Pleistocene origins of cultural and linguistic diversification: how Homo sapiens and Neanderthals differed

It is now widely assumed that Neanderthals possessed a human language-like communication system. What is yet unclear is how different this was from ours. Here we ask whether the communication system of Neanderthals shared a key feature of human languages: ergodicity. Ergodicity allows linguistic evolution to continue for purposes of social differentiation without changing the species-wide language faculty and hampering languages’ universal learnability. We first review the ergodic properties of human language and propose that they are co-indicated by social group differentiation, which are present since the Middle Stone Age. We then examine the archeological record and demography of Neanderthals, which suggest that they mostly lacked the relevant indicators and demographic conditions favoring ergodicity. Finally, we conclude that our findings are also consistent with recent genetic evidence for differences related to routinization and complexity in our species. Hence, the Neanderthal communication system may have differed in fundamental ways from ours, by accumulating changes that reduced learnability by other groups and increased differentiation into subspecies.