5.1 – Evolution and Biodiversity

5.1 – Evolution and Biodiversity 

Evolution: cumulative change in the heritable characteristics of a population

  • Cumulative change: small change over many generations
  • Heritable characteristics: gene-controlled factors
  • These traits cannot be acquired over a lifetime, they are heritable traits or alleles in an organism’s DNA

Evidence of evolution:

  • Fossil records – sedimentary rocks
  • Homologous structure
  • Vestigial structure e.g. appendix
  • Selective breeding
  • Comparative DNA
  • Observable change

Fossil records:

  • Fossils are the preserved remains of animals, plants, and other organisms from the past.
  • The fossil record shows the gradual change of species over time.
  • The timeline in which fossils appear are what scientists would expect, with bacteria and algae being the oldest in the fossil record. Followed later by shelled animals and trilobites, then dinosaurs and early reptiles, birds and mammals later still.

Selective breeding:

  • Breeding plants and animals for specific genetic traits.
  • Shows a good record of recent changes in genetic characteristics over a few dozens of generations that man has selected to breed.
  • For example, chickens that produce more eggs or cows that produce more milk are selected to breed, hopefully passing these traits onto next generations.
  • Plants can be bred in a similar manner based on useful or beneficial characteristics breeders would like to see in the next generation of plants.
  • The evolution of domesticated dogs has produced many different breeds through artificial selection

Homologous structure:

  • Common internal structures that are similar in seemingly dissimilar animals that have evolved from a common ancestor.
  • The standard example of homologous structures is the “Pentadactyl limb” which is the five digit limb found in animals such as humans, dolphins, bats, and dogs.
  • Even though the shape, size and function of this structure vary between species, the general structure and position of the bones in these limbs are the same.

Gradual diverge:

  • Within a population there is genetic variation
  • If two populations of the same species become separated so that they do not reproduce or interbreed because they become separated by geographical boundaries; for example one group migrates to an island or they became separated by a mountain range, then natural selection will act differently on those two separate populations
  • Over time, these populations change so that they are recognizably different and can or do not interbreed if they were to merge together again
  • This process is called speciation