Language—more specifically human language—refers to the grammar and other rules and norms that allow humans to make utterances and sounds in a way that others can understand, notes linguist John McWhorter, an associate professor of English and comparative literature at Columbia University. Or as Guy Deutscher said in his seminal work, "The Unfolding of Language: An Evolutionary Tour of Mankind's Greatest Invention," language is "what makes us human." Discovering what is language, then, requires a brief look at its origins, its evolution through the centuries, and its central role in human existence and evolution.