Some Undisputed Features of Evolution

1) Variation exists because heredity is not perfect. Variation arises primarily through random mutations and recombination.

2) All evolutionary changes depend upon changes within populations. These consist of alterations of the proportions of the genotypes, hence the genes (alleles), borne by the individual organisms that make up the population.

3) Allele frequencies remain constant unless forces change them. Factors that may alter allele frequencies in a population include: mutation, genetic drift and gene flow.

4) Another factor that may alter allele frequencies in a population is natural selection (which is defined as differential survival and differential reproduction of genotypes).

5) Evolution proceeds at different rates

6) Many mutations are advantageous in some contexts, disadvantageous in others, or neutral. The advantage of an allele or genotype depends upon the environment.

7) The chance (probability) that a mutation will occur is not affected by the advantage or disadvantage it confers.

8) Organisms cannot evolve adaptations in anticipation of future events nor do adaptations evolve for the "good of the species".

9) Not all characteristics evolved because they were adaptive.

10) Speciation generally requires barriers to gene flow.

11) If gene flow among local populations of a species is sufficiently restricted, the populations may so diverge that they will not or cannot interbreed. That is, speciation occurs.

12) If two populations have become different species, the genetic changes in one are usually not transmitted to the other, so they pursue independent evolutionary paths.

13) The principles of intraspecific evolution apply to all genetically controlled characters and at all taxonomic levels.

14) Biodiversity can be defined in terms of genetic diversity, species diversity and ecosystem diversity.

15) Systematics is involved with studying biodiversity and the evolutionary relationships that exist among organisms. The methods of cladistics are used by most systematists to formulate and test hypotheses of relationships.

(Modified after: Futuyma, D.J. 1998. Evolutionary Biology, 3rd Ed.. Sinauer Associates, Inc).