Natural selection lab by iyunp418

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									           Natural selection lab
           Mean size of        Mean size of          Mean size of
           galls with gall fly galls with gall fly   galls with gall
           v. obtuse wasp      v. giant wasp         fly v. beetle


P-value         0.900               0.0001               0.028



•You need to describe how you conducted these tests in your
methods section
•P-values need to be presented with results
    •i.e. We found a significant difference between mean size of
    galls containing surviving gall flies and those containing the
    giant wasp (p=0.0001).
Descent with modification:
 A Darwinian view of life
               Overview
People are naturally curious about nature.
  They ponder:
 “How did people and other living things
  come to exist?”
“Why do some organisms have abnormal
  traits or behavior?”
                     Overview
People are naturally curious about nature.
  They ponder:
 “How did people and other living things
  come to exist?”
“Why do some organisms have abnormal
  traits or behavior?”
For a long time the answer was typically that God or
the Creator was responsible (separate creation)
                    Overview
Separate creation

A     B    C   D




    Mechanism=God
       The answer then v. now
Why are the redwoods
 so tall?
Then: Because God created
them that way
        The answer then v. now
Why are the redwoods
 so tall?
Now:
•Redwoods competed with each
other and other trees for light.
•The tallest had a selective
advantage.
•They had higher reproductive
rates.
•The species became taller.
        The answer then v. now
Why are the redwoods
 so tall?
Now:
•Redwoods competed with each
other and other trees for light.
•The tallest had a selective
advantage.
•They had higher reproductive
rates.
•The species became taller.

What happened between then
and now?
         The theory of evolution
Two principles are at the core of this theory:
• Common descent with modification
   – groups or species undergo modification through
     successive generations and new species will form
   – All groups descended from a common ancestor
• Natural selection
   – Differential adaptation to an environment selects traits that will
     be passed on with greater frequencies from one generation to
     the next (ie. redwoods)
                    Overview
Separate creation             Descent with modification

A     B    C   D
                          A        B      C        D




    Mechanism=God        Mechanism=Natural selection
      How did the theory develop?
Georges Cuvier
• Provided fossil evidence of
  extinction
• Radical notion, most believed
  this would not happen to
  perfectly designed life forms
• He saw that new layers of rock
  held more complex life forms
  – He determined that these
    represented separate creation
    events
  – Proposed the idea of
    catastrophism
         How did the theory develop?
Charles Lyell
•Wrote the book Principles of
Geology (1830)

•Proposed that geological
forces still operating could
account for changes
geologists see in the past
Earth’s surface

•These processes happened
over BILLIONS of years

•Earth was not put into final
form at its creation and it is
old
         How did the theory develop?
Charles Lyell
•Wrote the book Principles of
Geology (1830)

•Proposed that geological
forces still operating could
account forIfchanges was gradually changing….couldn’t
              the Earth
             see in the past
geologists life be gradually changing too?
Earth’s surface

•These processes happened
over BILLIONS of years

•Earth was not put into final
form at its creation and it is
old
      How did the theory develop?
Jean-Baptiste de Lamarck
• Believed organisms changed
  by acquiring traits within their
  lifetime (ducks developed
  webbed feet to help them
  swim better)
• Acquired traits were passed
  on and a species could
  diverge into two
      How did the theory develop?
Jean-Baptiste de Lamarck
• Believed organisms changed
  by acquiring traits within their
  lifetime (ducks developed
  webbed feet to help them
  swim better)
• Acquired traits were passed
  on and a species could
  diverge into two
        How does this sit with your knowledge of genetics?
      How did the theory develop?
Jean-Baptiste de Lamarck
• Believed organisms changed
  by acquiring traits within their
  lifetime (ducks developed
  webbed feet to help them
  swim better)
• Acquired traits were passed
  on and a species could
  diverge into two
    Acquiring favorable traits is not consistent with our current
  understanding of evolution, descent from a common ancestor is
       How did the theory develop?
Charles Darwin articulated
the idea of evolution by
natural selection in 1859

•He had training in
medicine and theology

•He was always interested
in nature

•He joined the voyage of
the Beagle, a boat bound
for South America in his
twenties (this was a 5-year
journey)
       How did the theory develop?
What did Darwin see on his
voyage?
•Organisms were adapted to their
environments
•Similar species living close to
each other
•He found many unique fossils on
his journey
•Some of the extinct fossils
resembled living organisms
•Geological processes
       How did the theory develop?
What did Darwin see on his
voyage?
•Organisms were adapted to their
environments
•Similar species living close to
each other
•He found many unique fossils on
his journey
•Some of the extinct fossils
resembled living organisms
•Geological processes
        Clustering of like species spatially and
        similarities between species through time led
        Darwin to propose organisms arose by the
        process of evolution, descent from a
        common ancestor
         How did the theory develop?
The adaptations he saw                             Terminal
were clues about the                               bud    Lateral
mechanism of                                               buds
speciation….so was his              Cabbage                       Brussels sprout
                                               Flower
work with artificial selection                 clusters
•Humans have been
modifying species over time                                  Leaves

