When Darwin published the Origin of Species by means of Natural Selection he was not the first person to propose such ideas. However, Darwin was the first to propose a naturalistic mechanism to explain the variety and emergence of living lifeforms found on earth today. Darwin argued that all life was the product of undirected natural forces which happened over eons of time, through random and spontaneous actions which Darwin dubbed as “Natural Selection”.
While Natural Selection can be observed as an end result of genetic function as “survival of the fittest” or “variety within species” it cannot explain the arrival of life or the divergence of species. Minor changes within the same species, characteristics which help an organism to survive, such as thick fur in a cold environment or a heavier beak to break tough seeds for a bird, fail to move animals to new kinds or families. Such DNA diversity at reproduction occur within structures called alleles. These changes occur due to functions already present in the DNA and are not new to the organism nor do they occur by spontaneous mutations.
While natural selection can be used to explain simple observed end results within living organisms it cannot and does not explain the origin of life or the divergence of species as foreseen by Darwin as common ancestry of all life.