BSCI 124 Lecture Notes

I. Evidence for evolution [REQUIRED READING]- Extant organisms

• A. Comparative anatomy of different organisms
  • Definitions
    1. Homologous organs- organs similar in form in different organisms owing to a common evolutionary origin- example- same bone structure of bat's wing, dolphin's flipper, human's arm, bird's wing
    2. Analogous organs- organs that have similar functions in different organisms (do not share a common evolutionary origin)- lungs of mammals and trachea of insects; wings of insects and wings of birds
    3. Vestigial organs- organs or parts of organs that are nonfunctional and degenerate- wingless birds with vestigial wing bones, whales and pythons with vestigial hind leg bones; blind cave-dwelling animals with vestigial eyes
    • a. Occasional vestigial organ is to be expected as a species evolves and adapts to different modes of life
      b. When an organ loses its function, there is no selective advantage to possess it but there is no selective pressure to get rid of it

  B. Mimicry and protective coloration- examples of adaptive evolution brought about by natural selection

  • 1. Protective coloration- coloration that permits an organism to blend in with its surroundings
    • a. Walking stick insects look like branches
      b. Moths on bark in polluted England

    2. One type of mimicry [REQUIRED READING - Be sure to pull down page to Monarchs and Viceroys]- a harmless species resembles one that is dangerous or distasteful

    • a. Certain moths resemble wasps
      b. Many butterflies mimic the monarch, which is toxic to birds (the imitators are nonpoisonous)
    • Listen to an explanation.

  C. Developmental biology (looks at organisms from early embryos to adults)

  • 1. Early embryos of many vertebrates are strikingly similar in form- turtle, fish, chick, pig, human
    2. Common features of all of them- segmented muscles, gill pouches, a 2-chambered heart, tail
    3. Since higher vertebrates evolved from fish, they share the fish's basic pattern of development

  D. Biogeography- the unequal distribution of organisms on the earth

  • 1. Why are kangaroos in Australia but not elsewhere? Why are cacti in deserts of North America but not in deserts of Africa or Asia?
    2. Each species originated only once, in one place- called the point of origin
    3. From its point of origin, each species spread out until it encountered a barrier of some sort
    • a. Physical barrier- mountain, ocean
      b. Environmental barrier- unfamiliar climate
      c. Ecological barrier- presence of organisms that compete with it for food or shelter

    4. The portion of the earth over which an organism is found is its range
    5. Example of biogeographic evidence- plants and animals of the Galapagos Islands (volcanic, formed recently)

    • a. Resemble plants and animals of South America more than they resemble those of other places (Africa has a similar climate, for example, but Galapagos organisms don't resemble African organisms
      b. Often contain organisms unique to that particular habitat
      • Finches: in SA, large beaks to eat cacti seeds, in Gal. slender woodpecker-like to dig in bark
        
      • Change due to different food

      c. Explanation- some neighboring organisms migrated or were carried to the island; here they subsequently evolved into new species (in response to different selective pressures here than on mainland)

  E. Biochemistry and molecular biology

  • 1. Our genes contain evolutionary records every bit as dramatic as the fossil record
    2. If we all evolved from a common ancestor, then:
    • a. we should have the same genetic molecule (we do- DNA)
      b. we should use that molecule in the same way (we do- central dogma)
      c. portions of our DNA should be the same (it is)
      • 1) It won't be identical to our ancestral DNA because of mutations
        2) The longer the period of time since two species diverged, the greater the differences in their DNA
        3) Put another way, organisms that are close relatives will share large portions of DNA sequences, organisms that are distant relatives will share smaller portions of DNA sequences

    3. Because genes code for all the chemicals we make, a similar line of reasoning applies to proteins and other compounds

II. Evidence for evolution- Fossil organisms

• A. any trace left by a previous organism
  • 1. May be in rocks, in ice, in amber (ancient tree resin), in bogs, in tar, such as footprints
    2. Most are preserved in sedimentary rock, which is laid down as layers of sediment; over time, heat and pressure convert the sediment layers into rock
    • a. Oldest rocks- simplest life forms --> most recent rocks- more complex life forms
      b. Organisms must have been covered before decomposition occurs (ex- few fossils from tropical rain forests but lots from marine environments)

Other Sites of Interest:
An excellent, overall review [REQUIRED READING]
Five misconceptions about evolution

EvolvVision- traces microbe to man- fun!

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Last revised: 18 Sept 1998 - Straney