Presentation on theme: "Descent with Modification: A Darwinian View of Life"— Presentation transcript:
1 Descent with Modification: A Darwinian View of Life Chapter 22Descent with Modification: A Darwinian View of Life
2 Overview: Darwin Introduces a Revolutionary Theory A new era of biology began on November 24, 1859The day Charles Darwin published On the Origin of Species by Means of Natural Selection
3 The Origin of SpeciesFocused biologists’ attention on the great diversity of organismsFigure 22.1
4 Darwin made two major points in his book He presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral speciesHe proposed a mechanism for the evolutionary process, natural selectionThe basic idea of natural selection is that a population can change over time if individuals that possess certain heritable traits leave more offspring than other individuals.Natural selection results in evolutionary adaptation, an accumulation of inherited characteristics that increase the ability of an organism to survive and reproduce in its environment.
5 In order to understand why Darwin’s ideas were revolutionary Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging speciesIn order to understand why Darwin’s ideas were revolutionaryWe need to examine his views in the context of other Western ideas about Earth and its life
6 Resistance to the Idea of Evolution The Origin of SpeciesShook the deepest roots of Western cultureChallenged a worldview that had been prevalent for centuries• The Greek philosopher Aristotle (384–322 B.C.E.) opposed any concept of evolution and viewed species as fixed and unchanging.° Aristotle believed that all living forms could be arranged on a ladder of increasing complexity (scala naturae) with perfect, permanent species on every rung.
7 The Scale of Nature and Classification of Species The Greek philosopher AristotleViewed species as fixed and unchangingThe Old Testament of the BibleHolds that species were individually designed by God and therefore perfect• The Old Testament account of creation held that species were individually designed by God and, therefore, perfect.• In the 1700s, natural theology viewed the adaptations of organisms as evidence that the Creator had designed each species for a purpose.
8 Carolus LinnaeusInterpreted organismal adaptations as evidence that the Creator had designed each species for a specific purposeWas a founder of taxonomy, classifying life’s diversity “for the greater glory of God”• Carolus Linnaeus (1707–1778), a Swedish physician and botanist, founded taxonomy, a system for naming species and classifying species into a hierarchy of increasingly complex categories.° Linnaeus developed the binomial system of naming organisms according to genus and species.° In contrast to the linear hierarchy of the scala naturae, Linnaeus adopted a nested classification system, grouping similar species into increasingly general categories.° For Linnaeus, similarity between species did not imply evolutionary kinship but rather the pattern of their creation.
9 Fossils, Cuvier, and Catastrophism The study of fossilsHelped to lay the groundwork for Darwin’s ideasFossils are remains or traces of organisms from the pastUsually found in sedimentary rock, which appears in layers or strataFigure 22.3• Darwin’s views were influenced by fossils, remains or traces of organisms from the past mineralized in sedimentary rocks.° Sedimentary rocks form when mud and sand settle to the bottom of seas, lakes, and marshes.° New layers of sediment cover older ones, creating layers of rock called strata.° Erosion may later carve through sedimentary rock to expose older strata at the surface.° Fossils within layers of sedimentary rock show that a succession of organisms have populated Earth throughout time.
10 Paleontology, the study of fossils Was largely developed by French scientist Georges CuvierCuvier opposed the idea of gradual evolutionary changeAnd instead advocated catastrophism, speculating that each boundary between strata represents a catastrophe• Paleontology, the study of fossils, was largely developed by the French anatomist Georges Cuvier (1769–1832).• In examining rock strata in the Paris Basin, Cuvier noted that the older the strata, the more dissimilar the fossils from modern life.° Cuvier recognized that extinction had been a common occurrence in the history of life.° Instead of evolution, Cuvier advocated catastrophism, speculating that boundaries between strata were due to local floods or droughts that destroyed the species then present.° He suggested that the denuded areas were later repopulated by species immigrating from unaffected areas.
