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Evolution - Beyond the Popular Science
In Patterns and Processes of Vertebrate Evolution Carroll undertook an ambitious project - nothing less than to update George Gaylord Simpson's classic works from the 1940s and 50s, Tempo and Mode in Evolution and The Major Features of Evolution. The result is a "broad picture" overview of the processes of evolutionary change, centred on paleontology but attempting to integrate that with the rest of biology. Patterns and Processes is aimed at students of paleontology and specialists in that and related fields, but it should also be considered by general readers: while it goes into quite involved details, they are always used to illustrate broader ideas and there is solid motivation for persevering with them. It is especially recommended to those unhappy with the lack of substance in popular debates over the theory of punctuated equilibrium, which Carroll critically appraises. Patterns and Processes is effectively illustrated with line-drawings and figures and has a useful glossary.
Carroll begins with an overview of current problems in evolutionary theory and in particular of the "gap" between short- and long-term processes in evolution, and between paleontology and other disciplines. He also discusses the choice of the vertebrates as a testing ground (which is picked up at the end of the book in a brief comparison with invertebrate metazoa, prokaryotes, protists, and vascular plants). He then provides an overview of theories of evolution, at the level of populations and species, from Darwin through Dobzhansky and Mayr to Gould and Eldredge.
Two chapters present some essential background. The first looks at evolution in modern populations, in particular at rates of evolution among the Galapagos island finches, where significant directional change does occur and doesn't appear to be correlated with speciation. The second considers some of the limitations of fossil evidence, the irregularity of fossilization and other stratigraphic issues and problems with the dating of events and processes and the measurement of rates of evolution.
Next come two case studies. The rates and directions of change among late Cenozoic mammals are examined with an eye to testing theories of punctuated equilibrium and species selection. Many lineages exhibit stasis "of particular characters and character complexes," but in none is there stasis of all characters and phyletic evolution is common. And "no major trends involving a complex of character changes can be demonstrated as having resulted from species selection." In contrast, the rapid radiation of the cichlid fish of the East African Great Lakes provides some evidence for species level evolution, and a bridge between macroevolution and microevolution.
Four separate chapters focus on related disciplines, in an attempt to reunify different fields. Taxonomy influences our basic concepts of evolutionary patterns as well as providing tools for discovering them; phylogenetic systematics (cladistics) has been particular influential, offering "an objective way to compare patterns of large-scale evolution from group to group and within groups over time" and forcing reconsideration of traditional naming schemes in the vertebrates. With evolutionary genetics Carroll presents some basic models, focusing on quantitative traits; he touches on the enigma of low selection coefficients and on genetic constraints.
Turning to developmental biology, Carroll surveys heterochrony, homeobox and Hox genes, and the phylotypic stage. He then applies this to the origin of craniates and skull and axial skeleton development, but above all to tetrapod limbs, to their origins, developmental processes, morphogenesis, and evolution. He also considers the integration of developmental biology with the evolutionary synthesis and its possible connections with macroevolution. Other constraints are imposed by physics: Carroll considers vertebrate locomotion in water, in the air, and on land, and touches on membrane transport, heat transfer, and size scaling.
Three chapters then look at large scale structure and patterns in evolution. A chapter on "major transitions" focuses on movements between environments: the most detailed study is of the origin of birds, but others cover the origins of terrestrial vertebrates, mosasaurs, and whales. Critical periods saw rates of change exceeding those in ancestral and descendant groups, but not those observed in modern populations; more importantly, directions of change were sustained for long periods. Turning to radiations, Carroll treats at length the Cambrian explosion and the radiation of early Cenozoic mammals: occurring in intervals of 10 million years or less; these differ from other, slower radiations into already occupied environments and "can certainly be attributed to factors that were not considered by Darwin". At the largest scales, vertebrate evolution has been irregular, driven by "forces" that can't be extrapolated from those operating at the level of populations and species: among them sustained evolutionary trends, continental drift, and mass extinctions.
Among Carroll's overall conclusions:
"Evolutionary forces that can be studied in modern populations are sufficiently powerful to account for the amount and rate of morphological change throughout the entire course of vertebrate history."
and
"Transitions between environments governed by major differences in physical constraints do not necessarily require special evolutionary processes."
but at the same time
"Large-scale patterns of evolution cannot be fully explained by processes that are directly observable at the level of modern populations and species.... the patterns, rates, and controlling forces of evolution are much more varied than had been conceived by either Darwin or Simpson."
And macroevolution is essentially historical, with each major event "unique and worthy of detailed study in its own right".
Patterns and Processes in Vertebrate Evolution combines clear exposition of details - and what appears to be an encyclopedic knowledge of vertebrate history - with a willingness to tackle big questions. Sometimes Carroll seems to take both sides of debates, but that is a reflection of respect for complexity, not of unengaged fence-sitting. The result is a useful overview for students or outsiders; it also seems to have established itself as a minor classic within the field.
You might want to purchase Patterns and Processes in Vertebrate Evolution from bn.com or read some of Danny's other evolution book reviews. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
Calling evolution a religion is either dishonest or an exercise in destroying the meaning of "religion" and making the word so vague that you can call anything a religion. Take your pick.
XML causes global warming.
The entire concept of a "species" is the problem; the "loose grey zone" is the reality.
We classify organisms into species in order to make some sense of what we observe, but we should always keep in mind that the classification is artificially imposed, and somewhat arbitrary. The fossil record of any group of related organisms shows discrete snapshots of a continuous variation through time and geography (punctuated equilibrium does not refute this, it just says that the rate of evolution is not constant).
The species model describes evolutionary change as "creatures evolving from species A to species B to species C", with the implicit understanding that these are just arbitrary markers along the continuous evolutionary path, not coincidentally placed where there are well-preserved examples in the (incomplete) fossil record.
Unfortunately, this implicit understanding doesn't really get through to popular understanding of evolution; hence the many heated debates about speciation and how to tell when it occurs, when in fact speciation is not a real phenomenon at all, but a classification tool.
Liberal (adj.): Free from bigotry; open to progress; tolerant of others.
Without god, there are no moral absolutes, goes the argument. And without moral absolutes, why, what's to prevent all sorts of immorality?
Therefore, attempts to debate the theory of evolution with "christian" fundamentalists, or their fellow travelers, is pointless, because you are challenging their entire world view, not objectively evaluating competing scientific theories.
FWIW, almost all thinking non-fundamentalist Christians, as do most educated people regardless of religious belief/nonbelief, realize evolution is a scientific reality.
And we, the vast majority, further realize that evolution doesn't imply anything about morality, or the existence of god, one way or the other.
And therefore there is no reason to waste time in high school science classes teaching theories like creationism that are neither theologically nor scientifically interesting.