1. 1 Evolution Diversity of Life 7/8/2016 3:05 PMcoley - evolution

2. 2 “Nothing in biology makes sense EXCEPT in the light of evolution.” Theodosius Dobzhansky Evolution Charles Darwin in later years 7/8/2016 3:05 PMcoley - evolution

3. 3 History of Evolutionary Thought 7/8/2016 3:05 PMcoley - evolution

4. 4 Early Ideas On Earth’s Organisms Aristotle believed species were fixed creations arranged by their complexity Aristotle believed species were fixed creations arranged by their complexity Idea lasted 2000 years Idea lasted 2000 years 7/8/2016 3:05 PMcoley - evolution

5. 5 Early Ideas On Earth’s Organisms Linnaeus – 1 st to group similar organisms and assign them Latin names Linnaeus – 1 st to group similar organisms and assign them Latin names Two word name (Genus species) Two word name (Genus species) Known as Binomial nomenclature Known as Binomial nomenclature 7/8/2016 3:05 PMcoley - evolution

6. 6 : Contributor’s to Darwin’s thinking included: Charles Lyell – uniformatarianismCharles Lyell – uniformatarianism Georges Cuvier – species extinction (Catastrophism)Georges Cuvier – species extinction (Catastrophism) Thomas Malthus – struggle for existence (resources)Thomas Malthus – struggle for existence (resources) 7/8/2016 3:05 PMcoley - evolution

7. 7 : Contributor’s to Darwin’s thinking included: James Hutton - GradualismJames Hutton - Gradualism John Baptiste Lamarck – Inheritance of acquired Characteristics and Law of Use and DisuseJohn Baptiste Lamarck – Inheritance of acquired Characteristics and Law of Use and Disuse Alfred Russel Wallace – organisms evolved from common ancestorsAlfred Russel Wallace – organisms evolved from common ancestors 7/8/2016 3:05 PMcoley - evolution

8. 8 Evolutionary Timeline 7/8/2016 3:05 PMcoley - evolution

9. 9 Catastrophism Idea proposed by George Cuvier Idea proposed by George Cuvier Studied fossil in sedimentary rock strata of Paris Studied fossil in sedimentary rock strata of Paris Found some species completely disappeared in more recent layers Found some species completely disappeared in more recent layers 7/8/2016 3:05 PMcoley - evolution

10. 10 Catastrophism Stated that species disappear due to a catastrophic event of the earth’s crust (volcano, earthquake…) Stated that species disappear due to a catastrophic event of the earth’s crust (volcano, earthquake…) 7/8/2016 3:05 PMcoley - evolution

11. 11 Hutton’s Theory of Geological Change James Hutton, 1795, Scottish geologist James Hutton, 1795, Scottish geologist Studied invertebrate fossils in Paris Museum Studied invertebrate fossils in Paris Museum Described The Geological Forces That Have Changed Life on Earth Over Millions of Years (erosion, earthquakes, volcanoes…) Described The Geological Forces That Have Changed Life on Earth Over Millions of Years (erosion, earthquakes, volcanoes…) 7/8/2016 3:05 PMcoley - evolution

12. 12 Hutton’s Theory of Geological Change Changes in Earth’s crust due to slow continuous processes Changes in Earth’s crust due to slow continuous processes Idea Known as Gradualism Idea Known as Gradualism 7/8/2016 3:05 PMcoley - evolution

13. 13 Charles Lyell Proposed theory of Uniformitarianism Proposed theory of Uniformitarianism Geological processes at uniform rates building & wearing down Earth’s crust Geological processes at uniform rates building & wearing down Earth’s crust Proposed that the Earth was millions of years instead of a few thousand years old Proposed that the Earth was millions of years instead of a few thousand years old 7/8/2016 3:05 PMcoley - evolution

14. 14 Principles of Geology Published by Lyell Just Before The Beagle Set Sail & read by Darwin Published by Lyell Just Before The Beagle Set Sail & read by Darwin Explained Geological Processes That Shaped The Earth Explained Geological Processes That Shaped The Earth Helped Darwin Understand Sea Shells In The Andes Mountains At 12,000+ Feet Helped Darwin Understand Sea Shells In The Andes Mountains At 12,000+ Feet –Expanded Earth’s Age 7/8/2016 3:05 PMcoley - evolution

