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Comparing Artificial, Natural, and Sexual Selection Evolution A change in species over time But how does this happen? – 3 ways Artificial Selection Natural Selection Sexual Selection Artificial selection • Variation exists naturally in a population • Humans select the variations (traits) we found useful “descendants” of wild mustard Selective Breeding Humans create the change over time “descendants” of the wolf Natural Selection Three things needed A big, diverse population with heritable adaptations (variation of traits) Variations ultimately caused by mutation More born than survive: selection pressures that favor some individuals over others Examples Predation – may favor those who run faster Disease – may favor those with better immune systems Competition for resources (food, water, space, etc) – may favor those who are bigger/stronger/smarter Time Many generations needed to pass on traits Natural Selection Sexual Selection Instead of traits that help survival, they are traits to help reproduce Usually hurts ability to survive Two types Male competition Weapons for combat Large Size Female (mostly) choice Looking fancy Causes males and females to look very different Sexual Selection Male Competition Female Choice Sexual vs. Natural Selection http://www.youtube.com/watch?v=RxHdzw7E0wU Fitness The ability to survive AND reproduce Used to describe Natural and Sexual selection Survival of the Fittest Basic idea of evolution by natural selection The organisms that can survive and reproduce the most successfully pass on their adaptations Selection gone bad! Unexpected consequences of: Pesticide Resistance Antibiotic Resistance Resistance Spray the field, but… insecticide didn’t kill all individuals variation resistant survivors reproduce resistance is inherited insecticide becomes less & less effective