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Natural Selection

Natural Selection. Or, how did we get here…. Natural Selection. The Theory of Natural Selection is so simple that anyone can misunderstand it…. ( Anonymous ) Charles Darwin (1809-1882) saw three problems in need of a solution. Darwin was not the only one to see these problems BTW

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Natural Selection

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  1. Natural Selection Or, how did we get here….

  2. Natural Selection • The Theory of Natural Selection is so simple that anyone can misunderstand it…. (Anonymous) • Charles Darwin (1809-1882) saw three problems in need of a solution. • Darwin was not the only one to see these problems BTW • Other ‘Naturalists’ were struggling with the same issues

  3. Problem the First • There is change over time in the flora and fauna of the Earth • What we would commonly call ‘evolution’ today • The fossil record showed this to be pretty clear, even to people in the mid 1800s • This was not controversial in Darwin’s time, and is not now.

  4. The Second Problem • There is a taxonomic relationship among living things • People were big into classifying stuff • It was pretty obvious that there was a relationship between different species • Different birds, different grasses, different cats etc

  5. The Third Problem • Adaptation • Different kinds of teeth for different animals, say carnivore ripping teeth and herbivore grinding teeth • Different tissues within species • Heart vs. eye etc.

  6. The Solution! • Natural Selection provides a mechanistic account of how these things occurred and shows how they are intimately related. • It is one of those ‘oh man is that ever easy, why didn’t I think of that?’ type things.

  7. How’s it work? • There is competition among living things • More are born or hatched or whatever, than survive and reproduce • Reproduction occurs with variation • This variation is heritable • Remember, there was NO genetics back then, Chuck knew, he just knew…. • Realized that is wasn’t ‘blending’

  8. How’s it Work? • Selection Determines which individuals enter the adult breeding population • This selection is done by the environment • Those which are best suited reproduce • They pass these well suited characteristics on to their young

  9. How’s it Work? • REPRODUCTION is the key, not merely survival • If you survive to be 128 but have no kids, you are not doing as well as I am • I have reproduced… • Assuming the traits that made me successful will help them then I amore fit NOW than the 127 year old guy

  10. This lecture keeps evolving….. • Survival of the Fittest (which Chucky D NEVER said) means those who have the most offspring that reproduce • So, the answer to the trilogy of problems is: • ‘Descent with modification from a common ancestor, NOT random modification, but, modification shaped by natural selection’

  11. Different types of selection • Directional Selection • What most of us think about when we think about selection • An extreme value is selected for • Human brain size is a nice example

  12. Different kinds of selection • Stabilizing or Normalizing selection • The middle is selected for • Many examples here • Symmetry • Two eyes

  13. Different kinds of selection • Disruptive selection • Extremes are selected for • Might be where the two sexes come from • Trait was probably gamete sized • Two ‘mating types’

  14. Other Evolutionary Theories • Lamarckism • Inheritance of acquired characteristics • E.g., giraffes really wanted leaves, so they stretched their necks and….. • Sounds crazy, but a lot of people think this way • ‘We will all have giant heads and tiny bodies someday’ • ‘Cave swelling fish don’t use their eyes so they disappear’ • ‘We don’t use our appendix so it is disappearing’

  15. Silly incorrect evolutionary theories and ideas • Orthogenesis • There is some plan to evolution. • NO WRONG INCORRECT, THANKS FOR PLAYING • The idea of an ‘evolutionary ladder’ fits in here • It is wrong too……

  16. Still another silly idea • Intelligent Design • Just Creationism with a fancy name • God does not belong in a science class, any more than experiments belong in church • NOT A SCIENTIFIC THEORY

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