Describe the theory of natural selection. Who proposed this theory?

(N/A) Charles Darwin conducted a sea voyage around the world between $1831-1836$ on the ship $HMS$ Beagle.
During this period,Darwin explored the flora and fauna of various 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 in Earth's history. $(ii)$ Varying degrees of similarities exist between existing life forms and those that lived millions of years ago. $(iii)$ Populations of all organisms possess variations in characteristics,which help them adapt better to their environment. Characteristics that enable some individuals to survive better in natural conditions (food,climate,physical factors) allow them to outbreed others (survival of the fittest).
Thus,fitness,according to Darwin,refers ultimately to reproductive fitness.
Such fit individuals leave more progeny than others.
Consequently,organisms that are better adapted will survive more in nature and be 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,reached similar conclusions to Darwin.
Thus,they both jointly proposed the theory of 'Natural Selection' in $1858$.
It is based on the following factual observations: $(a)$ Natural resources are limited. $(b)$ Population sizes are stable except for seasonal fluctuations. $(c)$ Members of a population possess varying characteristics; no two members are identical,even if they appear superficially similar. $(d)$ Variations are generally inherited. $(e)$ Population size involves two facts: theoretically,it grows exponentially if everyone reproduces maximally,but in reality,population size is limited due to competition among individuals for resources.
Those that are better adapted survive and reproduce at the expense of those that are less adapted to the environment.