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AIM: How Do Scientists explain and support the theory of evolution? What is a theory? Is an explanation supported by observations and/or experiments, that can be used to explain related occurrences. Theory of Evolution Theory of Evolution 1)The process by which species change over time (simple to complex). 2)Present day species are related to ancient species. Scientists use this theory to explain a change in a species from simple to more complex organisms? What is the Theory of Evolution? • The gradual change of different organisms and species over time that allows them to adapt to a changing environment. What is the evidence that supports the Theory of Evolution? 1) Fossil Record - collection of fossils that provides clues to the history of Earth’s organisms. The fossil record spans much of geologic time (billions of years of Earth’s history). 2)Similarities in Structure (body structures) 3)Similarities in Development (Embryology) 4)Molecular Biology (DNA & Proteins) How do we know that we have evolved from ancestors distinctly different from us? Hint: How do we know dinosaurs existed? FOSSILS The fossil record (remains of dead organisms) have given scientists the clues they needed to determine an organisms ancestry by comparing them to present day species. The fossil record shows… Life has evolved from simple to more complex Newer Organisms: more complex Older Organisms: more simplistic What do we learn from fossils? http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html • How did behaviors evolve? • How long did individuals live? • How do features evolve over time? http://www.ucmp.berkeley.edu/education/explorations/tours/stories/middle/C7a.html Evolutionary Tree Species living at present time (top) Ancestral common species (bottom) Similar to a family tree • Descendents Descendents Common Ancestor Our Common Ancestor Unicellular Common Ancestor 100’s of Millions of year ago How closely related are they? • Which organisms • Which are distant are closely relatives? related? • Those who have • Those who have a distant common a recent common ancestor (a far ancestor (a close point of point of intersection in a intersection in a tree diagram) tree diagram) What organisms are our closest relatives? Why?