Write a short note on Darwinism.

(A) Charles Darwin made a sea voyage around the world between $1831-1836$ in a sailship $HMS$ Beagle.
During that period,Darwin explored the fauna and flora of a number of continents and islands.
Based on his observations,he concluded the following: $(i)$ There has been a gradual evolution of life forms with new forms arising at different periods of the history of Earth. $(ii)$ Varying degrees of similarities can be observed between existing life forms and those which existed millions of years ago. $(iii)$ Populations of all organisms have variations in characteristics,which make them adapt better to the environment. The characteristics which enable some populations or individuals to survive better in natural conditions (food,climate,physical factors) would outbreed others (survival of the fittest).
Thus,fitness of the individual,according to Darwin,refers ultimately to reproductive fitness.
Such fit individuals leave more progeny than others.
Thus,those organisms which are better fit or adapt well will survive more in nature and get selected by nature.
This is called natural selection.
Branching descent (e.g.,Darwin's finches) and natural selection are the two key concepts of the Darwinian theory of evolution.
Alfred Wallace,a naturalist who worked in the Malay Archipelago,came to similar conclusions as Darwin.
Thus,they both jointly propounded the theory of 'Natural selection' in $1858$.
It is based on the following factual observations: $(a)$ There are limited natural resources. $(b)$ Populations are stable in size except for seasonal fluctuations. $(c)$ Varying characteristics exist in members of a population,i.e.,no two members of a population are identical even though they look superficially similar. $(d)$ Variations are generally inherited. $(e)$ Population size involves two facts: theoretically,it grows exponentially if everyone reproduces maximally,and in reality,population size is limited due to competition among individuals for resources.
Those which are better adapted could survive and will reproduce at the cost of others,i.e.,those who are less adapted in the environment.