Darwin’s theory of evolution is based on the fact that all the different types of species of plants and animals found today are the descendants of common ancestors. Gradual variation among them occured due to changes in organism-environment relationship in both time and space. The organism- environment relationship is different for different populations at different places and time. If a homogeneous population living in a particular environment migrates to a new habitat the organism- environment relationship may change. Depending upon the organism-environmental relationship the nature may select out those combination of genes which are better adapted under the given circumstances. In long course of time a few members of the population may show distinct adaptation which is marked by variation of characters.
Key Principles of Darwinian Theory:
Variation Among Organisms:
(i) Individuals within a species show heritable variations.
(ii) These variations arise due to mutations, genetic recombination, and environmental factors.
Struggle for Existence:
(i) Organisms compete for limited resources (food, shelter, mates, etc.).
(ii) Those with favorable traits have a better chance of survival.
Natural Selection:
(i)Nature "selects" organisms best adapted to their environment.
(ii) Those with beneficial traits survive and reproduce, passing on their traits to the next generation.
Survival of the Fittest:
(i) Individuals better adapted to their environment thrive, while others perish.
Speciation:
(ii)Over long periods, accumulated changes lead to the formation of new species.
If a population becomes reproductively isolated, it evolves into a distinct species.
