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3. Human Evolution


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3. Human Evolution

  1. 1. Human Evolution
  2. 2. Overview <ul><li>Evolution of Primates </li></ul><ul><li>Evolution of Hominids </li></ul><ul><li>Focus on Homo </li></ul><ul><li>Human Variation </li></ul><ul><li>Humans as a selective agent </li></ul>
  3. 3. Early Primates <ul><li>Prosimians (~58mya) </li></ul><ul><li>Monkeys (35mya) </li></ul><ul><li>Apes (23mya) </li></ul><ul><li>Hominids (~6mya) </li></ul>
  4. 4. First Arboreal Mammals <ul><li>The first arboreal (tree dwellers) mammals probably resembled shrews: </li></ul><ul><li>Example of phylogeny (characteristics) </li></ul><ul><ul><ul><ul><ul><li>Long snouts. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Good sense of smell. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Probably nocturnal. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Very active. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>CLAWS </li></ul></ul></ul></ul></ul>
  5. 5. First Arboreal Mammals
  6. 6. Tarsiers Lemurs Loris Pottos Prosimians
  7. 7. Tarsier
  8. 8. Ring tailed lemur
  9. 9. Aye aye
  10. 11. Two main groups of primates: <ul><ul><li>1. Prosimians – lemurs, lorises, pottos & tarsiers </li></ul></ul><ul><ul><li>2. Anthropoids – monkeys, apes and man </li></ul></ul>
  11. 12. Tarsiers Lemurs Loris Pottos 1. Prosimians
  12. 13. <ul><ul><li>ANTHROPOIDS </li></ul></ul><ul><ul><ul><li>Monkeys: </li></ul></ul></ul><ul><ul><ul><ul><li>Old world monkeys </li></ul></ul></ul></ul><ul><ul><ul><ul><li>New world monkeys </li></ul></ul></ul></ul>New World Monkey: Flat face Wide nostrils Prehensile tail Old World Monkey: Long snout Close nostrils Non-prehensile tail 2. Anthropoids = monkeys + apes + man
  13. 14. Taxonomy <ul><li>Anthropoids= Hominoids + monkeys </li></ul><ul><li>Hominoids= Asian and African Apes + Hominids </li></ul><ul><li>Hominids= Humans </li></ul>
  14. 15. Primate Phylogeny <ul><li>What is the major selective pressure associated with life in the trees? </li></ul><ul><li>How are primates adapted to this life? </li></ul>
  15. 16. Primate phylogeny that Humans Share <ul><li>Evolved the opposable digits : thumb and forefinger, provide excellent grasp </li></ul><ul><li>Nails protect top of delicate fingers, which have sensitive fleshy pads on the reverse side </li></ul><ul><li>Long slender limbs suited to climbing and treetop mobility </li></ul><ul><li>Stereoscopic vision – needed to climb, capture food </li></ul><ul><li>Excellent hearing </li></ul><ul><li>Large brains </li></ul><ul><li>Social animals, work together as a group </li></ul><ul><li>Long life span </li></ul><ul><li>Females bear usually one baby ; long gestation and long post parturition nurturing and protection </li></ul>
  16. 17. Binocular Color Vision
  17. 18. Primate Hands
  18. 19. Mobile Limbs <ul><li>Most primates have flat nails as well as sensitive pads on the undersides of fingers and toes. </li></ul><ul><ul><li>Many also have both an opposable big toe and thumb. </li></ul></ul><ul><li>Mobile limbs and clawless opposable digits allow primates to freely grasp and release tree limbs. </li></ul>
  19. 20. Other important features <ul><li>Upright posture. </li></ul><ul><li>Small litter size. </li></ul><ul><li>Expanded forebrain, larger brain capacity. </li></ul><ul><li>Advantages? </li></ul>
  20. 21. Proconsul- Ancestor to Hominoids?
  21. 22. Proconsul A skull of Proconsul africanus from the Kenya National Museum.