15. 15 Lamarck’s Theory of Evolution Jean-Baptiste Lamarck, 1809 Jean-Baptiste Lamarck, 1809 One Of First Scientists To Understand That Change Occurs Over Time One Of First Scientists To Understand That Change Occurs Over Time Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime Said acquired changes were passed to offspring Said acquired changes were passed to offspring 7/8/2016 3:05 PMcoley - evolution

16. 16 Lamarck’s Theory of Evolution Idea called Law of Use and Disuse Idea called Law of Use and Disuse If a body part were used, it got stronger If a body part were used, it got stronger If body part NOT used, it deteriorated If body part NOT used, it deteriorated 7/8/2016 3:05 PMcoley - evolution

17. 17 Lamarck’s Theory of Evolution Inheritance of Acquired Characteristics Inheritance of Acquired Characteristics Proposed That By Selective Use Or Disuse Of Organs, Organisms Acquired Or Lost Certain Traits During Their Lifetime Proposed That By Selective Use Or Disuse Of Organs, Organisms Acquired Or Lost Certain Traits During Their Lifetime These Traits Could Then Be Passed On To Their Offspring These Traits Could Then Be Passed On To Their Offspring Over Time This Led To New Species Over Time This Led To New Species 7/8/2016 3:05 PMcoley - evolution

18. 18 Lamarck’s Theory of Evolution Use & Disuse - Organisms Could Change The Size Or Shape Of Organs By Using Them Or Not Using Them Use & Disuse - Organisms Could Change The Size Or Shape Of Organs By Using Them Or Not Using Them Blacksmiths & Their Sons (muscular arms) Blacksmiths & Their Sons (muscular arms) Giraffe’s Necks Longer from stretching) Giraffe’s Necks Longer from stretching) 7/8/2016 3:05 PMcoley - evolution

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20. 20 Lamarck’s Theory of Evolution Inheritance Of Acquired Traits Inheritance Of Acquired Traits –Traits Acquired During Ones Lifetime Would Be Passed To Offspring Clipped ears of dogs could be passed to offspring! 7/8/2016 3:05 PMcoley - evolution

21. 21 Lamarck’s Theory of Evolution Tendency Toward Perfection Tendency Toward Perfection Organisms Are Continually Changing and Acquiring Features That Help Them Live More Successfully In Their Environment Organisms Are Continually Changing and Acquiring Features That Help Them Live More Successfully In Their Environment Example: Bird Ancestors Desired To Fly So They Tried Until Wings Developed Example: Bird Ancestors Desired To Fly So They Tried Until Wings Developed 7/8/2016 3:05 PMcoley - evolution

22. 22 Lamarck’s Mistakes Lamarck Did NOT Know how traits were inherited (Traits are passed through genes) Lamarck Did NOT Know how traits were inherited (Traits are passed through genes) Genes Are NOT Changed By Activities In Life Genes Are NOT Changed By Activities In Life Change Through Mutation Occurs Before An Organism Is Born Change Through Mutation Occurs Before An Organism Is Born 7/8/2016 3:05 PMcoley - evolution

23. 23 Charles Darwin the Naturalist 7/8/2016 3:05 PMcoley - evolution

24. 24 Voyage of the Beagle Charles Darwin Born Feb. 12, 1809 Born Feb. 12, 1809 Joined Crew of HMS Beagle, 1831 Joined Crew of HMS Beagle, 1831 Naturalist Naturalist 5 Year Voyage around world 5 Year Voyage around world Avid Collector of Flora & Fauna Avid Collector of Flora & Fauna Astounded By Variety of Life Astounded By Variety of Life 7/8/2016 3:05 PMcoley - evolution

25. 25 A reconstruction of the HMS Beagle sailing off Patagonia. Darwin’s Voyage of Discovery 7/8/2016 3:05 PMcoley - evolution

26. 26 Darwin Left England in 1831 Darwin returned 5 years later in 1836 7/8/2016 3:05 PMcoley - evolution

