Download Evidence of Evolution

The Theory of Evolution
How did the animal on the next
slide get his amazing
camouflage?
Evolution sometimes has a bad rep…
• But it’s really simple.
– THINGS CHANGE! Animals, plants, algae, pond
scum, bacteria, viruses, and even humans! Every
species has the potential to evolve (change over
time) and everything has evolved.
• How do we know evolution is real?
– Just by looking at the world around us!
Before Darwin
Everybody believed that the world
never changed. Every plant, animal,
and organism was made in the
beginning exactly as it exists now. But
nature says differently…
Darwin and the Voyage of the Beagle
Charles Darwin- the scientists given credit for the discovery
of evolution through natural selection.
Darwin’s Observations
• Changing Geography –
The Earth is many
millions of years old and
has changed a lot over
time. It is still changing.
– If the earth changes,
shouldn’t life change too?
Darwin’s Observations
• The Fossil Record – we have evidence underground of
animals and plants that no longer exist (e.g.
dinosaurs) and sometimes we find fossils that look
like earlier versions of modern species
– If nothing ever changes, then why did they go away? Why
do they sometimes look similar but different to existing
species? Could they be an earlier version?
Darwin’s Observations
• Patterns of
Diversity –
populations show
variety among
individuals
– Even identical
twins are a little
different! If
nothing ever
changes, why
aren’t we all
exactly the same?
Natural Variation
Individuals, even of
the same species,
always contain
some differences.
New traits can even
be added through
genetic mutations.
Couldn’t this
variation lead to
big changes?
Darwin’s Observations
• Artificial Selection – humans have been
changing animals and plants drastically for
hundreds of years for our own use (e.g. wolves
to dogs)
– If we can make changes, why can’t nature?
Darwin’s Observations
• The Galapagos Islands contained different (but
VERY similar) species on different islands; did
they all come from the same original species?
– If nothing ever changes, why not have the same
tortoises on all the islands?
Can you see what Darwin saw?
What do these two islands
have such different tortoise
shells?
Hint: Check the backgrounds!
“Natural” Selection of the
Galapagos Tortoises
• An ancestral group of tortoises ended up on the
Galapagos islands. They contained variation among
the individuals. Some had dome and some had
saddle shells. The domes could not survive on the
harsh islands because they could not lift their head
to get food from shrubs. The saddles had a harder
time protecting their neck from predators on the
greener islands. Overtime, all of the unsuited
tortoises on each island died, leaving behind only the
tortoises that best “fit”. In the end, the tortoises are
selected by nature for their environment.
Evolution
• A change in the available genetics in a
population’s gene pool. Over long periods of
time, good genes become more common and
bad genes become less common in the group.
Occasionally new genes will arise (good or
bad)
– Population = all the animals of the same species
living within an area
– Remember: Populations evolve. Individuals
cannot.
Evolution is driven by
Natural Selection
Organisms best suited for their surroundings
will survive and reproduce more, producing
even more individuals in the next generation
with the good genes. Overtime, only the best
genes will remain.
PROOF: The Evolution of the Peppered Moth
In England a species of moth called the Peppered Moth had two
available, inheritable wing colors- a light color and a dark color.
(Through genetics, dark colored moths had dark colored babies,
and vice versa.) Prior to the industrial revolution, the light color
dominated with 99% of the moths displaying this phenotype. (See
below to find out why.) However, after the factories opened, the
light phenotype became almost extinct and the darker color began
to dominate. What changed? Why do you think this happened?
Problem…
Evolution can take a really long time.
How can we know it’s actually
happening if we can’t directly see it?
Evidence of Evolution
While we can’t watch evolution directly, we
CAN see the results of it. Darwin argued that
living things have been evolving on Earth for
millions of years. Evidence can be found in the
fossil record, the geography of living species,
homology between different species, and
similarities in early development.
Evidence of Evolution
The Fossil Record shows how species have changed. It
also enables us to create an evolution timeline through
radioactive or relative dating. It’s a way to peek into
the past and see what things *used* to look like.
How old is this fossil?
• Relative Dating: A fossil found deeper in the
ground is older than a fossil found near the
surface; can’t give an exact age, only “older”
or “younger”; can also be used for the same
fossil found in different locations
How old is this fossil?
• Radioactive dating: using the decay of special
chemicals called isotopes to determine an
exact age
– Half life: the time it takes for half of the isotope to
decay; after 1 half-life, 50% remains. After 2 halflives, 25% remains…
Evidence
of Evolution
Geographic Distributiondifferent regions have their
own variations of similar
organisms due to different
environments working on
common ancestry. All of these
giant rodents came from a
common ancestor. They look
different now because they
live in different areas. Just like
the Galapagos tortoises!
Evidence of Evolution
Homologous Body Structures – animals descended from the
same ancestor will have similarly built traits; they may work
differently, but they are built the same (e.g. bat wings and
human hands)
Evidence of Evolution
Molecular Homology – Since genetic relatives (like siblings)
have similar DNA, species related through evolution will also
have similar DNA
Careful!
• Sometimes two species look a
lot alike, but they are not
related. This is still evidence
for natural selection, because
their similarities came from
living in the same environment
BUT they do NOT have a
common ancestor.
• Analogous structures –
structures that work the same
way, but they are built
differently; these species are
NOT related! (e.g. butterfly
wings and bird wings)
Evidence for Evolution
Vestigial Structures- traits that were
used in an ancestor, but are not used
anymore (ex: whale pelvis)
Whale ancestors used to have legs!
Evidence of Evolution
Embryology – related
species develop in
similar ways and the
embryo can show
evidence of past
traits; sometimes
watching an embryo
grow is kind of like
watching evolution
in fast forward!