The Macroevolutionary Puzzle


  1. Fossils–Evidence of Ancient Life
      1. Fossilization

        1. Fossils are recognizable, physical evidence of organisms that lived long ago–skeletons, shells, leaves, seeds, imprints of leaves and tracks (trace fossils), and even fossilized feces (coprolites)
          1. For fossilization, body parts or impressions must be buried in rock before decomposition.
          2. Over time, chemical changes and pressure transform living structures into stony hardness.
        2. Obviously, fossils form in highly unusual situations and therefore, are very rare.
      2. Interpreting the Geologic Tombs
        1. Stratification, the layering of sedimentary deposits bearing fossils, is quite similar from continent to continent.
        2. Deepest rock strata are assumed to be the oldest, surface layers the youngest. (big leap of logic…)
        3. Abrupt changes in the fossils in the layers were the basis for dividing earth history into great eras, which formed a "geologic time scale" to which actual dates were added later.
      3. Interpreting the Fossil Record
        1. The fossil record is far from complete, but some lineages are extensive.
        2. Fossil records vary according to type of organism (hard parts preserve well, soft parts do not), stability of the geographical region (sea floor vs. eroding hill), and quality of the specimen.

  2. Evidence of a Changing Earth
    1. According to the theory of uniformity, mountain building and erosion had repeatedly changed the surface of the Earth in exactly the same ways through time.
    2. Plate Tectonics
      1. Alfred Wegener proposed a model of a single world continent, named Pangea, that at one time extended from pole to pole surrounded by a single huge ocean.
      2. The idea of continental drift explains the separation of the continents and the formation of great mountain ranges as the continents collided (all through mantle convection)
  3. Evidence From Comparative Embryology
    1. Developmental Program of the Larkspurs
      1. The common larkspur has a ring like array of petals to guide honeybees to the nectar, plus bulging reproductive structures for the bee to hold on to.
      2. A more recently evolved larkspur has tight flowers that discourage bees but are attractive to hummingbirds.
    2. Developmental Program of the Vertebrates
      1. Different organisms may show similarities in morphology during their embryonic stages that often indicate evolutionary relationships.
        1. The early embryos of vertebrates strongly resemble one another because they have inherited the same ancient plan for development (see Macroevolution intro…)
        2. Some of the variation seen in adult vertebrates is due to mutations in genes that control the rates of growth of different body parts. (see "From Fin to Hand")
      2. One illustration of changes occurring in the timing of development is the similarity in size of the skull bones of humans and chimps at birth, which becomes dramatically different as these two animals age. (see "Retardation of Maturation" )
  4. Evidence of Morphological Divergence
    1. Homologous Structures
      1. In morphological divergence, features have departed in appearance and/or function from the ancestral form.
      2. These are body features that resemble one another in form or patterning due to descent through common ancestors.
      3. A good example of homology is the similarity of the structure of the bones in forelimbs of birds and bats. (see Evidence of Evolutionary Thought )
    2. Potential Confusion from Analogous Structures
      1. Analogous body parts perform similar functions in dissimilar and distantly related species.
      2. Morphological convergence is the adoption of similar function over periods of time in animals of evolutionary remote lineages.
      3. A good example of analogy is the similarity of function but not structure of the wings of an insect, bat, and a bird.
  5. Evidence from Comparative Biochemistry
    1. Molecular Clocks
      1. Neutral mutations have no more measurable effect on survival and reproduction rates than do other alleles for the trait.
      2. These mutations accumulate in the DNA and can be used as a "molecular clock" for (back) dating times of divergence of species.
      3. This model has three important assumptions.
      4. The "Lucy" theory.

    2. Protein Comparisons
      1. Because genes dictate the sequence of amino acids in proteins, analysis of proteins can determine the similarity of genes between species.
      2. For example: The amino acid sequence of cytochrome c shows strong evidence for placing humans, chimps, and rhesus monkeys in the same group.
      3. See Dr. Doolittle's Hemoglobin analysis.
    3. Nucleic Acid Comparisons
      1. The degree of similarity of nucleotide sequences of DNA reveals information about evolutionary relationships.
      2. If a single strand of DNA from one species is allowed to recombine with a single strand of DNA from another species (DNA-DNA hybridization), the degree to which they match up is a measure of similarity.
      3. DNA and mDNA both are used (see Genetic Relationships of Micronesian Populations)
  6. Identifying Species, Past and Present
    1. Assigning Names to Species
      1. The binominal system was originated by Carl Von Linné, better known as Linnaeus.
        1. The first part is the genus (always capitalized and italicized) and signified very closely related organisms.
        2. The second part is the specific epithet (never capitalized but always italicized) often followed by the subspecies.
      2. The language used for scientific names is Latin.
    2. Groupings of Species—The Higher Taxa
      1. The main taxa of the hierarchy from most to least inclusive are:
    1. Kingdom………………………Animalia
    2. Phylum………………………...Chordata
    3. Class…………………………...Mammalia
    4. Order…………………………..Primates
    5. Family………………………….Homodinae
    6. Genus…………………………..Homo
    7. species, subspecies…....sapiens sapiens
        1. In time, the traditional classification schemes became modified to reflect phylogeny – the evolutionary relationships among species.
    1. Finding Evolutionary Relationships Among Species
      1. Actually, There Is No Single Systematics Approach
        1. In classical taxonomy, classification schemes and evolutionary tree diagrams are constructed to reflect the perceived degree of morphological divergences among major lineages.
        2. In cladistic taxonomy, groups are arranged by branch points in an evolutionary tree diagram
    2. How Many Kingdoms?
      1. Whittaker’s Five-Kingdom Scheme
        1. Robert Whittaker originated the widely adopted five-kingdom system in 1969.
      1. Monera - unicellular prokaryotes
      2. Protista - unicellular eukaryotes
      3. Fungi - multicellular absorptive heterotrophic eukaryotes
      4. Plantae - multicellular autotrophic eukaryotes
      5. Animalia - multicellular ingestive heterotrophic eukaryotes
        1. Along Came the Archaebacteria
          1. Archaebacteria thrive in unusually harsh environments and differ from other bacteria in chemical composition, cell wall, and membrane characteristics.
          2. Recent analysis of archaebacterial DNA has convinced most scientists to create a sixth kingdom—Archaebacteria—to separate them from the eubacteria (Monera).