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Evolution: Change in population characteristics over generations OUTLINE Evolution and common descent History of evolutionary thought Evidence for evolution Evaluating models Evolutionary novelty Goals: Be able to… Central tenets of evolution Explain the central tenets of evolution. Explain how natural selection leads to evolution. Describe how Darwin came up with the theory of common descent. 1. Populations have changed over time into the different species we see today 2. Theory of Common Descent: These populations changed from a common ancestor 1 Natural selection is a mechanism of evolution Mixed lice Resistant lice survive Resistant lice Apply permethrin Microevolution: Change over short periods Fig 9.2 Fig 9.1 OUTLINE Evolution and common descent Speciation: formation of new species History of evolutionary thought Evidence for evolution Evaluating models Natural selection Evolutionary novelty Fig 9.2 Historical ideas about evolution: Separate (“special”) creation: Species are fixed on a scale of complexity with humans on top. The world is perfect. -- Plato, Aristotle … Fig 9.7 2 Theory of Common Descent Lamarck: 1. Views of Lamarck (evolutionist) Organisms change over generations 2. Views of Lyell (geologist) 3. Fossil evidence 4. Travels to Galapagos Fossils of dinosaurs: some species don’t make it Lyell Due to the Biblical flood? Result: The world is not perfect Or, due to gradual changes over very long time periods? Result: Earth is much > 10,000 yo 5 year expedition around the world Galapagos giant tortoises Fig 9.4 Different kinds of giant tortoises on different islands Result: Giant tortoises must be related, but diverged over time 3 Darwin published “On the Origin of Species by Means of Natural Selection” in 1859 Giant Alfred Russell Wallace Darwin Fig 9.2 True/False: Fossils of species that don’t exist today, in combination with a lack of fossils of modern species, support the idea that organisms have NOT evolved over time. 1. True 2. False OUTLINE Evolution and common descent History of evolutionary thought Evidence for evolution Evaluating models Evolutionary novelty Goals: Be able to… Describe how classification, homology, biogeography, and fossils all provide evidence for the theory of common descent. Differentiate between analogy and homology. Apply your knowledge of radiometric dating to problems. Do you agree or disagree with the statement: “Human beings, as we know them, developed from earlier species of animals.” 1. Agree 2. Disagree 3. Don’t know Discuss evidence refuting various alternative hypotheses of evolution. Describe 3 ways in which evolutionary novelty can be generated by small changes. 4 Agree Disagree “Human beings, as we know them, developed from earlier species of animals.” Hypothesis 1: Static model Fig 9.7 Hypothesis 2: Transformation Hypothesis 3: Separate types Independent origins Fig 9.7 Fig 9.7 5 Hypothesis 4: Common descent Scientists investigate evolution, because 1. It is the only acceptable scientific explanation for the observed patterns of change in organisms over time. 2. They are not spiritual or religious people. 3. They want to disprove the existence of (a) Creator(s). 4. All of the above. Common origin of life Fig 9.7 Classification suggests relatedness Evidence for Evolution 1. Biological classification 2. Homology of features Why are we able to put organisms into groups? 3. Biogeography 4. Fossils! Fig 9.9 Evidence for Evolution 1. Biological classification 2. Homology of features 3. Biogeography Ancestry represented using trees 4. Fossils! More closely related = more recent common ancestor Fig 9.11 6 Homology: Similarity of features due to common ancestry Homology Vestigial structures: evolutionary baggage Fig 9.12 Vestigial structures Fig 9.13 Similar genetic sequences Fig 9.17 True/False: A fish fin and a whale flipper are homologous structures. 1. True 2. False Evidence for Evolution 1. Biological classification 2. Homology of features 3. Biogeography: Geographic distributions 4. Fossils! 7 Marsupials: Young develop in pouches Placentals Marsupials Analogy: similarity due to common function Porpoise: mammal Evidence for Evolution 1. Biological classification 2. Homology of features 3. Biogeography 4. Fossils! Icthyosaur: reptile Convergent evolution: similar features arise due to common environmental pressure, not ancestry. Transitions in the fossil record Transitions in the fossil record Archaeopteryx: transitional bird-lizard Fig 9.28 8 Fossilization: minerals replace organic matter Age of the Earth Radioactive elements “decay” at a predictable rate. Decay causes parent elements to turn into daughter elements Uranium Æ Lead How do we know how old fossils are? Half-life is the time it takes for ½ of the parts to decay Fig 9.21 Age of the Earth Age of the Earth 100% left 50% left 25% 12.5% left left 1 half-life = 1 million yr 200 years ago 150 years ago 100 years ago 50 years ago 19% left = 2.5 half-lives What is the half-life of this element? Fig 9.24 Age of the Earth Materials dated Shells, Limestone, organics Method Half-lives Carbon/ Nitrogen 5,730 yrs Potassium/ Argon 1.3 billion yrs Volcanic rock Rubidium/ Strontium 47 billion yrs Micas Uranium/Lead 4.5 billion yrs Zircon If an element has a half-life of 20 million years, and there is 25% of it remaining in a rock, how old is the rock? 1. 2. 3. 4. 