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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 22 Descent with Modification: A Darwinian View of Life Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Figure 22.1 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species • Darwin’s ideas had deep historical roots © 2011 Pearson Education, Inc. Figure 22.2 1809 Lamarck publishes his hypothesis of evolution. 1798 Malthus publishes “Essay on the Principle of Population.” 1812 1858 Cuvier publishes his extensive studies of vertebrate fossils. 1795 Hutton proposes his principle of gradualism. 1830 Lyell publishes Principles of Geology. While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection. 1790 1870 1809 183136 Charles Darwin is born. Darwin travels around the world on HMS Beagle. 1859 On the Origin of Species is published. 1844 Darwin writes his essay on descent with modification. The Galápagos Islands Ideas About Change over Time • The study of fossils helped to lay the groundwork for Darwin’s ideas • Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata © 2011 Pearson Education, Inc. Figure 22.3 Sedimentary rock layers (strata) Younger stratum with more recent fossils Older stratum with older fossils Lamarck’s Hypothesis of Evolution • Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics • The mechanisms he proposed are unsupported by evidence © 2011 Pearson Education, Inc. 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life • During his travels on the Beagle, Darwin collected specimens of South American plants and animals • He observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions © 2011 Pearson Education, Inc. Figure 22.5 The Voyage of the Beagle Darwin in 1840, after his return from the voyage HMS Beagle in port Great Britain EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA PACIFIC OCEAN Pinta Genovesa Santiago Fernandina Isabela 0 20 40 Kilometers Daphne Islands Pinzón Santa Santa Cruz Fe Florenza Equator SOUTH AMERICA Equator Chile PACIFIC OCEAN San Cristobal Española Andes Mtns. Marchena Brazil Malay Archipelago PACIFIC OCEAN AUSTRALIA Cape of Argentina Good Hope Cape Horn Tasmania New Zealand Darwin’s Focus on Adaptation • In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes – From studies made years after Darwin’s voyage, biologists have concluded that this is what happened to the Galápagos finches © 2011 Pearson Education, Inc. Darwin saw organisms adapted to their environment (b) Insect-eater (a) Cactus-eater (c) Seed-eater • In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification • Natural selection is a process in which individuals with favorable inherited traits are more likely to survive and reproduce • Published The Origin of Species • Explained three broad observations: – The unity of life – The diversity of life – The match between organisms and their environment © 2011 Pearson Education, Inc. • In the Darwinian view, the history of life is like a tree with branches representing life’s diversity – Darwin’s theory meshed well with the hierarchy of Linnaeus © 2011 Pearson Education, Inc. Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) †Moeritherium Descent with modification †Barytherium †Deinotherium †Mammut †Platybelodon †Stegodon †Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) 60 34 24 Millions of years ago 5.5 2 104 0 Years ago Artificial selection Cabbage Selection for apical (tip) bud Brussels sprouts Selection for axillary (side) buds Broccoli Selection for flowers and stems Selection for stems Selection for leaves Kale Wild mustard Kohlrabi Descent with modification : • Observation #1: Members of a population often vary in their inherited traits • Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing leave more offspring than others © 2011 Pearson Education, Inc. • Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce • Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations © 2011 Pearson Education, Inc. What happens at intersection? Natural Selection: A Summary • Natural selection is the mechanism which directs the process of descent with modification • Natural selection says: – Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals – Natural selection increases the adaptation of organisms to their environment over time – If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species © 2011 Pearson Education, Inc. An example of adaptation (a) A flower mantid in Malaysia (b) A leaf mantid in Borneo • Note: that individuals do not evolve; populations evolve over time • Note: Natural selection can only increase or decrease heritable traits that already exist and vary in a population © 2011 Pearson Education, Inc. 22.3: Evolution is supported by an overwhelming amount of scientific evidence • Evidence continues to fill the gaps identified by Darwin in The Origin of Species 1. Direct observations 2. Homology 3. Embryology 4. Vestigial Organs 5. Fossil record 6. Biogeography 7. Biochemistry (later chapters) © 2011 Pearson Education, Inc. Evidence 1: