Editing Thomas Hunt Morgan (section)

==Morgan and evolution==
Morgan was interested in evolution throughout his life. He wrote his thesis on the phylogeny of sea spiders ([[pycnogonids]]) and wrote four books about evolution. In ''Evolution and Adaptation'' (1903), he argued the anti-Darwinist position that selection could never produce wholly new species by acting on slight individual differences.<ref>{{cite book |first=Garland E. |last=Allen |editor1-first=Michael |editor1-last=Ruse |editor2-first=Joseph |editor2-last=Travis |year=2009 |title=Evolution. The First Four Billion Years |publisher=Harvard University Press |page=[https://archive.org/details/evolutionfirstfo00mich/page/746 746] |isbn=9780674031753 |url-access=registration |url=https://archive.org/details/evolutionfirstfo00mich/page/746 }}</ref> He rejected Darwin's theory of sexual selection<ref>"I think we shall be justified in rejecting it as an explanation of the secondary sexual differences amongst animals", pp. 220–221, chapter VI, ''Evolution and Adaptation'', 1903.</ref> and the Neo-Lamarckian theory of the inheritance of acquired characters.<ref>Chapter VII of ''Evolution and Adaptation'', 1903.</ref> Morgan was not the only scientist attacking natural selection. The period 1875–1925 has been called '[[The eclipse of Darwinism]]'.<ref>{{cite book |first=Peter |last=Bowler |year=2003 |title=Evolution. The History of an Idea |publisher=University of California Press |at=chapter 7 }}</ref> After discovering many small stable heritable mutations in ''Drosophila'', Morgan gradually changed his mind. The relevance of mutations for evolution is that only characters that are inherited can have an effect on evolution. Since Morgan solved the problem of heredity (1915), he was in a unique position to examine critically Darwin's theory of natural selection.

In ''[[s:A Critique of the Theory of Evolution|A Critique of the Theory of Evolution]]'' (1916), Morgan discussed questions such as: "Does selection play any role in evolution? How can selection produce anything new? Is selection no more than the elimination of the unfit? Is selection a creative force?" After eliminating some misunderstandings and explaining in detail the new science of Mendelian heredity and its chromosomal basis, Morgan concludes, "the evidence shows clearly that the characters of wild animals and plants, as well as those of domesticated races, are inherited both in the wild and in domesticated forms according to the Mendel's Law". "Evolution has taken place by the incorporation into the race of those mutations that are beneficial to the life and reproduction of the organism".<ref>'' A Critique of the Theory of Evolution'', Princeton University Press, 1916, pp. 193–194</ref> Injurious mutations have practically no chance of becoming established.<ref>''A Critique of the Theory of Evolution'', p. 189.</ref> Far from rejecting evolution, as the title of his 1916 book may suggest, Morgan, laid the foundation of the science of genetics. He also laid the theoretical foundation for the mechanism of evolution: natural selection. Heredity was a central plank of [[Charles Darwin|Darwin]]'s theory of natural selection, but Darwin could not provide a working theory of heredity. [[Darwinism]] could not progress without a correct theory of genetics. By creating that foundation, Morgan contributed to the [[Neo-Darwinism|neo-Darwinian]] synthesis, despite his criticism of Darwin at the beginning of his career. Much work on the Evolutionary Synthesis remained to be done.