change over time 7 th grade science. evolution – what science tells us process by which modern...
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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.