Descent with Modification: A Darwinian View of Life

Transcription

1 Chapter 22 Descent with Modification: A Darwinian View of Life PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp 1

2 Overview: Endless Forms Most Beautiful A new era of biology began in 1859 when Charles Darwin published The Origin of Species 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 2

3 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 3

4 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 4

5 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 5

6 Fig Layers of deposited sediment Younger stratum with more recent fossils Older stratum with older fossils 6

7 Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier 7

8 Geologists James Hutton and Charles Lyell perceived that changes in Earth s surface can result from slow continuous actions still operating today This view strongly influenced Darwin s thinking 8

9 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 9

10 Fig Acquired traits cannot be inherited 10

11 Darwin s Research As a boy and into adulthood, Charles Darwin had a consuming interest in nature Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle 11

12 The Voyage of the Beagle During his travels on the Beagle, Darwin collected specimens of South American plants and animals He observed adaptations of plants and animals that inhabited many diverse environments Darwin was influenced by Lyell s Principles of Geology and thought that the earth was more than 6000 years old His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America 12

13 Fig The Galápagos Islands Fernandina Isabela Pinta Marchena Santiago Pinzón Santa Cruz Florenza Genovesa Daphne Islands Santa Fe San Cristobal Española NORTH AMERICA PACIFIC OCEAN SOUTH AMERICA ATLANTIC OCEAN GREAT BRITAIN Cape Horn Tierra del Fuego Cape of Good Hope EUROPE AFRICA Equator AUSTRALIA Tasmania New Zealand 13

14 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 14

15 Beak variation in Galápagos finches Fig (a) Cactus-eater (c) Seed-eater (b) Insect-eater 15

16 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 16

17 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 17

18 Fig 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 18

19 Fig Hyracoidea (Hyraxes) Moeritherium Sirenia (Manatees and relatives) Barytherium Deinotherium Mammut Platybelodon Stegodon Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) Millions of years ago Years ago 19

20 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 20

21 Fig Terminal bud Lateral buds Cabbage Flower clusters Brussels sprouts Leaves Cauliflower Kale Stem Wild mustard Broccoli Flowers and stems Kohlrabi 21

22 Observation #1: Members of a population often vary greatly in their traits 22

23 Observation #2: Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than the environment can support 23

24 Fig Overproduction of offspring Spore cloud 24

25 Observation #4: Owing to lack of food or other resources, many of these offspring do not survive 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 25

26 Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources Thomas Malthus s ideas: In nature plants and animals produce far more offspring than can survive, and that Man too is capable of overproducing if left unchecked. Malthus concluded that unless family size was regulated, man's misery of famine would become globally epidemic and eventually consume Man. Malthus' view that poverty and famine were natural outcomes of population growth and food supply was not popular among social reformers who believed that with proper social structures, all ills of man could be eradicated. 26

27 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 27

28 Note that individuals do not evolve; populations evolve over time Adaptations vary with different environments (a) A flower mantid in Malaysia (b) A stick mantid in Africa 28

29 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 29

30 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 30

31 Fig a 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 31

32 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 32

33 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 33

34 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 34

35 Fig Patient No. 1 Patient No Patient No Evolution of drug resistance in HIV Weeks 35

36 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 36

37 The Fossil Record 0 2 The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time Bristolia insolens Bristolia bristolensis Bristolia harringtoni Bristolia mohavensis 1 Latham Shale dig site, San Bernardino County, California 37

38 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 (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor) 38

39 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 39

40 Fig Mammalian forelimbs: homologous structures Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat 40

41 Comparative embryology reveals anatomical homologies not visible in adult organisms Fig Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo 41

42 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 42

43 Vestigial Structures 43

44 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 44

45 Fig Branch point (common ancestor) Lungfishes 1 Amphibians Tetrapod limbs 2 Mammals Amnion 3 Lizards and snakes Homologous characteristic 4 5 Feathers 6 Crocodiles Ostriches Hawks and other birds Birds 45

46 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 46

47 Fig Sugar glider NORTH AMERICA AUSTRALIA Flying squirrel 47

48 Analogous structures 48

49 49

50 Aardvark (Orycteropus afer) 50 Fig a, p. 402

51 Giant anteater (Myrmecophaga tridactyla) 51 Fig b, p. 402

52 Pangolin (Manis crassicaudata) 52 Fig c, p. 402

53 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 Stenasellus asiaticus 53

54 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 54

55 Continental Drift 55

56 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 56

57 Fig. 22-UN2 57

58 Fig. 22-UN3 58

59 ??????? 59

60 Thank you for your attention and participation! 60

61 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 61

62 5. Explain why an individual organism cannot evolve 6. Describe at least four lines of evidence for evolution by natural selection 62