Download Monday, February 13th

Monday, February 13th
Proofs of Evolution
Chapter 21
Darwin’s Theory of Evolution
• Darwin studied Finches on the Galápagos
Islands.
• Each bird had seemed to perfectly match the
specifics of the island it was on
Modern Day Research
Humans Influence Evolution
Intro to Fossils, Types
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Specimens preserved in amber
Siberian permafrost fossils
Dry cave fossils
Your typical rock fossil
Quick overview of Rock Fossils
• First, the organism is buried in sediment
• Secondly, calcium is mineralized
• Lastly, the surrounding sediment hardens to
form rock
2 Ways to Date Fossils
• People in Darwin’s time used relative
dating – dated rocks by their position
with respect to one another (which
layer was on top of which other
layers?)
2 Ways to Date Fossils
• Today we can use radioactive decay and use
absolute dating to determine the age.
• Half-Life – amount of time needed for onehalf of the original amount to be transformed
• Once a rock is formed, no radioactive isotopes
can be added, so we can compare the
daughter isotope to the original, determine
how many times it has halved, and date the
sample.
How are Fossils used as Evidence for
Evolution?
• Once the fossils are lined up from oldest to
youngest, they show evidence of successive
evolutionary change.
• Prokaryotic (no nucleus)  eukaryotic 
fishes  land dwelling organisms  dinosaurs
 humans
The Gaps in the Fossil Record
• As previously stated, fossils rarely form.
Because of this, when we line up all the fossils
by age, there are still large gaps between one
organism and the next.
• There are still enough intermediate forms of
organisms available to show the major
transitions of evolution on Earth
To this Day we still find Transition
Fossils
• For a while we didn’t have any fossils that
showed the transition from hoofed land
animals to modern day whales
• But we were able to find some that helped
show the transition
Evolution of the Horse
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Evidence from fossils show the horse’s:
a. Change in body size
b. Decrease in toes
c. Change in teeth to accommodate browsers
to grazers
Homologous Structures
• As vertebrates have evolved, the same bones
have sometimes been put to different uses
• Homologous Structures – structures with
different appearances and functions that all
derived from the same body part in a common
ancestor
• Natural selection has modified the same initial
starting blocks to serve very different
purposes.
Embryonic Development
• Comparing how organisms develop also shows
strong evidence supporting evolution
• http://www.youtube.com/watch?v=h3Lkac89
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Vestigial Structures
• Vestigial Structures – structures that have no
apparent function, but resemble structures
their ancestors possessed.
• Example: Humans have muscles to “wiggle”
our ears
• These muscles allow other mammals to move
their ears to pinpoint sounds.. but for us…
these muscles don’t have much use
Vestigial Structures
• Boa Constrictors have hip bones and
rudimentary hind legs
• Whales have bones that resemble pelvic
bones of other mammals, but are weakly
developed and have no apparent function
Vestigial Structures
• These structures were helpful or useful to an
organism’s ancestor, but not for them. This is
used to prove descent with modification, or
evolution
Convergent Evolution and
Biogeographical Record
• Biogeography – study of the geographic
distribution of species
• Reveals that different geographical areas
sometimes exhibit organisms of strikingly
similar appearance even though the
organisms may only be distantly related
• Why do some organisms that don’t live near
each other, and aren’t closely related,
sometimes have similar body structures or
forms? – Convergent Evolution
Convergent Evolution
• Convergent Evolution – selection can tend to
favor parallel evolutionary adaptations in
similar environments