Explain 'natural selection'.
Darwin and wallace proposed that natural selection is the mechanism by which new species arise from pre existing ones. The theory of Natural selection states that there is "struggle for existence" within a population and variation exists within all population. The continuous competition between individuals for environmental resources creates a 'struggle for existence' and this struggle makes sure that certain organisms would fail to survive or reproduce. This would eliminate less suited organisms and better adapted organisms would survive and pass on their traits to next generation leading to evolution.