Recent work on Self-Replication in CAs
In the last 10 years or so, a lot of people have published
work on CA machines that are capable of self-replication, but are much
smaller than von Neumann's Universal Constructor, e.g.
- Chris Langton, 1984 (he started the recent trend with the
so-called "Langton's Loop")
Reggia et al, 1993
Ibanez et al, 1995
Sipper et al, 1996
and so on...
These simple machines are not universal constructors, and
(more seriously) they ignore many of the theoretical considerations about
evolvability that went into von Neumann's Universal Constructor.
McMullin discussed the shortcomings of Langton's work
at some length in his PhD thesis (1992)