Consider the newborn. Thrown abruptly into a blaze of bright lights and babble of novel noises, it faces the immediate job of understanding and controlling its world.
Understanding requires the newborn to interpret the strange noises that apparently occur when those giants open their mouths. And controlling means breaking that mysterious sound code that those giants use between themselves and with you.
Crying and fussing may be enough communication for a while, but soon the infant begins babbling by making a sound and rapidly opening and closing the mouth. By 11 to 12 months, the baby is making single words and then joining them into short phrases. By the age of 3 or so, many babies speak in complete sentences, and can express their needs with words (at least after shrieking fails).
How does the newborn learn language? Natural language, after all, is so sophisticated, yet almost all babies learn it faster and more thoroughly than the baddest computer around. Full of nuances, loaded with meaning and implication, language is a subtle but comprehensive mode of communicating.
To most people, it's a hallmark of being human.