Briefly explain how Darwin formulated his theory of evolution by natural selection.

Darwin made four key observations in his studies of wild populations: members of a population of the same species vary in their traits; traits can be inherited, or passed from parents to offspring; populations are capable of producing more offspring than the environment can support; and, due to a lack of food or other resources, many of the offspring do not survive. From these observations, Darwin made two deductions which form the basis of his theory of evolution by natural selection: individuals whose inherited traits give them a higher chance of surviving and reproducing in their environment tend to leave more offspring than other individuals, and this unequal ability of individuals to survive and reproduce will lead to the accumulation of favourable traits in the population over many generations.