Lectures 1 and 2 on Darwin and Natural Selection (Fall2011)

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Biological Sciences
Maydianne Andrade

BIOB51Fall2011 Chapter 3 Darwanian Natural SelectionLecture 1 and 2 o Before Darwin people believed in Special creation Judeo Christian Muslim Traditions 1800s o Special Creation all species are created independently do not change through time are all created recently and at the same timemechanism created by supernatural force GOD o They also believed that the Earth was very young less than 10000 years old o Early definition of evolution the development of new types of living organisms from preexisting typeso Darwin is considered the parent of modern evolutionary theory because he provided evidence that evlotuion had occurred proposed natural selection mechanism of evolution which could explain adaptation special creation could not explain how organisms were still adapted to their environments at the current day if they were created a long time ago and did not change at all and provided evidence that evolution would occur by natural selection o Darwin wrote in his On the origin of Species that each species had to been independently created but had descended from other specieso Darwin and early evolutionists indicated that both fossilized and living organisms were derivedwith modification from either a single common ancestor or a fewdescent with modificationSmall changes within a populations from generation to generation can accumulate over time and lead to the origin of a new species31 Artificial Selection Domestic Animals and Plants o To understand evolution in natureDarwin studied evolution under domesticationstudied the method plant and animal breeders used to modify their livestock and cropso Breeders employ artificial selection to increase the frequency of desirable traitsDarwin started breeding pigeonso Example the tomatoewild tomatoes are small but domestic ones have been artificially selected and breeded so now they are a LOT bigger than the wild ancestors the wild tomato carries a gene for repressor proteins which make it small in size while the big tomato has a low production of the protein and therefore a larger sizeyear by year farmers planted seeds from the largest tomatos they cultivated so eventually they eliminated all the small fruited alleles from their stocko Farmers practicing artificial selection can change more than size the domesticated broccoli brussel sprouts cauliflower kale and kohlrabi differ in architecture but all can interbreed and are part of the same family and are all derived from the wild cabbage 32 Evolution by Natural Selectiono Darwin and Wallace realized that a process similar to artificial selection happens automatically in natureo Darwin came up with 4 postulates o 1 individuals within a population are variable o 2 the variation among individuals are at least in part passed from parents to offspring heritable o 3 in every generation some individuals are more successful at surviving and reproducing than othersmany more offspring are produced than can survive and reproduceo How do we know thisdeduction and observation o Deduction quantifying the observations and then analyzing them and seeing what the result isex The reproductive potential of elephants is 19 million in 750 years but because not all of them survive there are not that manyo Observation biological factors competition predation and parasitism and physical factors climate catastrophic events habitatfood limitation o Ex wild dogs hunt impalastudy shows more of the impala with less stored fat were killedexample of biological factor as natural selection o 4 the survival and reproduction of individuals are not random instead they are tied to the variation among individuals The individuals with the most favourable variationsthose who are better at surviving and reproducing are naturally selected o Darwanian evolution gradual change in population over time
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