Understanding Natural Selection and Its Role in Evolution

Natural Selection:

Some variations are inherited (passed on from parents) and some are acquired (developed during life). Only inherited variation is passed on to the next generation.
Animals and plants produced by sexual reproduction will show variation from their parents, for example, in the size of the muscles in the legs of lions.
When new organisms are produced, not all of them are likely to survive because of competition for resources such as food, water, and shelter. The same is true for plants (they compete for resources such as nutrients, light, water, and space).
The individuals with the most favorable characteristics are most likely to survive.

The process of natural selection follows a sequence, as listed below:

• Some of the variations within a population may give some individuals an advantage over others in the population. Bigger muscles in the legs of a lion would enable it to run more quickly and get food more successfully.
• In an environment where there is a food shortage, the lion with the biggest leg muscles is most likely to survive to adulthood.
• The weaker individuals die before having the chance to breed, but the surviving adults breed and pass on the advantageous genes to their offspring.
• More of the next generation carry the advantageous genes, resulting in a stronger population, better adapted to a changing environment.

Slow changes in the environment result in adaptation in a population to cope with the change. Failure to adapt could result in the species becoming extinct. This gradual change in the species through natural selection over time, in response to changes in the environment, is a possible mechanism for evolution.

The theory of evolution states that species of an organism show descent with modification. It also states that all living things are related and have descended from a single common ancestor.

Charles Darwin accumulated a tremendous collection of facts to support the theory of evolution by natural selection. One of his difficulties in demonstrating the theory, however, was the lack of an example of evolution over a short period of time, which could be observed as it was taking place in nature. Although Darwin was unaware of it, remarkable examples of evolution, which might have helped to persuade people of this theory, were in the countryside of his native England.