Document: John von Neumann and the Evolutionary Growth of Complexity
Bibliography
John von Neumann and
4 Looking Backwards
By re-examining von Neumann's work in the light of his own
description of the problem he was working on, I have tried to
show that there is much more substance to it than has been
generally recognised. However, as Popper (1976) has
emphasised, the scientific enterprise is iterative: the solution
of any given problem gives rise to a new problem situation, which
is to say new problems to be addressed. It seems to me that von
Neumann's work is particularly fruitful in this regard, as it
poses a number of new and profound questions which need to be
addressed by the (still) fledgling field of Artificial Life. Among these
are:
- Can we clarify (or even formalise) the notion of
complexity. This of course is not specifically a problem for
Artificial Life, but rather underlies the entire discipline of
evolutionary biology (Maynard Smith, 1969).
- What is the precise significance of the self-reproductive
capability of von Neumann's machines? Technically, based on the
idea of a ``general constructive automaton'', growth of
complexity per se could take place in isolation from
self-reproduction. One simple scenario here would be to
imagine being made to simply grind through the
(countable) infinity of all description tapes, constructing
every described automaton in turn. This would require only a
trivial extension of the capabilities of . While this
would fail in practice due to the essential fragility of von
Neumann's automata (discussed further below) it is not clear
whether there is any fundamental problem with this
general idea. Nonetheless, it seems clear that if the growth of
complexity is to involve Darwinian evolution, then
self-reproduction surely is a necessary additional requirement.
- The problem of identity or individuality. In the alife
systems discussion above, the question of what constitutes a
distinct individual ``machine'' or ``automaton'' is addressed
in a completely ad hoc manner. In a real sense, these putative
individuals exist as such only in the eye of the human
observer. Whereas, the notion of a self-defining identity,
which demarcates itself from its ambiance, is arguably
essential to the very idea of a biological organism. Some
early and provocative work on this question, including
simulation models overtly reminiscent of von Neumann's CA, was
carried out by Varela et al. (1974). However, there has
been relatively little further development of this line since.
- The evolutionary boot-strapping problem: in the von Neumann
framework, at least, is already a very complicated
entity. It certainly seems implausible that it could
occur spontaneously or by chance. Similarly, in real biology,
the modern (self-consistent!) genetic system could not have
plausibly arisen by chance (Cairns-Smith, 1982).
It seems that we must therefore assume that something like
(or a full blown genetic system) must itself be the
product of an extended evolutionary process. Of course, the
problem with this--and a major part of von Neumann's own
result--is that it seems that something like a genetic system
is a pre-requisite to any such evolutionary process.
- Perhaps most importantly of all, what further conditions
are required to enable an actual, as opposed to merely
potential growth of complexity? It was well known even
to von Neumann himself that his system would not in
practice exhibit any evolutionary growth of complexity. The
proximate reason is that, in his CA framework, all automata of
any significant scale are extremely fragile: that is,
they are very easily disrupted even by minimal perturbation of
the external environment. The upshot is after the completion
of even a single cycle of self-reproduction the parent and
offspring would almost immediately perturb, and thus effectively
destroy, each other. This can be avoided by ad hoc mechanisms
to prevent all interaction (again, this was suggested by von
Neumann, and since shown in practice by Langton and others).
However, eliminating interaction eliminates the grist from the
darwinian mill, and is thus a non-solution to the substantive
problem (growth of complexity). Tierra offers a somewhat
different approach, whereby the integrity of the automata
(process images) is ``protected'' by the underlying operating
system, while still allowing some forms of significant
interaction. This has been very fruitful in allowing the
demonstration of some significant evolutionary
phenomena. However, any serious claim to substantively model
real biological organisms will inevitably have to confront
their capacity for self maintenance and repair in the
face of continuous perturbation and material exchange with
their environments. This, in turn, is clearly also related to
the earlier problem of biological individuality.
In conclusion, it seems to me that von Neumann's work in
Artificial Life--properly understood--is as profound and
important today as it was half a century ago; and that it should
continue to provide structure, insight and inspiration to the
field for many years to come.
Bibliography
John von Neumann and
4 Looking Backwards
Document: John von Neumann and the Evolutionary Growth of Complexity
Copyright © 2000 All Rights Reserved.
Timestamp: 2001-01-03
Barry.McMullin@dcu.ie