According to the socio-cognitive revolution hypothesis, humans but not other great apes acquire language because only we possess the socio-cognitive abilities required for Griceian communication, which is a pre-requisite of language development. On this view, language emerged only following a socio-cognitive revolution in the hominin lineage that took place after the split of the Pan-Homo clade.
Grice argues that the SCR hypothesis is wrong. The driving forces in language evolution were not sweeping biologically driven changes to hominin social cognition. Our LCA with non-human great apes was likely already a Griceian communicator, and what came with evolution was not a raft of new socio-cognitive abilities, but subtle tweaks to existing ones. It was these tweaks, operating in conjunction with more dramatic ecological changes and a significant increase in general processing power, that set our ancestors on the road to language.