Darwin's theory of natural selection was based on the following facts: 1) organisms increase more rapidly than their food supply. He quotes that there are finite number of resources, therefore making him a Neo-Malthusian. 2) Due to natural selection, there is never overpopulation in animals, because some of them will be eliminated at a young age due to unfavorable environment. 3) Due to limited resources, all life forms struggle to survive, but only the superior ones survive. 4) Those individuals that possess some characteristic that are useful in adapting the environment increase their chances of survival, and produce more offspring with the favorable characteristic and pass them to the next generations. Due to the variations in characteristic and physical changes, the new individual will eventually become so distinct that they will constitute different specie.