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DEFINING SPECIES AND SPECIATION

DEFINING SPECIES AND SPECIATION - species concept Typology...

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DEFINING SPECIES AND SPECIATION While Darwin entitled his book "On the Origin of Species", the book dealt primarily with a mechanism of evolution (natural selection) in which variation was critical. But what will selection do with this variation? Change the frequency of dark morphs of moths, or morphs of snow geese, or change the mean and the variance of the distribution of heights in human populations? What is the result of disruptive selection? How do we decide that natural selection has actually lead to the origin of new species? The answer to these questions depends on one's species concept . The concept of species is an important but difficult one in biology, and is sometimes referred to the "species problem". Some major species concepts are: Typological (or Essentialist, Morphological, Phenetic)
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Unformatted text preview: species concept. Typology is based on morphology/phenotype. Stems from the Platonic "forms". Still applied in museum research ( type method ) where a single specimen ( type specimen ) is the basis for defining the species. In paleontology all you have is morphology: typology is practiced and species are defined as morphospecies (e.g., snail shells in fossil beds). Problems: what about sexual dimorphism: males and females might be assigned to different species. Geographic variants: different forms viewed as different species? What about life stages: caterpillars and butterflies? If typology is let run it can lead to oversplitting taxa: each variant is called a new species ( Thomomys ) pocket gophers with > 200 subspecies ....
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