Intro to evolutionary thoughtsummer10

Intro to evolutionary thoughtsummer10 - 1. Why are there so...

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Unformatted text preview: 1. Why are there so many kinds of organisms? 1. 2. Why do organisms appear to be well-designed? Scala naturae from Charles Bonnet (circa 1760) • M an • Monkeys • Q uadrapeds ( mammals) • Bats • Ostrich • Birds • Aquatic birds • Flying fish • Fish • Eels • Sea serpents • Reptiles • Slugs • Shellfish • Insects • Worms • Polyps (hydras) • Sensitive plants • Trees • Shrubs • Herbs • Lichens • Mold • Minerals • Earth • Water • Air • Ethereal matter Non-evolutionary attempts to organize nature: ladders of life Being Realm of Being God Angels Demons Man Realm of Becoming Woman Animals Minerals Sea lions? Whales? Non-Being Nagging questions in the mid to late 1700’s: Nagging 1. Why do organisms appear to be designed? Why do organisms resemble each other, even in their underlying features? 2. Where do new species come from? 3. Why do organisms resemble each other, even in their underlying features? • An unknown designer or creator with limited creativity O R... • Shared ancestry and inheritance (homology) Does correspondence among parts reflect... • A divine plan OR • D escent from a shared ancestor (HOMOLOGY) Homology/shared ancestry vs. “divine plan” Homology/shared vs THE ARGUMENT FOR COMMON DESCENT (HOMOLOGY) Fi sh p Am hi an bi s M am l ma s Tu r s t le Li za s rd +S na ke s od ile s Cr oc Bi rd s Acanthostega, a stem tetrapod from the Devonian (≈ 365 mya) Nagging questions in the mid to late 1700’s: Nagging 1. Why do organisms appear to be designed? Vestigial organs: why do organisms have them? Ear muscles 2. Where do new species come from? 3. Why do organisms resemble each other, even in their underlying features? • An unknown designer or creator with limited creativity O R... • Shared ancestry and inheritance (homology) 4. Why do organisms have vestigial structures? • Evolutionary relicts (organisms are built on their ancestor’s body plans) O R • Undiscovered function Vermiform appendix Answer: historical baggage/evolutionary legacy Vestigial organs: why do organisms have them? Vestigial organs: why do organisms have them? Vestigial hindlimbs in whales Ear muscles Vestigial hindlimbs in boas and pythons Vestigial organs: why do organisms have them? Vestigial Vestigial wings in crane flies Nagging questions in the mid to late 1700’s: 1. Why do organisms appear to be designed? 2. Where do new species come from? 3. Why do organisms resemble each other, even in their underlying features? • An unknown designer or creator with limited creativity O R... • Shared ancestry and inheritance (homology) 4. Why do organisms have vestigial structures? • Evolutionary relicts (organisms are built on their ancestor’s body plans) O R • Undiscovered function 5. Why do organisms sometimes seem to be so badly designed? • Evolutionary legacy OR • A cruel designer or creator Bad design in nature: Is a creator cruel, or evidence of evolution? A tradeoff, perhaps? ORGANIC EVOLUTION DEFINED All living things have developed from pre-existing common ancestors •So, how do evolutionary lineages evolve so that organisms are adapted to their environments? Lamarck’s Proposal Lamarck 1. Principle of use & disuse • Disuse → vestigial organs • Use → A DAPTATION 2. Inheritance of acquired (through use & disuse) characteristics • Evolutionary change through time/across generations Inheritance of acquired characters??? Jean-Baptiste de Lamarck (1744-1829) Charles Robert Darwin (12 Feb. 1809-19 April 1882) Voyage of the Beagle (1831-1836): “It was not the best of boat journeys.” 1816 1860 1880 The word from John Gould: The mockingbirds were different The species, and each species lived on a different island. Darwin’s 1st breakthrough in 1837: representing evolution as genealogical change (a branching tree) A page from Darwin's Notebook B showing the first evolutionary tree diagram. Darwinian descent with modification: a tree • Elegant explanation for vestigial characters: • You get them from your ancestors • Elegant explanation for bad design in nature: • What your ancestors have determines what you have • In 1838, Darwin read Malthus’ (1798) Essay on the Principle of Population and basically understood the “struggle for existence” in ALL organisms (not just humans). Famine, disease, space & other resources eventually limit all populations But, what causes “good design”/adaptation? But, “If you accept that natural traits are variable, that variation is heritable and that there is a struggle for existence, evolution by natural selection must follow.” - Charles Darwin • Observation 1: Populations should increase exponentially if all offspring survived to reproduce (from M althus) Some observations that led to three inferences: • Observation 4: The individual members of a species always phenotypically differ • Observation 5: Offspring tend to resemble their parents Some of the resemblance is due to inherited factors Some is due to shared environments •INFERENCE 2: The best competitors win in the struggle for existence. There are predictable and STABLE differences in the There S TABLE traits possessed by those who do and those who do not survive. THERE IS DIFFERENTIAL SURVIVAL & HEREDITY! • Observation 2: Populations do NOT increase exponentially: they remain at a relatively constant size • Observation 3: Limited availability of resources, predation, or disease control population size: Most offspring do NOT survive. •INFERENCE 1: There is a “struggle” for existence INFERENCE due to excess fecundity • Observation 6: New and stable “varieties” with desirable qualities can be created by artificial selection (This was a rtificial HUGE in Darwin’ s argument!) <5,000 years of evolution by artificial selection (gets you broccoli, cabbage, sprouts, kale!) Wild “cabbage” 10,000 years of evolution by artificial selection (gets you a Chihuahua from a wolf) Artificial selection on pigeons: why not make it natural? Exhibition Fantail • Observation 6: New and stable “varieties” with desirable qualities can be created by artificial selection a rtificial • INFERENCE 3: Heritable traits that enhance survival and reproduction in nature will increase in frequency in the population through time THIS LEADS TO ADAPTATION Jacobin Mealy Horseman Pouter Volga Tumbler Adaptation is a process (by which changes in the relative frequencies of different phenotypes and genotypes in a population accumulate) Adaptation is also a state of being that describes a trait that increases an organism’s fitness (or reproductive success) Jacobin A formal statement of the conditions for natural selection: Individuals within a population must vary p henotypically. Individuals pass on at least some of their traits to their offspring: INHERITANCE Individuals with different traits differ in their survival or reproductive success The crisis of 1857-58: Alfred Russel Wallace C. DARWIN to A.R. WALLACE Down, Bromley, Kent, May 1, 1857. My dear Sir,—I am much obliged for your letter of Oct. 10th from Celebes, received a few days ago: in a laborious undertaking, sympathy is a valuable and real encouragement. By your letter, and even still more by your paper in the Annals,28 a year or more ago, I can plainly see that we have thought much alike and to a certain extent have come to similar conclusions. In regard to the paper in the Annals, I agree to the truth of almost every word of your paper; and I daresay that you will agree with me that it is very rare to find oneself agreeing pretty closely with any theoretical paper; for it is lamentable how each man draws his own different conclusions from the very same fact. This summer will make the twentieth year (!) since I opened my first notebook on the question how and in what way do species and varieties differ from each other. I am now preparing my work for publication, but I find the subject so very large, that though I have written many chapters, I do not suppose I shall go to press for two years. The Outcome = NATURAL SELECTION Traits that are heritable and that enhance survival and Traits reproduction relative to other members of the population will reproduction r elative increase in frequency from generation-to-generation, so long as a particular selective regime persists. Alfred Russel Wallace (1823-1913); photo taken when he was 25 “The Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Existence” 1859 THE BOOK THAT CHANGED THE WORLD: THE ...
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