Based on empirical research involving humans and great apes, Michael Tomasello proposes that human language emerged from the need for communication as part of collaboration. Collaboration and shared intentionality that it came to entail, was the basis. He does not think that language began as vocalizations, since the ability to refer to specific things is required, and how does one indicate that using just sound without a prior basis of meaning? Instead, gestures, and in particular pointing, is more likely as the precursor of language, in Tomasello's view.
Human communication is based on biological adaptions to the need for cooperative social interaction, and it relies heavily of cultural inheritance. Tomasello does not think that Chomsky's theory of innate grammar really provides much explanatory power. Instead, the focus should be in shared intentionality and the transmitting of cultural innovations.
I found this to be a more accessible text than usual for Tomasello. Not that he is usually difficult to understand, rather that his texts usually have rather high density. This one was a little lighter.