The key concepts of Darwin's theory of evolution include the following
(i) Over Production-Living beings process and innate ability of producing own kind for the continuty of race. It has been observed that more individuals of each kind are produced than could possibly survive.
(ii) Struggle for Existence-Individuals multiply in geometric ratio, whereas space and food remaiin almost limited. This causes competition and struggle for existence.
(iii) Variations No two individuals are alike. Members of a population vary in size, form and other characteristics even through they look superficially similar. These variations are gradual and those with adaptive value are passed on to next generation.
(iv) Survival of the Fittest and Natural Selection During struggle for existence only those individuals could survive which exhibit variations that are beneficial and adapt better to a changing environment. This is known as natural selection.
(v) Origin of Species Natural Selection results in modification of traits within a lineage, which can bring about evolution of original species into new one over a period of long time.