I.  The Issues

     A.      Is the equation for gene frequency change we have derived quantitatively correct, i.e. given that we can
               measure fitnesses accurately, does it actually predict the correct evolutionary trajectory a population will follow?

     B.     Are the qualitative predictionsof the equation acurate, i.e., given that we can rank fitness of different genotypes,
               even if we can't measure them with great accuracy, do the rankings predict the evolutionary outcome in
               natural populations?

      C.     Given that we have confidence, from answers to questions 1 and 2, that we understand how natural selection
               causes evolutionary change, what other types of evidence can be used to infer that populations have undergone
               divergent evolution due to natural selection?

II.  Laboratory Experiments: Demonstrating Quantitative agreement with equation for gene
      frequency change.

     A.  Laboratory experiments as microcosms

     B. Example: Drosophila melanogaster and the lt locus (B. Wallace.  1963.  American Naturalist 97: 65-66).

          1.  Characteristics of the lt locus

          2.  Experimental procedure

          3.  Theoretical expectations

          4.  Comparing theoretical expectations with observed gene frequencies.  (see Graph)

     C.  Example: Drosophila pseudoobscura and inversion polymorphisms (T. Dobzhansky.  1954.  Proc. 9th Int. Cong.
           Genetics, in Caryologia, 435-449).

          1.  Natural history

              a.  Polymorphisms for chromosomal inversions.
 `            b.  Inversion frequencies of these alleles undergo regular seasonal oscillations (see Graph).

          2.  Measuring Fitness (Handout).

          3.  Experimental procedure

          4.  Results (see Graph)

III.  Experiments in Nature: Demonstrating Qualitative Agreement with equation for gene
       frequency change.

     A.  Industrial melanism in Biston betularia (see H.B.D. Kettelwell.  1973.  Industrial Melanism.  Oxford Univ. Press,
           Oxford, U.K.)   (click here for Picture)

    B.  Other similar examples

          1.  Evolution of warfarin resistance in rats (see Explanation)
          2.  Evolution of DDT resistance in mosquitoes (see Explanation)

    C.  Sickle-Cell anemia and malarial resistance

         1.  Natural history.

         2.  Expected fitnesses of genotypes.

         3.  Alternative hypothesis:  the polymorphism is maintained by heterosis (J.B.S. Haldane).  (see Map).

         4.  Evidence supporting Haldane's hypothesis.

          5.  Conclusions

IV.  Inferring Evolution by Natural Selection without measuring fitnesses

     A.  Non-random associations between gene frequencies and environmental variables.

     B.  Example: variation in shell banding patterns in Cepea nemoralis.

     C.  Example: coordinate variation in gene frequencies in two species of crickets.
.

V. Adaptation

        Definition:  An adaptation is any trait that has evolved due to natural selection.