It may seem hardly surprising that no one has ever actually made a self-reproducing machine, even though Von Neumann laid down the design principles more than 40 years ago. You can imagine a clanking robot moving around a stock-room of raw components (wire, metal plates, blank tapes and so on) choosing the pieces to make another robot like itself. You can show that there is nothing logically impossible about such an idea: that tomorrow morning there could be two clanking robots in the stock-room.

Graham Cairns-Smith, Seven Clues to the Origin of Life
1985