Transcript Document
History of Evolutionary Thought
I. Early Ideas of Change
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the Greeks
II. Darwinian Revolution
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Intellectual environment pre-Darwin Change as a concept Darwin and contemporaries
III. Post Darwin
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Blending Inheritance Mendel Biometrics
IV. The Modern Synthesis
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Hardy-Weinberg Dobzhansky Haldane, Fisher, Wright Recent innovations
I. Early Ideas of Change A. Anaximander
-- 6th Century BC "Men first formed as fishes; eventually they cast off their fish skins and took up life on dry land."
B. Xenophanes
-- 6th Century BC recognized that fossils are the remains of organisms that once lived
I. Early Ideas of Change C. Empedocles
-- 5th Century BC – the father of the evolutionary idea
plants and subsequently animals rose from the earth
they arose as unattached organs and parts that joined together in haphazard fashion. Most conglomerates were freaks and monsters incapable of living, but occasionally a combination of organs appeared which could function as a successful living organism. These survived and reproduced.
I. Early Ideas of Change C. Empedocles Con’t.
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This bears elements that are still accepted, the first glimmerings of "survival of the fittest"
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included man in his ideas of formation
I. Early Ideas of Change
D. Aristotle -- 4th Century BC -- bit of a step back
maintained complete gradation in nature
lowest stage is inorganic
organic beings arise from inorganic by direct metamorphosis
(spontaneous generation, eg, flies from meat)
D. Aristotle -- 4th Century BC
first known organization of life, first tree of life although without limbs
Thinking then stood still for about 2000 yrs, most of the ancient Greeks forgotten, Christian belief of special creation dominated
II) DARWINIAN REVOLUTION
The intellectual environment in the 1600-1700's
Change as general concept
DARWINIAN REVOLUTION Con’t:
Plato and the "essence”
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Plato incorporated into Christian ideas
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the essence is the thing -- that which we have is not the true, but a reflection of the essence, VARIATION WAS MEANINGLESS the mean or the typical was the object
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the "essence" exists in the mind of god
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Extinction not possible, because extinction would be imperfect
DARWINIAN REVOLUTION
Scala Naturae (
the great chain of being)
Order is superior to disorder, complete gradation throughout life, without gaps, this translated into human society
to change the Order of life is unthinkable
the role of science was to catalogue the ladder, describe the adaptations by which organisms are so wonderfully suited to their functions ad majorem Dei gloriam (for the greater glory of God) (All of Linnaeus' work)
DARWINIAN REVOLUTION Con’t:
Change as general Concept
The Geologists
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Around the late 1700's, due to influence of astronomers, geologists began to question whether the earth was static (Catastrophism = creation.....flood......re-creation) or changing.
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Sedimentary rocks
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recognized that they had been laid down at different times
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Buffon (1779) suggested the world might be 168,000 yrs old!!! (Bishop of Usher mid 1800's declared the world created in 4004 BC)
Buffon
In 1753 raised the possibility that closely related species had developed from a common ancestor.
1766 all related organisms shared the same internal mold.
DARWINIAN REVOLUTION Con’t:
Change as general concept
James Hutton (1788) UNIFORMITARIANISM
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"same process responsible for both past and present events"
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implied very old age of earth, with "no vestige of a beginning -- no prospect of an end"
Charles Lyell (1830-1833)
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Principles of Geology Championed Uniformitarianism, but held a steady state view that could not admit biological evolution
DARWINIAN REVOLUTION Con’t:
Change as general concept
Jean-Baptiste Lamarck (1744-1829)
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Philosophie Zoologique (1809)
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Most important evolutionist (or "transformist") pre-Darwin
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Lineages persist indefinitely (ie, no such thing as extinction) but forms change from one into another. Lamarck's tree of life was unbranching
DARWINIAN REVOLUTION Con’t:
Lamarck…..(pre-Darwin)
Fossils were viewed as forms that had changed into something new, these were left from previous time
"Great alterations in the environment of animals lead to great alterations in their needs, and these alterations in their needs necessarily lead to others in their activities. Now if the new needs become permanent, the animals then adopt new habits which last as long as the needs that evoked them.
DARWINIAN REVOLUTION Con’t:
Lamarck…..(pre-Darwin)
Primary mechanism of change was "internal forces", an unspecified striving that caused individuals to produce offspring slightly different than themselves.
