They came from the radio shows that were performed in front of live audiences, and that came all the way back from vaudeville theater. After some time, it became too expensive to broadcast the comedy shows live at a theater, so they started to tape it, edit it, and add laughs to it, so that people would still think they were still live. Since TV comedy came from radio comedy, laugh tracks were incorporated to TV shows, the early ones still had the "theater" feel, like "I Love Lucy" and "Honeymooners".

And today, I can watch this piece of crap called "Friends", and see what has the laugh track evolved to. I watched 2 episodes of Friends, a long time ago, and I simply could not laugh, it was NOT funny, the actors were terrible, the writing was awful, and yet thanks to the laugh track that became the most successful sitcom in the world. I have NOTHING against sitcons, but if you have any talent, try it without the laugh track.

I did some stand ups experiences during college, and I had this tape recorder with me, on my right hand. After the first joke, which was the best one, I would stand my right hand and tape the laughs. People would laugh even more after I did it. After 2 or 3 minutes I would tell a bad joke on porpouse, and after 3 seconds with no laughs, I'd show the tape recorder, rewind it, put it on the microphone and press play, and the laughs would play. Then I'd say "See? I don't need you anymore. I've captured your laughs. They know what's funny."