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15.3 Darwin Presents His Case

15.3 Darwin Presents His Case. Darwin Presents His Case. The specimens Darwin brought back had the scientific community in a buzz Learned that Galapagos species are found nowhere else in the world They looked similar to South American mainland species but were clearly different.

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15.3 Darwin Presents His Case

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  1. 15.3 Darwin Presents His Case

  2. Darwin Presents His Case • The specimens Darwin brought back had the scientific community in a buzz • Learned that Galapagos species are found nowhere else in the world • They looked similar to South American mainland species but were clearly different

  3. Darwin’s Book • Published his ideas about species diversity and evolution in On the Origin of Species • Proposed a mechanism for evolution called natural selection • Many agreed with Darwin while others strongly opposed him

  4. Natural Variation • Scientists used to believe species were perfect and unchanging • Darwin argued natural variation (differences among species) is found in all types of organisms • Some cows give more milk • Some plants give larger fruit

  5. Artificial Selection • Darwin also studied English farmers and breeders • Used selective breeding to breed the “best” individuals • Largest hogs, fastest horses • Darwin called this artificial selection • Still used today!

  6. Evolution by Natural Selection • Darwin believed that evolution occurred through natural selection • Natural selection = the process by which only the organisms best adapted to their environment will survive and reproduce • 3 main parts to natural selection

  7. 1. The Struggle for Existence • There are more living things than resources • Results in competition • Competition = the struggle among living things to get their needs for life

  8. 2. Survival of the Fittest • Individuals that are better suited to their environments survive (high fitness) • Individuals not suited to their environment will die (low fitness) • Fitness – the ability of an individual to survive and reproduce in its environment • Is a result of adaptations

  9. 2. Survival of the Fittest • Adaptation – any inherited characteristic that increases an organism’s chance for survival • Long necks in giraffes • Long toes / webbed feet in birds • Coloring / Camouflage

  10. 3. Descent with Modification • Each living species has descended, with changes, from other species over time • Implies all organisms are related to one another • Known as common descent

  11. Evidence for Evolution • Fossil Evidence • When living things from the past are compared to living things today, we can see that change has occurred

  12. Evidence for Evolution • Geographic distribution of living things • Species are located in different parts of the world but share similarities • Beavers and capybara are similar • Muskrat and coypu are similar Beaver Beaver Muskrat Beaver andMuskrat Coypu Capybara Coypu andCapybara NORTH AMERICA Muskrat Capybara SOUTH AMERICA Coypu

  13. Evidence for Evolution • Homologous body structures • Limbs (arms, wings, legs, flippers) have different form and function but are constructed from the same bones Turtle Alligator Mammals Bird Typical primitive fish

  14. Evidence for Evolution • Vestigial structures • Body parts that no longer have functions • i.e. Pink lump in corner of eye • Remnant of a third eyelid • Frogs and turtles have third eyelid to see underwater • Appendix • In many mammals the appendix is used to help digest food

  15. Evidence for Evolution • Embryology • Studying embryodevelopment to look for similarities and differences

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