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  Other ‘Naturalists’ were struggling with the same issues 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. 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 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. 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. 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’ 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 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 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’ 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 Different kinds of selection  Stabilizing or Normalizing selection  The middle is selected for  Many examples here  Symmetry  Two eyes 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’ 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’ 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…… 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