5 million years 10 million years 20 million years 40 million years 9 Group Problem: M&Mite decay M&Mite spontaneously decays into the daughter product “beanus” over time OUTLINE Evolution and common descent 1. Using your samples (baggies), graph # of M&Mite molecules vs. Number of half-lives. History of evolutionary thought Evidence for evolution Evaluating models 2. If your oldest sample is 1000 years old, what is the half-life of M&Mite? Evolutionary novelty Hypothesis 1: Static model Hypothesis 2: Transformation What evidence refutes this theory? What evidence refutes this theory? Fig 9.7 Fig 9.7 Hypothesis 3: Separate types Hypothesis 4: Common descent What evidence refutes this theory? Independent origins Fig 9.7 Common origin of life Fig 9.7 10 We can reject the static hypothesis, because 1. We usually do not find fossils record that are exactly the same as living organisms. 2. Example Fossil evidence indicates that many organisms short answer: have gone extinct. 3. List Many diverse a basic structure 2 pieces of features evidenceshare that refute the static (bat wing &For whale flipper hypothesis. each piece,bones). state which aspect 4. ofWe findhypothesis fossils transitional between thecan status is refuted. different organisms that are currently alive. 5. All of the above. OUTLINE Evolution and common descent History of evolutionary thought Evidence for evolution Evaluating models Evolutionary novelty Exaptations: Features originally performed a different function than they currently do. Generation of evolutionary novelty • Exaptation • Developmental mutations • Intermediate forms Mutations in developmental genes… Intermediate forms Pigment cells Pinhole eye Complex camera eye Eyecup Primitive lens Amphistoma larva Have widespread effects Axolotl adult 11 True/False: Both bird feathers and the human eye are irreducibly complex 1. True 2. False Group Problem: Birds on Islands A = Red feathers, blue beaks A B C C = Yellow feathers, blue beaks Example short answer: In 1-2 sentences, describe how feathers on birds may have evolved. B = Red feathers, black beaks 1. Draw 2 possible phylogenetic trees for these 3 species. 2. What specific evidence would help you choose between these 2 hypotheses? Goals: Be able to… Primates Describe features that 1) we share with other primates, 2) differentiate apes from other primates, and 3) differentiate us from apes. • Grasping hands Describe the environment in which primate features evolved. • Large brains Explain why Lucy was such an important find. • Forward-facing eyes Why? Adaptation for forest life Discuss hypotheses about the origins of bipedalism and big brains. Tell me when modern humans arose, and about their Homo ancestors. Prosimians: Lemurs and tarsiers Monkeys and apes Earliest diverging Opposable thumb! 12 Apes • No tail • Long forelimbs • Larger brains Orangutans Gorillas Fig 9.11 Chimpanzees Bonobos What human features were probably adaptations for forest life? 1. Fingernails Example short answer: 2. Forward-facing eyes List 2 human features that were originally 3. Opposable adaptations for thumbs forest life. 4. Lack of hair -OR5. 2 and 3 Give 2 ways which apes are distinct from 6. All of thein above other primates. What does it mean to be human? 1) Large brain 2) Bipedalism 3) Short jaw 4) Reduced sexual differences 5) Monogamy 13 Hominins: Most closely related to us. Comparing humans vs. chimps Diverged from chimpanzee line: 5-7 mya? Fig 9.22 Fig 9.25 What features separate humans from other apes? Enlarging brain Example short answer: 1. Forward-facing eyes 2. Opposable thumbs What are the most critical 2 ways in which human anatomy 3. Long arms differs from other apes? 4. Largest brain Fig 9.27 Dry savanna provides more complexity? Looking for 2 major features: • Bipedal posture • Enlarged brain How did they evolve? Early ideas: + Bipedal posture Brain size + 14 Along came Lucy… Problem: Bipedal with small brain Fig 9.23 Australopithecus afarensis Fig 9.23 ~ 3.5 mya: Australopithecus afarensis Homo sapiens Why bipedalism? Early theories: + Environmental change Æ dry savannas Bipedal posture Brain size Why might bipedalism be favorable in a savanna (as opposed to forest) environment? + Bipedal posture is the key!!! Why bipedalism? Environmental change Æ dry savannas Not using hands for tree climbing? Bipedalism paved the way for large brain? Babies born smaller due to pelvis… Longer care of infants Æ more culture? Easier to see far away? Easier to carry things? Hands free to create tools…? Prevent overheating? 15 True/False: Looking at human evolution, we can see that bipedalism developed before large brain size. Genus: Homo 1. True 2. False Example short answer: What did the fossil Lucy demonstrate about the order of evolution of bipedalism and big brains? Fig 9.25 Homo habilis: “handy-man” Homo erectus First tool-maker Specialized tools Brain size: 47% of ours Brain size: 71% Neanderthals: 500,000 – 30,000 years ago? Homo sapiens neanderthalensis Homo erectus colonized Asia and Europe Brain size: 12% larger 16 Homo sapiens sapiens: 100,000 years ago. Origins of agriculture begin 9500 BC Cultural evolution… Homo floresiensus: The Hobbit Alive 13,000 years ago Example short answer: What scientific support is there that humans share a common ancestor with chimpanzees? What do you think about the statement: “God created man pretty much in his present form at one time within the last 10,000 years.” 17