11 Theories of Gradualism Is the idea that profound change can take place through the cumulative effect of slow but continuous processesTheories of geologic gradualism prepared the path for evolutionary biologists.• In contrast to Cuvier’s catastrophism, Scottish geologist James Hutton (1726–1797) proposed a theory of gradualism that held that profound geological changes took place through the cumulative effect of slow but continuous processes identical to those currently operating.° Thus, valleys were formed by rivers flowing through rocks and sedimentary rocks were formed from soil particles that eroded from land and were carried by rivers to the sea.• Later, geologist Charles Lyell (1797–1875) proposed a theory of uniformitarianism, which held that geological processes had not changed throughout Earth’s history.• Hutton’s and Lyell’s observations and theories had a strong influence on Darwin.
12 Geologists Hutton and Lyell Perceived that changes in Earth’s surface can result from slow continuous actions still operating todayExerted a strong influence on Darwin’s thinking• Later, geologist Charles Lyell (1797–1875) proposed a theory of uniformitarianism, which held that geological processes had not changed throughout Earth’s history.• Hutton’s and Lyell’s observations and theories had a strong influence on Darwin.
13 Lamarck’s Theory of Evolution Lamarck hypothesized that species evolveThrough use and disuse and the inheritance of acquired traitsBut the mechanisms he proposed are unsupported by evidenceFigure 22.4• He explained his observations with two principles: use and disuse of parts and the inheritance of acquired characteristics.° Use and disuse was the concept that body parts that are used extensively become larger and stronger, while those that are not used deteriorate.° The inheritance of acquired characteristics stated that modifications acquired during the life of an organism could be passed to offspring.° A classic example is the long neck of the giraffe. Lamarck reasoned that the long, muscular neck of the modern giraffe evolved over many generations as the ancestors of giraffes reached for leaves on higher branches and passed this characteristic to their offspring.
14 As the 19th century dawned Concept 22.2: In The Origin of Species, Darwin proposed that species change through natural selectionAs the 19th century dawnedIt was generally believed that species had remained unchanged since their creation, but a major change would challenge this thinkingthrough natural selection• Charles Darwin (1809–1882) was born in western England.° As a boy, he developed a consuming interest in nature.° When Darwin was 16, his father sent him to the University of Edinburgh to study medicine.• Darwin left Edinburgh without a degree and enrolled at Cambridge University with the intent of becoming a clergyman.
15 As a boy and into adulthood, Charles Darwin Darwin’s ResearchAs a boy and into adulthood, Charles DarwinHad a consuming interest in natureSoon after Darwin received his B.A. degreeHe was accepted on board the HMS Beagle, which was about to embark on a voyage around the world° At that time, most naturalists and scientists belonged to the clergy and viewed the world in the context of natural theology.• Darwin received his B.A. in 1831.• After graduation Darwin joined the survey ship HMS Beagle as ship naturalist and conversation companion to Captain Robert FitzRoy.
16 The Voyage of the Beagle During his travels on the BeagleDarwin observed and collected many specimens of South American plants and animalsDarwin observed various adaptations of plants and animalsThat inhabited many diverse environments
17 Darwin’s interest in the geographic distribution of species Was kindled by the Beagle’s stop at the Galápagos Islands near the equator west of South AmericaFigure 22.5EnglandEUROPENORTHAMERICAGalápagosIslandsDarwin in 1840,after his returnSOUTHCape ofGood HopeCape HornTierra del FuegoAFRICAHMS Beagle in portAUSTRALIATasmaniaNewZealandPACIFICOCEANAndesATLANTIC• Darwin had the freedom to explore extensively on shore while the crew surveyed the coast.• He collected thousands of specimens of the exotic and diverse flora and fauna of South America.° Darwin explored the Brazilian jungles, the grasslands of the Argentine pampas, the desolation of Tierra del Fuego near Antarctica, and the heights of the Andes.
