Quote:
To oversimplify, animal signals are aimed at the behavior and motivational states of others, whereas human symbols are aimed at the attentional and mental states of others.
Tomasello goes on to discuss how human linguistically communication is learned via different social and cultural methods. Animals rely on this type of "learning" less and therefore do not develop much learned communication as a species - some individuals or small social groups can/do learn communications in some animals. Animals, as a whole, have more "known" signals than learned signals. Given the humans' abilities to create ad understand visual symbols, the regression to a more basic function in the brain may trigger a much higher sensitivity to a set of "known" vs "learned" symbols.