There are many theories on how human language began. Some think it may have started from imitating sounds that already exist in real life. Others think it could have started with our sounds that come from natural reactions (pain, etc.). Or it could have been grunts and noises made when needed to work together. Or maybe even out of love.
The point is, there are a lot of theories on how language begin and no one really knows for sure. Arika Okrent and Sean O’Neill do their best to explain more of the beginnings of language below and think it may be a result of the combinations of skills that we have (that some animals have only in parts).