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Chapter 7
The Evolution of Living Things
Review
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What is a hypothesis?
A possible explanation or answer to a question
What is a theory?
A unifying explanation for a broad range of
hypotheses and observations that have been
supported by explanation
• What is a law?
• Theories that are proven time and time again
What is Evolution?
• Evolution is a widely accepted theory.
• It is not a law.
• You don’t need to believe anything I say in
this chapter.
• However you need to know the information
behind the theory to pass you SOL’s next
year.
Change over time
• These three frogs all
look different but live
in the same habitat
Differences Among Species
• All three frogs have different adaptations
that help them survive
• Adaptation
– A characteristic that helps an organism
survive and reproduce in its environment
• Can include structures for finding food, for
protection and movement
Stegosaurus
Dimetrodon
Brontosaurus
Species
• Groups of organisms that can mate with
one another and produce fertile offspring
• Share same characteristics and
adaptations
• Mule vs. horse vs. donkey
Do Species Change Over Time?
• Scientist estimate the Earth is 4.6 billion
years old
• Did the same animals and plants always
live here?
Evolution
• Process by which populations accumulate
inherited changes over time
• Because of evolution, scientists think all
living organisms have a common ancestor
Evidence of Evolution
• Fossils
• The solidified remains or imprints of once
living organisms are found in the layers of
the earth’s crust
• Mold – imprint
• Cast – mold filled in with sediment
Fossil Record
• A historical sequence
of life indicated by
fossils found in the
layers of the Earth’s
crust
Vestigial Structures
• Remnants of once-useful structures
• Hind limb bones in whales
• Other examples
– Wings on flightless birds (ostriches, rheas)
– Human tail bone
– Erector pilli muscles and body hair
– Wisdom teeth
Comparing Organisms
• Bones in the human
arm and a bat’s arm
are similar even
though they are used
in different ways
• Indicates a common
ancestor but the
bones have evolved
to perform different
functions
Birds Walk on Their Toes
Comparing DNA
• All living things made from the same
genetic material
• The more similar the species (closely
related) the more similarities in DNA codes
Comparing Embryonic Structures