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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 • Evolution can be viewed as both a pattern and a process • Three observations about life – Organisms are suited for life in their environments – Organisms share many characteristics – Organisms show a great diversity Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 22.1 How can this beetle survive in the desert, and what is it doing? 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 Fig. 22-6 (a) Cactus-eater • In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes (c) Seed-eater (b) Insect-eater 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 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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Artificial Selection, Natural Selection, and Adaptation • Darwin then described four observations of nature and from these drew two inferences Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-10 • Observation #1: Members of a population often vary greatly in their traits • Observation #2: Traits are inherited from parents to offspring Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 22-11 Observation #3: All species are capable of producing more offspring than the environment can support Spore cloud • 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 • 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 Natural Selection: A Summary • 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 • What is the ultimate source of genetic variation? Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence • One example includes the evolution of drugresistant HIV 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 • 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 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 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 The red dot shows change over time in the location and angle of the spines 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 Fig. 22-16 • • 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) • Vestigial structures are remnants of features that served important functions in the organism’s ancestors Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Homology is similarity resulting from common ancestry Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat • 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 Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo Fig. 21-11 Human chromosome 16 DNA sequences very similar to large blocks of human chromosome 16 are found on mouse chromosomes 7, 8, 16, and 17. This suggests that the DNA sequence in each block has stayed together in the mouse and human lineages since the time they diverged from a common ancestor. Blocks of DNA sequence Blocks of similar sequences in four mouse chromosomes: 7 8 16 17 Duplication, rearrangement, and mutation of DNA contribute to genome evolution Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 21.6: Comparing genome sequences provides clues to evolution and development • 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 • Fig. 21.15 – This tree diagram shows the ancient divergence of bacteria, archaea, and eukaryotes. A portion of the eukaryote lineage is expanded in the inset to show the more recent divergence of three mammalian species. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 21-15 Bacteria Most recent common ancestor of all living things Eukarya Archaea 4 3 2 Billions of years ago 1 0 Chimpanzee Human Mouse 70 60 50 40 30 20 Millions of years ago Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 10 0 Fig. 22-20 • • • 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 Sugar glider NORTH AMERICA AUSTRALIA The ability to glide evolved independently in these two distantly related groups of mammals Flying squirrel Fig. 26-7 An elongated body, enlarged front paws, small eyes, and a pad of thickened skin that protects a tapered nose all evolved independently in the marsupial Australian “mole” (top) and a eutherian North American mole (bottom). 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 (this term outdated, plate tectonics is now the proper term) • 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 Mid Ocean Ridge Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings