Principles of Evolution

What is evolution?

• possible definitions

• it's a scientific theory

• beneficial features are retained while detrimental features are lost

Development of the theory

• People were trying to answer the question: "How do you explain all of the biological diversity on Earth?"

• special creation

• Cuvier - catastrophism

• Lamarck - inheritance of acquired characteristics

• Lyell and Hutton - theory of uniformity

• Darwin - evolution by natural selection

  • members of populations have heritable trait variations

  • these variations are innate and due to chance

  • some variations have adaptive advantages

  • selective forces act upon individuals in the population

  • over generations, the population changes

Evidence for evolution

• artificial selection - humans choose traits to perpetuate

• fossils - layers show successive life-forms

• biogeography - study of geographic distribution of organisms

• comparative anatomy - anatomical similarities between organisms

How populations evolve

• gene pool - all of the genes in a population

• natural selection acts upon individuals, but the population evolves

• genes determine traits

• genes exist in 2 or more forms (alleles)

• in a population, the alleles are present at different frequencies

• in a stable population, these allele frequencies will NOT change unless there is:

  1. mutation - change in the DNA sequence

  2. gene flow - immigration and emigration

  3. genetic drift - random change in allele frequencies by chance alone

  4. non-random mating - choosing to mate with particular partners

  5. natural selection - preservations of favorable adaptations

• these 5 occurrences result in small-scale changes in allele frequencies - microevolution

© Carol L. Wymer, 2004