Natural Selection by Charles Darwin
Thomas Malthus, in his theory of population growth, argued that there is the replacement of living organisms that lead to the increase in population. Through this Darwin came up with the theory of natural selection known as ‘struggle for existence and survival for the fittest’. Many animals and plants are produced in the world compared to the available resources to sustain them. Thus there is a struggle between individuals of the same species or different species for limited resources in the ecosystem.
Due to pressure for these limited resources, living organisms with favorable traits are able to live, procreate and move to the next generation. Those organisms with unfavorable traits are unable to fight for resources and survive in the ecosystem. Thus, they cannot procreate young ones with favorable traits to survive in the ecosystem and move to the next generation. They are then eliminated leading to a lack of transfer of traits to the next generation. Thus nature selects organisms to survive in the ecosystem.
The older species changes to the new species through natural selections. Nature selects organism to live, move and continue the generation of organisms. Those organisms with favorable traits which enable them to compete for resources in the ecosystem are enabled to produce young ones and move them to the next generation. This young one with profitable variations in the ecosystem also breeds young ones who compete for resources in the ecosystem. Those with favorable traits than the other are also able to survive, produce young ones and move them to the next generation. The process repeats itself in many generations leading to the emergence of new species.