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BIOE 103 Common ancestry of life Great moments in evolution Unusual tooth, found in forest by a British doctor, Gideon Mantell (1822). Leading biologists could not identify it 2 The tooth looked liken an iguana’s But was 20x larger! Illustration by Mantell Teeth from a green iguana 3 Additional bones found in quarry in 1834. Mantell reconstructed animal. Named species “iguanodon” or “iguana tooth” Estimated it was 40’ long. (Keep in mind that no one had seen bones like this before) 4 Iguanodon In 1878, bones from Belgium quarry reconstructed. And it became obvious this was an extinct species. 5 By then, Mantell had died His medical practice had collapsed as he spent more time digging for fossils. His wife left him. He died of opium overdose in 1852. 6 Discovery of dinosaur skeletons in the 19th century shocked scientists and public 7 Mammoth skeletons also shocked everyone 8 Scientists wondered whether dinosaurs & mammoths were living creatures… or had gone extinct “Such is the economy of nature, that in no instance can be produced her having permitted any race of her animals to become extinct.” – Thomas Jefferson 9 Almost half of Americans believe humans and dinosaurs lived together This idea is common in popular culture, and is advocated by biblical literalists. 10 How could scientists test the hypothesis that humans lived at the same time as dinosaurs or mammoths? Propose a way to answer this question using methods you could actually do. 11 IF Humans and dinosaurs lived at the same time AND We note which rock layers contain signs of humans and dinosaurs THEN We should find human and dinosaur tracks, fossils, or remains in the same rock layers. Observation Human bones, fossils, tools, or footprints have never been found in the same rock layers as dinosaurs. Footprints of human ancestors 3.5 million years old 13 Distribution of fossils of humans and dinosaurs in actual rock layers Human fossils (young rocks) Dinosaur fossils in old rocks 14 Conclusion: Humans and dinosaurs do not appear to have lived together Dinosaurs appear to have lived a long time a before humans. 15 In contrast, archeologists have found numerous mammoth remains with spear points See “Naco kill site” & “Lehner Mammoth-Kill Site” 16 Eight spear tips found in mammoth skeleton in Arizona 17 2. Faunal succession In the early 19th century British constructed an extensive canal system 18 In 1816, canal surveyor William Smith noticed… Craig stratum …each layer of rock has distinctive fossils… Lower chalk stratum Upper Oolite stratum …and that rock layers could be identified by their fossils. 19 Smith made charts showing sequence of fossils. Principle of faunal succession The types of rocks varied, but sequence of fossils did not. 20 Smith called this: “faunal succession” Different rock layers contain different fossils Sequence of fossils is predictable & consistent. E.g. Human fossils are not found in rock layers with (or below) dinosaur fossils. See “faunal succession” 21 This was an example of faunal succession Human fossils in young rocks Dinosaur fossils in old rocks 22 Grand Canyon shows faunal succession Different rock layers have different fossils Trilobites, sponges + Fish, amphibians, reptiles Trilobites, sponges No fish, amphibians, reptiles No fossils except algae or bacterial mats 23 Grand Canyon Region shows faunal succession Bryce Canyon: Zion Canyon: Grand Canyon Bryce Zion Mammals Dinosaurs Invertebrates, fish, reptiles Grand Canyon 24 Geologists spent middle of 19th century identifying which fossils were present in which rocks And they identified a basic sequence that is present everywhere in the world 25 Geologists divided earth’s history into different time periods based on fossils This diagram shows the “geologic time scale”. It depicts divisions of the earth history inferred from fossils in rock layers. No single place on earth has rock layers from all of these periods. 26 Four major divisions in the Earth’s history Cenozoic “New Life” Dominated by modern mammals Massive extinction Mesozoic “Middle Life” Dominated by dinosaurs Massive extinction Paleozoic “Old Life” Trilobites, fish, amphibians Precambrian Very primitive organisms (e.g. sponges) 27 Example of faunal succession: dinosaurs Dinosaurs: 230 MYA – 65 MYA 28 Example of faunal succession: trilobites 17,000 species of trilobites in these rock layers 29 Fossil record showed several major extinction events Dinosaur extinction End Triassic extinction End Permian extinction End Devonian extinction Ordovician extinction And many less severe ones. 99.9% species extinct Most species live for 10 MY 30 There is also a trend towards increasingly complexity Birds Modern mammals Dinosaurs Reptiles Amphibians Fish Unicelluar organisms 31 Cenozoic “New Life” Dominated by modern mammals Massive extinction Mesozoic “Middle Life” Dominated by dinosaurs Massive extinction Paleozoic “Old Life” Trilobites, fish, amphibians 32 3. How to explain all this? These patterns could not be explained by a biblical creation 6000 years ago followed by a flood. French paleontologist Alcide d'Orbigny proposed in 1842 there had been 27 creations and floods. Alcide d'Orbigny 33 Darwin argued: **All living organisms are descended from a common ancestor **Different rock layers had different fossils because species evolved over time These diagrams show ancestry of living species. 34 Watch history of life video (available at: http://www.youtube.com/watch?v=5Q55z6EsL8M) 35 Evolution Definition. #1 The theory that all species are descended with modification from a common ancestor. 