GEOL 104 Dinosaurs: A Natural History

Fall Semester 2000
Evolution I: On the Origin of Species by Means of Natural Selection

  • Why does comparative anatomy work (i.e., where are their homologies)?
  • Why are there adaptations (specialized structures or behaviors that allow organisms to interact with their environment in certain specific ways)?
  • Why is Life so effectively organized under a nested hierarchy of groups?
  • Why should the Principle of Fossil Succession work?
  • Where should vestigial organs exist?
  • Why should groups closely related to each other have embryos similar throughout most of their development, while those of more distantly related forms have fewer shared stages?
  • Why does the fossil record hold evidence of creatures intermediate in form between distinct modern groups?
  • Why is there a biogeography (non-random distribution of living things)?
  • FROM WHERE DO NEW SPECIES COME?

    Historically have been two primary competing views about life:

    Both ideas can be found in ancient Greek writing, and might have been even older.

    Much new consideration of topic during Age of Enlightenment and afterwards:

    Prior to knowledge of geological ancient past and its extinct creatures, could only relate modern animals to each other; and thus assumed any transitions had to be between known modern forms.

    With rise of knowledge of both fossil creatures and geologic time, new models of evolution were proposed. In these models the earlier forms were the ancestors of modern taxa.

    Jean-Baptiste Lamarck (French: late 1700s-early 1800s): predominant theory of evolution prior to Darwin:

    Flaw with Lamarckian Evolution: characters acquired during the lifetime of an organism are not passed on to descendants!
    (The test: mice had their tails cut, bred with other de-tailed mice. However, mouse tail length did not decrease over time, but instead remained the same).

    Still, during the early 1800s was the best model available. Explained:

    During early-mid 1800s, two natural historians independently developed an alternative, and superior model: Natural Selection. Their basic observations: Thus, IF some variation gives the individual a slight advantage (bigger, stronger, smaller, smarter, less tasty, whatever) at surviving; and IF that variation is inherited; THEN there is a somewhat better than average chance that organisms with that variation will survive to bear the next generation. Over the long expanse of geologic time, the accumulation of these variations will change the population from one form to another: the origin of species.

    This process is analogous to artificial selection (i.e., domestication), and thus called natural selection.

    NOTE: Natural Selection is NOT “survival of the fittest”, as commonly thought.

    NOTE ALSO: Darwin did not use the word “evolution” very often; instead, preferred the phrase “descent with modification”.

    Darwin pointed out a subset of Natural Selection: Sexual Selection, where the variation is “being more sexy” (and thus have better than average chance of breeding, and thus passing on “sexiness”, compared to other members of the population): peacock tails, bird song, etc.

    Many similarities to Lamarckism: homology due to common ancestry, for example.

    Primary difference: adaptations due to differential survival of variations in a population, not to accumulation of characters acquired in the lifetime of the organisms.

    Evolution by natural selection explained a lot:

    For those interested in some of the original literature on the subject, click here for the joint Darwin & Wallace paper of 1858 (actually, it was a series of short papers and letters published together) and here for the text of the first edition of The Origin of Species.

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