27. 27 HMS Beagle’s Voyage 7/8/2016 3:05 PMcoley - evolution

28. 28 The Galapagos Islands Small Group of Islands 1000 km West of South America Small Group of Islands 1000 km West of South America Very Different Climates Very Different Climates Animals On Islands Unique Animals On Islands Unique »Tortoises »Iguanas »Finches 7/8/2016 3:05 PMcoley - evolution

29. 29 The Galapagos Islands Volcanic islands off the coast of South America Volcanic islands off the coast of South America Island species varied from mainland species & from island-to- island species Island species varied from mainland species & from island-to- island species Each island had long or short neck tortoises Each island had long or short neck tortoises 7/8/2016 3:05 PMcoley - evolution

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31. 31 The Galapagos Islands Finches on the islands resembled a mainland finch Finches on the islands resembled a mainland finch More types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects…) More types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects…) Finches had different types of beaks adapted to their type of food gathering Finches had different types of beaks adapted to their type of food gathering 7/8/2016 3:05 PMcoley - evolution

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33. 33 Darwin’s Observations & Conclusions The Struggle for Existence 7/8/2016 3:05 PMcoley - evolution

34. 34 Voyage of the Beagle During His Travels, Darwin Made Numerous Observations And Collected Evidence That Led Him To Propose A Revolutionary Hypothesis About The Way Life Changes Over Time 7/8/2016 3:05 PMcoley - evolution

35. 35 Darwin’s Observations Patterns of Diversity were shown Patterns of Diversity were shown Unique Adaptations in organisms Unique Adaptations in organisms Species Not Evenly Distributed Species Not Evenly Distributed »Australia, Kangaroos, but No Rabbits »S. America, Llamas 7/8/2016 3:05 PMcoley - evolution

36. 36 Darwin’s Observations Both Living Organisms & Fossils collected Both Living Organisms & Fossils collected Fossils included: Fossils included: »Trilobites »Giant Ground Sloth of South America This species NO longer existed. What had happened to them? 7/8/2016 3:05 PMcoley - evolution

37. 37 Evidence for Evolution – The Fossil Record 7/8/2016 3:05 PMcoley - evolution

38. 38 Definition Evolution is the slow, gradual change in a population of organisms over time 7/8/2016 3:05 PMcoley - evolution

39. 39 Darwin’s Observations Left unchecked, the number of organisms of each species will increase exponentially, generation to generation In nature, populations tend to remain stable in size Environmental resources are limited 7/8/2016 3:05 PMcoley - evolution

40. 40 Darwin’s Conclusion Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals Only a fraction of offspring survive each generation Survival of the Fittest 7/8/2016 3:05 PMcoley - evolution

41. 41 Darwin’s Observations Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike. Much of this variation between individuals is inheritable. 7/8/2016 3:05 PMcoley - evolution

42. 42 Darwin’s Conclusion Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals Called Natural Selection 7/8/2016 3:05 PMcoley - evolution

43. 43 The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection)The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection) New species evolveNew species evolve Darwin’s Theory of Evolution 7/8/2016 3:05 PMcoley - evolution

44. 44 Ideas That Shaped Darwin’s Thinking Thomas Malthus 7/8/2016 3:05 PMcoley - evolution

45. 45 Population Growth Thomas Malthus, 1798 Thomas Malthus, 1798 Economist Economist Observed Babies Being Born Faster Than People Were Dying Observed Babies Being Born Faster Than People Were Dying Population size limited by resources such as the Food Supply Population size limited by resources such as the Food Supply 7/8/2016 3:05 PMcoley - evolution

46. 46 The Struggle for Existence Malthus’ Influence: –High Birth Rates & Limited Resources Would Force Life & Death Competition Each Species Struggles For: –Food –Living Space –Mates 7/8/2016 3:05 PMcoley - evolution

47. 47 Population Growth Malthus Reasoned That If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone Malthus Reasoned That If The Human Population Continued To Grow Unchecked, Sooner or Later There Would Be Insufficient Living Space & Food For Everyone Death Rate Will Increase To Balance Population size & Food Supply Death Rate Will Increase To Balance Population size & Food Supply 7/8/2016 3:05 PMcoley - evolution