  22. 23. Selective pressures <ul><li>East Africa Rift Valley </li></ul>
  23. 25. Hominid Evolution <ul><li>Major Homo advances : </li></ul><ul><ul><li>I. Mouth development </li></ul></ul><ul><ul><li>II. Brain size </li></ul></ul><ul><ul><li>III. Bipedalism Hunting </li></ul></ul><ul><ul><ul><ul><li>Fire ( H. erectus ) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Tools </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>H. habilis </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>H. erectus </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>H. heidelbergensis </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>H. sapiens </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>Built shelters ( H. heidelbergensis ) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Clothing ( H. neandertalensis ) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Language (Neandertals) </li></ul></ul></ul></ul>Environmental Changes Cont Drift
  24. 26. <ul><li>IV. Changes in dentition based on dietary shifts </li></ul><ul><li>V. Reduced size differences between the sexes </li></ul><ul><ul><ul><li>a. male gorillas are 2x heavier than females, male chimps are 1.35X heavier and male humans are 1.2X heavier. </li></ul></ul></ul><ul><li>VI. Key changes in family Structure </li></ul><ul><ul><ul><li>a. Insights into social behavior are derived from comparisons between humans and extinct hominoids </li></ul></ul></ul><ul><ul><ul><li>b. In contrast to most ape species, monogamy or long term pair bonding prevails in most human cultures. </li></ul></ul></ul>
  25. 27. VII. Cultural Evolution: <ul><li>Tool use is more sophisticated </li></ul><ul><li>Use of fire </li></ul><ul><li>Cave paintings </li></ul><ul><li>Introduction of language </li></ul><ul><li>Agricultural advances </li></ul><ul><li>Skills learned from teaching and communication </li></ul>
  26. 28. I. Changes to the mouth <ul><li>Lost of vegetarians rectangle mouth shape </li></ul><ul><li>Reduce size in molars (4 times larger in early ancestors) </li></ul><ul><li>Reduce jaw muscle. </li></ul><ul><li>Teeth very mineralized. </li></ul><ul><li>Evolutionary Trends in Dentition </li></ul>Chewing
  27. 31. II. Changes in Brain Size <ul><li>Austrapithecus 500cc </li></ul><ul><li>Homo habilis 700cc </li></ul><ul><li>Homo erectus 1000cc </li></ul><ul><li>Homo sapiens 1000cc </li></ul><ul><li>Present day Homo sapiens 1300cc </li></ul>
  28. 34. A. afarensis A. africanus A. boisei A. robustus
  29. 35. Human Evolution
  30. 36. III. Bipedalism
  31. 37. <ul><li>3.8 myo fossil footprints </li></ul><ul><li>Represent at least two individuals of the A. afarensis species </li></ul><ul><li>Bipedal </li></ul>Laetoli Footprints
  32. 38. Anatomical Adaptations to Bipedalism
  33. 39. Human and Ape Skeletal Features <ul><li>Human skeletons show the need for upright walking – making a ground dwelling ape </li></ul><ul><ul><ul><li>Curvature of the spine is an adaptation to provide better balance and weight distribution for bipedalism </li></ul></ul></ul><ul><ul><ul><li>Foramen Magnum (hole for the spinal cord) located UNDERNEATH the skull rather then toward the back in apes. </li></ul></ul></ul><ul><ul><ul><li>Pelvis adjusted for upright walking (change in angle and shape like a bowl to support organs) </li></ul></ul></ul><ul><ul><ul><li>Hip Angle change and is angle in (knock knees) </li></ul></ul></ul><ul><ul><ul><li>Foot provides a better platform by losing opposable thumb (big toes) making it easier to running </li></ul></ul></ul>
  34. 40. Human Skeletal Adaptations
  35. 41. What are the anatomical features of bipedalism? <ul><li>Skull </li></ul><ul><ul><li>In both Ancient and Modern apes, the Spine enters the skull at the back </li></ul></ul><ul><ul><li>Human spines enters at bottom thru hole foramen magnum </li></ul></ul><ul><li>Pelvis </li></ul><ul><ul><li>Ancient and Modern apes have long flat Pelvises </li></ul></ul><ul><ul><li>Humans have bowl shaped </li></ul></ul><ul><ul><ul><li>Hold Organs </li></ul></ul></ul><ul><ul><ul><li>Lower center of gravity for better balance on 2 legs </li></ul></ul></ul><ul><li>Knee </li></ul><ul><ul><li>Apes are straight from pelvis, Humans slant in. </li></ul></ul><ul><ul><ul><li>Allow straight walking + Maintain balance. </li></ul></ul></ul><ul><li>Foot </li></ul><ul><ul><li>Enlarged ankle bones and arches to support pressure of walking </li></ul></ul>
  36. 42. Bipedal Pelvis
  37. 43. Bipedal Femur
  38. 44. Bipedal Foramen Magnum
  39. 45. Bipedal Foot
  40. 47. Why Bipedalism?
  41. 48. Remember the following… <ul><li>PELVIS! </li></ul><ul><li>FEET! </li></ul>
  42. 49. 1960 Up the ladder <ul><li>The idea that one species smoothly evolves from one into another is regarded today as an oversimplification </li></ul><ul><li>Unfortunately it is a very persistent view that continually resurfaces in cartoons </li></ul>Trends illustrated by fossils Environmental Changes Cont Drift
  43. 50. Human Origin Misconceptions : <ul><li>First, our ancestors were not chimpanzees or any other modern apes. </li></ul><ul><ul><ul><ul><li>Chimpanzees and humans represent two divergent branches of the hominoid tree that evolved from a common ancestor that was neither a chimpanzee nor a human. </li></ul></ul></ul></ul><ul><li>Second, human evolution did not occur as a ladder with a series of steps leading directly from an ancestral hominoid to Homo sapiens . </li></ul><ul><ul><ul><ul><li>If human evolution is a parade, then many splinter groups traveled down dead ends and several different human species coexisted. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Human phylogeny is more like a multi-branched bush with our species as the tip of the only surviving twig. </li></ul></ul></ul></ul><ul><li>Third, the various human characteristics, such as upright posture and an enlarged brain, did not evolve in unison. </li></ul><ul><ul><ul><ul><li>Different features evolved at different rates, called mosaic evolution . </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Our pedigree includes ancestors who walked upright but had brains much less developed than ours. </li></ul></ul></ul></ul>
  44. 51. 1960 Up the ladder Australopithecus Homo erectus Homo sapiens
  45. 52. 1970 Branching out <ul><li>The 1960s and 1970s were a fertile period for fossil hunting in Africa </li></ul><ul><li>The idea developed that more than one hominid species existed at the same time developed </li></ul>Homo sapiens Homo erectus Homo habilis Australopithecus africanus A. robustus A. boisei Australopithecus afarensis “Lucy” Added 1974
  46. 53. 1991 Changing status <ul><li>As more specimens were found a clearer idea developed of the relationships between them </li></ul>Homo sapiens Homo erectus Homo habilis A. africanus A. robustus A. boisei Australopithecus afarensis
  47. 54. 2001 From a tree to a bush ? ? ? 1 Ma 2 Ma 3 Ma 4 Ma Homo sapiens Homo erectus Homo habilis A. africanus P. robustus Paranthropus boisei Australopithecus afarensis Australopithecus anemensis Ardipithecus ramidus P. aethiopicus Homo rudolfensis H. ergaster H. heidelbergensis Homo neanderthalensis A. garhi ? ? ?
