Chapter 7Chapter 7

The Evolution of Living ThingsThe Evolution of Living Things

ReviewReview• 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?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 timeChange over time

• These three frogs all look different but live in the same habitat

Differences Among SpeciesDifferences 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

StegosaurusStegosaurus

DimetrodonDimetrodon

BrontosaurusBrontosaurus

SpeciesSpecies

• 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?Do Species Change Over Time?

• Scientist estimate the Earth is 4.6 billion years old

• Did the same animals and plants always live here?

EvolutionEvolution

• Process by which populations accumulate inherited changes over time

• Because of evolution, scientists think all living organisms have a common ancestor

Evidence of EvolutionEvidence 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 RecordFossil Record

• A historical sequence of life indicated by fossils found in the layers of the Earth’s crust

Vestigial StructuresVestigial 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 OrganismsComparing 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 ToesBirds Walk on Their Toes

Comparing DNAComparing 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 StructuresComparing Embryonic Structures