The RepRap is a selfreproducing 3D printer. The 3D printer 'prints' his own components by melting tiny plastic particles together.
Imagine what would happen if this 3D printer wouldn’t stop reproducing. At a certain point, the 3D printers will reproduce faster than we could destroy them. The RepRap will populate the world, the human race will die out and eventually the RepRap will evolve into smarter and better devices.
Happily the RepRap is still dependent on the human race