Lecture Outline: Descent With Modification

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  1. Introduction to Evolution and Life Concepts
    1. Unit Focus
      1. The entire unit is about evolution, a really important biological concept
      2. This introductory chapter provides an overview of evolution and a historical context
      3. The chapter largely concerns Darwin but covers many other major historical figures
    2. Core Concepts Illustrated
      1. Example of Camouflage
        1. The color of a camouflaged caterpillar is favored by evolution
        2. Evolution has selected for colors that provide camouflage, otherwise the individual would likely die out
      2. Variety of Life
        1. There is an enormous variety of organisms, both living now and those that have lived historically
        2. This variety ties in with evolution because evolution leads to speciation (the creation of new species)
      3. Unity of Life
        1. Despite the huge variety, there is a unity of all living things, sharing important features
        2. All organisms share a set of seven major characteristics, such as using energy and having a high degree of order
        3. This unity exists because all organisms descended from the same original successful ancestor lineage
  2. Historical Context Leading to Darwin
    1. Early Voyage and Galápagos Islands
      1. Darwin's famous voyage was a years-long process
      2. The Galápagos Islands were visited late in the voyage
      3. The organisms there were drastically different from those in England, which informed Darwin's way of thinking
    2. Paleontology and the Strata
      1. Strata are layers of soil, and stratified soil has layers
      2. Fossils are mineralized remains of past living organisms
      3. Historically, most people believed in a creation event where all species came into existence at once and did not evolve
      4. Different strata represent different ages, with the lowest layers being the oldest
      5. Finding different sets of fossils in different strata suggests that different species existed at different times, which disagrees with creationism
      6. Cuvier, the "father of paleontology"
        1. Believed in creationism but accepted that some species go extinct (fossils missing in newer strata)
        2. He could not reconcile creationism with new sets of fossils appearing in newer strata
    3. Faith Versus Science
      1. Science is belief based on evidence, requiring belief to change if new evidence contradicts it
      2. Faith is belief without evidence, sometimes despite evidence to the contrary
      3. Early evolutionary thinkers were often non-scientific because they asserted evolution occurred but did not offer a hypothesis (explanation) for how it happens
    4. Lamarck and Acquired Characteristics
      1. Lamarck was the first scientific evolutionary thinker because he offered a hypothesis to explain the mechanism of change
      2. Lamarck's hypothesis: Organisms gain certain traits through lifetime experience, and these acquired traits are passed on to offspring
      3. Example: Giraffes supposedly developed long necks by stretching for higher leaves during their lifetime, passing this longer neck trait to their young
      4. Lamarck's explanation was incorrect because the experience of an organism's lifetime (e.g., bulk from weightlifting, or training a bonsai tree) is not passed on genetically
  3. Charles Darwin and Natural Selection
    1. The Voyage and Geologic Influences
      1. The ship was called the Beagle; the voyage's original purpose was cartography (mapping the coast of South America)
      2. Darwin served as the ship's naturalist, cataloging wildlife during stops
      3. Darwin started as a creationist but changed his view during the years-long voyage
      4. He was influenced by geologists Lyell and Hutton, who proposed that Earth's physical features change gradually through normal processes (e.g., erosion)
      5. This suggested the Earth was much older (millions of years, rather than the thousands most people believed); the true age is about 4.5 billion years
    2. Natural Selection: The Core Mechanism
      1. Darwin is famous for his explanation of how evolution happens: through natural selection
      2. The full title of his famous book is On the Origin of Species by Means of Natural Selection
      3. Natural selection results in successive generations becoming, on average, more adapted to their surroundings
      4. Individuals with beneficial traits (high fitness) are more likely to survive and successfully reproduce
      5. Inheritance Mechanism
        1. DNA/Genes are passed on from parent to offspring
        2. Proteins directly give an organism its traits (acting as assembly instructions)
    3. Darwin's Major Observations
      1. Observation 1: Variation in Heritable Characteristics
        1. Individuals in any naturally occurring population are not identical in their traits (e.g., color/spotting differences in beetles)
        2. Only heritable variation (genetic variation) affects evolution
        3. Variation leads to differences in fitness (survivability)
      2. Observation 2: Overproduction of Offspring
        1. Species produce far more offspring (e.g., spore clouds, sperm) than can possibly survive
    4. Darwin's Inferences (Mechanism of Evolution)
      1. Inference 1: Individuals that are well-suited (adapted, high fitness) tend to leave more offspring
      2. Inference 2: Over time, favorable traits that lead to higher fitness accumulate in the population, resulting in better adaptation (evolution)
      3. Natural selection is the only way evolution occurs that reliably leads to an increase in fitness
  4. Supporting Concepts and Evidence
    1. Alfred Russel Wallace
      1. Wallace independently came up with essentially the same idea of natural selection
      2. He respected Darwin and yielded credit, which is why Darwin became the household name
    2. Phylogenetic Trees
      1. Darwin's diary included the first known phylogenetic tree
      2. A phylogenetic tree is a treelike representation showing species relatedness and how they came into existence
      3. Each branch point represents speciation (one lineage diverges into two new species)
      4. The overall Tree of Life shows that all organisms ultimately descended from one common ancestor
    3. Artificial Selection
      1. Artificial selection operates exactly like natural selection, but humans are doing the selecting
      2. Humans favor certain traits regardless of whether they aid natural survival
      3. Example: Wild mustard was selectively bred into drastically different forms, including kale, Brussels sprouts, cabbage, and broccoli
    4. Examples of Natural Selection
      1. Galápagos Finches
        1. Finches on different islands evolved distinct bill shapes corresponding to the local food source
        2. A broad, tough bill was selected for seed eaters (to crack tough seeds), while a narrow bill was selected for insect eaters (to reach into tight spaces)
      2. Soapberry Bugs
        1. These bugs feed by piercing fruit rind with their proboscis
        2. When thinner-rinded fruit (golden rain tree) was introduced, the average length of the proboscis decreased
        3. Shorter noses were favored because they are sturdier, reducing the chance of breakage and subsequent starvation, while still being long enough to pierce the thinner fruit
      3. Antibiotic Resistance
        1. Antibiotics (first mass-produced around World War II) change the environment for bacteria
        2. Bacteria with random genetic variations that confer resistance survive the selection event
        3. The next generation is immune to that antibiotic, requiring new drug development
    5. Homology and Analogy
      1. Homology (Homologous Structures)
        1. Structures are similar due to a common ancestry
        2. Example: The forelimbs of different mammals (human, cat, whale, bat) are made up of the same number and types of bones, despite being used for different purposes (throwing, running, swimming, flying)
        3. Example: Features shared in the embryonic stage, such as the post-anal tail present in all vertebrates
      2. Analogy (Analogous Structures)
        1. Structures are similar in appearance or use but not due to common ancestry
        2. Analogous structures result from convergent evolution
        3. Convergent evolution is the independent evolution of similar features in unrelated species because they are advantageous in similar environments
        4. Example: The gliding flaps of skin found in the marsupial sugar glider and the flying squirrel
        5. Example: Eyeballs, which evolved independently in many types of animals
    6. Importance of Fossils
      1. Fossils continue to be highly important in evolutionary studies, helping to fill in "missing links" in knowledge
      2. Example: Ankle bone structure suggests that marine mammals (whales, porpoises) are evolutionarily more related to even-toed ungulates (like pigs) than to other mammals
      3. Fossils representing extinct lineages clarify the evolutionary path of modern species