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Natural Selection in Action

Natural Selection in Action. Chapter 7 Section 3. Theory of Natural Selection explains how a population changes in response to its environment. Changes in Populations. Adaptation to Hunting 99% of elephants had tusks – 1% didn’t Fact: Elephants are hunted for ivory

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Natural Selection in Action

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  1. Natural Selection in Action Chapter 7 Section 3

  2. Theory of Natural Selection explains how a population changes in response to its environment.

  3. Changes in Populations • Adaptation to Hunting 99% of elephants had tusks – 1% didn’t Fact: Elephants are hunted for ivory Today: 15% don’t have tusks WHY?

  4. Insecticide Resistance • Why does this occur so quickly in insects?? • Because they reproduce so quickly Fact: Insecticides kill most insects Insects reproduce very quickly Some insects survive Result: Survivors pass insecticide resistant genes to offspring Over time what happens??

  5. Competition for Mates Fact: Sexual reproducing organisms can select certain adaptations for mates Female birds select colorful male mates Results: What happens over time??

  6. Speciation ? • Formation a new species as a result of evolution. Separation – separated by nature (mtn, lake, etc.) Adaptation – change with the environment Division – Over time the changes are so drastic they can no longer mate and reproduce

  7. Evolution of Galapagos Finches

  8. Gradualism vs Punctuated Equilibrium • Gradualism and punctuated equilibrium are two ways in which the evolution of a species can occur. A species can evolve by only one of these, or by both. Scientists think that species with a shorter evolution evolved mostly by punctuated equilibrium, and those with a longer evolution evolved mostly by gradualism.

  9. Gradualism • selection and variation that is slow, constant and consistent • Hard to notice over short period of time • Small variations that fit an organism slightly better to its environment are selected for: a few more individuals with more of the helpful trait survive, and a few more with less of the helpful trait die.

  10. Punctuated Equilibrium • Change comes in spurts • Period of very little change, then one or a few huge changes occur, often through mutations in the genes of a few individuals. • Mutations are helpful for survival • Species changes very rapidly over a few generations, then settles down again to a period of little change.

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