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The Organization of Life Section 2
NATURAL SELECTION AND RESISTANCE
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Objectives
• Explain the process of evolution by natural selection.
• Explain the concept of adaptation.
• Describe the steps by which a population of insects becomes resistant to pesticide.
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The Organization of Life Section 2
Evolution by Natural Selection
• Charles Darwin
• 1809 – 1882
• 1831 – sailed on an expedition to observe, collect and document organisms on various continents/islands
Why are there so many different kinds of things?
Why have some species survived and others died out?
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• Galapagos Islands
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The Organization of Life Section 2
• each island supported its own form of finch which were closely related but different in important ways.
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• organisms in a population differ slightly from each other
• Some of these differences are hereditary.
• However, environment exerts a strong influence over which individuals survive to produce offspring, and that some individuals, because of certain traits, are more likely to survive and reproduce than other individuals.
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The Organization of Life Section 2
Evolution by Natural Selection
• Natural selection is the process by which individuals that have favorable variations and are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do.
• Darwin proposed that over many generations, natural selection causes the characteristics of populations to change.
• Evolution is a change in the characteristics of a population from one generation to the next.
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Nature Selects
• Darwin thought that nature selects for certain traits, such as sharper claws, because organisms with these traits are more likely to survive.
• Over time, the population includes a greater and greater proportion of organisms with the beneficial trait.
• As the populations of a given species change, so does the species.
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Evolution by Natural Selection• Adaptation is the process of becoming adapted to an
environment. It is an anatomical, physiological, or behavioral change that improves a population’s ability to survive.
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Nature Selects
• An example of evolution is a population of deer that became isolated in a cold area.
• Some of the deer had genes for thicker, warmer fur. These deer were more likely to survive, and their young with thick fur were more likely to survive to reproduce.
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Evolution of Resistance
• Resistance is the ability of an organism to tolerate a chemical or disease-causing agent.
• An organism may be resistant to a chemical when it contains a gene that allows it to break down a chemical into harmless substances.
• Humans promote the evolution of resistant populations by trying to control pests and bacteria with chemicals.
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Pesticide Resistance
• A pesticide sprayed on corn to kill grasshoppers, for example, may kill most of the grasshoppers, but those that survive happen to have a gene that protects them from the pesticide. These surviving insects pass on this resistant gene to their offspring.
• Each time the corn is sprayed, more resistant grasshoppers enter the population. Eventually the entire population will be resistant, making the pesticide useless.
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Pesticide Resistance
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Literacy Standard: After copying your notes and watching the video, do the following:
Write a letter to a friend explaining to them:What natural selection is.What causes it.What is the end resultDiscuss at least one exampleWhat pesticide resistance isWhat causes it What is the end resultUse examples to get your point across.