From the Wiki article on
Homo erectus;
quote:
The discovery of Turkana boy in 1984 has shown evidence that despite H. erectus's human-like anatomy, they were not capable of producing sounds of a complexity comparable to modern speech. They may have communicated with a pre-language lacking the fully developed structure of human language but more developed than the basic communication used by chimpanzees.
How does that gel with a story that revolves around language?
Mutate and Survive