Khan Academy: Theories of the Early Stages of Language Acquisition

Language is the primary method of human communication, but there are also other ways to communicate without the use of language. Language in its most complex form is unique to humans, although some animals have been found to have basic communication patterns. Languages often have verbal and written components, but how we classify something like American Sign Language? Animals manage to communicate -- do they have language? How did language evolve? How do we learn enough language ourselves to begin to answer this question?