Human communication comprises two modes – speech, and movements of the arms and hands, termed gestures. Of these, the gestural mode is likely to have evolved substantially earlier than speech. Apes, which are ancestors of humans, lack speech but gesture on a regular basis in their natural communication. They develop a multifaceted repertoire of gestures, and like pre-linguistic human infants, they use their gestures as intentional acts to draw attention to themselves.
Which one of the following most accurately describes the role played in the argument by the claim that the gestural mode of human communication is likely to have evolved substantially earlier than the speech mode?
