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AP Biology •Chapter 22~ •Descent with Modification: A Darwinian View of Life Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Overview: Endless Forms Most Beautiful •The Origin of Species focused biologists’ attention on the great diversity of organisms •Darwin noted that current species are descendants of ancestral species •Evolution can be defined by Darwin’s phrase descent with modification •Evolution can be viewed as both a pattern and a process Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species • To understand why Darwin’s ideas were revolutionary, we must examine them in relation to other Western ideas about Earth and its life Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-2 In historical context Other people’s ideas paved the path for Linnaeus (classification) Darwin’s thinking Hutton (gradual geologic change) (population limits) , extinction) competition: struggle for survival population growth exceeds food supply land masses change over immeasurable time Scala Naturae and Classification of Species • The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae • The Old Testament holds that species were individually designed by God and therefore perfect • Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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 Video: Grand Canyon Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-3 Layers of deposited sediment Younger stratum with more recent fossils Older stratum with older fossils • Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier • Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today • Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time • This view strongly influenced Darwin’s thinking Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Lamarck’s Hypothesis of Evolution •Organisms adapted to their environments – through acquired traits – change in their life time • Use & Disuse organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm • Perfection with Use & Need the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat – transmit acquired characteristics to next generation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life • As the 19th century dawned, it was generally believed that species had remained unchanged since their creation • However, a few doubts about the permanence of species were beginning to arise Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Charles Darwin •1809-1882 •British naturalist •______________________ _______________________ _ •Collected clear evidence to support his ideas Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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 •Robert Fitzroy Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-5 GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA Pinta Genovesa Equator Marchena Santiago Fernandina Isabela Daphne Islands Pinzón Santa Santa Cruz Fe Florenza SOUTH AMERICA AUSTRALIA PACIFIC OCEAN San Cristobal Cape of Good Hope Tasmania Española Cape Horn Tierra del Fuego New Zealand Unique species Video: Galápagos Islands Overview Video: Blue-footed Boobies Courtship Ritual Video: Albatross Courtship Ritual Video: Galápagos Sea Lion Video: Soaring Hawk Video: Galápagos Tortoises Video: Galápagos Marine Iguana Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Darwin found… birds •Collected many different birds on the Galapagos Islands. •Thought he found very different kinds… Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Finch? Finch? Sparrow? QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Sparrow? Woodpecker? WleWarbler? pecker? r? 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! F Large Ground Finch S Small Ground QuickTime™ and a Finch parrow? inch? Photo - JPEG decompressor are needed to see this picture. How did one species of finches become so many different species now? Woodpeck Veg. Tree Finch Warbler Finch Warbler? er? Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Tree Thinking QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Correlation of species to food source Rapid speciation: new species filling new niches, because they inherited successful adaptations. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Darwin’s finches •Darwin’s conclusions – small populations of original South American finches land 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 ___________________________________________ •emergence of different species Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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 indeed what happened to the Galápagos finches In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s Darwin quickly finished The Origin of Species and published it the next year (a) Cactus-eater c) Seed-eater b) Insect-eater In 1858, Darwin received a letter that changed everything. Alfred Russel Wallace a young naturalist working n the East Indies, had written a short paper with a new idea. He asked Darwin o evaluate his ideas and pass it along for publication. November 24, 1859, Darwin published On the Origin of Species by Means of Natural Selection” The Origin of Species • Darwin developed two main ideas: – Descent with modification explains life’s unity and diversity – Natural selection is a cause of adaptive evolution Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Descent with Modification • Darwin never used the word evolution in the first edition of The Origin of Species • The phrase descent with modification summarized Darwin’s perception of the unity of life • The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past • 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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings More observations… Correlation of species to food source Whoa, Turtles, too! Many islands also show distinct local variations in tortoise morphology… …perhaps these are the first steps in the splitting of one species into several? Artificial Selection, Natural Selection, and Adaptation • Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection • Darwin then described four observations of nature and from these drew two inferences Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Selective breeding the raw genetic material (variation) is hidden there Four Observations •Observation #1: Members of a population often vary greatly in their traits Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Observation #2: Traits are inherited from parents to offspring • Observation #3: All species are capable of producing more offspring than the environment can support • Observation #4: Owing to lack of food or other resources, many of these offspring do not survive Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals • Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources • If some heritable traits are advantageous, these will accumulate in the population, and this will increase the frequency of individuals with adaptations • This process explains the match between organisms and their environment Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Natural Selection: A Summary • 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 Video: Seahorse Camouflage Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-12 (a) A flower mantid in Malaysia (b) A stick mantid in Africa • Note that individuals do not evolve; populations evolve over time • Natural selection can only increase or decrease heritable traits in a population • Adaptations vary with different environments Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 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 • 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 • 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 • 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 • 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) Anatomical and Molecular Homologies •Homology is similarity resulting from common ancestry •Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Comparative embryology reveals anatomical homologies not visible in adult organisms Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-18 Pharyngeal pouches Post-anal tail Chick embryo (LM) 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 • 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.