Speciation

4.2 Natural selection

5.1.1 Environmental change

Speciation

  1. Fossils

    1. Evidence of early forms of life comes from fossils
    2. Fossils are the “remains” of organisms from hundreds of thousands of years ago that are found in rocks

    3. Formation

      1. From parts of organisms that have not decayed because one or more of the conditions required for decay are absent
      2. When parts of the organism are replaced by other materials as they decay
      3. As preserved traces of organisms, such as footprints, burrows and rootlet traces
    4. Many early forms of life were soft-bodied, which means that they have left few traces behind, which were mostly destroyed by geological activity; this is why scientists cannot be certain about how life began on Earth
    5. Fossils show how much or how little different organisms have changed as life developed on Earth

  2. Causes of extinction

    1. Changes to the environment over geological time
    2. New predators
    3. New diseases
    4. New, more-successful competitors
    5. A single catastrophic event, such as massive volcanic eruptions or collisions with asteroids

  3. New species

    1. Isolation: two populations of a species become separated, such as by geographical isolation
    2. Genetic variation: each population has a wide range of alleles that control their characteristics
    3. Natural selection: in each population, the alleles that control the characteristics that help to organism to survive are selected
    4. Speciation: the populations become so different that successful interbreeding is no longer possible