variation and evolution

• Jean Baptiste Lamarck's theory was that changes to an animal within it's lifetime could be passed onto it's offspring.
• In 1859, Charles Darwin published his book called 'On the Origin of Species'.
• In 1859, Alfred Russel Wallace suggested a similar theory to Charles Darwin's natural selection.
• Fossils are evidence for evolution as they show how organisms have changed over time.
• In a population, differences in the characteristics of individuals is called variation.
• Variation can be due to:

  • the genes individuals have inherited (genetics)
  • the conditions in which individuals have developed (environment)
  • a combination of both genetic and environmental causes
• Sexual reproduction produces different combinations of alleles which leads to variation, although only mutations can create new alleles.
• Most mutations do not affect the phenotype of an organism, although a small number do.
• Evolution is the gradual change in the inherited characteristics of a population over time. This may also lead to a formation of a new species.
• Darwin's theory of natural selection took a long time to be accepted due to the lack of evidence.
• Process of natural selection:

  • There is variation within a population
  • The organisms with the best suited characteristics to the environment will survive and reproduce
  • These characteristics will be passed onto the offspring
  • This cycle continues until the whole species has changed over a long time.
• There are gaps in the fossil record as:

  • some species were soft-bodied and left few traces behind
  • traces may have been destroyed by geological activity
• Survival and reproduction

  Some of these variations may be advantageous or disadvantageous in a particular environment. Organisms with traits that give them an advantage in their environment are more likely to survive and reproduce.