Direct Observations of Evolutionary Change • Two examples provide evidence for natural selection: natural selection in response to introduced plant species, and the evolution of drug-resistant bacteria © 2011 Pearson Education, Inc. Natural Selection in Response to Introduced Plant Species • Soapberry bugs use their “beak” to feed on seeds within fruits • In southern Florida soapberry bugs feed on balloon vine with larger fruit; they have longer beaks • In central Florida they feed on goldenrain tree with smaller fruit; they have shorter beaks • Correlation between fruit size and beak size has also been observed in Louisiana, Oklahoma, and Australia © 2011 Pearson Education, Inc. • In all cases, beak size has evolved in populations that feed on introduced plants with fruits that are smaller or larger than the native fruits • These cases are examples of evolution by natural selection • In Florida this evolution in beak size occurred in less than 35 years © 2011 Pearson Education, Inc. Figure 22.13a FIELD STUDY Soapberry bug with beak inserted in balloon vine fruit Can a change in a population’s food source result in evolution by natural selection? RESULTS Beak 10 On native species, southern Florida 8 Number of individuals 6 4 2 0 Museum-specimen average 10 On introduced species, central Florida 8 6 4 2 0 6 7 8 9 Beak length (mm) 10 11 The Evolution of Drug-Resistant Bacteria • 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, two years after it was first widely used – S. aureus became resistant to methicillin in 1961, two years after it was first widely used © 2011 Pearson Education, Inc. • Methicillin works by inhibiting a protein used by bacteria in their cell walls • 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. aureus strains • MRSA strains are now resistant to many antibiotics © 2011 Pearson Education, Inc. Figure 22.14 2,750,000 1 250,000 base pairs 2,500,000 Chromosome map of S. aureus clone USA300 500,000 Key to adaptations 2,250,000 Methicillin resistance Ability to colonize hosts 750,000 Increased disease severity 2,000,000 Increased gene exchange (within species) and toxin production 1,750,000 1,500,000 1,250,000 1,000,000 • Natural selection does not create new traits, but edits or selects for traits already present in the population • The local environment determines which traits will be selected for or selected against in any specific population © 2011 Pearson Education, Inc. Evidence type 2: Homology • Homology is similarity resulting from common ancestry • Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor © 2011 Pearson Education, Inc. Figure 22.15 Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat Figure 22.16 Evidence 3: Comparative embryology reveals anatomical homologies not visible in adult organisms Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo • Evidence 4: Vestigial structures are remnants of features that served important functions in the organism’s ancestors – Human vestigial structures, ex. Coccyx, appendix, – Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor © 2011 Pearson Education, Inc. Homologies and “Tree Thinking” • Evolutionary trees are hypotheses about the relationships among different groups • Homologies form nested patterns in evolutionary trees • Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data © 2011 Pearson Education, Inc. Tree thinking: information provided in an evolutionary tree. Branch point Lungfishes Amniotes 2 Digitbearing limbs Amnion Mammals Lizards and snakes 3 4 Homologous characteristic Crocodiles Ostriches 6 Feathers Hawks and other birds Birds 5 Tetrapods Amphibians 1 Comparing physical structure might bring erroneous conclusions regarding relationships • 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 © 2011 Pearson Education, Inc. Figure 22.18 NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Evidence 5: The Fossil Record • The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time • Fossils can document important transitions – For example, the transition from land to sea in the ancestors of cetaceans © 2011 Pearson Education, Inc. Figure 22.19 Most mammals (a) Canis (dog) Cetaceans and even-toed ungulates (b) Pakicetus (c) Sus (pig) (d) Odocoileus (deer) Figure 22.UN01 Figure 22.20 Other even-toed ungulates Hippopotamuses †Pakicetus †Rodhocetus Common ancestor of cetaceans †Dorudon Living cetaceans 70 60 50 40 30 20 Millions of years ago 10 0 Key Pelvis Femur Tibia Foot Evidence 6. Biogeography • Biogeography, the geographic distribution of species, provides evidence of evolution • Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift • An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved © 2011 Pearson Education, Inc. • Endemic species are species that are not found anywhere else in the world • Islands have many endemic species that are often closely related to species on the nearest mainland or island • Darwin explained that species on islands gave rise to new species as they adapted to new environments © 2011 Pearson Education, Inc.