Change Over Time

7th Grade Science

Evolution – What Science Tells Us• Process by which modern organisms have

descended with modification from ancient organisms.

• Modified due to adaptations – a characteristic that helps an organism survive & reproduce in its environment.

• As populations change over time, new species form.

Evidence for Change Over Time

• Fossils & Fossil Record:

-fossils found in newer layers tend to be more similar to present-day organisms.

-all living species descended from common ancestors.

Fossil Record of the Horse

Evolution of Whales

• Whales are like fish……….

but unlike fish: they breathe air, give birth to live young & produce milk.

-WHALES ARE MAMMALS!

-Scientists believe whales evolved from ancient land mammals!

Pakicetus (pak-uh-SEE-tuhs)• Earliest whale

ancestor

-land-dwelling but went in water -ran on 4 legs

-about the size of a wolf

Ambulocetus (am-byoo-loh-SEE-tuhs)

• Lived mainly in coastal waters

-good swimmer, but also waddled on land

-about the size of a dolphin

Dorudon (DOH-roo-don)• Lived in oceans – did not get out of water

-propelled itself with massive tail

-had tiny hind limbs – couldn’t use for walking or swimming.

Modern Whale

• Don’t have hind limbs….but they have tiny hip bones!

Vestigial Structures – more evidence

• Inherited remnants or “leftovers” of ancestors.

• Usually serve little or no function.

-ex: hip bones in whales.

-Can you think of any?

Vestigial Structures

-Humans:

-Tailbones

-Wisdom teeth

-Appendix

-Tonsils

-Hind legs on boas

-Eye stalks in blind cave bats

Homologous Structures – more evidence

-Structures that may have different functions, but are very similar skeletally.

Early Development – more evidence-Many organisms look similar during embryonic

stages.

How Does Evolution Happen?

Charles Darwin

-Scientists before him saw evidence of evolution.

-He was the 1st to explain how it happens.

-Served as a naturalist aboard H.M.S. Beagle.

-Journeyed to Galapagos Islands.

Galapagos Islands

Darwin’s Observations

-Studied many plants & animals…but especially finches.

-Noticed they differed from island to island & those all differed from the ones in Ecuador.

Darwin’s Conclusion

-Environment & resources differed greatly from island to island.

-Finches arrived on different islands & adapted to specific environment.

-Different species formed over time.

Darwin’s Theory of Natural Selection

-Individuals that are better adapted to their environment survive & reproduce.

-Survival of the fittest

-“Survival” genes passed to offspring.

-Driving mechanism of evolution.