why do we laugh?

i have posted tons of retarded shit on here just to make fun of all you retards. but i am serious. i was just laughing at a joke one of my friends made that was in an email. and it was sort of funny but him saying it made it extra funny. and i was laughing.

but what social construct does laughing facilitate? why are we born to enjoy jokes, and others are skilled in performing them?

i don't have sci pictures so i just posted winona ryder she is very pretty.