How good was Darwin at making predictions?  A good scientific theory should make predictions, at least according to a common assumption about science.  PBS thinks Darwin hit a home run, according to an interactive feature on the website for Judgment Day, the documentary about evolution vs intelligent design shown on Nova this week (11/14/2007).  The commentary below will analyze these 13 predictions, but some other recent stories from science journals show Darwin scoring a much lower batting average:

  1. Island dwarfism:  Evolutionary biologists have long believed that animals trapped on islands would evolve into smaller versions of their mainland counterparts.  Not true, say researchers from Imperial College, London.  A catalog of island species shows no such trend; many factors are involved in the size distribution of island species.  The details can be found atPhysOrg and Science Daily.  (Note: the articles do not attribute the prediction to Darwin himself.)
  2. Arms race:  If Darwin intended his theory of natural selection to express a law of nature that applies everywhere, it might be difficult to correlate opposite results.  Many evolutionary biologists speak of predators, prey and parasites leading to an “evolutionary arms race” that drives speciation and adaptive radiation, leading to Darwin’s branching tree of life.  An article in Science Daily, however, says that predators and parasites can drive “evolutionary stability.”
  3. Parental guidance suggested:  The environment is supposed to drive evolutionary adaptation.  Offspring, facing the mean old world, should get by with the random genetic mutations that improve their survival – not a parental handout.  Taking loans from mom or dad’s genes would indicate a dependency on pre-adaptive resources, innate in the genetic information of the species.  A study at University of Virginia suggests, however, that maternal influences do help offspring adapt to their environment.
  4. Birds don’t talk:  What drives speciation in birds?  It should be Darwin’s mechanism of natural selection – of which the Galapagos finches are the textbook example.  In Sciencelast month,1 however, Loren Rieseberg reviewed a new book by Trevor Price, Speciation in Birds, and found that even the textbook case is not open and shut:

    Of perhaps greater interest are Price’s conclusions about the roles of ecology and social selection in speciation; these remain relatively unexplored subjects about which birds have much to offer.  Closely related species of birds often differ in ecologically important traits–such as body size, habitat preferences, and feeding and migratory behaviors–that are also likely to contribute to both premating and postmating reproductive isolation.  These observations, combined with classic studies of ecologically driven speciation in Darwin’s finches and crossbills, imply that ecological selection likelycontributes to most speciation events in birds.  However, Price cautions thatdivergence of most co-occurring bird species is too ancient to make inferences about the causes of speciation and that studies of recently diverged species, such as Darwin’s finches, highlight the fragility of ecological reproductive barriers. He concludes that “it is unclear if ecological causes are sufficient or even important in many speciation events.”  This somewhat negative assessment of the role of ecology in speciation is tempered by speculation in later chapters that rapid ecological speciation may account for short branch lengths detected early in the evolution of many bird genera….

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