Nervous fluid
Inheritance of acquired characters, probably less important to Lamarck, was his downfall. Believed that through use, individuals modified their phenotype, these transformations would then be transmitted to offspring, and the whole lineage would transform through time. GIRAFFE EXAMPLE.
DARWINIAN REVOLUTION Con’t:
Lamarck…..(pre-Darwin)
Rather uncharismatic, clashed severely with GEORGES CUVIER, famous French anatomist, who championed the idea of fixity of species (eventually established that forms do go extinct). Cuvier believed that each species has a separate origin, is constant in form, then goes extinct. Essentially kept Lamarck from becoming popular in France.
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
One of the most biographied, and storied scientist ever, some of which make great reading.
A very wealthy family, child of 1st cousins, Sent to the best schools and highly educated.
From a family of educated people (Erasmus Darwin, Grandad, early transformationist thinker, poet, naturalist and physician). Went to Cambridge to study theology, then back to become physician, but spent most of his time shooting, collecting beetles
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
palled around with J. S. Henslow, Botany prof at Cambridge, who got him on board the HMS Beagle as ship naturalist. Spent 5 yrs touring through South America, Galapagos collecting and describing.
This voyage often pointed to as convincing him of evolution, but in truth, his realizations came after return. He had seen much and it certainly prepared him to change his ideas, but the actual events came after his return to England in 1836
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
One of the first events was the identification of Galapagos mockingbirds (not finches) as different species on each island. He had noted resemblance to mainland forms, but this identification by John Gould caused him to doubt the fixity of species.
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
He still had no concept of a mechanism, that which he is now famous for.
The key event appears to be the reading of Malthus' (1798) Essay on the Principle of Population which argued that unchecked growth would lead to famine and destruction of the human race.
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In his autobiography "I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animal and plants, it at once struck me that under these circumstances favorable variations would tend to be preserved and unfavorable ones to be destroyed."
DARWINIAN REVOLUTION Con’t:
CHARLES DARWIN (1809-1882)
This was the key element to his theory of modification by descent. He sat on it for another 20 yrs, publishing monumental works on worms, molds, orchids, etc. but only in 1856 started writing his "big book".
Artificial selection by breeders, especially pigeons and cattle could produce almost any form, basic concept was the same as his idea of preservation of favorable variations
DARWINIAN REVOLUTION Con’t:
Alfred Russell Wallace (1823-1913)
Absolute opposite of Darwin. Grew up in large family, father died, very poor, but was a rabid naturalist. He traveled primarily in Malaysia, Amazonia, and financed trips through collecting and selling specimens to wealthy Brit. collectors. Spent his whole life in and out of financial ruin (eg, one boat burned on way back from Amazonia with 7 yrs of collections)
Simultaneously arrived at natural selection as a process (1858) during a malarial fever delirium in Indonesia. The vision came to him, he wrote it down (after getting stronger) in a few pages and sent it to Darwin to review .
DARWINIAN REVOLUTION Con’t:
Darwin sent this and abstracts of his own work to Charles Lyell and his friend Joseph Hooker who urged him to present the manuscripts to the Linnaean Society of London. He did, they received little reaction, but then he published an abstract of his ideas in 1859 "The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life"
DARWINIAN REVOLUTION Con’t:
Two Basic Tenets (in Origin…)
all organisms descended with modification from common ancestors
chief agent of modification is natural selection on variation. This was the first tree of life with branches, the first with a precise mechanism, and the first to emphasize variation as elemental
DARWINIAN REVOLUTION Con’t:
The influence of Malthus:
read by both Darwin and Wallace
emphasized exponential growth in populations
DARWINIAN REVOLUTION Con’t:
Ex. of Exponential Growth and Its Potential Role in Selection…
Wallace: 1 pair birds produces 4 young per year
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each pair produce 4 times in a life
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15 years each pair produces 10 million birds
Darwin: Elephant lives 100 yrs, produces about 6 progeny between 30-90
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1 pr produces 19 million in 750 yrs if all offsp. reproduce
DARWINIAN REVOLUTION Con’t: Brodie: 2 Bullfrogs-----50,000 eggs/life (frog = .5 lb; egg mass=25 cm2) if 10 survive (.02%)...........250,000 eggs if .02% surv. (50 frogs).......1,250,100 eggs 250 frogs.......6,250,000 eggs (4th generation) by 10th gen. 19,531,250......~500 billion eggs which is about 2 sq km of egs and about 10,000 (9,866 tons) of frog
DARWINIAN REVOLUTION Con’t:
Natural Selection
4 elements as described by Darwin and Wallace
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Variation
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Over reproduction
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Some variations advantageous, some deleterious
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Individuals with advantageous variations leave more offspring than others, thus give rise to next generation
DARWINIAN REVOLUTION Con’t:
Natural Selection
(by Darwin and Wallace)
Did not incorporate any element of inheritance, taken for granted that parents produce like offspring
DARWINIAN REVOLUTION Con’t:
Afterwards.....
