Atheist point of view on origination of languages?

as people became smarter they started to develop ways of communication, as they migrated to different regions they didn't keep in contact to other tribes of humans and their language evolved. more migrations happen and more development happened. The tribes that split up later in time have similar languages (french and spanish rather spanish and chinese). different languages develop as we lose comminication with the other peoples. think of how different the american language is now from england, even though we have only split recently in comparison, there is significant difference in the accents of people and some words despite the amount of communication that still occurs.