The social interaction source

Another proposal involving natural sounds has been called the “yo-he-ho” theory. The idea is that the sounds of a person involved in physical effort could be the source of our language,  especially  when  that physical  effort involved  several  people and the inter- action had to be coordinated. So, a group of early humans might develop a set of hums, grunts, groans and curses that were used when they were lifting and carrying large bits of trees or lifeless hairy mammoths.

The appeal of this proposal is that it places the development of human language in a social context.  Early people must  have lived in groups,  if only because  larger groups offered better protection from attack. Groups are necessarily social organizations and, to maintain those organizations, some form of communication is required, even if it is just grunts  and curses.  So, human sounds, however they were produced, must have had some principled  use within  the life and social interaction of early human groups. This is an important idea that may relate to the uses of humanly produced sounds. It does not, however, answer  our question regarding the origins of the sounds  produced.

Apes and other primates live in social groups and use grunts and social calls, but they do not seem to have developed the capacity for speech.

Taken from The Study of Language (George Yule).