Transcript Document
UNIT 6 SEMINAR Evolution and Natural Selection Agenda What is evolution? What drives evolutionary change? What is natural selection? What role do new mutations play in this process? Video: The Evolution of Homer Simpson Evolution resource: “Evolution 101” from UC Berkeley What is evolution? Evolution = What is evolution? Evolution = the change in inherited traits present in a population over time. What is evolution? Evolution = the change in inherited traits present in a population over time. Present day species evolved from earlier species What is evolution? Evolution = the change in inherited traits present in a population over time. Present day species evolved from earlier species The relatedness of organisms is a result of common ancestry What is evolution? Evolution depends on understanding a few concepts: Inheritance – genetic traits are passed from parents to offspring Variation – there is genetic variety within a population (polymorphism) Time – major evolutionary changes happen over hundreds or thousands of generations. http://galliform.bhs.mq.edu.au/~simon/_Graphics/Research/Three%20males.jpg What drives evolutionary change? Mechanisms of evolution include: Natural selection New mutations Genetic drift (small populations) Gene flow (migration) Hybridization What is natural selection? Natural selection = What is natural selection? Natural selection = process by which certain traits become more or less common depending on their effects on the “fitness” of individuals Fitness = What is natural selection? Natural selection = process by which certain traits become more or less common depending on their effects on the “fitness” of individuals Fitness = ability to reproduce and contribute to the gene pool. VS Artificial Selection “Survival of the Fittest” What are some factors that could affect the “fittness” of an individual? Natural selection: Example Imagine a population of beetles in which there are both green and brown varieties. If birds prefer to eat the green ones, then the brown ones have an advantage and will reproduce more. Natural Selection: Example Natural Selection: Example http://www.pbs.org/wgbh/evolution/library/01/6/images/l_016_02_l.gif Role of Mutations in Evolution Sometimes, a new mutation confers a selective advantage in an individual, resulting in increased reproduction and therefore increased prevalence of the new gene in the gene pool. Types of Selection Example: beak size in finches Example: human birth weight The “extremes” are preferred – leads to speciation. Speciation Species = group of individuals that actually (or potentially) interbreed Speciation Species = group of individuals that actually (or potentially) interbreed Speciation = the splitting of one lineage into two or more lineages Speciation Species = group of individuals that actually (or potentially) interbreed Speciation = the splitting of one lineage into two or more lineages Allopatric speciation geographic isolation Speciation Species = group of individuals that actually (or potentially) interbreed Speciation = the splitting of one lineage into two or more lineages Allopatric speciation geographic isolation Sympatric speciation members of a population become better adapted within a particular “niche” in the ecosystem. Speciation Species = group of individuals that actually (or potentially) interbreed Speciation = the splitting of one lineage into two or more lineages Allopatric speciation geographic isolation Sympatric speciation members of a population become better adapted within a particular “niche” in the ecosystem. Parapatric speciation individuals are more likely to mate with their geographic neighbors. http://evolution.berkeley.edu/evosite/evo101/VC1fEvidenceSpeciation.shtml Natural Selection Simulation Have a chat about the weather in your area. The only hitch is that you may not use the letter 'e' in anything that you type. Any words that contain the letter 'e' will be ignored. You and your classmates will talk about the weather in your area for five minutes total, after which your instructor will announce "STOP," and you will be allowed to use the letter 'e' again. Natural Selection Simulation In your new, 'e'-free environment, what adaptations to language did you and your classmates make? What things were more difficult to talk about, and why? If you were to live in a 'u'-free environment, what other letters might struggle and die out? Think about this experiment as a way to show how changes in environment force creatures (like you) to adapt and change. Now, think about squirrels. What might happen to them if all the oak trees (and therefore acorns) died out? What adaptations might they have to make to adjust to the acorn-free world? How might these changes affect their body structures? After 50,000 years of living in an acorn- free world, how might squirrels look? Why does this kind of evolutionary change take so long? Next week: Unit 7: The Human Practice of Science Reading: Atoms and Biochemistry