Evolution by natural selection


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Evolution by natural selection

  1. 1. Evolution byNatur al SelectionMrs. WilesApril 2009
  2. 2. Who was CharlesDarwin? Began as a medical student but changed to be a “naturalist,” or person dedicated to the study of nature. Voyage on The Beagle to study various species. Upon returning wrote The Origin of Species
  3. 3. What did he say? § Overpopulation: Every population is capable of producing more offspring than can survive. There are limited resources.
  4. 4. What did he say? 2. Variation: Variation exists within all populations. Much of it is inherited because it is created by crossing over during meiosis.
  5. 5. What did he say?  3. Selection: In an environment, having a particular trait can make individuals more or less likely to survive and have successful reproduction. So, some individuals leave more offspring than others.  4. Adaptation: Over time, those traits that improve survival and reproduction will become more common.
  6. 6. PopularMisconceptions1. “Evolution says man came from monkey” WRONG! Darwin never said that. Ever. All he said is that we are related species.
  7. 7. PopularMisconceptions2. “Evolution says that Earth began with the Big Bang” WRONG! Darwin never said that either. Evolution DOES NOT address how the Earth began. Only what happened after that. Darwin = Big Bang
  8. 8. More PopularMisconceptions3. “Evolution is just a theory” Recall that in science theories have been tested and proven. Yes Evolution is a theory and it has been proven. (More on the proof to follow!)Did you know… Darwin never even used the word Evolution in his book? He preferred “Descent with Modification.” So what does that mean?
  9. 9. Descent withModification The real definition of the word evolution: organisms change over time into order to adapt to a changing environment. This change can been passed on to the next generation. AKA descent with modification. How do they do this? Natural Selection
  10. 10. What is NaturalSelection?  Competition for resources: there isn’t enough food for everyone, those who are the best at getting the food survive and pass on their genes.  Traits that make them better at getting food are adaptations.
  11. 11. Natural Selection isCaused by theEnvironment  Pressure from the limited environment causes individuals to adapt.  Certain individuals are born with genes that make them more fitted for their environment. Those genes are passed on.  More favorable traits emerge generation after generation.
  12. 12. Natural SelectionExample 1  A Gazelle on the African Plains runs faster than any other Gazelle in the heard. A Cheetah comes after the heard for some dinner, who survives? The Gazelle who runs faster than the others. The slow ones get eaten.  The Gazelle does not have to be faster than the Cheetah, just faster than the guy next to him.
  13. 13. Natural SelectionExample 1  That Gazelle lives on to reproduce and give his offspring the fast running gene. This is an adaptation.  This Gazelle has better reproductive fitness. It is more able to reproduce and pass on genes.
  14. 14. Natural SelectionExample 2 Male peacocks have bright colorful tails. These tails enable them to attract female mates. The males with the biggest and brightest tails mate with more females. The females see the tails as a sign of a healthy male.
  15. 15. Natural SelectionExample 2  Therefore, males who have genes for those bright tails will have more offspring and pass on the bright tails to their offspring. They have adapted.  This is evolution at work! The key is to successfully reproduce and pass on your advantageous genes to as many offspring as possible.