, a single proto-language can evolve into various distinct languages over time. For example, the Indo-European family began as a single language, Proto-Indo-European, around 6,000 years ago. As populations migrated, their languages evolved and differentiated into the myriad languages we see today, such as the Romance, Germanic, and Slavic language groups.
In discussing why it's difficult to give an exact number for how many languages exist, one must consider factors like dialects, creole languages, and revived languages. For instance, Creole languages often form in colonial contexts, incorporating features from multiple languages and sometimes becoming the primary language of an area, as seen in Haiti. Furthermore, dialects such as the various forms of American English have distinct grammatical features and pronunciations. Lastly, language revival efforts demonstrate the fluidity of language usage and classification over time and reflect the integral connection between language and cultural identity.