Derek Bickerton is an emeritus professor in Linguistics at the University of Hawaii. His other works include Language and Species (1990), along with many publications on the character of pigdin and creole. This work synthesizes ideas from a long and productive career.
The evolution of language has proven to be a difficult topic. Bickerton's work refutes one thesis, proposed by Noam Chomsky and others, that language appeared suddenly by way of a fortuitous mutation. He does so by offering an alternate hypothesis, which turns out to be a parallel evolution of the symbolic operations of parole and langue. These operations were able to evolve once hominins adopted words (in the same fashion that pidgin is adopted, for lack of any other method to communicate.)
Here, the word "language" exclusively means "speech-alone talk". As it turns out, hand talk may be readily substituted in for "language" as well. To me, this makes more sense, since manual-brachial gestures were under voluntary control in the walking southern apes, but the vocal tract was not.
Also, Bickerton locates the start of "language" at the appearance of anatomically modern humans. To me, this works for the addition to speech to an already established hand talk.
In sum, Bickerton's proposals apply to a long period before the appearance of anatomically modern humans. The gracile australopithicenes (who discovered words) and the early Homo genus (who evolved syntactical operations for langue and parole) span two million years. Then, Homo heidelbergensis broke the slow increase in brain size by initiating grammar-dependent behaviors.
These comments re-articulate Bickerton's argument, using the category-based nested form plus a time-map for the evolution of talk that goes from protolanguage, to hand talk to hand-speech talk, then finally, with the first singularity, to speech-alone talk.