48. 48 Population Growth Darwin Realized Malthus’s Principles Were Visible In Nature Darwin Realized Malthus’s Principles Were Visible In Nature Plants & Animals Produce Far More Offspring Than Can Be Supported Plants & Animals Produce Far More Offspring Than Can Be Supported –Most Die –If They Didn’t – Earth Would Be Overrun 7/8/2016 3:05 PMcoley - evolution

49. 49 Darwin’s Theory of Evolution Organisms Change OverTime 7/8/2016 3:05 PMcoley - evolution

50. 50 Common Descent with Modification Darwin proposed that organisms descended from common ancestors Darwin proposed that organisms descended from common ancestors Idea that organisms change with time, diverging from a common form Idea that organisms change with time, diverging from a common form Caused evolution of new species Caused evolution of new species 7/8/2016 3:05 PMcoley - evolution

51. 51. Natural Selection Driving force for evolution Driving force for evolution During the struggle for resources, strongest survive & reproduce During the struggle for resources, strongest survive & reproduce Idea that at least some of the differences between individuals, which impact their survival and fertility, are inheritable Idea that at least some of the differences between individuals, which impact their survival and fertility, are inheritable 7/8/2016 3:05 PMcoley - evolution

52. 52 Origin of Species Darwin Presents His Case 7/8/2016 3:05 PMcoley - evolution

53. 53 Publication of “On The Origin of Species” Upon His Return To England, Darwin Developed His Observations Into The Theory of Evolution Upon His Return To England, Darwin Developed His Observations Into The Theory of Evolution But He Did Not Publish For 25 Years – But He Did Not Publish For 25 Years –Why? 7/8/2016 3:05 PMcoley - evolution

54. 54 Publication of “On The Origin of Species” Darwin Knew That His Theory Would Be Extremely Controversial And Would Be Attacked Darwin Knew That His Theory Would Be Extremely Controversial And Would Be Attacked His Theory Challenged Established Religious & Scientific Beliefs, Particularly About The Creation Of Man His Theory Challenged Established Religious & Scientific Beliefs, Particularly About The Creation Of Man 7/8/2016 3:05 PMcoley - evolution

55. 55 Publication of “On The Origin of Species” He Refused To Publish Until He Received An Essay From Alfred Wallace He Refused To Publish Until He Received An Essay From Alfred Wallace –Fellow Naturalist –Independently Developed The Same Theory –After 25 Years, Someone Else Had Come To The Same Conclusions From Their Observations Of Nature 7/8/2016 3:05 PMcoley - evolution

56. 56 Wallace’s Contribution Alfred Russel Wallace Independently came to same Conclusion as Darwin that species changed over time because of their struggle for existenceAlfred Russel Wallace Independently came to same Conclusion as Darwin that species changed over time because of their struggle for existence When Darwin read Wallace’s essay, he knew he had to publish his findingsWhen Darwin read Wallace’s essay, he knew he had to publish his findings 7/8/2016 3:05 PMcoley - evolution

57. 57 Publication of “On The Origin of Species” Darwin Presented Wallace’s Essay & Some Of His Work At A Scientific Conference of the Linnaean Society in July of 1858 Darwin Presented Wallace’s Essay & Some Of His Work At A Scientific Conference of the Linnaean Society in July of 1858 Then He Started On his book “Origin of Species” Then He Started On his book “Origin of Species” It Took Darwin 18 Months To Complete The Book It Took Darwin 18 Months To Complete The Book 7/8/2016 3:05 PMcoley - evolution

58. 58 Natural Variation and Artificial Selection Abandoned The Idea That Species Were Perfect & Unchanging Abandoned The Idea That Species Were Perfect & Unchanging Observed Significant Variation in All Species Observed Observed Significant Variation in All Species Observed Observed Farmers Use Variation To Improve Crops & Livestock Observed Farmers Use Variation To Improve Crops & Livestock Called Selective Breeding Called Selective Breeding 7/8/2016 3:05 PMcoley - evolution

