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Thursday, November 15th, 2012.docx

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York University
Natural Science
NATS 1840
Carol Bigwood

Science, Technology and the Environment (SC NATS 1840A) – th Thursday, November 15 , 2012 Readings: Chapter 5.4, 12, 13 Speciation, Evidence and Extinction Natural Variation determined at molecular level (alleles of genes) Prevalence, or frequency, of alleles in a population determined by environmental conditions Speciation (Macroevolution) New species result from long-term evolutionary divergence of populations  Might result from migrations, or other causes of physical/environmental isolation  Physical isolation, followed by long periods of microevolution, leads to reproductive isolation. Evolution – Common Misconceptions Clarified; 1) Populations evolve. Individuals do not. 2) “Fittest” does not refer to physical strength. The fittest individuals are those able to leave the most descendants 3) There is no “plan”. Genetic mutations underlying evolution appear to be completely random. Evidence for Evolution 1) Comparative Anatomy:  Structural features common to many species of plants or animals, suggesting a common lineage Eg. Limb structure in four-legged animals Eg. Insect mouth parts Eg. Basic structure of flowers 2) Fossil Record  Chronological arrangement reveals changes in structure and complexity  Reveals species that are now extinct  Comparison with today’s organisms shows progression of common features  Limited by rarity of fossils – there are gaps in the record Filling the Gaps – Example: Tiktaalik A link between fish and tetrapods (four-legged animals). Now extinct, the species named Tiktaalik had  Gills and scales;  Half-fish, half tetrapod limbs – wrist joint with fins instead of toes  Tetrapod ribs, lungs, and a mobile neck More Evidence of Evolution: Comparative Embryology:  Similarities in the early stages of embry
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