Last day… overview of what the course will cover,
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Transcript of Last day… overview of what the course will cover,
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Last day… overview of what the course will cover, started discussing historical development of
evolutionary thinking
- idea of evolution had been debated, but generally rejected
Buffon Erasmus Darwin Saint Hilaire Lamarck
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Charles Darwin
- provided evidence that evolution had occurred- first to develop a theory to explain how & why
evolution happens
Glyptodon
- left him last day on voyage of the Beagle (1832-36)
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4 spp. ofmockingbirdsfrom Galapagos
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What patterns of distribution would be expected if species are independently created (as opposed to what is expected if species are related by descent from a common ancestors)?
a) very similar species will be expected in similar habitatseven if on different continents
b) species in very different habitats will be very different,even if the habitats are geographically close
c) different species will be found on opposite sides of geographic barriers, even if the habitats are similar
d) endemic species on islands will be closely similar to those of the nearest continent
e) species will be found in environments that they are welladapted to
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- influence of geological theories Lyell: Uniformitarianism: geological patterns created by presently observable forces, ancient history of the earth
Charles Lyell: 1797-1875
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Started notebook (1837) to record ideas Many facts suggested evolution, but needed a theory...
- must produce change
- must account for adaptation
- must explain speciation
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Inspiration from Thomas Robert Malthus (1798)
- population growth will always tend to outrun food supply
- immediately suggested natural selection
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Darwin’s insight in 1838 - quickly developed this into theory explaining how all living things evolved into their diverse forms
and then... silence
"is the most powerful and the most comprehensive idea that has ever arisen on earth. It helps us understand our origins ... We are part of a total process, made of the same matter and operating by the same energy as the rest of the cosmos..." (Sir Julian Huxley)
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Who mailed the paper to Darwin?
a) Robert FitzRoyb) Thomas Henry Huxleyc) Alfred Russell Wallace d) Sir Charles Lyelle) Samuel Wilberforce
Delayed publishing - started outline 1842
…until he received a paper in 1858 outlining natural selection
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Friends arranged for joint reading of papers at Linnean Society - Darwin published ‘The Origin of Species’ in late 1859
Wallace’s paper stunned Darwin…
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Darwin & Wallace disagreed on many issues regarding the details of HOW natural selection would work, butboth were convinced that it was the primary mechanismby which evolution occurred
Wallace: 1823-1913Darwin: 1809-1882
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Basic outline of Darwin’s theory:
1. Individuals within a species differ in morphology, physiology, & behavior
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2. Some of this variation is heritable
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3. Organisms have a huge capacity for increase in numbers, but populations tend to remain +/- constant
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4. As a result of competition, some variants will leave more offspring than others
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5. If reproductive success is due to the varying trait, and that trait is heritable, it will be passed on to the offspring and become more common in the next generation
(Thus evolutionary change by natural selection)
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‘Origin’ controversial among public - human descent from apes stressed
Among many scientists, concept of evolution was largely accepted
Much supporting evidence collected from paleontology, morphology, etc. to establish the fact of evolution
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Mechanism of natural selection was not viewed as favorably - many doubted its power to produce evolution
Later, more serious objections e.g. about nature of heredity... do traits blend together in offspring?
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Is it a problem for Darwin’s theory if inheritance works by blending (e.g. tall parent & short parent producekids of medium height)?
a) yes, it will remove the potential for variationb) no, it does not affect the potential for natural selection as
best adapted individuals still leave the most offspring
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...and doubts about the age of the earth- Lord Kelvin estimated about 100 million years,
based on cooling of earth
Ooops. Didn’t know radioactivity continues to heat earth
What did Kelvin leave out of his calculations?
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Darwin’s arguments for evolution & natural selection
Variation in domesticated forms: - great variation in animal breeds & cultivated plants
- deliberate selection to modify varieties
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Variation in species in nature: - pointed to variation in individual traits (even in
‘important’ organs)- difficulty classifying: varieties vs. species
Eastern Screech-Owls
barnacles (Semibalanus)
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Increase in numbers and competition:- calculated expected # of offspring if all survive- gave examples of increase for plants & animals
introduced to new areas
Ox-eye Daisies
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Geological succession: - new species occur at intervals- ‘modern’ species may be found among extinct forms- intermediate forms between orders found- older forms differ more from modern species
trilobite
- fossils belong to same groups as modern species in same area
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Geographical distribution:- species isolated by strong barriers tend to be distinct,
though physical conditions are similar
Indigo Bunting Lazuli Bunting
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- species in the same area are related, even if occupying different habitats
Eastern Gray Kangaroo
Lumholtz’sTree Kangaroo