18 Darwin’s Focus on Adaptation As Darwin reassessed all that he had observed during the voyage of the BeagleHe began to perceive adaptation to the environment and the origin of new species as closely related processes
19 From studies made years after Darwin’s voyage Biologists have concluded that this is likely what happened to the Galápagos finchesFigure 22.6a–c(a) Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp.(c) Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground.(b) Insect eater. The green warbler finch (Certhidea olivacea) uses its narrow, pointed beak to grasp insects.• While on the Beagle, Darwin read Lyell’s Principles of Geology.
20 In June 1858 Darwin received a manuscript from Alfred Russell Wallace In 1844, Darwin wrote a long essay on the origin of species and natural selectionBut he was reluctant to introduce his theory publicly, anticipating the uproar it would causeIn June 1858 Darwin received a manuscript from Alfred Russell WallaceWho had developed a theory of natural selection similar to Darwin’sDarwin quickly finished The Origin of SpeciesAnd published it the next year• In June 1858, Alfred Russel Wallace (1823–1913), a young naturalist working in the East Indies, sent Darwin a manuscript containing a theory of natural selection essentially identical to Darwin’s.
21 Darwin developed two main ideas The Origin of SpeciesDarwin developed two main ideasEvolution explains life’s unity and diversityNatural selection is a cause of adaptive evolution• Darwin quickly finished The Origin of Species and published it the next year.• While both Darwin and Wallace developed similar ideas independently, the theory of evolution by natural selection is attributed to Darwin because he developed his ideas earlier and supported the theory much more extensively.° The theory of evolution by natural selection was presented in The Origin of Species with logic and supporting evidence.
22 Descent with Modification The phrase descent with modificationSummarized Darwin’s perception of the unity of lifeStates that all organisms are related through descent from an ancestor that lived in the remote past° Descent with modification. All organisms are related through descent from a common ancestor that lived in the remote past. Over evolutionary time, the descendents of that common ancestor have accumulated diverse modifications, or adaptations, that allow them to survive and reproduce in specific habitats.
23 In the Darwinian view, the history of life is like a tree With multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organismsFigure 22.7Hyracoidea(Hyraxes)Sirenia(Manateesand relatives)Years agoMillions of years agoDeinotheriumMammutStegodonMammuthusPlatybelodonBarytheriumMoeritheriumElephasmaximus(Asia)Loxodontaafricana(Africa)cyclotis
24 Natural Selection and Adaptation Evolutionary biologist Ernst MayrHas dissected the logic of Darwin’s theory into three inferences based on five observations
25 Observation #1: For any species, population sizes would increase exponentially If all individuals that are born reproduced successfullyFigure 22.8
26 Observation #2: Nonetheless, populations tend to be stable in size Except for seasonal fluctuationsObservation #3: Resources are limitedInference #1: Production of more individuals than the environment can supportLeads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving
27 Observation #4: Members of a population vary extensively in their characteristics No two individuals are exactly alikeFigure 22.9
28 Observation #5: Much of this variation is heritable Inference #2: Survival depends in part on inherited traitsIndividuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals
29 Inference #3: This unequal ability of individuals to survive and reproduce Will lead to a gradual change in a population, with favorable characteristics accumulating over generations
30 In the process of artificial selection Humans have modified other species over many generations by selecting and breeding individuals that possess desired traitsFigure 22.10TerminalbudLateralbudsBrussels sproutsCabbageFlowerclusterLeavesCauliflowerandstemsBroccoliWild mustardKohlrabiStemKale
31 Summary of Natural Selection Natural selection is differential success in reproductionThat results from the interaction between individuals that vary in heritable traits and their environment
32 In the adaptation of organisms to their environment Natural selection can produce an increase over timeIn the adaptation of organisms to their environmentFigure 22.11(a) A flower mantid in Malaysia(b) A stick mantid in Africa
33 If an environment changes over time Natural selection may result in adaptation to these new conditions
