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Transcript
Evolution, Darwin and Evidence • Descent with Modification: A Darwinian View of Life Evolution • Evolution: the change over time of the genetic composition of populations • Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) • Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction November 24, 1859 Evolutionary history • • • • • Linnaeus: taxonomy Hutton: gradualism Lamarck: evolution Malthus: populations Cuvier: paleontology • • • • Lyell: uniformitarianism Darwin: evolution Mendel: inheritance Wallace: evolution Charles Darwin • 1809-1882 • British naturalist • Proposed the idea of evolution by natural selection • Collected clear evidence to support his ideas Voyage of the HMS Beagle • Invited to travel around the world – 1831-1836 (22 years old!) – makes many observations of nature • main mission of the Beagle was to chart South American coastline Stopped in Galapagos Islands 500 miles off coast of Ecuador Darwin found… birds Collected many different birds on the Galapagos Islands. Thought he found Finch? very different kinds… Woodpecker? Sparrow? Warbler? But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Ground Finch Small Ground Sparrow? Finch How did one species of finches become so many different species now? Warbler Finch Woodpecker? Veg. Tree Finch Warbler? Darwin’s finches • Differences in beaks – associated with eating different foods – survival & reproduction of beneficial adaptations to foods available on islands Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Large insectivorous tree finch Small ground finch Cactus eater Medium ground finch Insect eaters Seed eaters Vegetarian tree finch Bud eater Large ground finch Darwin’s finches • Darwin’s conclusions – small populations of original South American finches landed on islands • variation in beaks enabled individuals to gather food successfully in the different environments – over many generations, the populations of finches changed anatomically & behaviorally • accumulation of advantageous traits in population • emergence of different species Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken & modified for different ends. Darwin’s finches • Differences in beaks allowed some finches to… – successfully compete – successfully feed – successfully reproduce • pass successful traits onto their offspring More observations… Correlation of species to food source Whoa, Turtles, too! Essence of Darwin’s ideas • Natural selection – variation exists in populations – over-production of offspring • more offspring than the environment can support – competition • for food, mates, nesting sites, escape predators – differential survival • successful traits = adaptations – differential reproduction • adaptations become more common in population Evolution evidence: Biogeography • Geographical distribution of species • Examples: Islands vs. Mainland Australia Continents Evidence supporting evolution • Fossil record – transition species • Anatomical record – homologous & vestigial structures – embryology & development • Molecular record – protein & DNA sequence • Artificial selection – human-caused evolution Fossil record • Layers of sedimentary rock contain fossils – new layers cover older ones, creating a record over time – fossils within layers show that a succession of organisms have populated Earth throughout a long period of time Evolution evidence: The Fossil Record • Succession of forms over time • Transitional links • Vertebrate descent Fossil record • A record showing us that today’s organisms descended from ancestral species Evolutionary change in horses 550 500 Body size (kg) 450 Equus 400 350 300 250 Merychippus 200 150 Mesohippus Hyracotherium 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 5 0 Millions of years ago Evolution of birds • Archaeopteryx – lived about 150 mya – links reptiles & birds Smithsonian Museum, Washington, DC Evolution evidence: Comparative Anatomy • Homologous structures (homology) • Descent from a common ancestor • • • • Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship – recent common ancestor Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Don’t be fooled by their looks! Solving a similar problem with a similar solution Vestigial organs • Modern animals may have structures that serve little or no function – remnants of structures that were functional in ancestral species – deleterious mutations accumulate in genes for noncritical structures without reducing fitness • snakes & whales — remains of pelvis & leg bones of walking ancestors • eyes on blind cave fish • human tail bone Vestigial organs • Hind leg bones on whale fossils Evolution evidence: Comparative Embryology • Pharyngeal pouches, ‘tails’ as embryos Evolution evidence: Molecular Biology • Similarities in DNA, proteins, genes, and gene products • Common genetic code Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships Comparative hemoglobin structure Human Macaque 8 Dog Bird Frog Lamprey 32 45 67 125 0 10 20 30 40 50 60 70 80 90 100 110 120 Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans Building “family” trees Closely related species (branches) share same line of descent until their divergence from a common ancestor Artificial selection • Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties” “descendants” of the wolf Natural selection in action • Insecticide & drug resistance – insecticide didn’t kill all individuals – resistant survivors reproduce – resistance is inherited – insecticide becomes less & less effective Final words…... • “Absence of evidence is not evidence of absence.”