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DarwinDarwinDarwinDarwin

I. PreI. Pre--Darwinian SceneDarwinian Scene

II Darwin’s Contribution toII Darwin’s Contribution toII. Darwin s Contribution to II. Darwin s Contribution to Evolutionary TheoryEvolutionary Theory

III. Refinement of Darwin’s TheoryIII. Refinement of Darwin’s Theory

Darwin is supposed, by those who have not read Darwin is supposed, by those who have not read him, to be the man who thought of evolution and him, to be the man who thought of evolution and

h id h d d d f kh id h d d d f k

Evolution was an Old Idea

who said that men were descended from monkeys. who said that men were descended from monkeys. Neither notion is even half true.Neither notion is even half true.

William Howells, 1949William Howells, 1949

[Source: Mankind So Far, American Museum of Natural History Series, Vol, 5, Doubleday, Garden City, NY[Source: Mankind So Far, American Museum of Natural History Series, Vol, 5, Doubleday, Garden City, NY]

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Darwin’s IdeasDarwin’s Ideas

•• Species are not fixed.Species are not fixed.

D t ith difi tiD t ith difi ti•• Descent with modificationDescent with modification

•• Evolution is gradual.Evolution is gradual.

•• Natural selectionNatural selection

AnaximanderAnaximander LamarckLamarck

MatthewMatthewMaupertuisMaupertuis

Erasmus DarwinErasmus Darwin

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 p yneeds; 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.....

Pierre Louis Pierre Louis MaupertuisMaupertuis ((Venus Physique ,1745) 1745)

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Darwin Lyell

MendelWallace

• Believed all species werecreated by God (in 6 days)

• Earth was very young

Catastrophism Georges Cuvier(1769-1832)

Earth was very young(6,000 years old)

• Extinctions were causedby local catastrophes

• Species are immutable

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The Mount at ShrewsburyThe Mount at ShrewsburyBirthplace of Charles DarwinBirthplace of Charles Darwin

(February 12, 1809)(February 12, 1809)

Voyage of the Beagle

Captain FitzroyCaptain Fitzroy

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… a polite fiction to explain his guest’s presence and an activity attractive enough to lure a

The Myth of the Naturalist

and an activity attractive enough to lure a gentleman on board for a long voyage.

H. L. Burstyn, 1975H. L. Burstyn, 1975

[Source: British Journal of the History of Science 8, 62-69]

Voyage of the Beagle

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Remains of the Cathedral of Concepcion, in Chile,Remains of the Cathedral of Concepcion, in Chile,after the Earthquake of 1835after the Earthquake of 1835

The Giant Sloth (The Giant Sloth (MegatheriumMegatherium))

Darwin collected and catalogued countless specimens.Darwin collected and catalogued countless specimens.

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Voyage of the Beagle

GalapagosIslands

Cactus finchGround finch

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, 1982Frank Sulloway, 1982

[Source: Journal of the History of Biology 15, 1-53]

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… the tortoises differed from the different islands, … the tortoises differed from the different islands, and that he and that he [Vice[Vice--governor of the Galapagos] governor of the Galapagos] could could with certainty tell from which island any one was with certainty tell from which island any one was brought. brought.

I did not for some time pay sufficient attention to this I did not for some time pay sufficient attention to this statement, and I had already partially mingled statement, and I had already partially mingled together the collections from two of the islands.together the collections from two of the islands.

Charles Darwin, 1845Charles Darwin, 1845Beagle VoyageBeagle Voyage

Down House at Downe in KentDown House at Downe in KentHome of Charles Darwin (1842Home of Charles Darwin (1842--1882)1882)

• Man is abundantly fertile.

• The world does not contain enough resources to satisfy

Darwin Gleans from MalthusDarwin Gleans from Malthus

Thomas MalthusThomas Malthus

enough resources to satisfy man’s needs.

• Human population is controlled by disease, famine, and war.

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Believing that is always best to study some special Believing that is always best to study some special group, I have, after deliberation, taken up domestic group, I have, after deliberation, taken up domestic pigeons. I have kept every breed which pigeons. I have kept every breed which I could purchase or obtain.… I could purchase or obtain.…

The key is man's power of accumulativeThe 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, 1859Charles Darwin, 1859

Alfred Russel WallaceAlfred Russel Wallace(1823(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.

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Charles Lyell presents both Charles Lyell presents both Darwin’s and Wallace’s work at Darwin’s and Wallace’s work at

the meeting of thethe meeting of theLinnaean SocietyLinnaean Society

(July 1, 1858)(July 1, 1858)

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Gregor Johann MendelGregor Johann Mendel(1822(1822--1884)1884)

Mendel’s gardenMendel’s garden

Genes for Eye ColorGenes for Eye Colorin in DrosophilaDrosophila

Red eyes = heterozygous

-OR-

homozygous dominant

White Eyes = homozygous recessive

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SummarySummary

• 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• 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.