As a result of many years of careful study and observations, Charles Darwin (1859) proposed his theory of evolution. He hypothesized that new species came about by a process called natural selection. In formulating his hypothesis, he assumed that
-Organism tends to increase in geometric ratio. Each generation of offspring produces more offspring than parent. So each generation should be larger than the one before, even with this, there was no evidence for an enormous population.
-He again assumed that population of any given specie remain constant except for minor fluctuations, he therefore concluded that a struggle for survival exists among many living organism i.e. a competition for food, space, water, light and other factors takes place and many organism do not survive the competition.