Natural selection is the theoretical concept of explaining mechanism of evolution which was deduced by famous evolutionist and naturalists Charles Darwin (1859). He explained the process of evolution through natural selection in his book “Origin of Species”.
Darwin’s theory of Natural Selection is based on the observed facts which experienced by him during his world exploring journey by Voyage of Beagle.
i) Enormous power of Fertility and Prodigality of Production:-
Every living Organism tends of multiply in geometric progression. A single Amaranthus plant under normal condition, i.e. free from environmental pressure could produce 20, 00,000 seeds in a season. A mushroom can scatter two billions of spores in a single breeze. An Oyster caw lay 60 million eggs per breeding season. Thus there is a continuous and progressive growth of species population take place.
ii) Competition or Struggle for existence:-
There is over production of species due to high reproductive rate and on the other hand space and food is very limited on the earth. Therefore a competition starts among the individuals of a species or between different species or between the environment and species. Such competition when reach the through then become struggle for existence.
iii) Survival of Fittest:-
In struggle for existence, individuals having several favorable variations with the changed habitat will have better chance of survival and tend to exist. But those which are not adopt or lack of variations proved to be less fit in the struggle, will be destroyed by physical and biotic factors. Those which proved themselves fittest only can survive and rest become extinct.
Thus the organisms of present day condition arose through the selection or scrutiny which automatically occurring in nature.
Darwin’s theory proves that environmental change is the principal cause of evolution of species.
Objections to natural selection:-
i) It does not explain the mechanism of variation.
ii) Natural selection is not the only cause of speciation.
iii) It does not considered the inheritance of new characters.
iv) Only useful variations are taken into account.
v) It does not considered arrival of fitness.