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Processes of Evolution Plato and Aristotle 427-347 BC 384-322 BC • Aristotle was the first to classify living animals. He observed patterns suggesting transmutation; new types could arise from older species • Western culture – life forms unchanged (immutable) since creation • Some accounts claim this was questioned 2000 years ago, even before Aristotle and Plato Early Beliefs – Chain of Beings- Life extended from lowest forms to humans, spiritual beings were highest. – Single Creation- All species were links created at the same time at one center of creation. Age of Exploration Led to new discoveries • 15th century world travel began • New species of plants and animals were discovered • Naturalists cataloguing them identified patterns in where species lived and whether they seemed related • Among first to ponder about ecology and evolution Evidence against concept of “immutable species” • Biogeography • Comparative morphology • Geologic discoveries Biogeography • Study of patterns in geographic distribution of species and communities • Accepted beliefs did not explain discovery of new organisms in previously unknown places Biogeography Comparative Morphology • Study of similarities and differences in body plans of major groups • Puzzling patterns: – Animals as different as whales and bats have similar bones in forelimbs – Some parts seem to have no function (vestigial structures) Comparative Morphology coccyx fossilized ankle bone ankle bone Comparative Morphology Comparative pelvic anatomy Geological Discoveries • Similar rock layers throughout world • Certain layers contain fossils • Deeper layers contain simpler fossils than shallow layers • Some fossils resemble known species 19th Century: New Theories • Scientists attempt to reconcile evidence of change with traditional belief in a single-creation event • Thoeries – Georges Cuvier: catastrophism – James Hutton: gradualism – Jean Lamarck: teleological evolution (evolution with a predetermined purpose!) Georges Cuvier (1769-1832) French anatomist • Fossil species from Paris Basin • older strata had flora and fauna increasingly dissimilar from modern life • extinction common occurrence new species appear, others disappear • theory of catastrophism – following creation global disasters destroyed species repopulated from other areas James Hutton (Scottish Geologist) Theory of Gradualism (1795) • profound change cumulative product of slow but continuous processes Jean Baptiste Lamarck Theory of Evolution (Philosophie Zoologique,1809) • Organisms had a drive to perfection evol. responds to “felt needs” • teleological - evolution has a goal, or directed purpose species changed over time because they "wanted" to be "better" • 1st to combine evolutionary and ecological thinking Lamarck’s Theories Proposed mechanism: 1. Use and disuse – body parts used extensively become larger and stronger, those not used deteriorate 2. inheritance of acquired characteristics modifications an organism acquires during its lifetime can be passed to offspring Credit deserved for his recognition that: 1. Evolution best explanation for both fossil record and current diversity 2. Recognition of great age of the Earth 3. Emphasis on adaptation to the environment Charles Lyell (Scottish geologist) Principles of Geology (1830) Uniformitarianism (Theory of Uniformity) – 1. Natural laws are constant in space and time. 2. Most geological change occurs slowly and gradually, not through sudden, catastrophic events. 3. Scientists should attempt to explain events of the past through the same sorts of natural processes that we observe today. • Challenged the view that Earth was only 6,000 years old Charles Darwin (1809-1892) 1. Father was wealthy Physician 2. Natural History interested in collecting insects, hunting fishing and reading 3. College University of Edinburgh studied medicine (age 16) transferred to Christ College, University of Cambridge studied theology BA in 1831 4. natural theology most naturalist and scientists belonged to the clergy Darwin’s History • Rev. John Henslow, Professor of Botany • 1831 – H.M.S. Beagle (Captain FitzRoy) • Professor Henslow recommended him as naturalist • Gave him Lyell's book Darwin’s Voyage • At age 22, Charles Darwin began a fiveyear, round-the-world voyage aboard the HMS Beagle • As ship’s naturalist, he collected and examined species that inhabited regions the ship visited Voyage of the Beagle EQUATOR Galapagos Islands Voyage of the Beagle 5 years • Darwin spent most of his time on shore, observing & collecting exotic and diverse specimens Wrote extensively on: • flora and fauna of So. America (very different from Europe) • Coral Reefs, Barnacles, Volcanic Islands Galapagos Islands Darwin Wolf • Volcanic islands far off coast of Ecuador Pinta Genovesa Marchena • All inhabitants are descended from species that arrived on islands from elsewhere Santiago Bartolomé Fernandia Seymour Baltra Rabida Pinzon Santa Cruz Santa Fe Tortuga San Cristobal Isabela Española Floreana Galapagos Islands Darwin’s Finches Many Endemic Species Galapagos Turtles Marine Iguanas Fossil Evidence • Darwin found Glyptodont fossils in Argentina • Proposed descent with modification Descent with Modification “Like confessing a murder” Voyage Ended in 1836 • Upon return home to England: • Darwin began discussing his observations as possible evidence for evolution with other naturalists • Also read Malthus essay Thomas Malthus An Essay of Population (1798) 1837 Darwin read Malthus’ Essay Human population growth would eventually be limited by: • War • Famine • Disease Reproductive Capacity and Competition • All populations have the capacity to increase in numbers • No population can increase indefinitely • Eventually, individuals of a population end up competing for resources Galapagos Finches Galapagos Finches • Darwin observed finches with a variety of lifestyles and body forms • On his return, he learned that there were 13 species • He attempted to correlate variations in their traits with environmental challenges Variation and Artificial Selection Heritable variation – is random, purposeless, and in no way subject to control. Farmers could not cause a variation to arise, but manipulation of existing variation is possible. Dog Artificial Selection Artificial Selection Variation in Populations • All individuals have the same genes that specify the same assortment of traits • Most genes occur in different forms (alleles), which produce different phenotypes • Some phenotypes compete better than others (fitness) Change over Time • Over time, alleles that produce the most successful phenotypes will increase in the population • Less successful alleles will become less common • Change leads to increased fitness – Increased adaptation to environment Natural Selection • Natural selection for various traits among individuals of a population affects which individuals survive and reproduce in each generation • Process results in adaptation to the environment (increases fitness) Alfred Wallace 1823-1913 British Naturalist Malay archipelago • 1858 Darwin received manuscript with developed theory of Natural Selection essentially identical to Darwin’s • Prompted Darwin to publish “On the origin of Species” • Darwin quickly finished Origin of Species, by Means of Natural Selection (1859) • Darwin received most of the credit 15 yr. earlier • developed and supported theory of Natural Select. much more extensively • Darwin’s success: science was shifting away from natural theology immaculate logic and an avalanche of evidence Summary: • Natural selection is differential success in reproduction. • Natural selection occurs through an interaction between the environment and the variability inherent among individual organisms making up the population. • The product of natural selection is the adaptation of populations of organisms to their environment.