Lecture 2 evolutionary fact and theory


Published on

Lecture 2 - Evolutionary Fact and Theory

Published in: Education, Technology
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Lecture 2 evolutionary fact and theory

  1. 1. Anthropology 101: Human Biological Evolution Lecture 2: Evolutionary Fact and Theory Dr. Leanna Wolfe LAWolfe@aol.com Office AHS Drop In Hours: 5:00-6:30 PM AHS 303
  2. 2. Darwin and the history of evolutionary thinking • Historical Context • Darwin’s theory of natural selection
  3. 3. Organisms are well-suited to their environment • Viceroy butterfly • Monarch butterfly
  4. 4. Complex adaptations require special explanation
  5. 5. The Scientific Revolution in Europe • Global exploration • Round Earth - 1492 etc. • Biological Diversity • Earth orbits the sun - 1541 Copernicus • Solar system in motion - 1600’s Galeleio • physics, medicine, chemistry advanced • Scientific methods • Measuring instruments
  6. 6. A problem emerges from the growing body of knowledge • Early Geology = Study of stratigraphy • Stratum (strata) = Layers of earth Within these layers find fossils of non- existing animals And many resemble living ones
  7. 7. A solution is proposed: James Hutton (1794) • Strata = gradual process  erosion  accumulation • Proposed “Deep Time”  Earth profoundly old
  8. 8. The solution is resisted: Georges Cuvier (1796) • Proposed “Catastrophism”  Strata formed by series of divine catastrophes  Species go extinct  Multiple creation events
  9. 9. The solution is refined: Lyell (1830) • Proposes “Uniformitarianism” • Natural processes same in past and present • Slow accumulation of changes  Requires deep time • Darwin’s friend & mentor
  10. 10. So if the earth isn’t young…maybe life isn’t either • Jean-Baptiste Lamarck • First to propose an evolutionary mechanism for species change • He was wrong in the details, but important nonetheless
  11. 11. Prior to Lamarck: Fixity of Species • Species: A group of organisms that can interbreed to produce viable off-spring Biblical understanding: • Every species was a unique act of creation • Once created, never changes
  12. 12. …so perhaps species aren’t fixed Lamarckian Evolution – Inheritance of Acquired Characteristics • Traits determined by their usefulness in an environment. • If environment changes, organisms acquire new traits • pass new traits on to their offspring
  13. 13. Meanwhile… • Thomas Malthus (1798) • An Essay on the Principle of Population • Population growth outstrips food supply • Population limited by limited resources • Writing about human population
  14. 14. Charles Darwin influenced by these ideas • Born to rich family in 1809 • Grandfather Erasmus proposed early idea of species evolution • Dropped out of med school • Studied religion • 1832 sailed on HMS Beagle • 5 year voyage to map coast of South America
  15. 15. The Voyage of the Beagle (1831-1836)
  16. 16. The HMS Beagle visited the Galapagos Island • Animals unique to each island • Similar to mainland species • Islands are volcanic, recent formations • Appearance of NEW FORMS
  17. 17. Darwin collected many birds on the Galapagos • A variety of finch species • Similarity in beak structure, body shape, and coloring • Perfect gradation between species • One species modified for different purposes Adaptive Radiation
  18. 18. Darwin returned to England in 1836 • Sort collections • Talked to scientific colleagues • Started a series of notebooks • Talked to plant and animal breeders • Growing evidence of gradation of forms in the fossil record • Read Thomas Malthus
  19. 19. Enter Wallace • Alfred Russel Wallace • Working-class family, b.1823 • little formal education • Expedition to Amazon in 1848 • Developed similar ideas in response to variety of natural phenomena
  20. 20. Publication • 1858: Enter Wallace…  Yawn… • 1859: Darwin published On the Origin of Species.  People noticed
  21. 21. The Theory of Evolution by Natural Selection • Evolution: Change over time  Can apply to many things besides biological organisms • Natural Selection: Process by which species evolve  Analogous with artificial selection • Darwin interested in change over time of biological forms via the process of natural selection • What is the process? How do biological forms change?
  22. 22. Darwin’s Theory of Natural Selection 1. The ability of a population to expand is infinite, but the ability of the environment to support populations is always finite. 2. Organisms within populations vary, and this variation affects the ability of individuals to survive and reproduce. 3. Variations are transmitted from parents to offspring. Darwin called this process natural selection Of course, long before you mature, most of you will be eaten “Bummer of a birthmark, Hal.”
