Chapters 22-25 Evolution

1. Chapters 22-25Evolution

2. Evolution The definition of Evolution is: • change over time Biological Evolution is: • genetic change in population over time • process by which modern organisms have descended from ancient organisms (slow change over long time) • Even relatively quick evolution takes hundreds of thousands of years

3. History of Evolutionary Theories • Plato (427-347 B.C.) 2 worlds – 1 perfect, 1 imperfect. No change in organisms • Aristotle (384-322 B.C.) Organisms placed on “ladder of complexity / perfection” (scala naturae) No change • Judeo-Christian culture tried to explain the Creator’s plan as observable, natural phenomena – Natural Theology

4. History of Evolutionary Theories • Carolus Linnaeus (1707-1832) Designed modern taxonomic system (binomial nomenclature) • From this system, we can (he didn’t) now infer evolutionary relationships between different groups • Geologists: • Georges Cuvier • James Hutton • Charles Lyell

5. History of Evolutionary Theories • Georges Cuvier (1769-1832) helped develop Paleontology – study of fossils • Discovery of fossils (extinct species, similarities to modern species) put some doubt into Earth’s age and the origin of species • Cuvier explained differences in strata with “catastrophism” – floods, droughts, volcanoes, etc. changed local areas drastically over short periods of time • Organisms did not change, just migrate

6. History of Evolutionary Theories • James Hutton (1726-1797) proposed that rocks, mountains, and valleys have been changed by water, wind, temperature, volcanoes, and other natural forces • He described the slow processes that shape Earth as “gradualism”

7. History of Evolutionary Theories • Charles Lyell (1797-1875) – agreed with Hutton and said that scientists must always explain past events in terms of observable, PRESENT events and processes (“uniformitarianism” – what happens today happened yesterday) • They theorized Earth was much older than a few thousand (6,000) years, which didn’t set well in the traditional timeframe of Creationism

8. Age of the Earth • We now know Earth is approximately 4.5 billion years old • Darwin used the work of Hutton and Lyell as a basis for his theories of slow change over time. Darwin’s work was a biological duplicate of Hutton and Lyell’s works in geology.

9. Geologists study Earth’s rocks • Fossils are preserved remains of ancient organisms • As fossils are found that don’t resemble organisms today, evidence increases that Earth has changed and that organisms have changed with it • Biologists and geologists date Earth’s past with the help of rocks

10. Geological Time Scale • RELATIVE DATING • Technique used to determine age of fossils relative to other fossils in different strata • This technique is VERY approximate

12. Geological Time Scale • ABSOLUTE (RADIOMETRIC) DATING • Using radioactive elements in rock that decay at a steady rate to determine age • Decay measured in terms of HALF-LIFE • Half-life – time required for half the radioactive atoms in a sample to decay

13. Radioactive Decay • During radioactive decay, the atoms of one element break down to form something else Lose a proton 6 protons 4 neutrons 5 protons 4 neutrons

14. Rocks contain radioactive elements, each having a different half-life EXAMPLES: Uranium-238 Lead-206 HL = 4.5 B yrs Potassium-40 Argon-40 HL = 1.3 B yrs Carbon-14  Nitrogen-14 HL = 5770 yrs

15. K-40 Ar-40 K-40 Ar-40 • Scientists often date rocks using Potassium-40, which decays to form the stable element Argon-40 • It has a half life of 1.3 billion years • This is used to date the oldest rocks on earth Formed 1.3 B yrs 2.6 B yrs

17. Uranium and Potassium are useful for dating rocks • Carbon-14 is useful for dating things that were once alive such as wood, natural fiber, or cloth • C-14 is in the atmosphere; living things take it in their cells. After the organism dies, it doesn’t take in any more C-14. We can then compare the amounts of C-14 to N-14, knowing its half-life, to determine the age of the sample

18. Fossil Evidence • Found in Sedimentary rock: layers of sand, silt, and clay in streams, lakes, rivers, and seas form rock that may have trapped living organisms • Fossil records – Show change over time. Some time frames are missing, but will show change of climate and geography. • Ex: Shark teeth in Utah • How can this be?

