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Transcript
Descent with Modification: A Darwinian View of Life Chapter 22 History of Evolution • Prior to November 24, 1859 and Charles Darwin: • The view of nature was determined by deep-seated beliefs held to be intractable truths rather than experimentation and observation • Biologists had slowly begun to accept various ideas of evolution (species change through time) • Evolution is the unifying principle of biology • Explains the unity and diversity of life History of Evolution • • • • • • • Aristole- scale of nature Linneaus- taxonomy Cuvier- catastrophism Hutton- gradualism Lamarck- inheritance of acquired characteristics Lyell- uniformitarianism Darwin- natural selection Lamarck’s Explanation of Evolution Jean Baptiste Lamarck (1744-1829) • Proposed that similar species descended from a common ancestor • Hypothesized that acquired traits were passed on to offspring • you would gain or lose features if you overused or didn't use them, and you could pass these new traits onto your offspring. • Not determined by your genes! (we know this is wrong) • Became known as the Inheritance of Acquired Characteristics Charles Darwin • • • • 1809-1882 (British) Attended medical school and studied to be a clergy. Became interested in natural history In 1831, set sail on the Beagle • A 5 year mapping and collection expedition to South America and the South Pacific. • Posed as the ships naturalist where he collected and recorded observations of specimens Voyage of the HMS Beagle • Invited to travel around the world • 1831-1836 (22 years old!) • makes many observations of nature • main mission of the Beagle was to chart South American coastline • Collected and observed many specimens of South America Findings • Observed massive geological changes • Concluded Earth must be VERY old • Went along with Hutton and Lyell’s findings Why should extinct armadillo-like species & living armadillos be found on the same continent? “This wonderful relationship in the same continent between the dead and the living will…throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.” Endemic organisms • Organisms that only live in one location Galapagos Islands • Darwin noted that there existed many finches on the islands, but while they had similarities, each was adapted to eating a particular type of island food Darwin’s Finches • Found 14 different birds, thought they were all different birds • Amazed to find out they were all finches But there is only one species of finch on the mainland! Descendant species Ancestral species Seed eaters Flower eaters Insect eaters Darwin’s Finches • Darwin’s conclusions • small populations of original South American finches landed on islands • variation in beaks enabled individuals to gather food successfully in the different environments • over many generations, the populations of finches changed anatomically & behaviorally • accumulation of advantageous traits in population • emergence of different species A Reluctant Revolutionary • Returned to England in 1836 • wrote papers describing his collections & observations • draft of his theory of species formation in 1844 • instructed his wife to publish this essay upon his death • reluctant to publish but didn’t want ideas to die with him • Then, in 1858, Darwin received a letter that changed everything… Alfred Russel Wallace a young naturalist working in the East Indies, had written a short paper with a new idea. He asked Darwin to evaluate his ideas and pass it along for publication. To Lyell— Your words have come true with a vengeance… I never saw a more striking coincidence…so all my originality, whatever it may amount to, will be smashed. The Origin of Species Darwin published this work to explain the variety of species that exist on the planet • On November 24, 1859, published after 21 years of refining • On the Origin of Species by Means of Natural Selection • Two main ideas: • Evolution explains life’s unity and diversity • Natural selection is a cause of adaptive evolution Descent with Modifications • Populations of organisms exhibit changes in characteristics that are passes on through inheritable means. • Summarized Darwin’s perceptions of the unity of life • States that all organisms are related through descent from an ancestor that lived in the remote past Darwin’s View of History • Darwin viewed the history of life like a tree, • With multiple branches from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms (1) Variation exists in natural populations (2) Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence - competition (4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations 5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species Natural Selection • Darwin concluded that evolution occurs by Natural selection. • Organisms best suited to their environment reproduce more successfully than other organisms. • This occurs over time and the environment “selects” the traits that will increase a population • Can not occur without genetic variations among species. 4 Main Principles 1. Variation exists among individuals in a species. 2. Individuals of species will compete for resources (food and space) 3. Some competition would lead to the death of some individuals while others would survive 4. Individuals that had advantageous variations are more likely to survive and reproduce. Natural Selection in Action • In humans, the use of drugs selects for pathogens that through chance mutations are resistant to the drugs’ effects • Natural selection is a cause of adaptive evolution • Researchers have developed numerous drugs to combat HIV but using these medications selects of viruses resistant to the drugs • The ability of bacteria and viruses to evolve rapidly poses a challenge to our society Evidence: Homology, Biogeography, and the Fossil Record Homology • Used to explain why certain characteristics in related species have an underlying similarity even though they may have VERY different functions. • Anatomical Homologies • Homologous structures • Vestigial organs • seemingly functionless parts, snakes have tiny pelvic and limb bones, humans have a tail bone • Molecular Homologies • When comparing the DNA of one species to another, more similarities are found in species that are more closely • Amino acid sequence in hemoglobin is one different between gorillas and humans • Humans and frogs differ by 67 A.A Evidence: Homology, Biogeography, and the Fossil Record • Biogeography • Biogeography is the study of the range and distribution of plants and animals throughout the world • distributions are consistent with the hypothesis that related forms of life evolved in one locale and then spread to accessible regions • A different mix of plants and animals would be expected whenever geography separates continents, islands, seas, etc. Sugar glider, Petaurus breviceps, is a tree-dweller and resembles the placental flying squirrel. The Australian wombat, Vombatus, Kangaroo, Macropus, is an herbivore is nocturnal and lives in burrows. It that inhabits plains and forests. It resembles the placental woodchuck. resembles the placental Patagonian cavy of South America. Evidence: Homology, Biogeography, and the Fossil Record • Fossil Record • Fossils are the remains and traces of past life or any other direct evidence of past life such as trails, footprints, or preserved droppings • Fossils record the history of life from the past • Document a succession of life forms from the simple to the more complex • Sometimes the fossil record is complete enough to show descent from an ancestor