34 Concept 22.3: Darwin’s theory explains a wide range of observations Darwin’s theory of evolutionContinues to be tested by how effectively it can account for additional observations and experimental outcomes
35 Natural Selection in Action Two examplesProvide evidence for natural selection
36 Differential Predation in Guppy Populations Researchers have observed natural selectionLeading to adaptive evolution in guppy populationsReznick and Endler transplanted guppies from pike-cichlid pools to killifish poolsand measured the average age and size of guppies at maturity over an 11-year period (30 to60 generations).EXPERIMENTPools with killifish,but not guppies priorto transplantExperimentaltransplant ofguppiesPredator: Killifish; preysmainly on small guppiesGuppies:Larger atsexual maturitythan those in“pike-cichlid pools”Predator: Pike-cichlid; preys mainly on large guppiesGuppies: Smaller at sexual maturity thanthose in “killifish pools”Figure 22.12
37 Control Population: Guppies from pools with pike-cichlids as predators RESULTSAfter 11 years, the average size and age at maturity of guppies in the transplantedpopulations increased compared to those of guppies in control populations.161.5185.667.5Weight of guppiesat maturity (mg)Age of guppiesat maturity (days)92.348.5Control Population: Guppiesfrom pools with pike-cichlidsas predatorsExperimental Population:Guppies transplanted topools with killifish aspredators76.1MalesFemales85.758.2CONCLUSIONReznick and Endler concluded that the change in predator resulted in different variationsin the population (larger size and faster maturation) being favored. Over a relatively short time, this alteredselection pressure resulted in an observable evolutionary change in the experimental population.
38 The Evolution of Drug-Resistant HIV In humans, the use of drugsSelects for pathogens that through chance mutations are resistant to the drugs’ effectsNatural selection is a cause of adaptive evolution
39 Percent of HIV resistant to 3TC Researchers have developed numerous drugs to combat HIVBut using these medications selects for viruses resistant to the drugsPatientNo. 1Patient No. 2Percent of HIV resistant to 3TCPatient No. 3WeeksFigure 22.13
40 The ability of bacteria and viruses to evolve rapidly Poses a challenge to our society
41 Homology, Biogeography, and the Fossil Record Evolutionary theoryProvides a cohesive explanation for many kinds of observations
42 HomologyHomologyIs similarity resulting from common ancestry
43 Anatomical Homologies Homologous structures between organismsAre anatomical resemblances that represent variations on a structural theme that was present in a common ancestorFigure 22.14HumanCatWhaleBat
44 Comparative embryology Reveals additional anatomical homologies not visible in adult organismsFigure 22.15PharyngealpouchesPost-analtailChick embryoHuman embryo
45 Vestigial organs Are some of the most intriguing homologous structures Are remnants of structures that served important functions in the organism’s ancestors
46 Molecular HomologiesBiologists also observe homologies among organisms at the molecular levelSuch as genes that are shared among organisms inherited from a common ancestor
47 Homologies and the Tree of Life The Darwinian concept of an evolutionary tree of lifeCan explain the homologies that researchers have observed
48 Anatomical resemblances among species Are generally reflected in their molecules, their genes, and their gene productsFigure 22.16SpeciesHumanRhesus monkeyMouseChickenFrogLamprey14%54%69%87%95%100%Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide
49 BiogeographyDarwin’s observations of the geographic distribution of species, biogeographyFormed an important part of his theory of evolution
50 Some similar mammals that have adapted to similar environments Have evolved independently from different ancestorsSugargliderAUSTRALIANORTHAMERICAFlyingsquirrelFigure 22.17
51 The succession of forms observed in the fossil record Is consistent with other inferences about the major branches of descent in the tree of life
52 The Darwinian view of life Predicts that evolutionary transitions should leave signs in the fossil recordPaleontologistsHave discovered fossils of many such transitional formsFigure 22.18
53 What Is Theoretical about the Darwinian View of Life? In science, a theoryAccounts for many observations and data and attempts to explain and integrate a great variety of phenomena
54 Darwin’s theory of evolution by natural selection Integrates diverse areas of biological study and stimulates many new research questions
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