which relied little on fossils, accepted uniformitarianism which gives time for gradual changes, documenting the fact that evolution has occurred. who established that all of life have descended over time from , and proposed the that this of resulted from a process that he called . Asa Gray (1810-1888) American Botanist and major adviser and supporter of Darwin Moritz Wagner (1813-1887) German Naturalist and geographer Among the first to emphasize the benefit of geographical isolation to species formation; failed in convincing his contemporaries that geographical isolation was important for speciation Joseph Dalton Hooker (1817-1911) English Botanist and major adviser and supporter of Darwin Louis Pasteur (1822-1895) French Microbiologist who in 1859 drove the final nail in the coffin of spontaneous generation with his “swan necked flasks” demonstrating that bacteria in the air are necessary for sterile broth to spoil Alfred Russel Wallace (1823-1913) British spent 5 years in South America, 1848-1852; the ship he was on, Helen, burned on homeward voyage along with all of his work collected over the 5 years (1854-1862) explored the east indies contracted malaria in the indies dispersalist Wallace wrote letters to Darwin outlining his independent conception of
Ideas of artificial selection were in the air centuries before Darwin’s time. Darwin made enormous use of artificial selection in explaining his theory. Darwin was among the first to see the significance of small, continuous variations in Nature. Darwin grappled with how selection could get started, invoking the concept of Preadaptation. The writings of the Rev. Thomas Malthus showed Darwin and Wallace how limited resources could lead to competition for these resources. Competition would result in some individuals leaving more offspring than other individuals and those parents would be the ones best adapted to the current environment. Slowly, natural selection would increase the numbers of individuals best adapted to the resources and to the environment: survival of the fittest. Darwin saw that such slow change could lead to the origin of new species. Darwin placed his emphasis on mechanisms including` geographical isolation behavior and sexual selection as necessary for speciation. Darwin initially lacked a mechanism by which phenotypic changes could be inherited and so proposed a form of pangenesis without the support of data. Publication of the On the Origin of Species in 1859 revolutionized understanding of the relationships between organisms and how organisms arise and change through geologic time. On the Origin of Species initiated widespread public discussion concerning science and the place and role of science in society. Darwin elaborated an evolutionary mechanism – natural selection – but was not the first think about selection in relation to living organisms. Darwin continuously referred to natural selection and artificial selection through combinations of: The ease of effecting change via artificial selection, The vastness of geological time, The application of the geological principle of uniformitarianism by which present day processes could be extrapolated back in time, Identification of a natural selector – the pressure of continuously limited resources – and with brilliant intuition Many more individuals of each species are born than can possibly survive. Consequently, there is a recurring struggle for existence. Any individual that varies however slightly in any way that is advantageous will have a better chance of surviving, of being naturally selected, and of leaving offspring.