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Title: Sudden Origins : Fossils, Genes, and the Emergence of Species by Jeffrey H. Schwartz ISBN: 0-471-32985-1 Publisher: Wiley Pub. Date: 19 March, 1999 Format: Hardcover Volumes: 1 List Price(USD): $27.95 |
Average Customer Rating: 3.69 (16 reviews)
Rating: 5
Summary: Hox genes, and the new origin of the species
Comment: This is a very important source of information both as to the history of the Neo-Darwinian Synthesis and the recent discoveries of regulatory hox genes and the light they throw on the riddles of speciation and large scale evolutionary change. The realization that major morphological changes do not in fact occur in the fashion of microevolution (as presented by traditional Darwinists), due to the effect of homeobox genes, is a revolutionary discovery and confirmation of the importance of the developmental tradition moving in parallel to standard Darwinism. This data creates a foundation for the various theories of macroevolution and punctuated equilibrium proposed almost a generation ago but still sidelined by the Darwinian mainline. The book contains an invaluable review of paleoanthropological theories, issues of neotonous evolution, and the various genetical theories of Mendelism, from de Vries and Bateson, to Haldane, Wright, and Fisher. The views of Goldschmidt, and his near miss of this new perspective, is also treated. This confusing history of Mendelism sorted out is invaluable, and shows how cogent (in part) where the intimations of Bateson and Morgan. The new perspective both confirms the concept of 'macroevolution' while suggesting this can be seen as a microevolution of regulatory genes, a point open to debate perhaps. The next mystery is the evolution of these complex sequences of development. But that does not distract from the great usefulness of this account. One can dispense with much of the erroneous literature on evolution, a great saving in brain space. The endless debate over the slow evolution of the eye, etc, that went on and on and drove all parties batty is hopefully over if we know the right combination of homeobox genes will control the development of this and other organs. Times are changing in Darwin land. Highly recommended.
Rating: 3
Summary: Hoxgenes to the rescue?
Comment: The first ten chapters is merely a historical survey of evolutionary discourse, and I shall not comment on them. It is the two final chapters that are supposed to offer a hopeful alternative to the beleaguered neo-Darwinian approach to evolution. Here the author relies on the role of homeobox genes, and highlights their effects on changes in morphology. His argument can be briefly summarised by referring to two of the examples he gives: the Rx gene in eye development, and the Manx gene in the development of the notochord during the larval stage of a species of tunicate.
Experiments with mice showed that individuals which carry a mutated (and therefore non-functioning) Rx gene failed to develop either an eye or its bony socket if the condition is homozygous, but individuals that are heterozygous in Rx undergo normal eye development. Schwartz argues that the reverse situation must have occurred in the past, i.e., a precusor mutated into the Rx gene. This was initially in the recessive state, as mutated genes generally are. This then spread widely through the population via heteroxygotes, until eventually homozygotes were produced in sufficient numbers to mate with each other. The mutant gene, i.e. Rx, was then expressed in the homozygotes, which developed eyes.
It is helpful to juxtapose the facts that the author appeals to, and the inferences he draws from them. The facts are that mutations in functioning genes render them non-functional - a loss of information. Schwartz turns this on its head and hypothesises that a mutation in a non-functioning DNA segment could render it functional - the emergence of novel information by natural processes.
One can get any complex multi-functioning mechanism, make a random change to one of its components, and render a part of the mechanism non-functional. It does not follow from this fact that the faulty component could have come about by chance, waiting for a random change to put it into working order. This is the kind of inverted logic employed above. The real world abounds in examples of natural processes producing degeneration, and causing malfunction in previously functioning mechanisms. The reverse process, however, has no basis in fact.
The case of the tunicate illustrates the importance Schwartz attaches to embryonic development in evolution. The homeobox gene, Manx, is responsible for the development of the notochord during the tunicate's larval stage. At a later stage the gene is deactivated and the adult tunicate does not possess a notochord. Schwartz hypothesises that at some point in the tunicate's evolution a mutation in some regulatory gene extended the duration of activation of the Manx gene, resulting in an adult with a notochord. This is a case of heterochrony, specifically paedomorphosis. Such a discrete change would be consistent with what one finds in the fossil record.
