Pim makes a very good point here. Suppose we considered three
variations of a question regarding increasing complexity in
evolution:
1) Does evolution sometimes result in an increase in complexity?
I believe practically everyone would answer yes to this question.
2) Does evolution always result in an increase in complexity?
Most evolutionary scientists would undoubtedly answer no to
this question. The interesting question is somewhere between
these extremes, but closer to (2)
3) Is there a general trend (with a few possible exceptions)
towards increasing complexity during evolution?
This question is very controversial. My own opinion is yes and
I suspect the majority of evolutionists might also say yes.
There are notable individuals (Steve Gould) who argue in the
negative though. A key point is that this may be only an
apparent trend due to our perceptions being influenced by faulty
sampling. i.e., the cases we tend to be most interested in are
those involving increasing complexity.
This point is well argued by Dan McShea in the following
article:
========================================================
McShea, Daniel W., "Complexity and Evolution: What
Everybody Knows," Biology and Philosophy, vol. 6,
pp. 303-324, 1991.
ABSTRACT: The consensus among evolutionists seems to
be (and has been for at least a century) that the
morphological complexity of organisms increases in
evolution, although almost no empirical evidence for
such a trend exists. Most studies of complexity have
been theoretical, and the few empirical studies have
not, with the exception of certain recent ones, been
especially rigorous: reviews are presented of both
the theoretical and empirical literature. The paucity
of evidence raises the question of what sustains the
consensus, and a number of suggestions are offered,
including the possibility that certain cultural and/or
perceptual biases are at work. In addition, a shift in
emphasis from theoretical to empirical inquiry is
recommended for the study of complexity, and guidelines
for future empirical studies are proposed.
=======================================================
Various proposed mechanisms for increasing complexity
mentioned by McShea:
<internalist mechanisms>
1. Invisible fluids. [Lamarck!, included for sake of
completeness I suppose ;-)]
2. The instability of the homogeneous. [Spencer]
3. Repetition and differentiation of parts.
4. The path of least resistance.
5. Complexity from entropy.
<externalist mechanisms>
1. selection for complexity
2. selection for other features.
3. niche partitioning.
<undriven mechanisms>
1. random walk
2. diffusion
3. the ratchet
More readily accessible is an article about McShea available on the
WWW:
========================================================
Frank Zoretich (1996). "Dan McShea and the Great Chain of
Being: Does Evolution Lead to More Complexity?," The Bulletin of
the Santa Fe Institute, summer 1996, volume 11, number 2.
http://www.santafe.edu/sfi/publications/Bulletins/bulletin-fall96/mcshea.html
========================================================
The article above mentions a paper by McShea recently published in
the journal <Evolution>. I haven't seen this article, nor do I
know the volume etc., but I do have the abstract:
==========================================================
"Metazoan Complexity and Evolution: Is There a Trend?"
Daniel W. McShea
Abstract: The notion that complexity increases in evolution
is widely accepted, but the best-known evidence is highly
impressionistic. In this paper, I propose a scheme for
understanding complexity which provides a conceptual basis
for objective measurement. The Scheme also shows complexity
to be a composite term covering four independent types. For
each type, I describe some of the measures that have been
devised and review the evidence for trends in the maximum
and mean. In metazoans as a whole, there is good evidence
only for an early-Phanerozoic trend, and only in one type of
complexity. For each of the other types, some trends have been
documented but only in a small number of metasoan subgroups.
==============================================================
Brian Harper
Applied Mechanics
Ohio State University
214 Boyd Lab
155 W. Woodruff Ave
Columbus, OH 43210
"God forbid that we should give out a dream of
our own imagination for a pattern of the world"
-- Francis Bacon