Our current views on evolution in plants are firmly rooted in Darwin's theory of evolution by natural selection. Before Darwin and Wallace formulated their concept of evolution, it was assumed that species had been individually created in a single act of Special Creation. They fitted perfectly their environment, and any deviations in morphology that occurred were the result of accident. Species were essentially unchanging and unchangeable ‘ideal types’. Moreover, the world had been created very recently. Thus, by counting scriptural generations, Archbishop Ussher came to the conclusion that the Earth originated in 4004 BC (Mayr, 1991, 16).

The first critical appraisals of Special Creation predated Darwin's theory of evolution (Briggs & Walters, 1997), but Darwin provided the most formidable challenge to the former orthodoxy, by suggesting not only a plausible mechanism of evolution but also by assembling a wide array of evidence. The naturalist Wallace independently arrived at the concept of natural selection, but with different emphases (Sheppard, 1975). In 1858, before Darwin had published his ideas, Wallace sent him an essay on evolution by natural selection. The question of priority was resolved by Darwin's friends, who arranged a meeting at the Linnean Society of London in July 1858 at which Wallace's essay was presented and Darwin's ideas were represented by unpublished extracts from his writings. Then, over the next few months, Darwin (1901) wrote an extended account of his work: On The Origin of Species by Means of Natural Selection. The main strands of the concept are as follows.