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Ch. 22: Descent with Modification - A Darwinian View of Life Slide 2 I.Intro A. Charles Darwin published On The Origins of Species in 1859. B.Evolution: C.Natural Selection: Slide 3 D.Evolutionary adaptation: a prevalence of inherited characteristics that enhance organisms survival and reproduction. Examples: Katydid - mimicry Creosote bush - toxins Bats - echolocation Slide 4 II.The Historical Context for Evolutionary Theory Slide 5 A.Western culture resists evolutionary views: 1.Plato and Artistotle 2.Judeo-Christian culture: natural theology a.Carolus Linnaeus (1707-1778): Swedish botanist tried to put in order the diversity of life for the greater glory of God. -Taxonomy: 3.Georges Cuvier (1769-1832): French anatomist who developed paleontology, the study of fossils. a.Fossils: relics or impressions of organ- isms found in sedimentary rock. Slide 6 b.New layers of sediments cover older ones, creating layers of strata. Fossils within layers show that a succession of organisms have populated Earth throughout time. c.Cuvier opposed evolution. He advocated catastrophism: strata due to a catastrophe (flood/drought) then area repopulated by immigrating species. Slide 7 B.Theories of geologic gradualism helped clear the path for evolutionary biologists: 1.Scottish geologist James Hutton (1726- 1797) proposed gradualism: 2.Scottish geologist Charles Lyell (1797- 1875) incorporated gradualism to form a theory called uniformitarianism. Slide 8 3.Hutton and Lyell had a large influence on Darwin. If geological changes result from slow, continuous processes, then the Earth must be far older than the 6000 years assigned by theologians from biblical inference. C.Jean Baptiste Lamarck published his theory of evolution in 1809. 1.Lamarck compared current species of organisms with fossil forms and noticed several lines of descent. 2.Lamarcks method of evolution: 3.Example: Giraffes long neck Slide 9 III.Darwinian Evolution A.Born in 1809 in western England. 1.After graduating college, Darwin was chosen to be a conversation companion to Captain Robert FitzRoy, on the survey ship Beagle for a voyage around the world. B.Field research on the Beagle helped him develop his view of evolution. Slide 10 1.The Beagles main mission was to chart S. Americas coast. 2.Darwin had a lot of time to explore the areas. He collected thousands of exotic specimens. 3.Darwin noticed that the organisms living on the Galapagos Islands resembled organisms found on the mainland S. America. 4.Darwin took notice of the 13 types of finches he collected. Their different beak shapes correlated to the foodsource found on the island they lived on. Slide 11 Slide 12 C.By the early 1840s, Darwin had developed the major features of natural selection. D.In 1858, Alfred Wallace, a young naturalist, sent Darwin a manuscript containing a theory of natural selection essentially identical to Darwins. E.The next year, Darwin published The Origin of Species. 1.Two main points: Slide 13 2.Descent with Modification = evolution Based on fossil evidence Slide 14 3.Natural Selection: Ernst Mayr, an evolutionary biologist, has dissected the logic of Darwins theory into three inferences based on five observations. 5 observations: 1 - Exponential fertility 2 - Stable population size 3 - Limited resources 4 - Individuals vary 5 Heritable variation Slide 15 3 inferences: 1 - Struggle for existence 2 - Non-random survival 3 - Natural selection (differential success in reproduction) 4.We can summarize Darwins main ideas in 3 points: a.Natural selection is differential success in reproduction (unequal ability of individuals to survive and reproduce). b.Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population. Slide 16 c. The product of natural selection is the adaptation of populations of organisms to their environment. Slide 17 5.In each generation, environmental factors filter heritable variations, favoring some over others. a.Differential reproduction: b.Artificial selection: Slide 18 Slide 19 6.While natural selection involves interactions between individual organisms and their environment, it is not individuals, but populations that evolve. a.Population: b.Therefore, evolution is measured as the change in relative proportions of heritable variation in a population over a succession of generations. Slide 20 F.Examples of natural selection provide evidence for evolution: 1.Insecticide- resistance in insects: a.Over time, insecticides become less effective as the percentage of insecticide- resistant individuals increases with each generation. b.Ex: DDT and malathion Slide 21 2.Drug-Resistance HIV: a.Natural Selection favors viruses with a resistance to the many HIV drugs being developed. b.For patients treated with the drug 3TC, which interferes with genome replication in HIV, 3TC-resistant strains become 100% of the population of HIV in just a few weeks. Slide 22 a.Vestigial organs: Ex. whale/snake hindlimbs; wings on flightless birds G. Other evidence for evolution: 1.Homology: Forearm: homologous structures Slide 23 b.Homologies in embryonic development: -pharyngeal pouches Slide 24 Pharyngeal Pouches and Tails Slide 25 c.Homologies on a molecular level: Slide 26 d.Homologies reflect the taxonomic tree of life. Slide 27 Slide 28 e.Evolutionary relationships among species are documented in their DNA and proteins - in their genes and gene products. 2.Biogeography: a.Species tend to be more closely related to other species from the same area than to other species with the same way of life, but living in different areas. b.Marsupials of Australia Slide 29 The sugar glider and flying squirrel are similar in appearance. However, the sugar glider is more similar to other marsupials in Australia. This is an example of convergent evolution. Slide 30 c.Islands provide good evidence for evolution; islands often have species that are found no where else in the world. These species are called endemics. Island organisms usually resemble species found on the nearest mainland. d.Island chains or archipelagos, individual may have different, but related species as the first mainland invaders reached one island and then evolved into several new species as they colonized other islands in the archipelago. Slide 31 Ex. Drosophila of Hawaii Finches of the Galapagos Islands Slide 32 Slide 33 3.Fossil evidence of evolution: a.The succession of fossil forms is compatible with the branches of the tree of life. Ex. Fish Amphibians Reptiles Mammals, Birds b.Fossils show changes that occurred.