An influential position in linguistics is that human language has not evolved primarily as a communication device, but as a “system of thought.” This system enables humans to refer to the outside world in ways that cannot be reduced to a “peculiar nature belonging to [a] thing” and to construct an infinite number of internal structures by merging (Chomsky 2005). Whether such an evolutionary scenario is plausible will depend much on comparative research with primates. Recent field experiments suggest that mental concepts of nonhuman primates can do more than refer to the physical properties of the outside world; there is evidence for distinct idiosyncratic qualities coined by the “cultural” background of their bearers. There is also evidence that primates perform basic mental operations when attending to each other’s calls, and that they combine elements of their repertoire to generate meanings that are independent of the constituent parts. Finally, there is a consensus that evolution has shaped primate communication as a device to pursue social goals, and it is unclear why humans should have been exempt from this process. In conclusion, contrary to the “cognition over communication” hypothesis, there is evolutionary continuity in mental operations and communicative versatility, suggesting that language evolved gradually from a nonlinguistic precursor in ancestral human population that also underwent an unprecedented increase in relative brain size and mental capacity.