Natural Selection and Evolution The observation of variations within species that were made in the 19th century led to the proposal of “Natural Selection” by Charles Darwin and Alfred Wallace. This theory explained how evolution could occur.
The Theory of Natural Selection Proposes that it is the environment that selects favourable variations and eliminates ones that are a disadvantage to an organism. After many generations of “selection”, the characteristics of a population might change and the population becomes adapted to their environment
The 4 Points • Darwin’s Theory had 4 main points: 1. In any population there are variations, all members of a species are not identical (prac - meal worms and giraffe example)
2. In any population their are offspring that die before they can reproduce, the characteristics of these organisms are removed from the population
3. Those organisms that survive and reproduce are well adapted to that environment (they have favourable variations) (survival of the fittest)
4. Favourable variations are then passed on to their offspring and will become more common on the population
In Summary Therefore, as the climate becomes hotter, colder, wetter or drier etc, the distribution and abundance of living things will change. The characteristics which were once favourable may no longer be favourable and the organisms that are not well adapted to the new environment will slowly die out and a change in the species will occur (evolution).
Evolution in Australia Australia has undergone physical (isolation, landforms) and environmental (hotter and drier) changes which has affected the flora and fauna. Changes are still occurring. Evidence of this can be seen by studying the geography and geology of Australia and also its fossils records.
Geological and Geographical Evidence that Australias Environment has Changed Rock and landform studies show sea levels have risen and fallen meaning mainland Australia and Tasmania have been joined and separated at least 8 times in the last 30 million years Continual erosion has lead to Australias Earth becoming lowered and flattened Black coal deposits in Sydney basin are evidence swampy environments in the precambrian era (298 mya) and contain fossils of plants growing there Sediments, soils and structures along with marine fossils found in Aust. outback show a great inland sea broke Australia up in the cretaceous period (approx. 65-141 mya) splitting it into 4 islands.
Fossil Evidence Kangaroo fossils found in the Naracoorte caves, SA show a great reduction in diversity and numbers since the Pleistocene changes reduced their habitats. Plants in the same area have changed from eycalypts and scrub plants to woodland trees and grasses to Casuarinas.
Question In your own words explain the theory of natural selection Compare Lamarck and Darwin’s theories Outline Darwin’s 4 points in no more than 1 sentence each Explain how a gradual change in environmental conditions can lead to evolution of a species Outline 1 piece of geological evidence and 1 piece of fossils evidence that shows that Australia’s flora and fauna have changed as a result of an environmental change over a period of time.