Humans are the only species that has evolved an advanced system of communication between individuals.
Whereas other species communicate through ritualized and repetitious songs, calls, or gestures, humans have developed linguistic systems that can express a literally infinite variety of separate and distinct thoughts. This incredible evolutionary leap is what distinguished humans from all other organisms on earth.
Language first appeared between 30,000 and 100,000 years ago in the species Homo sapiens. But how did language evolve? Currently, there are two rival answers to this question: the first and more common explanation is that language was an adaptation of some sort; the second (chiefly espoused by Stephen Jay Gould) is that language is a spandrel, a nonadaptive element arising as a byproduct of other processes.