Explain the terms
(i) Speciation (ii) Natural selection

Explanation

(a) Speciation : It is the evolution of reproductive isolation among once-interbreeding populations i.e., the development of one or more species from an existing species.
Factors which can lead to speciation are :
(i) Genetic drift may accumulate which lead to speciation.
(ii) Natural selection may work differently in different location which may give rise to speciation.
(iii) Severe DNA change.
(iv) A variation may occur which does not allow sexual act between two group.
(b) Natural Selection : (i) There is natural variation within any population and same individuals have more favourable variations than others.
(ii) Population remains fairly constant even though all species produce a large number of offsprings.
(iii) This is due to .competition. or struggle for existence between same and different species.
(iv) The struggle for survival within population eliminates the unfit individuals and those with .favourable variations. survive and pass on these variations to their progeny to continue. This is called natural selection. The favourable variations are accumulated over a long time period leading to the origin of a new species.