Question

briefly discuss the theory of natural selection as given by darwin

Answer 1

Postulates:

Three Postulates

Darwin's theory is based on three postulates:

The ability of a population to expand is infinite, while the resources available to sustain said population are finite. This dynamic causes a struggle for existence among individuals as they compete for resources.

Organisms vary in their physical qualities; these variations allow some members to reproduce more successfully than others.

These variations are inherited by offspring from their parents



Rejection:
when all was done evolution by natural selection seemed to be a plausible explanation of the wide variation and diversity both between and among organisms. However, the theory remained controversial because variation, and its inheritance, could not be adequately explained in terms of the existing body of knowledge. The current of the times favored a blending mode of inheritance, which would effectively deplete a population of organisms of all variation. 
Darwin could not provide a counterargument to the question of blending inheritance during his lifetime. At first glance, blending seems to be a good theory. Do not many human children appear to look like both their mother and father? , though, blending would have grave implications for any evolutionary novelty or variation; descendants would merely become increasingly homogenized with each passing generation. However, as Gregor Mendel would point out, while phenotypic variation may indicate blending of sorts, the inherited material—namely the genes—remains discrete.