Download evolution - Chaparral Middle School

EVOLUTION:
Descent with
modification
Age of the Earth
Scientists estimate Earth to be 4.6
billion years old
 Does not look today as it once did,
nor do the organisms on it

Change over time
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Earth is very old!
Has changed a
great deal.
Different
atmosphere
Different temp.
Collisions from
outer space
• Some organisms have stayed about the same as they were millions of
years ago (sharks). Some have changed. Some have disappeared.
Adaptation

Traits that an organism uses to survive and
reproduce. They are passed on from parent to
offspring.
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Example: How are Polar bears adapted to life in
the Arctic? Why would they not be well adapted
to life in Hawaii?
Can include structures or behaviors
Sea Turtles bury their eggs in the sand.
How is this behavior an adaptation?
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Species
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Living things that share the same
characteristics and adaptations
Can mate with one another to produce
offspring
Species have changed over time
Species change too…
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Many different life forms have existed through
Earth’s history
Evidence for this comes from fossils
Why do species change? Due to evolution
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Small changes in a species because of natural
selection add up over millions of years!
Mutations in an organism’s DNA, although most
often bad, can sometimes result in an adaptation.
If this mutation helps the organism survive it will
be selected and passed on to its offspring.
Evidence!

Key evidence to support evolution comes from
fossils
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Generally found in sedimentary rock (particles of
sand, dust and soil form layers, with oldest at the
bottom)
Fossils tell us that some species have died out,
while some have changed greatly
Why??
Because of EVOLUTION
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“Descent with Modification”
Organisms change over time, to what suits
their survival the best
Example: Giraffe
Must Have:
C Overproduction (too many
babies)
C Variation (different traits
C "Struggle for Existence"
C “Success = Reproduction
and passing on the trait”
C Giraffes with longer
necks get better food,
have more babies
(have an advantage in
the struggle for existence)
C Longer necks make more
long necks
(so that trait gets inherited)
Results:
Over time,
average neck
length increases
Other conditions:
**New species can form
**Extinctions may occur,
which allow others to
take over
*Extinction happens
when adaptations fail
to keep up with
changes to the
environment.
Okapi
(relative
of the
giraffe)
How do New Species Form?
Steps to a New Species
1.
2.
3.
Separation
Adaptation
Selection (reproductive isolation)
More evidence for evolution

Comparing
Skeletons:

Different organisms
have same basic
structure = common
ancestor

Fossil Evidence

At first glance, whales may seem similar to fish.
But whales have all the characteristics of a
mammal.

Scientists believe that the ancient ancestor of
whales was a land mammal. A more recent
ancestor was a mammal that spent some time in
water and some time on land.

There is fossil evidence to support this hypothesis.
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Comparing DNA from different species
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All organisms have the same type of DNA
Organisms that are more closely related have more
similar sequences of DNA (example: humans and
chimpanzees, only 40
million
base pair differences
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Embryonic Structures

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Early in development
all embryos look
amazingly similar
Common ancestor?
Branching Tree Diagrams
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Scientists use branching tree diagrams to show
how they think organisms are related.
They are kind of like family trees.
They use fossil evidence, comparative anatomy
(comparing skeletons), and DNA comparisons
Which animal is most closely
related to whales?
Which groups of animals
are still alive today?
How can you tell?
Why do the lines get wider
or thinner?
What does the branching
tree diagram tell us about
snakes and lizards?