In this paper, we complement proximate or ‘how’ explanations for the origins of language, broadening our perspective to include fitness-consequences explanations, i.e. ultimate, or ‘why’ explanations. We identify the platform of trust as a fundamental prerequisite for the development of a language-like system of symbolic communication. The platform of trust is a social niche in which cheap but honest communication with non-kin is possible, because messages tend to be trusted as a default. We briefly consider the place of the platform (...) of trust on the road map as laid out in the Mirror System Hypothesis. We then turn to recent research on turn-taking in primates, which has been proposed as a precursor of the cooperative structuring of conversation in humans. We suggest, instead, that human turn-taking, in its full richness that makes it an interesting explanatory target, may only appear in a communicative system that is already founded on a community-wide, cooperative platform of trust. (shrink)