19. Jean Baptiste de Lamarck (1744-1829) • He also recognized that organisms were adapted to their environments and that they change • He relied on three ideas: • A desire to change (innate drive for perfection) • Use and disuse (Giraffe’s necks and vestigial organs) • Inheritance of acquired characteristics

20. Darwin’s Dilemma • Set sail around the world in 1831 on HMS Beagle on a 5 year voyage • He had prior knowledge of geology (Lyell was a good friend) and agriculture that helped influence the development of his theory • Anchored all along the way and took samples from each place

21. Darwin’s Dilemma • He collected and studied beetles from Brazil, birds from Chile, and iguanas, tortoises, and finches from the Galápagos Islands • He noticed similarities between mainland (Ecuador) and Galapagos finches • Later, he noticed differences in beak size among finches from different islands in the Galapagos

22. Darwin’s Dilemma • Thomas Malthus – wrote paper on population growth in Great Britain • Population grows exponentially • Limiting factors on growth (carrying capacity) • Food • Area • Resources

23. Darwin’s Dilemma • Darwin applied Malthus’, Hutton’s, and Lyell’s work to species’ ability to change, and called the mechanism Natural Selection • Nat.Sel.: Process by which organisms with favorable variations survive and produce more offspring than less well-adapted organisms • He was sure Nat.Sel. was true, but he feared public ridicule. So, he kept his ideas to himself

24. Darwin’s Dilemma • Alfred Russel Wallace (1823-1913), working independently, came to the same conclusions as Darwin • He sent a manuscript to Darwin, basically for proofreading • “I never saw a more striking coincidence… so all my originality, whatever it may amount to, will be smashed.” – Charles Darwin • Letter to Charles Lyell, June 18, 1858 • Darwin quickly abridged and published his work “On the Origin of Species”

25. Darwin’s Natural Selection • Ernst Mayr, an evolutionary biologist, has dissected the logic of Darwin’s theory into three inferences based on five observations (Pg. 435) • Observations: • Tremendous fecundity • Stable populations sizes • Limited environmental resources • Variation among individuals • Heritability of some of this variation.

26. Darwin’s Natural Selection • Observation #1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully.

27. Darwin’s Natural Selection • Observation #2: Populations tend to remain stable in size,except for seasonal fluctuations. • Observation #3: Environmental resources are limited.

28. Darwin’s Natural Selection • Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population, with only a fraction of the offspring surviving each generation.

29. Darwin’s Natural Selection • Observation #4: Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike. • Observation #5: Much of this variation is heritable.

30. Darwin’s Natural Selection • Inference #2: Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the individuals. • Those individuals whose inherited characteristics best fit them to their environment are likely to leave more offspring than less fit individuals.

31. Darwin’s Natural Selection • Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations.

32. Evidence in Living Organisms • Comparative embryology: • All vertebrate embryos look similar to one another in early development, with the development of a tail and gill arches • Ernst Haeckel made early drawings – later exposed as frauds. • Gave fuel to anti-evolutionists

33. Evidence in Living Organisms • Comparative embryology: • These anatomical similarities indicate similar genetics are at work • Become more dissimilar as they grow • Cell specialization and differentiation • Common ancestor?

34. Evidence in Living Organisms

35. Evidence in Living Organisms • Comparative anatomy: • Homologous Structures • Analogous Structures • Vestigial Organs

36. Evidence in Living Organisms • Homologous Structures – structures that are similar in anatomy, but may serve very different functions • Ex: cat, whale, and human forearm

37. Homologous Structures Flying Swimming Running Grasping

38. Evidence in Living Organisms • Analogous Structures – structures that serve similar functions, but have evolved independently of each other

39. Not homologous;analogous Not homologous;not analogous Homologous;not analogous Homologous; analogous

40. Evidence in Living Organisms. • Vestigial organs – organs that have little or no purpose in the organism; may become smaller or even disappear • Ex: Tailbone or appendix in humans • Ex: Tiny leg bones in snakes (boas and pythons) thought to come from 4 legged ancestor

41. Evidence in Living Organisms • Comparative biochemistry and molecular biology: • All cells have DNA, RNA, ribosomes, the same 20 amino acids and use ATP to do work • Similarities in biochemistry indicate relationship

42. Evidence in Living Organisms • Cytochrome c is a highly conserved respiratory protein containing 104 amino acids in humans

43. Evidence in Living Organisms • Amino acid differences of hemoglobin between species

44. What Homologies tell us… • Similarities in structure and chemistry provide powerful evidence that all living things evolved from a common ancestor • Darwin Concluded: • Living organisms evolved through gradual modifications of earlier forms  descent with modification

45. What Similarities tell us… • Two types of evolution can account for homologous AND analogous structures • Convergent evolution • Divergent evolution

46. What Similarities tell us… • Divergent evolution – two species evolve from a common ancestor (speciation) • They share similarities in anatomy, biochemistry, and embryology due to common ancestry • Explains homologous structures

47. What Similarities tell us… • Convergent – two species apparently becoming more similar • Two species have adapted in similar ways to similar environmental conditions • NOT due to common ancestry • Explains analogous structures

48. Convergent Evolution • Ocotillo from California and allauidi from Madagascar have evolved similar mechanisms for protecting themselves

49. Convergent Evolution • Adaptive radiation of anoles has occurred on the islands of the Greater Antilles in a convergent fashion. On each island, different species of the lizards have adapted to living in different parts of trees, in strikingly similar ways.

50. Convergent Evolution