36 Many students wonder: “Isn’t evolution just a theory?” “Don’t many scientists doubt it?” 37 4. Testing Evolutionary Theory Characteristics of a good theory • Simple • Explains available observations • Makes testable predictions 38 Let’s see what this theory can EXPLAIN 39 On odd observation: Animals with very different lifestyles have similar sets of bones Can evolution explain this? 40 Can evolution explain?: Why vertebrates have similar limbs? These animals have very different bodies, but similar limb structure. 41 Can evolution explain: Why humans have “tail” bones? 42 Darwin sailed around the world 1831-1836 Made observations that led to theory of evolution His stop in the Galapagos Islands proved to be particularly influential. See “Second voyage of HMS Beagle” 43 Observations that intriguied Darwin “The most striking and important fact for us in regard to the inhabitants of islands, is their affinity to those of the nearest mainland, without being actually the same species. [In] the Galapagos Archipelago... almost every product of the land and water bears the unmistakeable stamp of the American continent. There are twenty-six land birds, and twenty-five of these are… distinct species, supposed to have been created here; yet the close affinity of most of these birds to American species in every character, in their habits, gestures, and tones of voice, was manifest.... The naturalist, looking at the inhabitants of these volcanic islands in the Pacific, distant several hundred miles from the continent, yet feels that he is standing on American land. Why should this be so? why should the species which are supposed to have been created in the Galapagos Archipelago, and nowhere else, bear so plain a stamp of affinity to those created in America? There is nothing in the conditions of life, in the geological nature of the islands, in their height or climate, or in the proportions in which the several classes are associated together, which resembles closely the conditions of the South American coast: in fact there is a considerable dissimilarity in all these respects.” - Charles Darwin, On the Origin of Species (1859) 44 Can evolution explain? Why Galapagos and Cape Verde Islands have similar climate, soil, size, but different birds. Galapagos Islands: birds similar to S. America Cape Verde Islands: birds similar to Africa 45 How could the common descent hypothesis explain these observations? Galapagos Islands: birds similar to S. America Cape Verde Islands: birds similar to Africa 46 Evolutionary explanations Vertebrates have similar limbs because all evolved from a common ancestor. Birds on islands similar to mainland because mainland birds colonized island and then evolved Galapagos Islands: birds similar to S. America Cape Verde Islands: birds similar to Africa Humans have a tailbone because human ancestor had a tail, and it never evolved away completely. 47 Humans apparently still have genes for a tail. (although they are usually not expressed) For more information, see http://www.anatomyatlases.org/AnatomicVariants/SkeletalSystem/Images/19.shtml 48 Humans have many “vestigial” genes E.g. Humans have half a gene for L-gulonolactone oxidase (The enzyme that synthesizes vitamin C) 49 Another vestigial trait: Blind mole rats have small eyes covered with skin 50 Another vestigial trait: Leg bones in whales 51 What does this theory PREDICT? 52 One prediction of common descent hypothesis Fossil record should show transitional species. 53 Horse lineage shows many transitional fossils 54 55 Time Transitional fossils: Archaeopteryx A dinosaur-like skeleton with feathers Archaeopteryx, discovered 1861 56 Transitional fossils: Early amphibian Tiktaalik 57 Transitional fossils: early humans Ardipithecus ramidus “Ardi” 4.4 MYA Brain: 325 cc Transitional fossils: Early whales “Evolution of cetaceans” 59 5. Darwin developed theory of evolution before DNA discovered Evolutionary theory and genetics predicts that closely related species will be genetically similar 60 DNA sequences provided an independent test of evolution theory Human Chimp Mouse Bird Frog Trout Fly Corn CTACAACTCTTTCCGTTCTTCTAAAAATAATACTTCACAAGGGTCACGGTG ..................................................A ........T..................C..GT.......C........... ...T.......C...............C.GGT...T..............A ....................TC.G...C.GGT...T............... ...T...GA..C..T......CGT...C.GGT.......C.......A..A ...........C..T......G.C..GC.CGT.GCG..GC........... T.GGGTTGACGA...C.......G..G.TC.GG.....GC.C......... Humans are genetically similar to chimpanzees and other mammals Less similar to fish, insects, and corn. 61 6. Could the earth and organisms have been created this way? 62 Sure. E.g., Douglas Adams suggested that the entire earth was made in a giant factory with all fossils built into place. The Matrix suggested “reality” was a computer simulation. Testing hypotheses like these is probably impossible because they do not make any predictions. In other words, they can not be refuted. 63 But how do species change? That is what we will discuss next lecture. 64 Study guide Read the section on evolution in the book (Ch. 5) Be able to describe evidence for common ancestry of all living organisms. Be able to use evolutionary theory to explain seemingly odd observations. Be able to interpret an evolutionary “tree.” Be able to explain the difference between evolution and natural selection. Be able to describe the requirements for natural selection and describe how natural selection occurs in nature. Be able to analyze a change in a population and determine whether it is evolution. 65 Sample exam questions Describe some of the fossil evidence that species have evolved, and explain how this evidence is interpreted. Cheetahs (large African cats) are able to run faster than 60 miles per hour when chasing prey. How would a biologist explain how the ability to run fast evolved in cheetahs, assuming their ancestors could run only 20 miles per hour? 66 The end 67