it is, the harder it is to reproduce, and thus the more complicated it 

 must still be — that particular kind of trouble was once and for all 

 eliminated by the arguments of the mathematician John 

 von Neumann 30 years ago. His argument was well-summarized by 

 Freeman Dyson: 



"Von Neumann did not live long enough to bring his 

 theory of automata into existence. He did live long 

 enough to see his insight into the functioning of living 

 organisms brilliantly confirmed by the biologists. The 

 main theme of his 1948 lecture is an abstract analysis 

 of the structure of an automaton which is of suffi- 

 cient complexity to have the power of reproducing 

 itself. He shows that a self-reproducing automaton 

 must have four separate components with the follow- 

 ing functions. Component A is an automatic factory, 



an automaton which collects raw materials and pro- 

 cesses them into an output specified by a written 

 instruction which must be supplied from the outside. 

 Component B is a duplicator, an automaton which 

 takes a written instruction and copies it. Compo- 

 nent C is a controller, an automaton which is hooked 

 up to both A and B. When C is given an instruction, it 

 first passes the instruction to B for duplication, then 

 passes it to A for action, and finally supplies the 

 copied instruction to the output of A while keeping 

 the original for itself. Component D is a written 

 instruction containing the complete specifications 

 which cause A to manufacture the combined sys- 

 tem A plus B plus C. Von Neumann's analysis showed 

 that a structure of this kind was logically necessary 

 and that it must also exist in living cells. Five years 

 later Crick and Watson discovered the structure of 

 DNA, and now every child learns in high school the 

 biological identification of Von Neumann's four com- 

 ponents. D is the genetic material, DNA; A is the 

 ribosomes; B is the enzymes RNA and DNA poly- 

 merase; and C is the repressor and derepressor con- 

 trol molecules and other items whose functioning is 



