BIOLOGY
EVIDENCE OF EVOLUTION

1. Outline the impact on the evolution of plants and animals of: - changes in physical conditions in the environment - changes in chemical conditions in the environment - competition for resources

Changes in the environment of living organisms can lead to the evolution of plant and animal species. These environmental changed in condition may be physical, such as temperature changes, or chemical, such as changes in water salinity. Change may also be triggered by competition, for example, competition for resources such as food and water or competition to reproduce.

Changes in physical conditions in the environment include natural conditions, such as temperature and the availability of water. Since life first evolved on Earth it has seen many changes. Given that the environment at the time was so antagonistic to life it is a wonder that life evolved at all. The physical environment has changed frequently. Sea levels have risen and fallen. Oceans or dry land has, at various times, covered parts of Australia. Such drastic changes in the environment influence evolution. Fossil evidence indicates that much mass extinction have resulted from changed in the Earth’s physical environment, for example, at the beginning of Pangaea about 90% of marine mammals became extinct. Over a period of 10 million years, dinosaurs along with other organisms became extinct. One theory as to why this occurred is that a meteorite struck the Earth producing a dust cloud that may first have killed many of the plants and animals that dinosaurs ate, causing them to starve and die. Other scientists argue that climate change could have occurred from continental drift, changing patterns in oceanic circulation, or possibly volcanos. Whatever the cause, the environmental change favoured the organisms that survived. The story of life on Earth us change, extinction and diversification. Environmental change can favour certain species. The Australia landmass has become drier over time and this has lead to changes in the species of kangaroos that are present today. Approximately 25 million years ago, Australia was considerably wetter than today with large areas of rainforest. During this time, kangaroos were small and omnivorous, with unspecialised teeth, eating a variety of foods from the forest floor. Food was nutritious and abundant; there was no need for specialised grinding teeth. As Australia became more arid and grass became the dominant vegetation in some areas, environmental selective pressure resulted in larger kangaroos favouring teeth suitable for grass. These teeth, high-crested molars, efficiently grind low-nutrition grass into a more easily digestible paste. Slicing pre-molars are of little use and so became much reduced from the ancestral kangaroos.

Changes in chemical conditions in the environment have also affected evolution. When life first evolved, it developed in an environment free from oxygen. These primitive organisms metabolised simple organic molecules in shallow seas. A product of this metabolism was carbon dioxide. Over millions of years the carbon dioxide accumulated in the environment and at some stage organisms capable of using CO2 in photosynthesis evolved and multiplied. They produced oxygen as a product of their metabolism, creating a chemical environment, which simple animals could exploit. These animals obtained energy from aerobic respiration. The evolution of organisms, as a consequence of chemicals in the environment, is not just ancient history by affects us now. Humans change the environment rapidly. Change and the capacity of populations of organisms to evolve in response to chemicals is sometimes a frustration to humans. Chemicals that can affect the evolution of species include salts and elements, such as iron. For example, many parts of Australia have soils that have a high salinity. There is a range of salt tolerant plants that have evolved to inhabit those areas.