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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.
Someone did. His name was Boltzmann. The more ordered a system is, the fewer microstates available to it. What does that mean? Well, a macroscopic example is this: imagine you have a bunch of books you're putting on a shelf. There's only one way to put the books alphabetically (assuming you have no duplicate copies). But there's a really large number of ways to put them on if you put them every which way. So let's compare the order of two systems. Our first system is our books on the shelf, restricted to alphabetical ordering. The second is our books on the shelf. The first system has only one way it can be arranged; the second (assuming we have more than one book) has more. So the first system is more ordered.
This is a little simplistic, but it gets the point across.
Trust me, entropy really is a well-defined concept. Or don't trust me; read for yourself.
Read Bujold. Free (as in
The concept of a species is an artificial classification scheme imposed upon a continuous reality. Therefore saying when a "speciation" occurs is entirely a matter of opinion. That said, there are plenty of examples of so-called macroevolution in the fossil record (hell, the entire fossil record is one big macroevolutionary record!); you have only to open your eyes and see it.
Evolution is a fact. Things change.
The "theory of evolution of biological species by natural selection" is a scientific theory to explain the observed variation and "relatedness" of biological organisms, and their change through time as observed in the fossil record.
The "theory" of creationism is a load of pseudo-scientific mumbo-jumbo used to prop up some people's faith in the Almighty in the face of evidence that contradicts the primary literary source of their belief.
Ergo, stating the belief that the theory of evolution and the theory of creationism are both scientific theories of equal merit demonstrates a profound lack of understanding of science and its rigid reliance on fact and observation. Q.E.D.
Liberal (adj.): Free from bigotry; open to progress; tolerant of others.
That has never been the scientist's definition of species. The definition of species is not, "A group of animals that can interbreed and produce viable offspring."
The definition of species is, and always has been, "A group of animals that can and do produce viable offspring."
If this seems vague to you, good! The definition of species *is* vague. It has to be. "Species" is a concept that humans invented to help them describe the world around them. Very very often, it doesn't work. There's no way to change it so that it will work.
There are no trails. There are no trees out here.
Darwin certainly did not claim to have discovered evolution. The evidence for evolution of some sort was accepted by a large number (though far from all) scientists and interested people for some time before Darwin - amongst them, Darwin's Grandfather, Josiah Wedgewood, so the idea was far from new.
What Darwin did was find an explanation for evolution - a mechanism by which it occurred. Undoubtedly Lyell believed in, and pointed out to Darwin, the operation of evolution. And the ornithologist certainly pointed that all the finches he had brought back (and carelessly jumbled up) appeared to be descended from a singel ancestor. His book is titled "On The Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life", and it is the "Means of natural Selection" bit that is original.
To assert that Darwin claimed to have discovered Evolution is like claiming that Columbus discovered the Atlantic. Columbnus dicovered how to cross the atlantic, and Darwin discovered hopw to explain Evolution.
Consciousness is an illusion caused by an excess of self consciousness.
All things short of a methematical 'proof' in science is theory, including gravitation and even cause-and-effect itself. The word 'theory' in science has an entirely different connotation to what it has in common parlence, and in particular to the way you use it here.
What you are equating evolution with is a hypothesis, not a theory, and the two are very different. Or, put another way,
The theory is not did evolution happen. We already know evolution did and does happen, there is a mountain of factual data underscoring that point. What is theoretical and debated (by scientists) is what the mechanism is by which primates became human and dinasaurs became birds. The fact that it happened is denied only by those with a religious agenda, whose fragile beliefs are challenged by the factual data collected by thousands of researches all over the face of the planet.
And I know this non-fundamental Christian believes God could have used evolution to create us.
And I know this Athiest believes aliens could have seeded the Earth with proto-human life, but until I see some sensible evidence indicating that such might be the case, I'm not going to pay the notion much heed.
The Future of Human Evolution: Autonomy
The delineation of species boundaries necessarily takes into consideration more than the ability to interbreed and produce viable offspring. Indeed, the taxonomic definition of the "species" classification is very plastic, and differs with the groups of organisms considered.
The advent of the use of genetic markers for classification provides some greater degree of accuracy and standardization in the process, but it does not eliminate the inherant flexibility in the definition. (From a bioinformatic standpoint, there is a whole other set of problems with trying to accurately portray evolutionary distances from genetic variation.)
Consider a group of animals with a continuous distribution over a very large area. All the members of this population are capable of interbreeding, and the uninterrupted distribution allows for genetic drift throughout the entire population. Individuals from different geographic regions will have subtly different physical characteristics, but the whole population is still considered a single species. This is a fairly classic situation. (The benefit of a large gene pool likely outweights the benifit of these subspecies differentiating into wholly different species, if you want to look at it that way.)
Then, consider a group of animals with a discontinuous distributuion over a large range. Individual populations may be able to interbreed with one another, but there is no natural genetic exchange among these separate populations. Subtle differences between the groups may, in this case, warrent classification as separate species, because they represent different gene pools drifting in different directions.
The complexity of the issue compounds when one looks outside the animal kingdom. For instance, essentially the entire family or orchids, with some 1000 genera and 20,000 species, exhibits a high degree of genetic plasticity, with species readily hybridizing across genera. And again, the definition of "species" must be reevaluated when one considers the bacterial world.
Anyway, the point of all this is to show that the grey zone is there for a reason. The alternative is to explicity redefine taxonomic criteria for every different group of organisms, which defeats the entire purpose of a single classification system.
The angel in the oatmeal.
I know it's nitpicky but evolution is a scientific "possibility". It is still regarded as a theory after all.
Evolution is a fact - it has been observed to happen, which cannot be disputed. HOW it happens is the theory of evolution by natural selection.
BTW, a theory in science isn't anything like the commonplace notion of a theory. Theories aren't haphazard guesses, they are fully supported by fact and represent the most powerful explanation that we can devise.
Example: The theory of gravity is "only" a theory, but does anyone go around saying that it's hardly proven to exist?
If tits were wings it'd be flying around.