Organic evolution.

What is Evolution?

A given species is a geneological descendent of some other species.

All forms of life on earth descended, geneologically, from one or a few original forms.

Why do we think that evolution has occurred?

  • Organisms exhibit a range of similarities to each other.
  • Domestic animals and plants can be changed.
  • Organisms are limited by their heritage and by compromise:
    • People poorly adapted to upright walking.
    • Are four legs optimal? Why do ostriches use 2? Why do insects have 6?
    • compare the wings of insects, birds, bats, pterosaurs.
    • panda's "thumb"
  • Vestigial Organs-body parts that serve a function in some animals, but not in related animals.
    • horse' "splint" bones.
    • the appendix in humans
    • whale's hips

"Darwinism": an Evolutionary Mechanism

Variation exists in populations of organisms

  • Variation exists in any population
  • Unique traits can be passed from parents to offspring
  • Mechanism of variation: In the genes
    • DNA
      • self replicating blueprints
      • Mutations: "bad" copies
    • Genotype and phenotype

Organisms tend to over-reproduce

    • How many cockroaches can two cockroaches generate in a year?
    • Some offspring must die.

Natural Selection: "Survival of the Fittest"

    • Survival, on average, depends on existence of favorable traits
    • Creatures with favorable traits survive to pass those traits on to the next generation.

How does Evolution Happen?

  • Gradualism: Evolution happens in imperceptible steps over a long period of time.
  • The problem of Allopatric Speciation (Ernst Mayr)
  • Punctuated equilibrium (Stephen Gould, Niles Eldrigde)
    • Stasis
    • sudden appearance of new species.

Major Evolutionary patterns recognized in the fossil record

  • Adaptive radiations
  • Parallel evolution
    • when two or more lineages follow similar evolutionary paths
  • Convergent evolution
    • when two or more lineages become similar
    • heterochronous homeomorphs
    • Synchronous homeomorphs
    • Analogous structures
    • Homologous structures

How do we study evolution in fossils?

Studying fossils is different than studying living organisms

  • We don't have:
    • a complete, gap free fossil record
    • genetic material
    • behavior or soft parts (usually).
  • We do have:
    • changes over vast periods of time.
    • lineages that have left no surviving members.