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Chapter 22

Chapter 22. Evidence for Evolution. Evolution occurs by natural selection…. Darwin’s finches Found on Galapagos Descent with modification. Natural selection has 3 conditions that must be met:. 1.) variation within the population

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Chapter 22

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  1. Chapter 22 Evidence for Evolution

  2. Evolution occurs by natural selection… • Darwin’s finches • Found on Galapagos • Descent with modification

  3. Natural selection has 3 conditions that must be met: • 1.) variation within the population • 2.) variation must lead to differences among individuals in survival and reproductive success • 3.) variation must be genetically inheritable

  4. Found with finches: • variation is within the population • changed from one year to the next depending on the weather and plant seed production • drought = fewer seeds, birds with large beaks survived b/c could eat bigger seeds • wet = many more small seeds, birds with small beaks survived ok • Traits were passed down according to those who survived – fluctuated within the population

  5. Peppered moths and industrial melanism • Industrial melanism is the darkening of a species due to industry • Two main forms: peppered and melanic • In areas of industry, the tree bark is darker – the dark moths do better • Non-industrial areas, the light moths do better

  6. Kettlewell –did experiment with industrial melanism • Raised both colors of moths • Marked their abdomens and released equal amounts of each color into an area of industry and a rural area. • Waited a a few weeks and recaptured as many moths as possible in each area. • Results: • light moths more in rural area • dark moths more in industrial area

  7. Artificial Selection • Lab experiments: • Used to test if selection can produce evolutionary change… • Used fruit flies • Chose flies with many bristles - Only bred the ones with the most • Over 86 generations, increased the bristle # from 9 to over 40!!

  8. In Agriculture… • Only allow the plants that produce the best seeds to breed • Ex: corn, wheat, strawberries

  9. Domestication… • Taking a once wild animal and breeding those with desirable traits to eventually spawn a desirable offspring • Has been done with wolves, foxes, cats and more!

  10. The fossil record… • Most direct evidence for evolution • Can get from rock, amber, permafrost, dry caves or deserts • Problem: fossilization does not occur easily! • Must have very specific conditions • Usually the remains are scavenged or eroded before the process can be completed

  11. Must have very specific conditions • Usually the remains are scavenged or eroded before the process can be completed • Here’s a bird in the process of being fossilized!

  12. Dating fossils • Date the rocks in which they are preserved: • Absolute dating – uses U238 • Relative dating – uses rock layers in respect to one another

  13. Gaps in the record • Even though gaps exist, links have been found between: • Reptiles and birds • Ex: Archaeopteryx

  14. Snakes and lizards - pelvic girdles still visible in snakes Whales and land mammals - flippers with homologous structures, pelvic girdle

  15. Anatomical record • Homology – homologous structures are structures with different appearances and functions that are all derived from the same body part in a common ancestor • Ex: forelimbs of mammals

  16. Vestigial Organs - Rudimentary structures of marginal, if any, use.

  17. Human Example

  18. Evolution Viewpoint • Remodeling of ancestral structures as their functions or adaptations changed.

  19. Comparative Embryology • Problem - closely related organisms go through similar stages in their embryonic development. • Ex: Gill pouches in vertebrates

  20. Molecular Biology • Study of Evolution at the DNA or protein levels. • Problem - related species have similar DNA sequences.

  21. Evolution Viewpoint • Related species share a common ancestrial DNA. The closer the relationship, the more similar the DNA sequences should be.

  22. Convergent evolution

  23. Horse evolution… • For example, we can trace the evolution of the modern horse through fossils. • First horses: • small, short legs, broad feet • lived in woods and ate leaves and berries We will look at the changes in these animals…

  24. Size • First horses were the size of dogs or smaller • Now they weigh on average about 1000 lbs! • Let’s see the fossils for this change… • http://chem.tufts.edu/science/evolution/HorseEvolution.htm

  25. Toe reduction • Primitive horses had 4 toes with fleshy pads like a dog’s • Modern horses have one toe encased in bone and keratin • This allowed the horse to run faster for longer distances • First row = forefoot • Bottom row = hindfoot

  26. Tooth size and shape • Primitive horses had small and simple teeth for the vegetation of the time • Modern horses now have more complex teeth that are longer and have ridges for chewing grasses which evolved along with the horse • The grasses are tough and the teeth need to tough to withstand the chewing of these materials

  27. Only one genus of horse still exists today…Equus • All others died out long ago – naturally selected against in the changing environment

  28. Summary • Know Darwin’s “facts” and “inferences”. • Be able to discuss the various evidences of Darwinian evolution.

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