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Early Evolutionary Theory Where did the Theory of Evolution Come From? Jean-Baptiste Lamarck (1744-1829) Created an incorrect Theory of Evolution based on the inheritance of Acquired Characteristics Lamarck Incorrectly Believed… Giraffes originally had short necks & since food was scarce, they reached for leaves in tall trees. This caused their necks to stretch. Offspring inherited this trait. Special use of a body part does not change the genetic make-up of that part! Charles Darwin (1809 – 1882) “Father of Evolution” Voyaged to the Galapagos Islands on H.M.S. Beagle (18311836) as the ship’s naturalist. Recognized that populations respond (over many generations) to changes in their environments. Example: Finches The finches he studied had differently shaped beaks depending on where they lived and what they ate. Who is Charles Darwin? Video Jot Clip! down some key points about Darwin and his discoveries! Alfred Russell Wallace Was also voyaging and observing similar things to Darwin. Sent an essay to Darwin that did not use the term “natural selection” but described the same ideas. Darwin published their ideas in a paper on the theory of evolution. Natural Selection Conditions in nature determine which organisms survive and reproduce (a process that leads to evolutionary change) 4 components of natural selection… 1. Variation – individuals in populations differ from one another. 2. Heritability – Variations are inherited from parents. 3. Overproduction: Populations produce more offspring than can survive. May result in competition between offspring for resources. 4. Reproductive Advantage – Variations that increase reproductive success will be more common in the next generation. Example: Porcupines evolved to have quills because they help to avoid predators and therefore reproduce. Natural Selection results in only some individuals surviving… Survival of the Fittest! (fitness – not necessarily the strongest…the fittest individuals leave the most offspring) What do you think will happen over time to this beetle population? What leads to variation among species? Mechanisms of Evolution 1. Mutations 2. Genetic Drift 3. Gene Flow/Migration 4. Natural Selection 1. Mutations Changes in DNA sequences that can result from environmental factors (chemical exposure/ radiation) or simply by chance Mutation Cont’d… Can lead to no change in phenotype When the mutation occurs on a stretch of DNA that does not code for anything Can lead to small changes in phenotype When cat’s ear has a slight curl Can lead to big changes in phenotype Death Gene Pool A collection of genes for all the traits in a population If gene mutations persist, they may become a standard part of that population. 2. Genetic Drift Affects the genetic make-up of a population through an entirely random process “Lucky” individuals survive, not necessarily the healthier or more “fit” individuals. May decrease genetic diversity! 3. Gene Flow Also called Migration Movement of individuals into or out of a population (variations are distributed among the populations) Examples: People moving to a new city Reasons for Migration Overcrowding of organisms in one area Lack of food/water Reproduction Ex. Male lions migrate before reaching maturity. If the lion leaves, it’s genetic make-up will be lost from its population, but will be added to a new population. 4. Natural Selection Conditions in nature determine which organisms survive and reproduce. Necessary if genes are to stay in a population Speciation How do new species emerge? Species A group of organisms that breed with one another and produce fertile offspring Geographic Isolation When a natural, physical barrier separates a population and they evolve separately from each other Physical barriers: body of water, landslides, mountains, deserts, etc. Cont’d… Without the flow of genes, the separated species differentiate (change) to enable them to survive in their environments. Ex: Reproductive Isolation The inability of formerly interbreeding organisms to produce offspring Ex. Ringed Salamander of California * Geographic Isolation can lead to Reproductive Isolation Ex: Wood frog & Leopard frog In captivity, they will breed, but in the wild they will not because of different breeding seasons Wood frog – early April Leopard frog – mid April Their species diverged because they did not breed at the same time. Population Bottleneck Occurs when a population’s size is reduced for at least one generation. Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. Killer Whale Article February 4, 2014 1. 2. 3. 4. 5. Describe what is meant by “upwelling system.” What is believed to have caused a genetic bottleneck in whale populations? Why? Why did the population of killer whales off the coast of South Africa retain it’s genetic diversity? Why was hunting ruled out as an effect on the bottleneck in populations? What additional evidence does the author suggest, could be used to support the claim that reduced genetic variation is a result of the last glacial period?