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15-1 The puzzle of Lifes Diversity

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					Notes 10.3 Theory of Natural Selection




   After the voyage, he spent over 20 years gathering
    data for his ideas
   Darwin noted Natural Variation—differences among
    individuals
   In artificial selection nature provided that variations
    among different organisms, and humans make use of
    the variations that they desirable…(creating dog
    breeds, seedless fruit, race horses, etc)
   Darwin performed experiments and concluded that
    these variations had habitability (could be passed on to
    future generations)
   Disproved that species were fixed



   Natural selection—Individuals that have inherited
    beneficial adaptations produce more offspring on
    average than do other individuals
   In nature, characteristics are only selected for if they
    give advantages to individuals in the environment.




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Notes 10.3 Theory of Natural Selection




   Thomas Malthus
        Economist: Noted that limited resources and
         disease kept the population in check.
   Darwin reasoned that members of each species
    compete regularly to obtain food, living space, and
    other necessities of life even more than humans.
   He proposed that adaptations arose over many
    generations—“descent with modification”


   Alfred Wallace—letter prompted Darwin to complete
    his book.

   Variation—heritable differences
   Overproduction—produce more offspring that can
    actually survive
   Adaptation—certain variations allow an individual to
    survive better…more selected individual are “naturally
    selected”, live longer, produce more offspring that
    share those adaptations
   Descent with Modification—over time, natural selection
    will result in species with adaptations are well suited
    for survival and reproduction
   Fitness- ability to survive AND reproduce.
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Notes 10.3 Theory of Natural Selection




   Natural section works only on phenotypes… NOT genotypes
   New alleles are not made by natural selection—they occur by
    mutations.
   Natural selection acts only on traits that already exist.


1. Individual organisms in nature differ from one another. Some
   of this variation is inherited.
2. Organisms in nature produce more offspring that can survive.
3. Because more organisms are produced that can survive,
   members of each species must compete for limited resources.
4. Because each organism is unique, each has different
   advantages in the struggle for survival.
5. Individuals best suited to their environment survive and
   reproduce most successfully. The characteristics that make
   them best suited to their environment are passed on to
   offspring. Individuals whose characteristics are not as well
   suited to their environment die or leave fewer offspring.
6. Species change over time. Over long periods, natural
   selection causes changes in the characteristics of a species,
   such as size and form. New species arise, and other species
   disappear.
7. Species alive today have descended with modifications from
   species that lived in the past.
8. All organisms on Earth are united into a single tree of life by
   common decent.
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