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Great Ideas in Science: Lecture 14 – Ecosystems

Explore the definitions of evolution, common descent, and natural selection in living systems. Understand creationist perspectives and the evidence supporting the theory of evolution. Discover the role of genetic code and cell theory in evolutionary biology.

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Great Ideas in Science: Lecture 14 – Ecosystems

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  1. Great Ideas in Science:Lecture 14 – Ecosystems Professor Robert Hazen PROV 301 All living systems live in ecosystems of many interacting organisms.

  2. Three Definitions of Evolution • Evolution as Change: Life on Earth has changed over time. • Common descent: All living things on Earth descended from a common ancestor. • Natural selection: The process by which life evolved is Darwinian natural selection.

  3. First Definition of Evolution: Change Over Time Observational evidence overwhelmingly supports the theory that life originated on Earth billions of years ago as a single cell, and has been changing ever since. • Fossils • Molecular Biology • Cellular biology • Genetics • Comparative anatomy • Observations of nature and of breeding

  4. Extinct Animals

  5. If you accept observational evidence, then the unambiguous conclusion is that life has changed over time. TRILOBITES

  6. Objections to Evolution are sometimes voiced by “Creationists.”

  7. Three Related Terms • Creationism • Young Earth Creationism • Scientific Creationism

  8. 1. Creationism • Creationists believe that God created the universe and life. • Many creationists accept the Bible’s creation story as a metaphor; they rely on empirical evidence (Psalm 19). • Many scientists are also creationists in this sense.

  9. 2. Young Earth Creationism • Young-Earth creationists believe in a literal reading of Genesis. • Earth is about 10,000 years old. • Geology features caused by Noah’s Flood. • All species were created in modern form. • Only minor evolutionary changes occur. • For many young-Earth creationists, the findings of science are irrelevant at best, and possibly dangerous and subversive.

  10. Created Antiquity, or Prechronism • Philip Goss (1857) “Omphalos” • Heavens and Earth were created 10,000 years ago to look much older. • No measurement you can make could disprove prechronism.

  11. 3. Scientific Creationism • Scientific creationists search for empirical evidence that supports the tenets of young-Earth creationism. • SC is not science, because its basic tenets are not subject to change based on empirical evidence. • Even if its tenets conformed to observational evidence, “scientific” creationism would not be science.

  12. 3. Scientific Creationism Given the religious beliefs of some people, should creationism be taught in the science classroom?

  13. Second Definition of Evolution: Common Descent • Common descent means that all living things descended from the first living cell. • Tree diagrams reveal ancestral relationships.

  14. Tree Diagrams

  15. Second Definition of Evolution: Common Descent • Common descent means that all living things descended from the first living cell. • Tree diagrams reveal ancestral relationships. • The search for fossil intermediates supports common descent.

  16. Fossils Strata Younger = higher

  17. Gradual Evolution

  18. Objections to Common Descent “Darwinists rarely mention the whale because it presents them with one of their most insoluble problems. They believe that somehow a whale must have evolved from an ordinary land-dwelling animal, which took to the sea and lost its legs. … A land mammal that was in the process of becoming a whale would fall between two stools – it would not be fitted for life on land or sea, and would have no hope of survival.” Alan Haywood, 1985

  19. Whale Evolution Ambulocetus

  20. Whale Evolution Ambulocetus

  21. Whale Evolution Rodhocetus

  22. Whale Evolution Basilosaurus

  23. Whale Evolution The power of the theory of evolution by natural selection is its predictive power. If we see a gap in the fossil record, then we can predict what kind of rock and what age of rock to search, and we can make a good guess as to what kind of fossil we’re likely to find.

  24. The Genetic Code

  25. The Cell Theory, 1839 • All living things are composed of cells • The cell is the fundamental unit of life • All cells arise from previous cells

  26. CONCLUSIONS: Observational evidence overwhelmingly supports the hypothesis of common descent for all known life forms, living and fossil, on Earth.

  27. Third Definition of Evolution: Natural Selection (Darwin) • Populations exhibit variation. • More individuals are born than will survive. • The most fit individuals are more likely to reproduce.

  28. Charles Darwin (1809-1882)

  29. Charles Darwin:The Beagle at Galapagos

  30. Microevolution Phacops trilobites: Almost unchanged from 440 to 370 million years!

  31. Microevolution

  32. Unanswered Questions about Evolution How does macroevolution occur? What is the rate of evolution? What is the rate of extinction? What causes mass extinctions?

  33. 1. Macroevolution How did such an amazing diversity of trilobites arise?

  34. Eye Evolution “To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree …” Charles Darwin, On the Origin of Species

  35. Eye Evolution Selection rules for model eye evolution: 1. Vary curvature, aperture, and central refractive index randomly by 1%. 2. If visual acuity (spatial resolution) increases, then retain that variation. D. Nilsson & S. Pelger, “A pessimistic estimate for the time required for an eye to evolve.”Proc. R. Soc. Lond. B 256, 53-58 (1994).

  36. Eye Evolution This evolutionary sequence is continuously driven by selection.

  37. 2. What is the Rate of Evolution? Punctuated Equilibria (a) versus Gradualism (b)

  38. 3. Extinctions: Fast and Slow

  39. 4. What Causes Mass Extinctions At least 5 major extinction episodes have occurred in the past 500 million years. Each episode resulted in the loss of from 30% to 90% of species. All models of mass extinctions involve significant changes to Earth’s atmosphere.

  40. 4. What Causes Mass Extinctions Evidence from Asteroids

  41. 4. What Causes Mass Extinctions Evidence from Iridium

  42. What Causes Mass Extinctions Evidence from Volcanoes

  43. What Caused Mass Extinctions Evidence from Foraminifera: Volcanoes versus Asteroids

  44. What Causes Mass Extinctions? Human Activities

  45. What Causes Mass Extinctions? Human Activities

  46. Ecology and Ecosystems Ecology:“The study of natural living systems” Ecosystems: They consist of biotic and abiotic components. Community: Includes all of the organisms in an ecosystem.

  47. Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms • Ecosystems consist of both living and nonliving parts

  48. Every Ecosystem Consists of Both Living and Nonliving Parts Abiotic: The chemical and physical environment Biotic: All living organisms that form the ecological community

  49. Ecosystems Key Idea: Living things live in ecosystems of many interdependent organisms • Ecosystems consist of both living and nonliving parts. • Energy flows through ecosystems.

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