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Biology 120 Lab Cerritos College DARWINIAN EVOLUTION (revised 11.17.03) Darwin Proposed “The Origin Of Species By Natural Selection": OBSERVATION 1: "Organisms tend to increase in a geometric ratio." OBSERVATION 2: "However, in spite of this, population numbers tend to remain more or less constant over a long period of time." DEDUCTION 1: "Since not all of the individualists produced can survive, there must be a struggle for existence." OBSERVATION 3: "There is variation in every species." DEDUCTION 2: "In the struggle for existence, those individuals that are better adapted to the environment leave behind more offspring than the less adapted individuals." *********************************************************************************************************** Theory of Natural Selection Made Simple A. The reproductive potential is great, but a. Rabbits should cover the Earth, but B. population tends to remain constant in size, because b. they don't, because C. populations suffer a high mortality. c. many are caught by predators. D. Populations exhibit variation which leads to d. Some rabbits run faster than others E. differential survival of individuals. e. and escape from predators; F. Individual traits are inherited by their offspring. f. so do their young. G. The composition of the population changes by the selective elimination of unfit individuals. g. Populations of rabbits, as a whole, tend to run faster than their predecessors. *********************************************************************************************************** Summary of Main Points: 1. 2. 3. 4. Variation – Differences exist within a population. Overproduction – More offspring are produced than can possibly survive. Struggle – Competition for survival. Survival of the "Fitter" – Nature selects the best variations Vocabulary: evolution – ________________________________________________ natural selection – __________________________________________ _________________________________________________________ adaptation – ______________________________________________ _________________________________________________________ differential reproduction – _____________________________________ _________________________________________________________ genetic polymorphisms – _____________________________________ _________________________________________________________ gene pool – _______________________________________________ fossil – ___________________________________________________ homologous feature – _______________________________________ ____________________________________________________ analogous feature – ________________________________________ ____________________________________________________ genotype – ________________________________________________ phenotype – _______________________________________________ allele – ___________________________________________________