Well, what are they? Of course, clapping is universally used by people to show that they appreciate something. It can also be used to show approval, such as when the audience claps on a show such as Jerry Springer or Montel.
But what the origins of this? My guess is that clapping evolved as the most convenient method of making a sustained noise. The noise is easily heard by the person(s) being clapped, and from that they know how much people enjoyed whatever they were doing.
When did clapping first become common, and how did this happen?