Answer:
Natural selection was proposed by Darwin.
Step-by-step explanation:
He stated that when the limiting factor exist then different species of organism have to compete with each other and the species that is able to survive the competition stays and adapt themselves according to the condition.
Darwin studies natural selection in birds of Galapagos island. He must have faced difficulties and they are: complex environment is difficult to study, it may take longer to study different generations of a population and the birds may be dependent on other species that also might have evolved.