The author argues convincingly for the discrete nature of the fossil record, as many others have done before him. In doing so he poses an effective challenge to the neo-Darwinian model. But the substitute he offers is hardly able to provide the solution. Schwartz hypothesises on the possible discrete evolutionary changes that could be brought about by changes in the control genes, given a fully functioning genetic apparatus to start with. The real problem for evolution, however, is to explain how that fully functioning apparatus got there in the first place. Deactivation of a homeobox gene may possibly explain the reduction of a three-toed horse into a one-toed horse, as Schwaltz suggests, but it can hardly account for the origin of horses.
Since mutant genes are useless or lethal, it is hardly surprising that they are recessive rather than dominant. It is most reasonable to infer that this is part of life's defense mechanism, designed to protect the organism from potential damage from mutations.
Rating: 4
Summary: Sits atop an important trend, but maybe too history-heavy
Comment: This is an excellent book that provides a reasonable introduction and much historical context to the concepts behind a class of theories of speciation that are gradually becoming less controversial.
The notion of cumulative gradual change in allele frequencies as the only source of variety has been a thorn in the side of serious biology for some time. Not least because it leaves the door open to claims that speciation itself is "improbable" in higher species. Richard Dawkins' brave attempts to rescue biology from "Mount Improbable" may very well turn out to be partly an exercise in futility.
Schwartz joins a number of recent authors and researchers to face head on the challenge of improving our understanding of evolutionary biology by recognizing that it makes perfect sense of much otherwise confusing data to allow for sudden "saltational" changes in species. As hard as it remains for many to swallow, S.J. Gould was probably right about much of this, and deserves credit for bucking the "received" view of Darwinism.
This book is disappointing however, in that it seems to revel in telling the history rather than describing the new concepts. There's just so much politics behind this issue that authors can't seem to avoid the temptation to add their own spin to the history in every book. But that part has been done already. Sterlny and Griffiths' "Sex and Death" does a great job of discussing all of the various chinks in the armor of the received view of how evolution works, without spending so much time interpreting intellectual history yet again.
The new part that is most exciting is the details of how regulatory genes work, their duplications and mutations, and the role they play in speciation. There is sadly relatively little of that in Schwartz's otherwise useful presentation.
A very recent release in the U.K. by Mark Ridley, "Mendel's Demon," looks like it handles similar deep questions but goes far more deeply into the genetics that forms the foundation for theories of sudden origins and other alternatives to simple cumulative gradual interpretations of Darwinism.
One point I wanted to make as a comment to a previous review. It was claimed at one point that this kind of theory is more congenial to the way many people view creation by God. That's something I think is a welcome sign. But they also commented that "creationists" is a meaningless label, and it seems to me that claim is simply nonsense. "Creationists" deny that speciation occurs at all, at least in the origin of humans. They don't argue that it could only occur suddenly. Whatever else they may accept or reject from evolutionary biology or genetics or paleoscience, it seems to me that they cannot accept that humans were not special creations of God separate from other animals. The United States is divided into those who find the close relationship of humans and apes ridiculous and those who pretty much take it for granted. That's not an easy line to cross, much less pretend it doesn't exist.
It would be very heartwarming and reaffirming to my faith in human reason of some people who consider themselves "creationists" were to find the theory of sudden origins in this book an acceptable version of evolutionary theory, but I'm not going to hold my breath waiting for it to happen.
The difference is critically important scientifically because the power of evolutionary thinking is not in whether we happen to be related to apes, but in the value of being able to apply adaptational thinking to species characteristics and describe and predict how characteristics relate to environments. Creationist interpretations deny the central concept of evolutionary thinking, that natural selection explains adaptation. The details of how it works and where other explanations supercede adaptational ones is what is left to ongoing research to discover.
That's where Schwartz contributes best to the literature, by placing "sudden origins" into its rightful historical context, (though I don't agree with some of his intellectual history in the medieval period). This is not something that creationists can honestly take any credit for, or honestly use in support of their agenda it is a theory of speciation not a denial of speciation.
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