Theory of Evolution

Previous Theories of Evolution

The Present Theory of Natural Selection

  1. The gene pool is the total of all the genes of a population of a species in a given area. The gene pool includes genes for both better-adapted and poorly-adapted characteristics. The gene pool has genetic variation as a result of:
    • Mutations
    • Chromosomal changes during meiosis and mitosis
    • Variations of combinations of gametes in sexual reproduction

  2. Gene frequencies are the frequencies or numbers of genes of particular types in a population. Gene frequencies alter because of 3 factors:
    • Migration into or out an area
    • Isolation
    • Adaptation

  3. Isolation is of 3 types:
    • Geographic Isolation (e.g. birds on different islands, wind-pollinated plants on different sides of a mountain)
    • Behavioural Isolation (e.g. nocturnal and diurnal feeders)
    • Reproductive Isolation (i.e. a social or structural difference that prevents mating)

  4. Adaptations are characteristics possessed by an organism that causes it to be better suited or better able to survive in its surroundings. Adaptations may be:
    • Structural Adaptation (e.g. streamlined shape of fish)
    • Physiological Adaptation (e.g. hibernation of bears in cold climates)
    • Colour Adaptation (e.g. camouflage, mimicry)
    • Behavioural Adaptation (e.g. nocturnal feeders in hot climates)
    • Reproductive Adaptation (e.g. peacock's fanning display to attract a mate)

    Organisms with better-adapted characteristics will breed, passing the better-adapted gene to future generations, and increasing the gene frequency of the better-adapted gene.
    Organisms that are poorly-adapted will breed less if at all, reducing the gene frequency of the poorly-adapted gene, possibly to the point of extinction.

  5. Speciation - New species that can no longer interbreed with the original species develop over time in different areas.

Theory of Continental Drift and Plate Tectonics