BIOLOGY 103
      Chapter 23:  SPECIATION

 
 
most important concept:

Scientists' theories about species and speciation are evolving, but natural selection in isolated gene pools is still the main focus.

 TEXTBOOK, important parts

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What is a species?  Before Darwin, scientists thought of species as recognizable descendents of an "ideal type" created by God, and even today scientists often use "species" to mean a visibly distinctive group of plants or animals.  But after Darwin, scientists realized that many species have so much genetic diversity it becomes impossible to define the "ideal" or even "typical" member.  As scientists learned more about genetics, they began to define a species as all the members of a gene pool.  By the time you finish this chapter and start thinking about time on an evolutionary scale, you may come to the conclusion that gene pools and species are very fluid categories. 

MAIN POINTS FROM THE TEXTBOOK

  • pp. 449:  The second and third paragraphs are critical; make sure you understand them.
  • pp.  450-451:  How many definitions of species can you find?  
  • pp. 451-452:  An example of why the definitions are important
  • pp. 453-460  :  Most of this part concentrates on one idea:  isolation of small gene pools so that natural selection and genetic drift produce enough change for speciation to occur.  
    • The examples are much more important than the technical terms, but you need to make sure you can use the technical terms.  Check to see how many kinds of speciation you can define; then how many kinds of isolation can you describe?  
    • CD activity 23.1 and 23.2 could help.
    • Another way of looking at these topics is from the point of view of an ecologist interested in biodiversity.  How do each of these contribute to species diversity?
      1. divergent selection
      2. isolation
      3. vicariance
  • pp. 460-462:  Can members of two species hybridize to produce a third species?
  • p. 463:  The book describes some interpretations of human races.  What is Freeman's point?  Are races subspecies?  In your own opinion, why does it matter?  Should we encourage research about genetic differences among different ethnic groups?
    • Genetic biodiversity is important in populations of plants and animals and humans, as the text pointed out in its discussion of inbreeding on pages 439 ff.  Be prepared to discuss these points:
      • Relation to endangered species
      • Relation to the Human Genome Project 
      • Relation to human "racial" identities.  Note:  The genetic differences between two members of the same ethnic group are often greater than the genetic differences between two people in different ethnic groups.   From www.theatlantic.com/genetic :  "The chimpanzees living on a single hillside in Africa have twice as much variety in their DNA as do the six billion people scattered across the globe."
        "Geneticists have never found a genetic marker that is of one type in all the members of one large group and of a different type in all the members of another large group. That's why ethnically targeted biological weapons would never work. Every group overlaps genetically with every other."
  • Summary:  So what's the current status of evolutionary theory?  Except for the minor problem of gradual rates, evolutionary theory is almost exactly what Darwin said.  We just connect it to more details of genetics and ecology, and we keep testing new hypotheses about phylogenies, speciation, and gene pool isolation.    The ideas and the "stories" about how speciation could have occurred are much more important than trying to differentiate the various technical terms which describe them.  
  • CHECKLIST:  species, speciation, gene pool, gene flow, genetic drift, natural selection, isolation, divergence, biological species concept, sexual species, asexual species, fossil species, reproductive isolation, morphospecies concept, phylogenetic species concept, evolutionary history, common ancestry, phylogenetic tree, phylogeny, monophyletic group, subspecies, Endangered Species Act, sympatry, sympatric speciation, exotic species, nonnative species, polyploidy, allopatry, allopatric speciation, vicariance, dispersal, colonization, isolated populations, , geographic distribution, ranges, refuges, Pleistocene refugium hypothesis, secondary contact, prezygotic isolation, reinforcement, postzygotic isolation, hybrid zones, mitochondrial DNA (mtDNA), hybridization
  • PREVIEW of TEST and QUIZ QUESTIONS

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