It was originally thought that smurfs reproduced much like humans with separate male and female genders, however this leads one to wonder why there are so few female Smurfs one of which being created by an evil wizard who is trying to eradicate them. The Smurf Stacker theory takes an entirely different approach theorizing that every smurf has both sets of genitalia, allowing them to both impregnate and be impregnated. It is believed that each smurf, under their each of their white hats, has a phallus and also a vaginal organ in their crotchal region. It is further theorized that during a mating event all of the smurfs in the village gather and assemble into a "Smurf Stack" which involves every smurf standing one on top of the other allowing simultaneous penetration.
Due to the elusiveness of the smurfs during mating season no one can either prove or disprove this theory and while it continues to be a hugely controversial subject among smurfologist it is quickly being accepted as the most plausible theory as to how smurfs reproduce.
note: wikipedia rejected this article claiming it was "unsalvageably incoherent"
"Lets make like smurfs and stack!"