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Chapter 15 – Evolution: Evidence and Theory • The Fossil Record • Theories of Evolution • Evolution in Process Section 15-1 The Fossil Record • Fossil evidence shows a long history of life on Earth. The fossil record shows that forms of organisms appeared, lasted for long periods of time, and then disappeared, only to be followed by newer forms of life that also eventually disappeared. The history of life is one of constant change and a tremendous diversity of life-forms Nature of Fossils • A fossil is a trace of longdead organisms. • Fossils are often found in layers of sedimentary rock, which is formed when sediment, such as dust, sand, or mud is deposited by wind and water. • Usually develop from the hard body parts which are replaced by minerals over time Nature of Fossils • Mold is essentially an imprint in rock in the shape of an organism. • Some molds eventually are filled with hard minerals, forming a cast, a rock-like model of the organism Nature of Fossils • Robert Hooke (1635-1703) published his conclusion that fossils are the remains of plants and animals. He hypothesized that living organisms had somehow been turned to rock Distribution of Fossils • Nicolaus Steno (1638-1686) made an important contribution toward a modern understanding of Earth’s geological and biological history. • In 1669, he proposed the law of superposition, which states that successive layers of rock or soil were deposited on top of one another by wind or water Distribution of Fossils Distribution of Fossils • The lowest stratum, or layer, in a cross section of Earth is oldest, while the top stratum is the most recent. • Fossils found within a single stratum are of the same approximate age. • Relative age of a fossil says that a given fossil is younger or older than another based on what stratum it is found • Absolute age could be estimated from radioactive dating Distribution of Fossils • The fossil record indicates that there were several mass extinctions, brief periods during which large numbers of species disappeared. • Mass extinctions probably resulted from drastic changes in the environment, perhaps following periods of volcanic activity or collisions with asteroids. Distribution of Fossils • Biogeography is the study of the geological distribution of fossils and of living organisms. • A comparison of recently formed fossil types with types of living organisms in the same geographic area shows that new organisms arise in areas where similar forms already lived. Natural Selection 15-2 A Critical Thinking Approach Start Thinking??? (Write answers in your notes) • Define Evolution in your own words • How do you think evolution happens? (What is the mechanism) • How long do you think evolution takes??? Problem Solving • Cheetahs are the world’s fastest land mammal. They have the ability to run almost 70 mph in pursuit of prey. All other big cats can only run about 35 mph over very short distances – Do you think the cheetah’s speed is important to its survival? Why or why not? – How do you think a biologist would explain the cheetah’s speed, based on the fact that their ancestors (and all other cats) only run 35 mph) – Remember, you are trying to think of a way that all cheetahs got faster over time Georges Cuvier (1769-1832) Georges Cuvier • Saw org. as complete wholes, w/ each body part fully integrated into the entire org. No single part could be altered w/o damaging the entire org. • Also suggested appearance of new org. in fossil record occurred through special creation events following natural catastrophes Questions • How do you think Cuvier would explain the cheetah’s speed? • Do you think Cuvier’s explanation is scientific? Why or why not? • How could test Cuvier’s ideas • “Same as it ever was” Jean-Baptiste Lamarck (17441829) Jean-Baptiste Lamarck-part 1 • 3 basic ideas: 1. A change in the envir causes a resulting change in the org. behavior 2. The behavior change causes the org. to use or not use various organs 3. The added use of an organ will cause it to grow & become more complex, the disuse of an organ will cause it to atrophy or waste away For Example, Lamarck thought that giraffes got longer necks by stretching to reach food. By using all of the muscles in the neck, their necks got longer. The giraffes would then pass on the extra height to their offspring, who would be born just as tall as their parents. “Use it or lose it” Questions • Do you think Lamarck’s explanation is scientific? Why or why not? • How could you test Lamarck’s ideas? • How do you think Lamarck would explain the cheetah’s speed? • How could you test the ideas about inheritance? Doberman Tail Docking? Body Builders? War Amputees? John Stackable or the Governator? Charles Darwin 4 Basic Ideas: 1. There are variations w/in populations of org. 2. Variations can be passed to offspring 3. Each generation produces more offspring than survive to adulthood 4. The org. w/ the favorable characteristics survive better and reproduce more often, thus transmitting their traits to the next generation Charles Darwin 1809-1882 Questions • How do you think Charles Darwin explained the cheetah’s speed? • Do you think Charles Darwin’s explanation is scientific? Why or why not? • How could you test Charles Darwin’s ideas? “NATURAL SELECTION” Reflection • Cheetahs are the world’s fastest land mammal. They have the ability to run almost 70 mph in pursuit of prey. All other big cats can only run about 35 mph over very short distances – Review your answer to this question: How do you think a biologist would explain the cheetah’s speed, based on the fact that their ancestors (and all other cats) only run 35 mph? – Which of the 3 evolutionary thinkers does your explanation sound like??? Classwork Scientist Ideas Scientific Y/N Hypothesis Supported/Refuted Cuvier Darwin Lamarck Who Said This??? • “The fennic’s ears grew large b/c the heat of the desert caused the fenic to use its ears to release heat. The ears grew b/c of this new added use. • After its ears grew it passed the trait for bigger ears onto its offspring, which also used their ears more which caused more growth & over time the fennic’s ears became what we see today.” Who said this??? • The viper became wonderfully camouflaged b/c each generation of vipers has variations in their camouflage. • The vipers w/ the best camo are more likely to escape becoming dinner for some predator. Also the vipers w/ the best camo are more likely to get more food b/c they were better able to sneak up on their prey. • Meanwhile the poorly camo’d vipers are more likely to be eaten & to suffer from lack of food. • The result is that the better camo’d vipers survive better and reproduce more often than their poorly camo’d counterparts. • Each generation of vipers receives its genes from the survivors of previous generations, so the collection of genes is being filtered, in a sense, w/ the genes for poor camo being removed & genes for good camo being maintained. Who said this??? Feathered feet are an advantage for a bird in a cold climate. • • In the past the snowy owl pop. Had lots of variation in the amount of feathers on their feet, but in each generation the owls w/ the most feathers on their feet (& therefore the best insulated feet) had the best chance of surviving the cold & enetually reproducing. • The owls w/ less insulated feet would have difficulty in surviving the cold and consequently reproduced less than other owls. • Over many generations of owls, the characteristic of highly feathered feet became prominent 15-3 Evidence of Evolution • Homologous Structures – similar features originated in shared ancestor. – i.e. beaks of birds, forelimbs (fig. 15-7) • Analogous Strucures – same function & look alike, but different structures. – i.e. (fig. 15-8) Hummingbird & humming moth • Vestigial Structures – Useful to ancestors but not to modern organism. – i.e. Whales evolved from land animals (hind legs Homologous Structures Analogous Structures Vestigial Structures Patterns of Evolution • Coevolution – change of 2 or more species in close association w/ each other. – i.e. bats & flowers (fig. 15-10) • Convergent Evolution – Look similar, but not related at all. – i.e. Shark & porpoise • Divergent Evolution – 2 or more related populations or species become more & more dissimilar ( Can result in new species) – i.e. Galapagos Finches, dogs (fig. 15-11)