Why we do not speak one language?

Why we do not speak one language?
Perhaps, at the very beginning of history the mankind spoke one language. But later time this language changed. Because of what it occurred? Reasons a little. People in search of food looked for new areas of dwelling. Arriving to new places and growing roots, they spoke language of ancestors, a pronunciation over time, the name of subjects changed, old and unnecessary words went out of use on a new place. New vital conditions demanded new words for their description. And if people moved in already populated places, two languages merged, both changed.
Approximately thus appeared from Latin - English, Norwegian, Swedish, Danish.
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