Bio1151 Chapter 21 Genomes and Their Evolution
  1. Genome comparisons can reveal               relationships among species.
Bio1151 Chapter 22 Descent with Modification
  1. Charles Darwin explained the diversity of life by            through          with               from a common ancestor.

      Three domains of life. Genome comparisons of species help us understand evolutionary events evolutionary relationships. This tree diagram shows the ancient divergence among the three domains based on genome evidence. Mammals diverged within the eukaryote lineage about 65 million years ago.
      Chimpanzees are the closest relatives to humans.


      Charles Darwin published The Origin of Species in 1859, after a five-year voyage on the HMS Beagle, and after receiving an essay from Alfred Russel Wallace describing similar ideas.


      After graduating from Cambridge University, Darwin took an unpaid position as a naturalist on the HMS Beagle for a 5-year (1831 - 1836) around-the-world voyage. He observed a wide diversity of organisms, especially at the Galápagos Islands.


      The Galápagos Islands are home to 14 species of related finches; differing mainly on their beaks, which are adapted for specific diets.
    • The long beak of the cactus finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp.
    • The green warbler finch (Certhidea olivacea) uses its narrow beak to grasp insects.
    • The large ground finch (G. magnirostris) has a large beak adapted for cracking seeds. One explanation was that the different birds evolved from a common ancestor: descent with modification.
     
     
     
     
  2. Humans have modified other species over generations by            and breeding individuals that possess desired traits. Darwin called this             selection.

      Artificial selection. These vegetables have all been selected from one species of wild mustard. By selecting variations in different parts of the plant, breeders have obtained these divergent results.


      From the wild European rock dove Columba livia, pigeon breeders produced varieties such as fantails, tumblers, pouters, and croppers, by artificial selection.
     
     
     
     
  3. Darwin proposed          selection as the mechanism driving evolution. He formed this hypothesis by drawing two             based on four               .

      Darwin formed his hypothesis of natural selection by drawing two inferences based on his observations.
     
     
     
     
    • Observation #1: Members of a population exhibit            in their traits.

        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.
       
       
       
       
    • Observation #2: Much of this variation is            .

        Heritable variation. The family of Sissy Spacek and Jack Fisk exhibits genetic variation. Sexual reproduction produces variation in the gametes and unique combinations of genes in the offspring, even though the offspring inherit traits from both parents.
       
       
       
       
    • Observation #3: Most species tend to              of offspring.

        Overproduction of offspring. A single puffball fungus can produce billions of offspring. If all of these offspring and their descendants survived, they would quickly carpet the surrounding land surface.
       
       
       
       
    • Observation #4: Resources are          ; many of these offspring do not survive.
       
       
       
       
      • Inference #1 (          selection): Individuals whose inherited traits give them a high probability of surviving ( struggle for            ) and              are likely to leave more offspring than others:.

          Inference #1: struggle for existence. Inherited traits give an advantage to some individuals over others in a struggle for existence.


          The struggle for existence applies to plants in many forms: competition for sunlight, moisture, nutrients, pollinating insects, etc. Winners of such struggles are likely to produce more offspring than their neighbors.


          The struggle for existence ultimately is reflected in differential reproductive success. The winner of this struggle among Bighorn Sheep males is likely to produce more offspring than his competitor.
         
         
         
         
      • Inference #2 (             ): A population will gradually accumulate favorable characteristics over generations and become more          to its environment.


      Inference #2: adaptation. Over time, populations (NOT individuals) accumulate favorable characteristics 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). Video: SeaHorses
     
     
     
     
  4. 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 each case is 3TCresistant.


      HIV, a retrovirus. The Human Immunodeficiency Virus (HIV) is a retrovirus. It has the enzyme reverse transcriptase to copy the RNA genome into DNA, which can be integrated into the host genome as a provirus.
     
     
     
     
  5.             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 basic skeletal elements: one large bone, attached to two smaller bones, attached to several small bones, attached to five phalanges.
     
     
     
     
  6. 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.
     
     
     
     
  7. Unrelated species that occupy similar ecological         may look similar by             evolution.

      Convergent evolution. The sugar glider is a marsupial mammal (young finish development in a pouch) 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 2 distantly related mammals.
     
     
     
     
  8. 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. Paleontologists digging in Egypt and Pakistan have identified extinct whales that had hind limbs. Pakicetus and Rhodocetus had ankle bones similar to that of hippos.
     
     
     
     
  9. 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 that had four limbs.