Machines making other machines: new twist on self-replication

How can we best build self-replicating machines? The past few decades have witnessed self-replicating virtual automata, ranging from the benign Game of Life by Conway to malicious computer viruses. Self-replicating physical constructs are, however, currently both delicate and rare. The work of mathematicians such as John von Neumann and Roger Penrose, around the birth of automata theory in the middle of the past century, revealed no limits in principle to constructing such devices. The main obstacles appear to be the substantial engineering challenges.