Darwin became an invalid and a recluse, never got used to the criticism but continued to write. Took every criticism of his theories to heart. Did not completely abandon his Deism until death of his daughter at about age 5.
Wallace continued to travel and collect, always had the utmost respect for Darwin, and tended to give him all the credit (Wallace's version had only one example, Darwin's literally thousands), Became increasingly interested in the occult and eventually wrote on mysticism and traveled the world attending séances......
III. Post Darwin (Blending Inheritance )
Most biologist of Darwin's day accepted BLENDING INHERITANCE, assuming that the stuff of inheritance was some sort of fluid, which when mixed together produced an average between parents.
Fleeming Jenkin, critic of Darwin, pointed out that selection could not sort out a superior liquid from a mixture, one of the most damning criticisms.
Post Darwin
B. Mendelian inheritance
Gregor Mendel (Czech Monk) performed experiments demonstrating particulate inheritance in mid 1800's but they were unknown until "rediscovered" by De Vries and Tschermak
Initially a great blow, because characters that are controlled by one or a few loci exhibit discrete variation -- differences between genotypes was too big to fit into Darwin's theory
Post Darwin
Biometricians
Karl Pearson, August Weismann, Francis Galton were demonstrating that most genes have only small effect, and that most variation is continuous
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(eg, body size, speed, vs eye color) this fit fine into Darwinian theory
The MODERN SYNTHESIS
Again around the 1930's, Natural Selection and gradual evolution started to come back into vogue, primarily through the efforts of a few geneticists responsible for what is now called the New Synthesis or Neo Darwinian theory.
Primarily combines genetics, mathematics and evolutionary theory into a set of ideas called population genetics
The MODERN SYNTHESIS
Hardy-Weinberg (-Castle) theorem
A demonstration that frequencies of genes do not change from one generation to the next if all members mate at random and there is no advantage to any gene. This is the foundation of all population genetics, because by adding terms for selection and migration, it can be shown that gene frequencies do change in the face of very weak forces.
The MODERN SYNTHESIS
Theodosius Dobzhansky
(1900-1975)
With fruitflies, revealed hidden genetic variation and demonstrated that the differences between races and species were genetic --- led to the understanding that species are not "morpho types" but variable populations that are reproductively isolated from one another
One of the main fathers of the New Synthesis, by combining genetics with the more established views of evolutionary process
The MODERN SYNTHESIS
Other Major Players
JBS Haldane: drinker, brawler, and theoretician
famous quotes: “the creator had an inordinate fondness for beetles" "I would not save a man from drowning, but I would save 2 brothers, or eight cousins" (in reference to average relatedness)
The MODERN SYNTHESIS
Other Major Players
Sewall Wright: used Guinea pig as eraser, worked on polydactyly and coat color in guinea pigs, intimidating mathematician, pioneer in multivariate approaches to evolution, Shifting balance theory of maintenance of variation
R. A. Fisher: competing mathematician and father of linear statistics (Regression); "The Genetical Theory of Natural Selection"
Tenets of the Synthesis
See Page 26-27 in Futuyma
Recent Challenges or Innovations
Cladistics -- Willi Hennig, a new and more rigorous means of approaching questions of relationship founded on a specific model of evolution including parsimony
Neutral Theory -- Mootoo Kimura, suggested that most evolution is neutral and has no effect on the phenotype, based on the idea that most DNA does nothing
Recent Challenges or Innovations
Punctuated equilibrium -- Stephen Jay Gould & Niles Eldridge, later Stephen Stanley; motivated by observation that fossil record tends to reflect a less continuous change than expected by gradual change. Referred to by some as evolution by jerks. Non-constant mode and rate of evolution, at times suggested that most evolutionary change occurs at level of species-selection
Recent Challenges or Innovations
Group selection
-- Wynne-Edwards, Rensch, rescued by Wilson, Wade: units other than the individual are the unit of selection and evolutionary change