59. 59 Natural Variation and Artificial Selection Natural Variation Natural Variation –Differences Among Individuals Of A Species Artificial Selection Artificial Selection –Selective Breeding To Enhance Desired Traits Among Stock or Crops 7/8/2016 3:05 PMcoley - evolution

60. 60 Natural Variation and Artificial Selection Key Concept: In Artificial Selection, Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful 7/8/2016 3:05 PMcoley - evolution

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62. 62 Origin of Species Concepts and Controversy 7/8/2016 3:05 PMcoley - evolution

63. 63 Evolution By Natural Selection Concepts The Struggle for Existence (compete for food, mates, space, water, etc.) The Struggle for Existence (compete for food, mates, space, water, etc.) Survival of the Fittest (strongest able to survive and reproduce) Survival of the Fittest (strongest able to survive and reproduce) Descent with Modification (new species arise from common ancestor replacing less fit species) Descent with Modification (new species arise from common ancestor replacing less fit species) 7/8/2016 3:05 PMcoley - evolution

64. 64 Survival of the Fittest Fitness –Ability of an Individual To Survive & Reproduce Adaptation –Inherited Characteristic That Increases an Organisms Chance for Survival 7/8/2016 3:05 PMcoley - evolution

65. 65 Survival of the Fittest Adaptations Can Be: – –Physical »Speed, Camouflage, Claws, Quills, etc. –Behavioral »Solitary, Herds, Packs, Activity, etc. 7/8/2016 3:05 PMcoley - evolution

66. 66 Survival of the Fittest Is Central To The Process Of Evolution Fitness Is Central To The Process Of Evolution Individuals With Low Fitness Individuals With Low Fitness –Die –Produce Few Offspring Survival of the Fittest AKA AKA Natural Selection 7/8/2016 3:05 PMcoley - evolution

67. 67 Survival of the Fittest Key Concept Over Time, Natural Selection Results In Changes In The Inherited Characteristics Of A Population. These Changes Increase A Species Fitness In Its Environment 7/8/2016 3:05 PMcoley - evolution

68. 68 Natural Selection Cannot Be Seen Directly Cannot Be Seen Directly It Can Only Be Observed As Changes In A Population Over Many Successive Generations It Can Only Be Observed As Changes In A Population Over Many Successive Generations –Radiation –Fossil Record 7/8/2016 3:05 PMcoley - evolution

69. 69 Descent With Modification Takes Place Over of Time Takes Place Over Long Periods of Time Natural Selection Can Be As Changes In Natural Selection Can Be Observed As Changes In –Body Structures –Ecological Niches –Habitats 7/8/2016 3:05 PMcoley - evolution

70. 70 Descent With Modification Species From Their Ancestors Species Today Look Different From Their Ancestors Each Living Species Has Each Living Species Has –Descended –With Changes –From Other Species –Over Time 7/8/2016 3:05 PMcoley - evolution

71. 71 Descent With Modification 7/8/2016 3:05 PMcoley - evolution

72. 72 Descent With Modification Implies Implies –All Living Organisms Are Related –Single Tree of Life »DNA, Body Structures, Energy Sources Common Descent –All Species, Living & Extinct, Were Derived From Common Ancestors 7/8/2016 3:05 PMcoley - evolution

73. 73. Major Problem in Darwin’s Theory No mechanism to explain natural selection How could favorable variations be transmitted to later generations? With the rediscovery of Mendel’s work in the first half of the 20th century, the missing link in evolutionary theory was found 7/8/2016 3:05 PMcoley - evolution

74. 74 Opposition to Evolution The upheaval surrounding evolution began with Darwin’s publication of On the Origin of Species By Means of Natural Selection The debate continues nearly 150 years later 7/8/2016 3:05 PMcoley - evolution

75. 75 Theory of Evolution Today Supporting Evidence 7/8/2016 3:05 PMcoley - evolution

76. 76 Homologous Structures 7/8/2016 3:05 PMcoley - evolution

77. 77 Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development 7/8/2016 3:05 PMcoley - evolution

78. 78 Similarities in DNA Sequence 7/8/2016 3:05 PMcoley - evolution

79. 79 Evolution of pesticide resistance in response to selection 7/8/2016 3:05 PMcoley - evolution

