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Evolution: Evidence and Theory Chapter 15 Section 15-1: The Fossil Record Fossils, Paleontology, & Geology • The study of fossils helped to lay the groundwork for Darwin’s ideas • Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier • Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe • Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today • Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time • This view strongly influenced Darwin’s thinking Nature of Fossils • Fossil: trace of long-dead organism; often found in layers of sedimentary rock which forms when sediment (dust, sand, mud) is deposited by wind or water • Minerals that form sedimentary rock slowly replace hard body parts or organism (shell, bones, teeth) • Over time, hard minerals replace tissue, leaving rocklike structure • Mold: type of fossil- imprint in rock of shape of organism; some eventually filled with hard minerals, forming cast: rocklike model of organism • 1668, Robert Hooke concluded that fossils are remains of plants & animals; one of first to study fossils • hypothesized that living organisms had somehow turned to rock Distribution of Fossils • Law of superposition: states that successive layers of rock or soil were deposited on top of one another by wind or water – Lowest stratum (layer) is oldest – Top stratum is most recent – Fossils in same stratum are approximately same age – Using law of superposition, observers could establish relative age of fossil: could say a fossil was younger or older than another fossil – Absolute age: could be estimated from amount of sediment deposited above the fossil Succession of Forms and Biogeography • Extinct: species that disappeared • Fossil record indicates there were several mass extinctions: brief periods during which large numbers of species disappeared – Resulted from drastic changes in environment, perhaps periods following volcanic activity • Biogeography: study of geographical distribution of fossils and living organisms • Comparison of recently formed fossil types and types of living organisms in same geographic area shows that new organisms arise in areas where similar forms already lived Section 15.2: Theories of Evolution Fig. 22-2 Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) American Revolution French Revolution U.S. Civil War 1800 1900 1750 1850 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population.” 1809 Lamarck publishes his hypothesis of evolution. 1830 Lyell publishes Principles of Geology. 1831–1836 Darwin travels around the world on HMS Beagle. 1837 Darwin begins his notebooks. 1844 Darwin writes essay on descent with modification. 1858 Wallace sends his hypothesis to Darwin. 1859 The Origin of Species is published. A Historical Perspective • The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae • The Old Testament holds that species were individually designed by God and therefore perfect • Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms Not the First Theory • Jean-Baptiste Lamarck (late 1700s) hypothesized that species evolve • Purposed that similar species descended from a common ancestor • Hypothesized that acquired traits were passed on to offspring • Acquired trait: one that is not determined by genes but develops during an organism’s lifetime as result of organism’s behavior or experience • Ex: Giraffes stretch necks • First to state that types of organisms change over time and that types of organisms are modified descendants of older types • The mechanisms he proposed are NOT SUPPORTED by evidence *BE VERY CAREFUL NOT TO USE LAMARCKIAN LANGUAGE. Darwin • As a boy and into adulthood, Charles Darwin had a consuming interest in nature • Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University • After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5year around the world voyage on the Beagle. Voyage of the Beagle • Collected specimens of South American plants and animals • Observed adaptations of plants and animals that inhabited many diverse environments • Influenced by Lyell’s Principles of Geology • Emphasized Earth was 6000 years old • Principles of uniformitarianism: geological structure of Earth resulted from cycles of observable processes and that these same processes operate continuously through time • Ex. Silt deposited by modern day rivers was deposited same way by ancient rivers • Began to believe that geologic changes require many years • Reasoned that formation of mountain ranges would slowly change habitats, requiring organisms to adapt to these changes which would be very slow and difficult to detect • Interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America Voyage of the Beagle Focus on Adaptation • Darwin perceived adaptation to the environment and the origin of new species as closely related processes • • 1844: Darwin wrote an essay on the origin of species and natural selection • • Did not introduce his theory publicly, anticipating an uproar June 1858: Darwin received a manuscript from Alfred Russell Wallace • • • From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches Developed a theory of natural selection similar to Darwin’s Darwin’s and Wallace’s hypotheses were presented side by side to Linnaean Society of London in 1858 The Origin of Species was published the next year • • In the Darwinian view, the history of life is like a tree with branches representing life’s diversity Darwin’s theory meshed well with the hierarchy of Linnaeus Artifical Selection, Natural Selection, and Adapation • Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits • artificial selection • Darwin then described four observations of nature and from these drew two inferences Observation #1: Members of a population often vary greatly in their traits Observation #2: • Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than the environment can support Observation #4: • Owing to lack of food or other resources, many of these offspring do not survive Two Inferences • 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 • 2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations 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 • • • BUT: This is not an ACTIVE process by the organism. Nature selects! If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species • • • • • 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 • Favorable traits have an adaptive advantage 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