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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. Earth is very old! Has changed a great deal. Different atmosphere Different temp.

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Descent with


Age of the earth
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
Change over time

  • 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.


  • Traits that an organism uses to survive and reproduce in it’s environment. They are passed on from parent to offspring.

    • 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?


  • Living things that share the same characteristics and adaptations

  • Can mate with one another to produce offspring that are fertile (can reproduce)

  • Species have changed over time

Species change too
Species change too…

  • Many different life forms have existed through Earth’s history

  • Evidence for this comes from fossils

  • Why do species change? Due to evolution

    • 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.


  • Key evidence to support evolution comes from fossils

    • 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
Because of EVOLUTION

  • “Descent with Modification”

  • Organisms change over time, to what suits their survival the best

  • Example: Giraffe

Must Have:

  • Overproduction (too many babies)

  • Variation (different traits

C "Struggle for Existence"

  • “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)


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


Okapi (relative of the giraffe)

Steps to a new species
Steps to a New Species

  • Separation

  • Adaptation

  • Selection (reproductive isolation)

More evidence for evolution
More evidence for evolution

  • 1. Comparing Skeletons:

    • Different organisms have same basic structure = common ancestor

  • 2. 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.

3. Vestigial Structures

  • Physical structures or behavior that is no longer necessary for an organism to survive or reproduce in it’s environment.

  • Things that have been left over as evolution takes place.

  • Scientists

    think that the

    appendix may

    be a vestigial






4. Comparing DNA from different species

  • 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

5. Embryonic Structures

  • Early in development all embryos look amazingly similar

  • Common ancestor?

Were you paying attention
Were you paying attention?

1. What is evolution?

2. Organisms are considered members of the same species if….

  • A.

  • B.

Were you paying attention cont
Were you paying Attention Cont.

3. What are the 3 steps to speciation (the forming of a new species)

4. What are 5 examples of evidence in support of the Theory of Evolution?

Branching tree diagrams
Branching Tree Diagrams

  • 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 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?