Bio1151 Chapter 22 Descent with Modification
  1. Charles Darwin explained the diversity of life by            through          with               from a common ancestor.

    Charles Darwin published The Origin of Species in 1859, after a five-year voyage on the HMS Beagle.

      After graduating from Cambridge University, Darwin took an unpaid position as naturalist on the HMS Beagle for an around-the-world voyage (1831 - 1836). He observed a wide diversity of organisms, especially at the Galapagos Islands.

    The Galapagos Islands are home to 14 species of finches; differing mainly on their beaks, which are adapted for specific diets.

  2. The long beak of the cactus finch helps it tear and eat cactus flowers and pulp.
  3. The warbler finch uses its narrow beak to grasp insects.
  4. The large ground finch has a large beak adapted for cracking seeds.

    Darwin hypothesized that the different birds evolved from a common ancestor: descent with modification.

  5. Humans have modified other species over generations by            and breeding individuals that possess desired traits.

    Artificial selection. These vegetables have all been selected from one species of wild cabbage. By selecting variations in different parts of the plant, humans managed to breed divergent varieties.

      From the wild European rock dove, pigeon breeders produced varieties such as fantails, tumblers, pouters, and croppers, by artificial selection.
  6. Darwin proposed          selection as the mechanism driving evolution.

    Natural selection.

    Darwin formed his hypothesis of natural selection by drawing two inferences based on his observations.

  7. Observation #1 : Individuals of a population exhibit variation in their traits.
  8. Observation #2 : Many traits are heritable.
  9. Observation #3 : Many species overproduce offspring.
  10. Observation #4 : Resources are limited; many of these offspring do not survive due to competition for those resources. _________________________________________________________________

  11. Inference #1 (natural selection): Individuals whose traits give them a high probability of surviving and reproducing are likely to leave more offspring than others.
  12. Inference #2 (adaptation): A population will accumulate favorable traits over generations and become adapted to its environment.

      Heritable variation. To the extent that the variation in color and banding patterns in this snail population is heritable, it can be acted on by natural selection.

      Overproduction of offspring.

      A single puffball fungus can produce billions of spores.

      If all of these spores produce viable offspring, they would quickly carpet the surrounding land surface.

      Resources are limited.

      The billions of spores from a single puffball mushroom do not all find suitable habitat and enough nutrients to survive.

      Inference #1: natural selection.

      Inherited traits give an advantage to some individuals over others in a struggle for existence.

      Inference #2: adaptation.

      Over time, populations (NOT individuals) accumulate favorable traits such as camouflage and evolve by adapting to their environment.

      These species of insects called mantids have diverse shapes and colors that are adapted to different environments.

      Different species adapt to unique ecological niches (environmental resources).


  13. Drug resistance in bacteria and viruses such as HIV are probably due to            and            for individual organisms that possess the resistance.

    Evolution of drug resistance in HIV.

    When patients are treated with the HIV drug 3TC, mutations in the virus population allow some to be resistant to the drug and reproduce.

    Within weeks, 100% of the virus population in all 3 patients is 3TC-resistant.

  14.             anatomical structures, such as the            among mammals, provide evidence of common ancestry with modifications.

    Homologous structures. Even though these anatomical structures have been adapted for different functions, the forelimbs of all mammals are constructed from the same skeletal elements: one large bone, attached to two smaller bones, attached to several small bones, attached to phalanges.

    Reconstructing Forelimbs activity:

  15. Comparative             reveals anatomical             not visible in adults.

    Anatomical homologies revealed by comparative embryology. At some stage in their embryonic development, all vertebrates have a post-anal tail (located behind the anus), as well as pharyngeal (throat) pouches. Descent from a common ancestor can explain such similarities.
  16. Unrelated species that occupy similar ecological         may look similar by             evolution.

    Convergent evolution.

    The sugar glider is a marsupial mammal that evolved in Australia.

    While sugar gliders superficially resemble the eutherian flying squirrels of North America, the ability to glide through the air evolved independently in these unrelated mammals.

  17. Darwin's theory of evolution predicts               forms during the evolution of species, and this is supported by         records.

    Transitional fossils.

    Whales are mammals that must have evolved from terrestrial ancestors.

    This hypothesis predicts that their ancestors had four legs, as shown in these transitional fossils..

    Pakicetus and Rhodocetus had ankle bones unique to even-toed land mammals such as hippos.

    More recent fossils such as Dorudon and Balaena had reduced limbs more adapted to an aquatic lifestyle.

  18. Homologous characteristics derived from a common           can be used to establish evolutionary relationships among organisms.

    Evolutionary tree.

    Homologous characteristics that are inherited from a common ancestor are strong indications of evolutionary relationships.

    For example, "Tetrapods" all possess four limbs, presumably because they evolved from an ancestor (#2) that had four limbs.