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Evolution

Evolution. Chapter 23. Biological evolution. A heritable change in one or more characteristics of a population or species across many generations Small scale: relating to changes in a single gene in a population over time Larger scale: relating to formation of new species or groups of species.

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Evolution

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  1. Evolution Chapter 23

  2. Biological evolution • A heritable change in one or more characteristics of a population or species across many generations • Small scale: relating to changes in a single gene in a population over time • Larger scale: relating to formation of new species or groups of species

  3. Species • Group of related organisms that share a distinctive form • Members of the same species are capable of interbreeding to produce viable and fertile offspring

  4. Empirical thought • Relies on observation to form an idea or hypothesis, rather than trying to understand life from a non-physical or spiritual point of view

  5. Jean-Baptiste Lamarck realized that some animals remain the same while others change • Believed living things evolved upward toward human “perfection” • Inheritance of acquired characteristics • Giraffe neck example

  6. Charles Darwin • British naturalist born in 1809 • Theory shaped by several different fields of study • Geology • Economics • Voyage of the Beagle

  7. Geology: • Uniformitarianism hypothesis • Slow geological processes lead to substantial change • Earth was much older than 6,000 years Economics: • Thomas Malthus: only a fraction of any population will survive and reproduce

  8. Beagle (1831-1836)

  9. Formulated theory of evolution by mid-1840s • 1856, began writing his book • 1858, Alfred Wallace sends his manuscript to Darwin • Darwin’s and Wallace’s papers published together • Darwin’s The Origin of the Species is published detailing his ideas with observational support

  10. Biological species change over the course of many generations • Hypothesized that existing life forms are the product of the modification of pre-existing life forms

  11. Descent with modification • Evolution based on • Variation within a given species • Natural selection • Leads to adaptation • Population’s characteristics change to make its members better suited to an environment

  12. Darwin’s theory preceded Mendel’s genetics work • Modern synthesis of evolution • Natural variation caused by random changes in the genetic material • May be positive, negative or neutral

  13. Observations of evolutionary change • Fossil record • Biogeography • Convergent evolution • Selective breeding • Homologies • Anatomical • Developmental • Molecular

  14. Fossils • Recognizable remains of past life • Paleontologists • Sediments pile up and become rock • Organisms buried quickly and hard parts replaced by minerals • Older rock is deeper and older organisms are deeper in the rock bed

  15. Biases to the fossil record Table 22.1 More likely to be fossilized: • Organisms with hard body parts • Larger organisms • Those that existed in greater numbers • Those that lived in a marine environment • Geological processes may favor the fossilization of certain organisms • Human error: search for only certain organisms

  16. Fossils • Even with an incomplete fossil record, evolutionary changes are demonstrated • Fishapod • Glyptodonts and armadillos • Horse family • Cetaceans

  17. Fishapod (Tiktaalik roseae)

  18. Glyptodont

  19. Adaptive changes: • Dog sized to more than half a ton • 4 front toes/ 3 hind toes to single toe in a hoof • Small teeth to much larger ridged teeth

  20. Biogeography: Geographical distribution of extinct and modern species. During last Ice Age (16,000 to 18,000 years ago) Santa Barbara channel was frozen.

  21. Convergent evolution • 2 unrelated species show similar characteristics due to similar environments • analogous or convergent traits • similar structures, but not genetically related.

  22. Selective breeding/artificial selection • Programs and procedures designed to modify traits in domesticated species

  23. The Grants Have Observed Natural Selection in Galapagos Finches • Since 1973, the Grants have studied natural selection • Focused much of their work on Daphne Major – moderately isolated, undisturbed habitat and resident finches • Compared beak sizes of parents and offspring over many years • Birds with larger beaks survived better during drought years • In the year after drought, average beak depth increases

  24. Homology • Fundamental similarity due to descent from a common ancestor • Anatomical • Developmental • Molecular

  25. Anatomical homologies

  26. Vestigial Structures

  27. Developmental homology • Different organisms have pharyngeal slits when embryos. FISH REPTILE BIRD MAMMAL All shared a common ancestor with slits.

  28. Molecular homology • Similarities in genes, enzymes, etc. • All living species use DNA to store information • Certain biochemical pathways are found in all or nearly all species

  29. Horizontal gene transfer • Exchange of genetic material among different species • Prokaryotes to eukaryotes, eukaryotes to prokaryotes, between prokaryotes and between eukaryotes • Widespread among bacteria • Vertical gene transfer: evolution from pre-existing species

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