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Transcript
12/19/13 Why is Evolution So Controversial? Descent with Modification ! Darwinian View of Life ! Chapter 22 Often evolution (and science in general) is pitted against religion in “winner take all” stance Modern debate mostly involves the teaching of evolution rather than the theory itself ! ! 3 Key Observations About Life 1. Organisms are suited for life in their environments. 2. Organisms share many characteristics of life (unity). Plenty of misconceptions and confusion surround evolution, adding to controversy Endless Forms Most Beautiful • • 3. There is a rich diversity of life. These observations led Charles Darwin to develop a scientific explanation for these observations. And that means mixing science, religion and politics, etc.---Never an easy combination! Study of biology upended in 1859 when Darwin published The Origin of Species Darwin proposed: Descent with modification • • Species are descendants of ancestral species which were different from present day species Evolution: change in genetic composition of population from generation to generation 1 12/19/13 Intellectual Context of Darwin’s Ideas Summary of Other Ideas Many scientists before and during the time of Darwin theorized on what was the cause of the unity and diversity of living organisms • 1809 Lamarck publishes his hypothesis of evolution. 1798 Malthus publishes Essay on the Principle of Population. 1790 Some ideas supported Darwin’s theories while some did not • 1812 Cuvier publishes his extensive studies of vertebrate fossils. 1795 Hutton proposes his principle of gradualism. 1830 Lyell publishes Principles of Geology. 1809 Charles Darwin is born. 1831-36 Darwin travels around the world on HMS Beagle. 1858 While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection. 1870 1859 On the Origin of Species is published. 1844 Darwin writes his essay on descent with modification. The Galápagos Islands Not in Darwin’s “Camp” • Aristotle viewed species as unchanging • • Arranged them on a scala naturae, ladder of permanent “rungs” Linneaus: Developed taxonomy and the binomial classification system • Believed in a divine placement of organisms in this classification, not necessarily changing either Lamarck’s Hypothesis of Evolution • Other scientists were thinking about life forms evolving over time • Lamarck hypothesized: • • Use and disuse of body parts could change organisms over their lifespan These changes could be passed to offspring by Inheritance of Acquired Characteristics • Cuvier (geologist): Founded of modern paleontology (study of fossils) • • Saw that fossils are deposited in strata (layers) of rocks with older layers containing fossils of species that may be extinct now Believed in catastrophism, the sudden loss of local species due to disasters 2 12/19/13 Scientists in Darwin’s “Camp” Lamarck’s Hypothesis of Evolution • • Lamarckism unsupported by much of genetic Hutton and Lyell believed: • evidence • • BUT emerging field of epigenetics may prove to support some of Larmarck’s ideas! • Earth’s surface changes from cumulative, SLOW continuous actions still operating today (uniformitarianism) Strongly influenced Darwin’s thinking • He reasoned the Earth must be much older than previously believed • Also reasoned biological organisms may also have slow, continuous change Malthus (economist): • Voyage of the HMS Beagle Darwin in 1840, after his return from the voyage Limited resources shape population sizes Darwin’s Focus on Adaptation HMS Beagle in port Great Britain • During the voyage, Darwin observed many adaptations: EUROPE NORTH AMERICA • Inherited characteristics of organisms which increase their ATLANTIC OCEAN The Galápagos Islands AFRICA PACIFIC OCEAN Pinta Genovesa Fernandina Isabela 0 20 40 Kilometers Daphne Islands Pinzón Santa Santa Cruz Fe Florenza Chile PACIFIC OCEAN San Cristobal Española survival and reproduction in different environments Equator SOUTH AMERICA Equator Andes Mtns. Marchena Santiago Brazil Malay Archipelago PACIFIC OCEAN AUSTRALIA Cape of Argentina Good Hope Cape Horn Tasmania New Zealand • Darwin saw how adaptation to environment and the origin of species is closely related • Theorized: Could new species arise from gradual accumulation of adaptations to different environments? 3 12/19/13 Example of Speciation in Galapagos Finches Darwin’s Focus on Adaptation How do adaptations arise? Largely dependent on: (a) Cactus-eater (b) Insect-eater Natural selection: Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits (c) Seed-eater Artificial Selection • Humans have modified other species by selective breeding for 1000’s of years, a process called artificial selection The Reason Why You Shouldn’t Procrastinate • In 1844, Darwin wrote an essay on natural selection--but did not publicize it • In June 1858, Wallace sent Darwin a paper to review with an almost identical theory of natural selection • Darwin quickly finished The Origin of Species by Means of Natural Selection and published it • Wallace graciously stepped away so now we call it “Darwinism” and not “Wallacism”! 4 12/19/13 Observations of Darwin • Observation #1: Members of a population often vary in their inherited traits Observations of Darwin Observation #2: All species can produce more offspring than the environment can support • Many offspring fail to survive and reproduce Important Points About Natural Selection • Note that individuals do not evolve; but populations evolve over time • Natural selection can only increase or decrease heritable traits that vary in a population • If everyone is genetically identical, no basis for selection • Adaptations vary with different environments Direct Observations of Evolutionary Change • The bacterium Staphylococcus aureus is commonly found on people • One strain, methicillin-resistant S. aureus (MRSA) is a dangerous pathogen • S. aureus became resistant to penicillin in 1945 and resistant to methicillin in 1961 • Single adaptation not preferred for all environments 5 12/19/13 Homology Direct Observations of Evolutionary Change • Methicillin works by inhibiting a protein used by • Homology is similarity resulting from common bacteria in their cell walls ancestry • But MRSA bacteria use a different protein in their cell walls • When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. • Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor aureus strains • MRSA strains are now resistant to many antibiotics Mammalian Forelimbs: Homologous Structures Embryonic Homologies Humerus Pharyngeal pouches Radius Ulna Post-anal tail Carpals Metacarpals Phalanges Chick embryo (LM) Human Cat Whale Human embryo Bat • Comparative embryology reveals anatomical homologies not visible in adult organisms 6 12/19/13 Vestigial Structures Lungfishes Amphibians 1 important functions in the organism’s ancestors Appendix • Male nipples • Wisdom teeth • Body hair and goosebumps • Ear muscles Mammals Lizards and snakes 3 4 Homologous characteristic Crocodiles 5 Feathers Different Cause of Resemblance: Convergent Evolution Ostriches 6 Birds • 2 Digitbearing limbs Amnion Amniotes • Common human vestigial structures: Tetrapods • Vestigial structures are remnants of features that served Evolutionary Tree Branch point Hawks and other birds Examples of Convergent Evolution • Convergent evolution is the evolution of similar, or analogous, features in distantly related groups • Analogous traits arise when groups independently adapt to similar environments in similar ways • Convergent evolution does not provide information about ancestry 7 12/19/13 Homology vs. Convergent Evolution • Both are evidence of evolution • Analogous features (convergent evolution) share similar function but not common ancestry • Homologous features (homology) share common ancestry but not necessarily similar function 8