Natural selection is a theory that seeks to explain how evolutionary change takes place in a gradual manner; with changes in time. The theory was put forward by Charles Darwin in the quest to explain on why species in different geographical locations did not have similar characteristics. According to the theory, evolutionary change arises because each generation has variation and the survival of populations. The gradually changing environment is enhanced by possession of the best combination of variable characteristics that are best suited to the then existing environment. According to the theory, therefore, the individuals of the population, which possess characteristics that are best suited or adapted to the existing conditions of survival have a higher probability of surviving in that given environment, where they will undergo reproduction to produce offspring that inherit such traits from their parents, thus enhancing the procreation of the species that best suits the existing favorable conditions. .
In any natural environment, organisms reproduce offspring of a larger number than the number required to replace the already existing organisms. Thus, this implies that the population of the given species will face a gradual increase. However, the population of every species appears to be of a constant number at all times. This shows that despite the rapid reproduction rate, the level of the number of organisms of any given species does not show any significant increase. The contributing factor to the above is the fact that in any given environment, the amount of resources is limited. The resources here refer to food, space, water, and any other type of resource that the organism needs for survival in a given environment. This thus implies that the individual organisms will have to compete for the access of the limited resources in the given ecological location, and organisms that possess the most suited characteristics will access the resources, and those with less fitting characteristics and traits would be eliminated, a term that Darwin named survival of the fittest.