1. Change Over Time 7 th Grade Science

2. 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.

3. 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.

4. Fossil Record of the Horse

5. 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!

6. Pakicetus (pak-uh-SEE-tuhs) Earliest whale ancestor -land-dwelling but went in water -ran on 4 legs -about the size of a wolf

7. Ambulocetus (am-byoo-loh-SEE-tuhs) Lived mainly in coastal waters -good swimmer, but also waddled on land -about the size of a dolphin

8. 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.

9. Modern Whale Don’t have hind limbs….but they have tiny hip bones!

10. 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?

11. Vestigial Structures -Humans: -Tailbones -Wisdom teeth -Appendix -Tonsils -Hind legs on boas -Eye stalks in blind cave bats

12. Homologous Structures – more evidence -Structures that may have different functions, but are very similar skeletally.

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

14. How Does Evolution Happen?

15. Charles Darwin -Scientists before him saw evidence of evolution. -He was the 1 st to explain how it happens. -Served as a naturalist aboard H.M.S. Beagle. -Journeyed to Galapagos Islands.

16. Galapagos Islands

17. 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.

18. 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.

19. 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.