From NPR's 13.7 Cosmos & Culture Blog (an awesome blog, by the way)
"Most organisms communicate, but humans are unique in communicating via symbolic language. This entails relationships between signifiers (e.g. words) and what's signified (e.g. objects or ideas), where what's special is the construction of a system of relationships among the signifiers themselves, generating a seemingly unlimited web of associations, organized by semantic regularities and constraints, retrieved in narrative form, and enabled by complex memory systems.
Humans are thus a symbolic species: symbols have literally changed the kind of biological organism we are. We think and behave in ways that are quite odd compared to other species because of the way that language has defined us. Symbolic language has become the dominant feature of the cultural environment to which we must adapt in order to flourish; the demands imposed by this niche have favored mental capacities and biases that guarantee successful access to this essential resource."
Read the rest here.