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1. Evidence of evolution suggests that the mechanisms of inheritance, accompanied by selection, allow change over many generations 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 physical conditions in the environment * These include natural conditions, such as temperature and the availability of water. * 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 have been reduced.
Changes in chemical conditions in the environment * 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 are a range of salt tolerant plants that have evolved to inhabit those areas. The animals that feed from these plants have also evolved to inhabit those areas. * The sheep blowfly, Lucilia cuprina, is a major problem to the Australian sheep industry. It stresses, weakens and can be lethal to sheep when larvae, laid by females, burrows into wounds and wet wool. Chemicals, such as dieldrin and organophosphates, have been used extensively to control the blowfly. However, genetic