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Darwin proposed his theory of evolution to explain life on earth and he proposed natural selection as the process of evolution. This theory is one of the most well accepted theories in science so, why is that… What is the evidence to support evolution? 420 mill yr old sea star fossil How do we use that evidence to understand evolutionary history and relationships between organisms. Evidence of Change Through Time I. Fossils -any trace of an organism that lived in the past -e.x. bones, branches, shells, tracks, impressions & dung Fig 24.3 Evidence of Change Through Time http://videos.howstuffworks.com/hsw/12698-windows-into-the-past-how-fossils-form-video.htm http://www.pbs.org/wgbh/evolution/library/04/3/l_043_01.html Evidence of Change Through Time I. How do fossils form? Organism (that makes it way to the ocean) dies and sinks to bottom. If not scattered by scavengers, gets covered by sediment Once safely buried in sediment, soft parts decompose and then hard parts become replaced by dissolved minerals. Fish pics: http://www.discoveringfossils.co.uk/whatisafossil.htm Evidence of Change Through Time I. How do fossils form? What’s left is a cast of an organism that becomes compressed into rock by pressure of sediments settling on top When sediments are raised and exposed by erosion (wind, rain) then fossils accessible to paleontologists. Evidence of Change Through Time The layer of rock in which the fossil is found and radiometric dating (of rock) can tell us how old the fossil is Evidence of Change Through Time Learning from fossils is not an easy process http://www.pbs.org/wgbh/nova/beta/evolution/b ecoming-human-part-1.html http://www.pbs.org/wgbh/nova/beta/evolution/building-fossils-faces.html Evidence of Change Through Time I. Fossils: Crazy Example Joesephoartigasia monesi (freakishly big rat) Lived 4 mya in South America Fossil discovered in Uruguay 1989, studied and reported in Jan 08 Est 1700 to 3000 lbs, preyed on saber-tooth cats (cbsnews.com) Evidence of Change Through Time Misconception: “Gaps in the fossil record disprove evolution.” Response: The fact that some transitional fossils are not preserved does not disprove evolution. Evolutionary biologists do not expect that all transitional forms will be found and realize that many species leave no fossils at all. Evidence of Change Through Time I. Limitations of Fossils •Fossilization is an extremely low probability event and it is nonrandom meaning not all organisms are equally likely to fossilize. •For instance any species with hard body parts such as shells or teeth or coating of pollen may fossilize, whereas soft-bodied like earthworm usually won’t 500,000 million yr old Jellyfish fossil (rare). •Also requires that the organism make it’s way to the water for fossilization process to work Evidence of Change Through Time II. Extinction Fossils that were unlike any structures from any known animal or plant Of all the species that ever lived ~ _98_ % are extinct. Dodo late 1600s Human activity Irish Elk 11,000 ya Glaciation Evidence of Change Through Time III. Transitional Forms: Fossil species with traits that are intermediate between those of older and younger species. •Archaeoptreryx lithographica: earliest bird fossil (1891) • Transitional form between dinosaurs and birds • 150 million year ago Evidence of Change Through Time III. Transitional Forms • Transitional Form between fish and tetrapods (land animals) • Discovered in Ellesmere Island, CA • 375 million years old Recent Discovery (2004): Tiktaalik Lived about 12 million yrs before 1st tetrapod which is ~363 million years old Tiktaalik significant b/c shows earliest appearance of tetrapod features- features that are not seen in their fish ancestors. Evidence of Change Through Time ribs Fins Fin skeleton resemble bones of forearm, shoulder, elbow and wrist http://tiktaalik.uchicago.edu/meetTik.html Evidence of Change Through Time Evidence of Change Through Time IV. Vestigial traits reduced or incompletely developed structure with no function, reduced function or completely different function but is structurally similar to functioning structures in closely related species Evidence that Species are Related I. Geographical Relationships- closely related species often live in same geographical area Common ancestor but over time, mockingbirds diversified into several distinct species on different island groups Fig 24.6 Evidence that Species are Related II. Homology: Similarity that exists in species descended from a common ancestor Three types: A. Genetic B. Developmental C. Structural A. Genetic Homology Evidence that Species are Related Significant similarity in DNA, RNA or proteins in species descended from a common ancestor. Expect more DNA changes over longer period of time 1.2% difference 1.6% difference 50% difference 0.1% difference Evidence that Species are Related A. Genetic Homology •Nearly identical sequence in genes for determining eye development in humans and Drosophila •Yet humans and flies have completely different eyes •Humans and and flies descended from common ancestor that had this gene for formation of a simple lightgathering organ, structure diverged, but same gene responsible for location of eyes Evidence that Species are Related B. Developmental Homology Similarity in embryonic traits in species descended from a common ancestor Patterns of early embryological development don’t change readily so early patterns of animals are still similar even when organisms look very different as adults Movie Fig 24.8 Evidence that Species are Related B. Developmental Homology: Why are developmental stages so preserved? Think of the early stages as the foundation of a house. * ** ** * *** *** A mutation in DNA (remove a few bricks from the foundation) is likely to be more detrimental than if a brick is removed from the top of the house Evidence that Species are Related C. Structural Homology Similarities in adult morphology All vertebrate limbs modified from same # and arrangement of bones Fig 24.9 Evidence that Species are Related aquatic terrestrial Why is all of this important? Fossils, vestigial traits, transitional forms, geographical relationships, structural, genetic and developmental homologies •Provide evidence that organisms are all related. Gives us clues about which ones are more closely related and how along ago they diverged •Provide evidence that organisms change over time Gives us clues about how long it took for certain changes to occur and why they occurred. For example: “Did land animals evolve from fish?” *Fish have a gill gene that forms gills, which fish need. Land animals have the same gene causing their formation during early development even though land animals have no use for gills. So if they didn’t inherit this gene from fish- why would they have it? The change over time: gills not needed in land animals, having them in adulthood was selected against by natural selection The primary type of evidence mentioned above: Developmental Homology For example: “Did land animals evolve from fish?” Discovery of tiktaalik demonstrates there was at once time a fish-like species that evolved tetrapod features demonstrating how this evolution could have occurred. This organism lived about 12 million years before tetrapods appeared telling us how long this evolution took. Evolution from fish to tetrapod not an instant event so without an intermediate form, we couldn’t understand how that evolution occurred even though we have genetic, develop. and structural homology data to support that they are related. The primary type of evidence mentioned above: Transitional Forms and Fossils 3. Which of the following is the most compelling support for Darwin’s theory of evolution? 1. There are fossils of once living organisms. 2. Fossils are found throughout geologic strata. 3. Evidence shows that some fossilized species are extinct. 4. Evidence shows that extinctions occurred throughout history. 4. Which of the following could be used as evidence of descent from a common ancestor? 1. Species of tortoise living in close proximity are more similar than tortoise species living far apart. 2. Genes for limb formation have almost identical sequences in salamanders and chimpanzees. 3. Antibiotics can cure the same diseases in rabbits and humans. 4. All of the above could be used as evidence. 5. Which of the following is a true statement? 1. An individual with an adaptation is said to have evolved. 2. An individual who is naturally selected has more offspring than an unselected individual. 3. An individual that needs an adaptation to survive is more likely to evolve it. 4. Over time organisms will become