80. 80 Evidence for Evolution – Evolution Observed Evolution of drug-resistance in HIV 7/8/2016 3:05 PMcoley - evolution

81. 81 Evidence for Evolution – Evolution Observed Selection against small guppies results in an increase in average size 7/8/2016 3:05 PMcoley - evolution

82. 82 Evolutionary Time Scales Long time scale events that create and destroy species. Macroevolution: Long time scale events that create and destroy species. 7/8/2016 3:05 PMcoley - evolution

83. 83 Microevolution: Short time scale events (generation- to-generation) that change the genotypes and phenotypes of populations Evolutionary Time Scales 7/8/2016 3:05 PMcoley - evolution

84. 84 Evidence of Evolution Key Concept Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. Evidence For This Process Could Be Found In: –The Fossil Record –The Geographical Distribution of Living Species –Homologous Structures of Living Organisms –Similarities In Early Development 7/8/2016 3:05 PMcoley - evolution

85. 85 Fossil Record Earth is Billions of Years Old Earth is Billions of Years Old Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time 7/8/2016 3:05 PMcoley - evolution

86. 86 Geographic Distribution of Living Species Different Animals On Different Continents But Similar Adaptations To Shared Environments Different Animals On Different Continents But Similar Adaptations To Shared Environments 7/8/2016 3:05 PMcoley - evolution

87. 87 Homologous Body Structures Scientists Noticed Animals With Backbones (Vertebrates) Had Similar Bone Structure Scientists Noticed Animals With Backbones (Vertebrates) Had Similar Bone Structure May Differ In Form or Function May Differ In Form or Function Limb Bones Develop In Similar Patterns Limb Bones Develop In Similar Patterns »Arms, Wings, Legs, Flippers 7/8/2016 3:05 PMcoley - evolution

88. 88 Homologous Body Structures Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues Strong Evidence That All Four- Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor Strong Evidence That All Four- Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor Help Scientist Group Animals Help Scientist Group Animals 7/8/2016 3:05 PMcoley - evolution

89. 89 Homologous Body Structures 7/8/2016 3:05 PMcoley - evolution

90. 90 Homologous Body Structures Not All Serve Important Functions Not All Serve Important Functions –Vestigial Organs »Appendix In Man »Legs On Skinks 7/8/2016 3:05 PMcoley - evolution

91. 91 Similarities In Early Development Embryonic Structures Of Different Species Show Significant Similarities Embryonic Structures Of Different Species Show Significant Similarities Embryo – early stages of vertebrate development Embryo – early stages of vertebrate development 7/8/2016 3:05 PMcoley - evolution

92. 92 Human Fetus – 5 weeks 7/8/2016 3:05 PMcoley - evolution

93. 93 ChickenTurtle Rat 7/8/2016 3:05 PMcoley - evolution

94. 94 Review 7/8/2016 3:05 PMcoley - evolution

95. 95 Darwin's Theory 1. Individual Organisms In Nature Differ From One Another. Some Of This Variation Is Inherited 2. Organisms In Nature Produce More Offspring Than Can Survive, And Many Of These Offspring Do No Reproduce 7/8/2016 3:05 PMcoley - evolution

96. 96 Darwin's Theory 3. Because More Organisms Are Produced Than Can Survive, Members Of Each Species Must Compete For Limited Resources 4. Because Each Organism Is Unique, Each Has Different Advantages & Disadvantages In The Struggle For Existence 7/8/2016 3:05 PMcoley - evolution

97. 97 Darwin's Theory 5. Individuals Best Suited To Their Environment Survive & Reproduce Successfully – Passing Their Traits To Their Offspring. 6. Species Change Over Time. Over Long Periods, Natural Selection Causes Changes That May Eventually Lead To New Species 7/8/2016 3:05 PMcoley - evolution

98. 98 Darwin's Theory 7. Species Alive Today Have Descended With Modifications From Species That Lived In The Past 8. All Organisms On Earth Are United Into A Single Tree Of Life By Common Descent 7/8/2016 3:05 PMcoley - evolution