Gould's book is essentially an expansion of an idea that was presented in
germ form in his Scientific American article a couple of years ago. There
is no direction to evolution--the apparent direction toward increased
complexity is simply an artifact of there being a left wall of minimum
complexity and that there is only one way for evolution to go and it will
go that way as variation increases. The last chapter is a fascinating
discussion of the dominance of bacteria in the biosphere. It's also a must
read for baseball fans because he links this evolution argument with a
statistical explanation for why 0.400 hitting has disappeared from
professional baseball.
Rudy Raff is a leader in the evo-devo field (that's evolution and
development). Here's a bit from the preface to whet your appetite. I'd be
interested in a plug from Paul Nelson who knows Raff's work well. If
anything, this book demonstrates that evolutionary theory is alive and well
even when dealing with the kinds of problems that intelligent design folks
are throwing at us.
TG
___
"I've organized this book around the two related themes of the origins of
the major animal body plans in the great Cambrian radiation and their
subsequent modifcation through the evolution of developmental processes
during the ensuing 530 million years. The first chapter reviews the
historical origins of the relationship between the disciplines of
evolutionary biology and developmental biology. Our attitudes toward the
great problems of biology are conditioned by historical contingencies.
These contingencies have had a particularly powerful impact on the outlooks
of the two disciplines that I'm attempting to synthesize here. When
history dictates the form experiments take, it's important to take note.
"The second chapter introduces animal body plans and the use of
phylogenetic methods. I do that because it is impossible to consider the
evolution of developmental features and processes without placing them in a
phylogenetic context. The use of phylogenetic reasoning has not been a
part of developmental biology, and many readers may not have given it much
thought, nor realized the pervasiveness of phylogeny in evolutionary
studies, nor understood the need to know the direction of evolutionary
changes being studied. The following three chapters consider the origins
of the animal phyla in the Cambrian radiation and the use of gene sequence
data in resolving phylogentic problems, especially the origins of major
groups, that are not amenable to other methods.
"Chapters 6 and 7 deal wit the developmental problems posed by body plans
and their modifications. These chapters present evidence on the
evolvability of different stages of development and consider the
significance of the freedom of early development to evolve rapidly and
radically. Evolutionary observations provide quite a different perspective
on the structure of development than do observations from developmental
genetics based on single species used as model systems. Chapters 8 through
10 consider the mechanistic relationship between development and evolution.
In chapter 8, I propose that heterochrony has been vastly oversold as a
universal evolutionary mechanism. The consequence has been the
substitution of labels for explanations in all too many studies of
evolutionary lineages. In chapters 9 and 10, I present the mechanistic
issues posed by the hypothesis that the internal architecture of the genome
and of developmental processes and their controls constrains the course of
evolution. This issue is a central one in the study of development and
evolution. If externally applied natural selection is the only force
required to produce evolutionary change, then developmental processes don't
matter except as features upon which selection can act. If internal
organization and processes govern modes of change, then development must be
incorporated into any complete theory of evolution. I propose that
internal organization and a set of distinct evolutionary processes acting
to sort internal variation produce nonrandom morphological variation in
evolution, and I identify and characterize these processes.
"The eleventh chapter examines special topics that reveal the rich and
unexpected fluidity of genomes and developmental processes in evolution.
The examples discussed reveal that genes can be readily co-opted for new
functions and that regulatory circuitry can be radically changed while
continuing to perform a conserved function. It is important to know as
much about function as possible. Apparently identical developmental
phenomena can prove to be quite distinct when their mechanistic bases are
known. Knowledge of function and of gene sequence homology are both
required. Different genetic systems might converge functionally, as they
do, for example, in sex determination in flies and nematodes. Conversely,
homologous genetic systems can be "wired in" differently and play quite
different roles. This chapter explores the extent to which the fluidity of
genomes allows evolutionary reversals in developmental processes.
"In the final chapter I discuss some examples of the evolution of
novelties. The underlying genetic mechanisms are relatively well known for
some of these, but not for others. The point to be made is that scenarios
about the origins of novel features in evolution can now be cast in terms
that will allow their investigation with the increasingly powerful tools
provided by molecular biology and developmental genetics. The commonality
of genetic controls in animal development has provide an important new
impetus to the study of "nonstandard" animals drawn from nature in addition
to model systems."
_____________________________________________________________
Terry M. Gray, Ph.D. Department of Chemistry and Biochemistry
Calvin College 3201 Burton SE Grand Rapids, MI 40546
Office: (616) 957-7187 FAX: (616) 957-6501
Email: grayt@calvin.edu http://www.calvin.edu/~grayt
*This mission critical message was written on a Macintosh with Eudora Pro*
A special message for Macintosh naysayers:
http://www.macworld.com/pages/july.96/Column.2204.html