  23. 23. The Theory of Evolution by Natural Selection 1. Competition: Malthus: Capacity of populations to increase is unlimited. Resources are not 2. Variation: In all species, individuals vary in some of their physical or behavioral characteristics 3. Fitness: Some members of a population have a variant that grants an advantage over others
  24. 24. The Theory of Evolution by Natural Selection 4. Heritability: Some portion of this trait variation is inherited 5. Differential Reproductive Success: Individuals with favorable traits produce more offspring than those who don’t, leading to more members of the population who inherited the trait 6. Adaptation: Highly favorable traits will eventually become widespread in the population, building new species-typical features 7. Speciation: Over time, as new variants accumulate and old ones disappear, new species develop
  25. 25. Time x NO YES Evolution changes the characteristics of a population, NOT an individual
  26. 26. The Vocabulary of Evolution by Natural Selection • Evolution: Change over time • Natural Selection: Process by which species evolve • Reproductive Success: The number of offspring an individual produces and rears to reproductive age • Fitness: A measure of relative reproductive success • Adaptation: An anatomical, physiological, or behavioral trait which improves an organism’s fitness in a given environment • Selective Pressures: Forces in the environment that influence reproductive success in individuals
  27. 27. Birds of the Galapagos show us how natural selection works Daphne Major Medium Ground Finch
  28. 28. Postulate 1: Environment constrains population growth • Severe drought occurred 1976- 78 • Drought affected seed availability and quality • Many birds died of starvation
  29. 29. Postulate 2: Individuals vary in ability to survive and reproduce • Beak size varies • Small beaked birds have trouble with large seeds • During drought, larger beaked birds were at advantage Before Selection Frequency of each Beak Depth Beak Depth After Selection
  30. 30. Postulate 3: Variation is transmitted from parents to offspring • Beak size is inherited
  31. 31. Characteristics of population changed over time • Large beaked adults survived better • Large beaked birds had large beaked offspring • Mean beak size increased in population
  32. 32. But, natural selection can: produce change (Directional Selection) or maintain status quo (Stabilizing Selection) • Small beaked birds can’t find enough food • Large beaked birds have higher juvenile mortality • Selection favors intermediate beak size • At equilibrium, selection will maintain stasis (no change)
  33. 33. Adaptations evolve in many small steps each favored by natural selection • The key to natural selection is variation + selective retention • Small changes occur • Selection retains beneficial changes • Complexity emerges • Each step must be favored by natural selection
  34. 34. We can see these steps in the fossil record and among living creatures Abalone: Crude image Spiny Murex: Better image Limpet: Directional information Beyrich Split Shell: Better directional information
  35. 35. Evolution can produce rapid change • Examples in nature  Radiation of Darwin’s finches ( 500,000 yrs)  Radiation of African cichlids ( 12,000 yrs)
  36. 36. Loss and Imperfection • Natural Selection can remove complexity  Cave fish lose eyesight  Penguins have small wings • Imperfect features  Human fondness for sugar, fat, salt  Peacock’s tail  Human appendix
  37. 37. MYTH: ‘Survival of the fittest’ justifies everyone for themselves • Survival of the fittest is NOT natural selection • Fittest does NOT always mean most aggressive, strongest, most selfish • Don’t use the NATURALIST FALLACY  “because its natural its the right way to behave, or its moral or good” • Natural selection describes what happens in the world, NOT how we should chose to live our lives
  38. 38. MYTH: Evolution cannot be disproved What would disprove evolution? • Major jumps or different ordering in the fossil record • Novel combinations that counter the predicted trajectory of evolutionary history • Animals & plants that don’t change • Young earth = not enough time for all that we see to have evolved • Variety in the building blocks used by life and perfect forms
  39. 39. Key points • Without variation, there can be no evolution • Characteristics acquired during life are not heritable • Whether a trait is favorable or not is determined by the environment • Natural selection acts on individuals  Even at a cost to the population or species  No “good of the species” • Populations evolve • Small steps add up to more complex traits