WTF? My friend just called me a few minutes ago and asked me this question!
I told him its relieves stress just like a good stretch does. But are there any other answers to this question?
Re: Why do we laugh?
Yeah because we find something funny. I truly pity the human race. 
Re: Why do we laugh?
Get help for the friend of yours. :)
Re: Why do we laugh?
Its a good question...would be interested in the scientific reasons.
Laughter is beautiful
Re: Why do we laugh?
easy :D
Laughter, a physiological response to humor, can be broken down into two parts.
The first is a set of gestures, and the second is the production of sound. The brain forces to conduct both responses simultaneously. From a physiological standpoint, a "sensor" in the brain responds to laughter by triggering other neural circuits in the brain, which, in turn, generate more laughter.
Oddly enough, laughter is an orderly response, and almost occurs "spontaneously" during pauses at the end of phrases, earning it the name the punctuation effect. Human beings are the only species capable of laughter, and the average adult does so approximately 17 times per day.
Good health is one of the many benefits of laughter. Laughter reduces our stress levels by reducing the level of stress hormones, and also helps us cope with serious illnesses.
Physiologically, laughter promotes healing, by lowering the blood pressure, and by increasing the vascular blood flow and the oxygenation of the blood.
Physical fitness stemming from laughter is a benefit known to few. Scientists estimate that laughing 100 times is equivalent to a 10-minute workout on a rowing machine, or to 15 minutes on a stationary exercise bike. The mere act of laughing exercises the diaphragm, as well as the abdominal, respiratory, facial, leg, and back muscles.
Another benefit of laughter is that it improves our over-all mental health. Pent up negative emotions, such as anger, fear, and sadness, can cause biochemical changes in our bodies that can produce a harmful effect.
Laughter provides a harmless outlet for these negative emotions, and provides a coping mechanism for dealing with difficult or stressful situations.
Re: Why do we laugh?
dutch_paki, u wrote all that for this. 
i hope u copy pasted some of this junx.
thread starter, i think your friend is on crack. does he start laughing without a reason? puffing the magic dragon can make you laugh and unfortunately blows dutch_paki’s research on the subject. get him help.
Re: Why do we laugh?
Sometimes we laugh because our heart is smiling ( when you see your beloved, or you are heading towards your favourite picnic spot or shopping mall, when you are with your mother after so many days, when you are having cup of tea with your father, when you are fighting with your siblings on petty things, when you hang out with your friends, when you were missing someone and that person comes right infront you all of the sudden, etc)
and sometimes, you laugh because your mind orders you to laugh( when you are with your business rival for big business deal, when you have to show people that you are happy when you are NOT HAPPY, when you are in wedding ceremony where you didnt want to come, when you have to go with your beloved's friend for shopping etc)
and sometimes we laugh for absolutely no reason at all!!!!!
Re: Why do we laugh?
Normal people laugh when they find something funny. for people laughing without a reason we do have some treatments like electric shocks etc.
Re: Why do we laugh?
And I can see you have done YOUR research very well. Puffing the magic dragon?
I hope you use that line for kids. 
Re: Why do we laugh?
^ mann what is WITH your avator 
and then you go complaining whenever i accidentally call u auntie 
Re: Why do we laugh?
DP: Thanks for your effort. I appreciate.