system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did we go from grunting noises to a bunch of different languages?
gpt
You're referring to 'behavioural evolution', the process by which a species evolves in terms of behaviour (such as talking, using tools, etc) without *necessarily* having to express the physical changes that most people expect in evolution. In very early hominids (our ancestors ancestors) there was a very small population that lived close together, and so only one 'language' (likely very simple, even grunts as you've described). However, an aspect of evolution is 'divergence', whereby two groups of the same species (let's say tribes) that are removed for a long enough period of time will slowly turn into different species. A popular theory for the formation of language follows the same train of thought: if two groups spend enough time apart, their language will slowly diverge, as the language of each group slowly evolves to fit the needs of the group. 

This is just a theory, however, because language doesn't really show up well on the fossil record.