Starting with the Malthusian struggle for existence, Darwin argued that successful organisms in life's battles will tend to differ from the unsuccessful. There will thus be a 'natural selection' of the 'fittest' - the successful giraffe will have a longer neck than the unsuccessful giraffe. It was Darwin's claim that, over time, this will lead to significant permanent change. Darwin, however, had no adequate theory of heredity. This gap was filled in the twentieth century by the new science of genetics, which itself dates back to the middle of the nineteenth century and the ideas of Darwin's then unknown contemporary the monk Gregor Mendel.
Evolution raises questions of considerable philosophical interest and much controversy.
Most obviously, there are matters to do with the science itself. Comments of this ilk play on an equivocation on the word theory . If one is asking whether evolution as such is well established, then this is a matter beyond reasonable doubt. Palaeontology, biogeography, embryology, anatomy, and more all point to evolutionary origins. But if one is asking about a particular theory, then serious debate continues.