|MadSci Network: Evolution|
You ask about modern challenges to Darwinís theory of the origin of species. Let me begin by reminding you that there is a distinction to be made between the theory of evolution (i.e. that organisms arise by Ďmodification by descentí), which was around long before Darwin, and Darwinís theory of natural selection which purports to explain how this happens. Challenges to Darwin have come both from outside biology and from within biology itself. The major modern challenge from outside biology is scientific creationism. For more information on this subject you may wish to consult Pennock, R. T. 1999. "Tower of Babel: The Evidence Against the New Creationism" MIT Press. Other challenges from outside biology come from social scientists who suggest that the theory of evolution is a construct of the human mind rather than a valid description of objective reality. Take a look at Ruse, M. 1999. "Mystery of Mysteries: Is Evolution a Social Construction?" Harvard University Press, for more background to this idea. Challenges from outside biology tend to be challenges to the entire theory of evolution by modification by descent. The remainder of my answer will deal solely with challenges to Darwinís theory of natural selection from within biology itself.
Evolutionary biology can be divided into two subdisciplines; microevolution and macroevolution. Microevolution describes what happens to populations over short time-scales measured in generations. Macroevolution describes what happens over long time-scales measured in millions of years. No serious evolutionary biologists (and not even all creationists) doubt that natural selection is a major force behind microevolution and most also believe that it also has an important role in macroevolution. (Creationists who accept a role for natural selection in microevolution tend to deny it a role in macroevolution.) Some biologists, however, believe that natural selection is not the only, or even most important, driving force in evolution. Another force that is widely accepted is genetic drift. This is the idea that random factors have a role in deciding which genes are passed between the generations. It is no good my having some marvellous new adaptation to my environment if I get run over by a bus before I get the chance to pass the gene for this adaptation to my offspring. Biologists argue about the relative importance of random events in evolution. It seems likely that genetic drift is very important in small populations. This has implications for conservation. Its role in larger populations, particularly at the macroevolutionary level, remains a matter of debate. You can read about this in any evolutionary biology textbook.
At the time "Origin of Species" appeared, the main challenge to Darwinís theory from within biology was Lamarckism, and it seems that every generation of biologists since has thrown up a few mavericks to champion its cause. In the late 1980ís this was manifest in the debate about directed evolution, also called adaptive mutation. It was discovered that in some laboratory situations, bacteria and yeast appeared to behave as if they had mechanisms for choosing which mutations would occur, such that mutations became more likely when their effects were beneficial. This is contrary to Darwinís theory of natural selection, which supposes that mutations are random with respect to fitness and that it is selection amongst these random mutations, which drives the evolution of new adaptations. More recently however, these experiments have been shown to be entirely consistent with the modern Darwinian model of adaptation by natural selection on randomly occurring variation. For more information see Lenski, R. E. and Mittler, J. E. 1993. The directed mutation controversy and neodarwinism. Science 259: 188-194 and Sniegowski, P. D. and Lenski, R. E. 1995. Mutation and adaptation: the directed mutation controversy in evolutionary perspective. Annual Review of Ecology and Systematics 26: 553-578. A more recent manifestation of Lamarckianism is Lamarckís signature, which you can read about at http:// www.biomednet.com/hmsbeagle/56/viewpts/op_ed . This site has links to lots of other useful information about neolamarckism. Another good source is Jablonka, E. and Lamb, M. J. 1995. "Epigenetic Inheritance and Evolution: The Lamarckian Dimension" Oxford University Press. You might also want to check out McLaren, A. 1999. Too late for the midwife toad: stress, variability and Hsp90. Trends in Genetics 15: 169-171, for a description of some more recent evidence for the inheritance of acquired characters.
One final challenge to Darwin that should be mentioned is Gabriel Doverís theory of molecular drive. If I understand him correctly, Dover thinks that the molecular mechanisms by which genetic material is passed between the generations are biased in such a way as to drive evolution in certain directions. He explains this rather complicated theory in his new book, Dover, G. 2000. "Dear Mr. Darwin: Letters on the Evolution of Life and Human Nature" Weidenfield and Nicolson, which consists of a series of imaginary letters between himself and Charles Darwin in which he brings the old man up to date with modern ideas in genetics and evolutionary biology. Iíve only just got hold of this book myself and I havenít read it yet so I canít promise you itís any good, but it does have a bibliography, which should lead you into some of the more technical literature.
I hope this answers your question,
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