Chapter 17: Introduction to Darwinian Evolution

1. Chapter 17: Introduction to Darwinian Evolution

2. Evolution • Accumulation of inherited changes within populations over time • NOT changes in an individual in its lifetime • Changes in characteristics of populations over many generations

3. 2 perspectives: • 1) MICROEVOLUTION: short-term adaptations of population to changes in the environment • 2) MACROEVOLTUION: long-term formation of different species from common ancestors

4. Contributing Scientists • Jean Baptiste de Lamarck • 1st – organisms undergo change because of natural phenomena • Organisms endowed with vital force to change toward complexity over time • Organisms could pass traits acquired during their lifetimes to their offspring • Giraffes – stretch necks • Discredited when basis for heredity discovered

5. Thomas Malthus • Population growth not always desirable • Outstrip food supply • Famine, disease, war – stop growth • “struggle for existence” •  strong and constant check on human population growth • Charles Lyell • Slow geological processes  Old Earth

6. Charles Darwin • HMS Beagle – South America – 5 years • Naturalist – plants, animals, fossils, geology • Galapagos Islands – compared species to mainland and other Galapagos Islands • Artificial selection: breeders develop varieties in a few generations • Dogs, plants • Similar process in nature – model for natural selection

7. Fig. 22-9 Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters Leaves Kale Cauliflower Stem Wild mustard Flowers and stems Broccoli Kohlrabi

8. Fig. 22-5 GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA Pinta Genovesa Equator Marchena SOUTH AMERICA Santiago Daphne Islands AUSTRALIA Pinzón Fernandina PACIFIC OCEAN Cape of Good Hope Andes Isabela Santa Cruz Santa Fe San Cristobal Tasmania Florenza Española Cape Horn New Zealand Tierra del Fuego

9. Favorable variations would be preserved, unfavorable eliminated •  adaptation : evolutionary modification that improves the chances of survival and reproductive success in a give environment • Accumulation of modifications  maybe new species • Time required for new species to originate • Old Earth

10. Fig. 22-6 (a) Cactus-eater (c) Seed-eater (b) Insect-eater

11. Fig. 22-2 Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) American Revolution French Revolution U.S. Civil War 1800 1900 1750 1850 1795 Hutton proposes his theory of gradualism. Malthus publishes “Essay on the Principle of Population.” 1798 1809 Lamarck publishes his hypothesis of evolution. Lyell publishes Principles of Geology. 1830 Darwin travels around the world on HMS Beagle. 1831–1836 1837 1837 Darwin begins his notebooks. 1844 Darwin writes essay on descent with modification. Wallace sends his hypothesis to Darwin. 1858 The Origin of Species is published. 1859

12. Natural Selection (Darwin) • Better adapted organisms are more likely to survive and become parents • Population changes over time; frequency of favorable traits increase with each generation

13. 4 observation for Natural Selection • 1) Variation – each individual is unique • Some advantageous traits - inherited • 2) Overproduction – each species can produce more offspring than can survive • 3) Limits on Population Growth – (struggle for existence) more individuals than resources  competition • 4) Differential reproductive success – (survival of the fittest) better adapted individuals will survive and reproduce

14. Fig. 22-10

15. Evidence for Evolution • Fossil Record • Comparative Anatomy • Biogeography • Developmental biology • Molecular evidence

16. Fossil Record • Fossils – remains/traces of previously existing organisms • Sedimentary rock, bogs, tar, amber, ice • Conditions slow or prevent decay • Covered quickly – water, sand • Hard body parts • Record biased – location, body

17. Dating Fossils • 1) Relative Age – position in rock • Index fossils – • characterize a specific layer over large geographical areas • Existed short time, preserved in large numbers • With this info  arrange rock layers and fossils in chronological order and identify comparable layers in widely separated locations

18. Fig. 22-3 Layers of deposited sediment Younger stratum with more recent fossils Older stratum with older fossils

19. 2) Absolute Age – • Radioisotopes – emit radiation – nucleus changes into nucleus of different element with decay • Half-life – time required for ½ of the atoms to change to a different atom • Potassisum-40 (1.3 billion years) • Uranium-235 (704 million years) • Carbon-14 (5730 years)

20. Comparative Anatomy • Similar structures  related organisms (common ancestor) • Homologous structures – features derived from same structure in a common ancestor • Ex: limb bones of mammals, modified leaves • Similar structure, different function • Homoplastic features (Analogous features) – structurally similar features that are not homologous but have similar functions in distantly related organisms • Ex: wings of insects/birds, spines and thorns • Same function, evolved separately (different structure)

21. Fig. 22-17 Humerus Radius Ulna Carpals Metacarpals Phalanges Human Whale Bat Cat

22. Fig. 22-20 NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel

23. Show organisms with separate ancestries may adapt in similar ways to similar environmental demands  Convergent evolution • Ex: aardvarks, anteaters, pangolins • Vestigial structures – organs or parts of organs that are seemingly nonfunctional and degenerate, undersized or lacking some essential part • Remnants of parts that were functional in ancestors • Ex: • Human - appendix, coccyx, 3rd molars, ear muscles • Whales/pythons – hind limb bones • Pigs – vestigial toes • Kiwi – wingless bird – vestigial wing bones • Burrowing/cave-dwelling – vestigial eyes Vestige usually not harmful so selective pressure to completely eliminate is weak

24. Biogeography • Study of past and present geographical distribution of organisms • Not all animals/plants found in all environments where they could survive • Spread from origin • Continental drift / Pangaea

25. Developmental biology • Genetic similarities reflect shared evolutionary history • Vertebrates – embryological development similar  common ancestor • (segmentation, gill pouches, aortic arches)

26. Fig. 22-18 Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo

27. Molecular evidence • Confirms structural and fossil evidence • Universal genetic code • Similar amino acid sequences, proteins, nucleotides • More similarities  common ancestor • Phylogenetic trees - diagrams showing lines of descent • Derived from differences in DNA sequences • Whales and hippos closely related

28. Evolution is happening NOW! • Can be observed in our lifetime • Ex: • Resistant Bacteria • Finch beaks • Guppy study