Natural Selection

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Natural Selection

• Or, how did we get here.

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(No Transcript)
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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

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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 Darwins time, and
  is not now.

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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

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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.

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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
  didnt I think of that? type things.

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Hows 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 wasnt blending

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Hows 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

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Hows 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

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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

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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

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Different kinds of selection

• Stabilizing or Normalizing selection
• The middle is selected for
• Many examples here
• Symmetry
• Two eyes

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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

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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 dont use their eyes so they
  disappear
• We dont use our appendix so it is disappearing

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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

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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