Darwin I. Pre-Darwinian Scene II. Darwin s Contribution to Evolutionary Theory III. Refinement of Darwin s Theory Evolution was an Old Idea Darwin is supposed, by those who have not read him, to be the man who thought of evolution and who said that men were descended d d from monkeys. Neither notion is even half true. William Howells, 1949 [Source: Mankind So Far, American Museum of Natural History Series, Vol, 5, Doubleday, Garden City, NY] Darwin s Ideas Species are not fixed. Descent with modification Evolution is gradual. Natural selection Erasmus Darwin Anaximander Lamarck Could one not say that, in the fortuitous combinations of the productions of nature, as there must be some characterized by a certain relation of fitness which are able to subsist, it is not to be wondered at that this fitness is present in all the species that are currently in existence? Chance, one would say, produced an innumerable multitude of individuals; a small number found themselves constructed in such a manner that the parts of the animal were able to satisfy its needs; in another infinitely greater number, there was neither fitness nor order: all of these latter have perished. Animals lacking a mouth could not live; others lacking reproductive organs could not perpetuate themselves... The species we see today are but the smallest part of what blind destiny has produced... Maupertuis Matthew Pierre Louis Maupertuis (Venus Physique,1745) 1
Darwin Lyell Wallace Mendel Catastrophism Believed all species were created by God (in 6 days) Georges Cuvier (1769-1832) Earth was very young (6,000 years old) Extinctions were caused by local catastrophes Species are immutable Voyage of the Beagle The Mount at Shrewsbury Birthplace of Charles Darwin (February 12, 1809) Captain Fitzroy 2
The Myth of the Naturalist Voyage of the Beagle a polite fiction to explain his guest s presence and an activity attractive enough to lure a gentleman on board for a long voyage. H. L. Burstyn, 1975 [Source: British Journal of the History of Science 8, 62-69] Remains of the Cathedral of Concepcion, in Chile, after the Earthquake of 1835 The Giant Sloth (Megatherium) Darwin collected and catalogued countless specimens. 3
Voyage of the Beagle Ground finch Cactus finch Galapagos Islands Woodpecker finch As for Darwin s supposed insight into evolution by adaptive radiation while he was still in the Galapagos, the more the various species of finch exhibited this remarkable phenomenon, the more Darwin mistook them at the time for the forms they were mimicking. Frank Sulloway, 1982 [Source: Journal of the History of Biology 15, 1-53] 4
the tortoises differed from the different islands, and that he [Vice-governor of the Galapagos] could with certainty tell from which island any one was brought. I did not for some time pay sufficient attention to this statement, and I had already partially mingled together the collections from two of the islands. Charles Darwin, 1845 Beagle Voyage Down House at Downe in Kent Home of Charles Darwin (1842-1882) 1882) Darwin Gleans from Malthus Man is abundantly fertile. The world does not contain enough resources to satisfy man s needs. Human population is controlled by disease, famine, and war. Thomas Malthus Believing that is always best to study some special group, I have, after deliberation, taken up domestic pigeons. I have kept every breed which I could purchase or obtain. 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. Charles Darwin, 1859 Alfred Russel Wallace (1823-1913) 1913) Wallace traveled extensively about the world collecting biological specimens. In 1855, he published ideas that were dangerously close to natural selection. In 1858, Darwin received an essay by Wallace that was specifically focused on evolution by natural selection. 5
Charles Lyell presents both Darwin s and Wallace s work at the meeting of the Linnaean Society (July 1, 1858) Genes for Eye Color in Drosophila Red eyes = heterozygous -ORhomozygous dominant White Eyes = homozygous recessive Mendel s garden Gregor Johann Mendel (1822-1884) 1884) 6
Summary Darwin s theory of evolution by natural selection and Mendel s theory of inheritance transformed our understanding of life. Darwin had not set out to discover the mechanism for evolution; rather, he was provided unique opportunities to observe an overwhelming amount of evidence. In Darwin s case, chance favored the prepared mind. However, numerous individuals played key roles in Darwin s realization that species evolved by natural selection. 7