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)
Still, Darwin did not know about the basic laws of inheritance. It was the monk Gregor Mendel, who in 1865 published the results of his studies of genetic inheritance in garden peas. He showed that genetic material is inherited from both parents, independently of each other. And that each (diploid) individual thus carries 2 copies of the same gene, of which only 1 is passed on to their offspring. Which one is a result of chance (independent assortment). He also showed that these gene copies (alleles) can be dominant (only 1 copy determines the expression of the gene), recessive (2 copies are required for expression), or additive (a copy of both alleles result in an expression that is intermediate to that of having 2 copies of either of the alleles). These findings had no immediate impact on animal breeding and were not recognised as important until 1900.
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