In 1859, Charles Darwin (1809 – 1882) published his book 'On the origin of species', based on the findings that he collected during his voyage on 'the Beagle'. He discovered the forces of natural selection. He also concluded that the individuals that fit best in their environment have the highest chance to survive and reproduce: they are the fittest. Consequently, different environments result in different directions of selection pressure. He based this on his findings on the Galapagos islands, where finches on one island were different from finches on the next island. His conclusion was that the difference in food source, predators present, etc. between the islands had made the finches develop differently over very many generations. They adapted to their specific environments.
Darwin translated his ideas to domesticated species as well: "We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we see now them; indeed, in several cases, we know that this has not been their history. The key is man's power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him. In this sense he may be said to make for himself useful breeds" C. Darwin. On the Origin of species (1859, p.30)
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