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AP BIOLOGY Big Idea #1 – Part A – Section #4 Evolution is Supported by Scientific Evidence Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence • New discoveries continue to fill the gaps identified by Darwin in The Origin of Species Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Direct Observations of Evolutionary Change • Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drugresistant HIV Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Predation and Coloration in Guppies : Scientific Inquiry John Endler has studied the effects of predators on wild guppy populations • Brightly colored males are more attractive to females • However, brightly colored males are more vulnerable to predation • Guppy populations in pools with fewer predators had more brightly colored males Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-13 EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Guppies: Adult males have brighter colors than those in “pike-cichlid pools” Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools” RESULTS 12 Number of colored spots 12 10 8 6 4 2 0 Source population Transplanted population 10 8 6 4 2 0 Source population Transplanted population Fig. 22-13a EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Guppies: Adult males have brighter colors than those in “pike-cichlid pools” Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools” Fig. 22-13b RESULTS 12 Number of colored spots 12 10 8 6 4 2 0 Source Transplanted population population 10 8 6 4 2 0 Source Transplanted population population • Endler transferred brightly colored guppies (with few predators) to a pool with many predators • As predicted, over time the population became less brightly colored • Endler also transferred drab colored guppies (with many predators) to a pool with few predators • As predicted, over time the population became more brightly colored Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolution of Drug-Resistant HIV • The use of drugs to combat HIV selects for viruses resistant to these drugs • HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome • The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Some individual HIV viruses have a variation that allows them to produce DNA without errors • These viruses have a greater reproductive success and increase in number relative to the susceptible viruses • The population of HIV viruses has therefore developed resistance to 3TC • The ability of bacteria and viruses to evolve rapidly poses a challenge to our society Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-14 100 Patient No. 1 Patient No. 2 75 50 Patient No. 3 25 0 0 2 4 6 Weeks 8 10 12 • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Fossil Record • The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-15 0 2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10 12 3 2 Bristolia harringtoni 14 16 18 1 Bristolia mohavensis 3 2 1 Latham Shale dig site, San Bernardino County, California Depth (meters) Fig. 22-15b 12 2 Bristolia harringtoni 14 16 18 1 Bristolia mohavensis 2 1 Latham Shale dig site, San Bernardino County, California Fig. 22-15c 0 4 3 Depth (meters) 2 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10 • The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record • Paleontologists have discovered fossils of many such transitional forms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-16 (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor) Fig. 22-16ab (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Fig. 22-16cd Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor) Homology • Homology is similarity resulting from common ancestry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Anatomical and Molecular Homologies • Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor Comparative embryology reveals anatomical homologies not visible in adult organisms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-17 Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat Fig. 22-18 Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo Fig. 22-18a Pharyngeal pouches Post-anal tail Chick embryo (LM) Fig. 22-18b Pharyngeal pouches Post-anal tail Human embryo • Vestigial structures are remnants of features that served important functions in the organism’s ancestors • Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Homologies and “Tree Thinking” • The Darwinian concept of an evolutionary tree of life can explain homologies • Evolutionary trees are hypotheses about the relationships among different groups • Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-19 Branch point (common ancestor) Lungfishes Amphibians 1 Mammals 2 Tetrapod limbs Amnion Lizards and snakes 3 4 Homologous characteristic Crocodiles Ostriches 6 Feathers Hawks and other birds Birds 5 Convergent Evolution • 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 • Convergent evolution does not provide information about ancestry Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-20 Sugar glider NORTH AMERICA AUSTRALIA Flying squirrel Biogeography • Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution • Islands have many endemic species that are often closely related to species on the nearest mainland or island Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings What Is Theoretical About Darwin’s View of Life? • In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena • Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions • Ongoing research adds to our understanding of evolution Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 22-UN1 Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals and Over time, favorable traits accumulate in the population. Fig. 22-UN2 Fig. 22-UN3 You should now be able to: 1. Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace 2. Describe Lamarck’s theories, and explain why they have been rejected 3. Explain what Darwin meant by “descent with modification” 4. List and explain Darwin’s four observations and two inferences Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5. Explain why an individual organism cannot evolve 6. Describe at least four lines of evidence for evolution by natural selection Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings