Re: Book review: The Plausibility of Life (Marc W. Kirschner and John C. Gerhart) (CORRECTED VERSION PLEASE!)
- From: John Latter <jorolat@xxxxxxxxx>
- Date: Mon, 6 Feb 2006 13:59:26 -0500 (EST)
On Fri, 3 Feb 2006 12:12:25 -0500 (EST), Anthony Campbell
<ac@xxxxxxxxxxxxxxxx> wrote:
An HTML version of this review is available at:
http://www.acampbell.org.uk/bookreviews/
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More W. Kirschner and John C. Gerhart
THE PLAUSIBILITY OF LIFE
Resolving Darwin's dilemma
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Book review by Anthony Campbell. The review is licensed under a Creative
Commons License.
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Critics of evolution, including advocates of "intelligent design", often
point to the complexity of life and say that it could not have arisen by
the progressive accumulation of small genetic changes, especially random
changes. And they do seem to have a point. Even the vast stretches of
geological time do not seem to have been long enough. Also, how would
random genetic changes be coordinated to give rise to a new kind of
organism, one that functioned properly in its environment?
The answer proposed by Kirschner and Gerhart is that this is not how
evolution works. They put forward instead a theory which they call
facilitated variation. This draws on new information about molecular
biology that only became available at the end of the twentieth century.
One of the most surprising things about evolutionary biology is the
extent to which what the authors call "core processes" have been
conserved from the earliest times - in fact, probably from the
pre-Cambrian. As an example, more than 50% of the metabolic enzymes in
the bacterium E.coli are identical to those in humans.
There are several hundred "core processes" that generate the anatomy,
physiology, and behaviour of the organism during its development. Some
of these have been unchanged for hundreds of millions or even billions
of years. Yet although they are so strongly conserved, the way in which
they behave can be altered by signals that are often quite simple. A
process may just have two states, on or off, and the signals merely
switch it from one state to the other. Hence the presence or absence of
these signals, and their timing, can produce large changes in the
organism's phenotype.
An important concept here is that of "weak regulatory linkage"; the term
refers to reconfigurability (the linkages are not fixed) and also to
instability. Instability might seem to be a bad thing, but Kirschner and
Gerhart think that it has important advantages biologically. It provides
flexibility. Weak regulatory linkage is important in evolution, the
authors believe, because it plays a large part in core processes. It is
not necessary for genes to provide detailed instructions for how the
organism should develop. Instead, they can modify the way in which the
conserved core processes function during development.
The book provides several examples of how this works, which are explored
in some detail. They include the arrangement of microtubules in
eukaryotic cells, the distribution of whiskers on the faces of mice and
their central connections, and the limb proportions of different
vertebrates. (Incidentally, I learnt here that a normal mouse has
precisely 33 whiskers on each side.) The role of Hox genes and other
selector genes in embryology is also considered. The embryological
compartments which they control are remarkably similar in humans, fish,
birds, frogs, reptiles and even sea squirts.
Even if the theory described here is correct, deep questions remain. How
did the core processes originally arise? What was the origin of the
first prokaryotic cell? And, most difficult of all, how did life itself
originate? For these matters we are reduced to speculation, but
evolution since the Cambrian, Kirschner and Gerhart believe, "is
supported by irrefutable evidence and a compelling fossil record."
This is an important book, not least because it provides a pretty
comprehensive answer to criticisms of Darwinism based on its alleged
inability to explain variation. Whether or not it is ultimately
accepted, it does at least offer a plausible mechanism. "[T]here are no
gaping holes in our theoretical understanding of evolution and no
conspiracy of silence on scientific findings." Unfortunately, it will
probably not be widely read by non-specialists. The authors would like
it to be, and say that they have tried to avoid jargon (and a glossary
is provided). However, it is not exactly popular science, and the
authors acknowledge that close attention from the reader is required
and that "there is no short cut to understanding," In other words, you
have to work to get a grasp of their ideas, but the journey is worth the
effort.
3 February 2006
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%T The Plausibility of Life
%S Resolving Darwin's dilemma
%A More W. Kirschner
%A John C. Gerhart
%I Yale University Press
%C New Haven and London
%D 2005
%G ISBN 0-300-10865-6
%P xiii + 314 pp
%K biology
%O line drawings
I haven't read the book yet (although my first impressions are that
its a step in the right direction) but I found this review from Cell
quite interesting:
U-MsSWYVW-UUA-U-AAVUYVYCEZ-AABYVWEBEZ-ZAVWYCYEW-WU-U&_fmt=full&_coverDate=10%2F21%2F2005&_rdoc=2&_orig=browse&_srch=%23toc%237051%232005%23998769997%23608591%21&_cdi=7051&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=57a84b5448b51e8bcec185b879a8923d
PDF version:
rowse&_coverDate=10%2F21%2F2005&_sk=998769997&view=c&wchp=dGLbVlb-zSkzk&md5=47b05838b80d7f101a917be968937964&ie=/sdarticle.pdf
(taken from http://groups.yahoo.com/group/evomech/message/487)
John
--
John Latter
Model of an Internal Evolutionary Mechanism (based on an extension to homeostasis) linking Adaptive (Stationary-Phase) Mutations to the Baldwin Effect.
http://members.aol.com/jorolat/TEM.html
'Where Darwin meets Lamarck?' Discussion Egroup
http://groups.yahoo.com/group/evomech
.
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