Evidence for Evolution

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Transcript Evidence for Evolution

Wednesday May 5, 2010
Entry task (please write in your notebook)
Natural selection is sometimes described
as “survival of the fittest”.
Lilly says that “fit” means “bigger,
faster, stronger” like an Olympic
• Do you agree or disagree? Why? Give
an example.
Now try this:
• The DNA of a certain deer has a
mutation that causes the deer to have
white fur.
– Is this a favorable trait?
• When would each mutation be favorable?
a. Mutation that makes a mouse bigger
b. Mutation that makes birds with toes that are slightly webbed
Evidence for Evolution
How do we know evolution
Fossil Record
• Provides a peek at the past shows
how living things have changed
over the past 3.5 billion years.
• May have bits missing, but fossil
evidence clearly shows that life is
old and has changed over time.
Transitional Fossils
Early whale ancestor.
Land mammal, but clearly related to whales
and dolphins based on specializations of
Gray Whale:
lives today.
The position of nostrils has changed over time.
We would expect to see fossils that show intermediate forms.
Geographic Distribution
• Some species are only found in certain
parts of the world, likely because they
evolved there
•Alligators in United States
•Marsupials on the islands of Australia and
New Zealand
Geographic Distribution
• Organisms show more similarity to
species nearby than in similar climates
but far apart.
• Implies ancestry
– Example: species on Galapagos Islands
share more similarities with species on
mainland South America than they do with
species that live on other islands with
similar climates across the world
Homologous Structures
• Similar characteristics due to
Homologous Structures
• The leaves look and function differently from
each other, but are all derived from a common
ancestral form.
QuickTime™ and a
are needed to see this picture.
Homologous Structures
• Frogs, birds, rabbits, and lizards have different
forelimbs, but they all share the same set of bones.
Extinct, but
Homologous Structures
Each species has a different function for their limb. Does it seem
possible that they all developed the same bone structure
independent of each other?
“What could be more curious…?”
Vestigial Organs
• Traits that are not useful to an
organism, but remain from a useful
ancestral trait
•Ear-wiggling muscles
•Tail in human and all vertebrate embryos.
•Wisdom teeth
•Hip bone of a whale
• Which of
these is a
show striking
similarities in
early stages of
• Snakes have legged ancestors
– Hind limb buds as embryos, but lose them before
– Fossil evidence also shows snakes with hind limbs
Cellular/ Molecular Evidence
• All organisms are made of cells
–Membranes filled
with water,
proteins, lipids,
genetic material
–Most use
sugar for fuel
proteins as
blocks and
Molecular Evidence
• DNA: simple four-base code that
provides instructions for all living
• All life is linked to a common
• Different species share some of
the same genes
– Worms share 25% of their genes with
Molecular Evidence
• The more similar the DNA of two
living organisms, the more closely
they may be to one another
– Note: many other factors play a role as
• Activity:
– study the amino acid sequence in the
hemoglobin of humans, gorillas, and
– use the data to show the similarities in
DNA of these organisms