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Descent with Modification: A Darwinian View of Life

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1 Descent with Modification: A Darwinian View of Life
Chapter 22 Descent with Modification: A Darwinian View of Life

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 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

3 Figure 22.1 How can this beetle survive in the desert, and what is it doing?

4 Figure 22.5 The voyage of HMS Beagle
GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA Pinta Genovesa Marchena Equator SOUTH AMERICA Santiago Daphne Islands Pinzón AUSTRALIA Fernandina PACIFIC OCEAN Isabela Figure 22.5 The voyage of HMS Beagle For the Discovery Video Charles Darwin, go to Animation and Video Files. Santa Cruz Andes Cape of Good Hope Santa Fe San Cristobal Tasmania Florenza Española Cape Horn New Zealand Tierra del Fuego

5 (a) Cactus-eater (c) Seed-eater (b) Insect-eater
Fig. 22-6 (a) Cactus-eater (c) Seed-eater In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater

6 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

7 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

8 Artificial Selection, Natural Selection, and Adaptation
Darwin then described four observations of nature and from these drew two inferences

9 Fig Observation #1: Members of a population often vary greatly in their traits Figure Variation in a population

10 Observation #2: Traits are inherited from parents to offspring

11 Fig Observation #3: All species are capable of producing more offspring than the environment can support Spore cloud Figure Overproduction of offspring

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

13 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

14 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 Figure Camouflage as an example of evolutionary adaptation

15 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?

16 Concept 22.3: Evolution is supported by an overwhelming amount of scientific evidence
One example includes the evolution of drug-resistant HIV

17 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

18 Fig 100 Patient No. 1 Patient No. 2 75 Percent of HIV resistant to 3TC 50 Patient No. 3 Figure Evolution of drug resistance in HIV 25 2 4 6 8 10 12 Weeks

19 The Fossil Record 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 Depth (meters) 2 Bristolia harringtoni 14 16 18 1 Bristolia mohavensis 3 Figure Fossil evidence of evolution in a group of trilobites 2 1 Latham Shale dig site, San Bernardino County, California

20 Fig 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) Figure The transition to life in the sea Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)

21 Vestigial structures are remnants of features that served important functions in the organism’s ancestors

22 Homology is similarity resulting from common ancestry
Humerus Radius Ulna Carpals Metacarpals Figure Mammalian forelimbs: homologous structures Phalanges Human Cat Whale Bat Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

23 Comparative embryology reveals anatomical homologies not visible in adult organisms
Pharyngeal pouches Post-anal tail Figure Anatomical similarities in vertebrate embryos Chick embryo (LM) Human embryo

24 Blocks of similar sequences in four mouse chromosomes:
Fig 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 Figure Similar blocks of sequences on human and mouse chromosomes Duplication, rearrangement, and mutation of DNA contribute to genome evolution

25 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 – 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.

26 Bacteria Most recent common ancestor of all living things Eukarya
Fig Bacteria Most recent common ancestor of all living things Eukarya Archaea 4 3 2 1 Billions of years ago Chimpanzee Figure Evolutionary relationships of the three domains of life Human Mouse 70 60 50 40 30 20 10 Millions of years ago

27 Convergent evolution does not provide information about ancestry NORTH
Fig 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 NORTH AMERICA Sugar glider AUSTRALIA Figure Convergent evolution The ability to glide evolved independently in these two distantly related groups of mammals Flying squirrel

28 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). Figure 26.7 Convergent evolution of analogous burrowing characteristics

29 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

30 Mid Ocean Ridge


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