Charles Darwin’s theory of evolution

Darwin’s theory of evolution is also called the theory of evolution by natural selection. His theory was based on accurate observations. The theory is resolved into three components: • Over-production of offspring and subsequent struggle for existence among the offspring • Variations in natural populations • Elimination of unfavourable variations, which result in the survival of the best adapted or survival of the fittest. If all the offspring of plants and animals survived, there would be geometric increase in the number of organisms, i.e. organisms would continue to increase in number in an unlimited manner. If the number of organisms increased at this rate, food supply, water and space would soon be insufficient. A struggle for existence would ensue as a result of competition fro the limited resources. No two individuals in a species are identical. There are always variations, however slight. Some variations are better suited to the environment while others are not. These slight variations are preserved and passed on to the offspring. In the struggle for existence, individuals with favourable variations are more likely to survive and transmit their characteristics to their offspring, i.e. they have greater survival value. Individuals with less favourable variations are more likely to perish before they can reproduce and pass on any of their variations to offspring. This is the idea of the survival of the fittest. The survivors in each generation may be different from those of the previous generation and thus they are better adapted to their environment. Gradual change of this type in isolated populations may result in them differing more and more, eventually being recognised as a new species. In the case of the giraffe, the ancestral giraffes showed variation in neck length. Natural selection favoured those with long necks which were best adapted to reach their food and thus survived. Those with short necks, unable to compete for food with the longer-necked varieties, dies. Eventually only longer-necked giraffes remained.