                                                                    Kale
•We have selected for            Cauliflower
certain traits in the plants                                 Stem
and animals we use
                                                   Wild mustard

•Taught Darwin about                           Flowers
                                               and stems
variation and heritability       Broccoli                           Kohlrabi
       How did the theory develop?
At home in the study….
•Darwin read Malthus, an
economist

Malthus
•Humans run out food, space,
and other resources when they
reproduce beyond their capacity
•When this happens they
compete for limited resources

Darwin transferred this idea to
all populations
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
• Traits are heritable
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
• Traits are heritable
•Some traits may make the bearer more competitive at
securing limited resources (adaptive)
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
• Traits are heritable
•Some traits may make the bearer more competitive at
securing limited resources (adaptive)
•Highly adapted individuals tend to have more offspring
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
• Traits are heritable
•Some traits may make the bearer more competitive at
securing limited resources (adaptive)
•Highly adapted individuals tend to have more offspring
•Adaptive traits will become more common
       How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
• Traits are heritable
•Some traits may make the bearer more competitive at
securing limited resources (adaptive)
•Highly adapted individuals tend to have more offspring
•Adaptive traits will become more common

  Darwin proposed that this mechanism would lead to speciation
        How did the theory develop?
Principles of natural selection
•Populations tend to increase in size
•Resources will become limited and individuals will compete
•There is variation among traits
• Traits are heritable
•Some traits may make the bearer more competitive at
securing limited resources (adaptive)
•Highly adapted individuals tend to have more offspring
•Adaptive traits will become more common
  Darwin proposed that this mechanism would lead to speciation

 This explanation of evolution (descent with modification) explains:
 • Why organism are adapted to their environments
 •The unity of life
 •The diversity of life
    Descent with modification
    (by natural selection)

A        B      C        D
Modern evidence for evolution
    EXPERIMENT

    Predator: Killifish; preys             Experimental
    mainly on juvenile                     transplant of                      Pools with
    guppies (which do not                  guppies                            killifish,
    express the color genes)
                                                                              but no
    Guppies: Adult males have                                                 guppies prior
    brighter colors than those                                                to transplant
    in “pike-cichlid pools”




                                 Predator: Pike-cichlid; preys mainly on adult guppies
                                         Guppies: Adult males are more drab in color
                                         than those in “killifish pools”



    RESULTS

            12                                               12

                                             colored spots
            10                                               10
                                              Number of
             8                                                8
             6                                                6
             4                                                4
             2                                                2
             0                                                0
                 Source     Transplanted                          Source     Transplanted
                 population population                            population population
     Modern evidence for evolution
Fossils
• Mineralized teeth, bones,
  spores, shells
• Can also be impressions
Fossil evidence for evolution
• Similarity of fossil types in
  similar layers of rock across
  the globe
• Movement to complexity in
  newer layers (we don’t find
  humans in the same strata as
  trilobites)
• This evidence has not been
  falsified, it has been verified
  with radiometric dating
    Modern evidence for evolution
Morphology and vestigial
  characteristics
• We see evidence for
  evolution when we compare
  anatomy across species
   – Shared forelimb structure
     of diverse mammals
     (1,2,5)
   – Indicates descent from a
     common ancestor
     (homologous traits)
• Some traits don’t have a
  function, but they remain
  (vestigial traits)
   – Human appendix
   – Un-perfect designs
    Modern evidence for evolution
Morphology and vestigial
  characteristics
• We see evidence for
  evolution when we compare
  anatomy across species         (a) Pakicetus (terrestrial)
   – Shared forelimb structure
     of diverse mammals
     (1,2,5)
   – Indicates descent from a    (b) Rhodocetus (predominantly aquatic)
     common ancestor
     (homologous traits)                            Pelvis and
• Some traits don’t have a                          hind limb
                                 (c) Dorudon (fully aquatic)
  function, but they remain
  (vestigial traits)
   – Human appendix                         Pelvis and
                                            hind limb
                                 (d) Balaena
   – Un-perfect designs             (recent whale ancestor)
               Summary
• Understand evolution by natural selection
• Understand how Darwin came to this
  conclusion
• Modern evidence for evolution

								
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