What is the mechanism for evolution proposed by Darwin?

The mechanism for evolution proposed by Darwin is natural selection. It occurs when individuals with heritable traits that improve survival or reproduction leave more offspring than individuals without those advantages.

Darwin developed the idea after observations from the 1831–1836 voyage of HMS Beagle and after reading Thomas Malthus’s 1798 argument that populations can grow faster than their food supplies. He published the theory in On the Origin of Species in 1859, describing natural selection as the preservation of useful variations during the struggle for existence.

Natural selection requires variation, inheritance, and differences in reproductive success. It is not a conscious force and does not mean that the physically strongest individual always survives; in biology, “fitness” primarily means reproductive success. Mutation creates some variation, while genetic drift can also change populations, but those are not interchangeable with natural selection.

Darwin contrasted natural selection with artificial selection, in which humans deliberately breed plants or animals for chosen traits. Alfred Russel Wallace independently developed the same mechanism, and their work was presented jointly in 1858.