  48. 55. 2003 DEEPER ROOTS ? ? ? ? ? ? ? ? 1 Ma 2 Ma 3 Ma 4 Ma 5 Ma 6 Ma 7 Ma Homo sapiens Homo erectus Homo habilis A. africanus Paranthropus robustus Paranthropus. boisei Australopithecus afarensis Australopithecus anemensis Ardipithecus ramidus P. aethiopicus Homo rudolfensis H. ergaster H. heidelbergensis Homo neanderthalensis A. garhi Orrorin tugensis Gorilla gorilla Sahelanthropus tchadensis “ Toumai” Pan trogolodites
  49. 56. How many more? <ul><li>An estimated number of 16 hominid species is thought to have existed </li></ul><ul><li>This is based on the evolutionary patterns of other primates </li></ul><ul><li>Our family tree is similar to other species </li></ul><ul><li>Periods of radiation </li></ul><ul><li>Separated by periods of extinction </li></ul>
  50. 57. Hominid Fossil Record <ul><li>All known hominid (human) fossils older than about 1.5 million years are from eastern and southern Africa. </li></ul><ul><ul><li>Most consist of teeth and fragments of jaws, skulls, and other skeletal pieces, with a few spectacular exceptions. </li></ul></ul><ul><ul><li>Researchers must try to reconstruct human phylogeny from an incomplete record , revising their hypotheses to account for new fossil evidence and data from new research strategies such as molecular systematics (DNA and Protein studies). </li></ul></ul>
  51. 58. Hominid Fossil Record <ul><li>The various pre- Homo hominids are classified in the genus Australopithecus (“southern ape”) and are known as australopithecines. </li></ul><ul><ul><li>The first australopithecine, A . africanus , was discovered in 1924 by Raymond Dart in a quarry in South Africa. </li></ul></ul><ul><ul><ul><li>From this and other skeletons, A . africanus probably walked fully erect and had humanlike hands and teeth. </li></ul></ul></ul><ul><ul><ul><li>However, the brain was only about one-third the size of a modern human’s brain. </li></ul></ul></ul><ul><li>In 1974, a new fossil, about 40% complete, was discovered in the Afar region of Ethiopia. </li></ul><ul><ul><li>This fossil, nicknamed “Lucy,” was described as a new species, A. afarensis . It was discovered by Don Johanson and his team of paleoanthropolgists. </li></ul></ul>
  52. 59. Human Evolution is Complex <ul><li>Several human species known to have existed over the past 4 million years, although only Homo sapiens exists today </li></ul><ul><li>Probably a single lineage not true for humans </li></ul><ul><li>Most ancient genus called Ardipithecus ramidus , 4.4 mybp from East Africa </li></ul><ul><li>Appears to have given rise to Australopithecus spp. (the ‘southern ape’ which dominated from 4-1 mybp </li></ul>
  53. 60. Australopithecines 3.6 mya <ul><li>Much evidence for australopithecine structure, evolution </li></ul><ul><li>Show sexual dimorphism in the skeleton, notably in the overall size and in the tooth structure </li></ul><ul><li>Oldest is Australopithecus afarensis </li></ul><ul><ul><li>One is ‘Lucy’ 3.2 mybp </li></ul></ul><ul><li>Several Australopithecus species </li></ul><ul><ul><li>Thought to be omnivores, except the robust (larger) species, thought to be vegetarian </li></ul></ul>
  54. 62. South Africa Skull
  55. 63. Gorilla Skull
  56. 64. Homo habilis 2.3 MYA <ul><li>First hominid clearly & obviously human enough to be genus Homo </li></ul><ul><li>Small hominid, ~2.3 mybp and lasted ~0.75 my </li></ul><ul><li>Site had chipped tools </li></ul><ul><li>Tools probably developed to cut hides, break bones to obtain the marrow </li></ul><ul><li>Classification difficult, due to few bones and damage to skulls </li></ul>
  57. 65. Homo erectus 1.7 mya <ul><li>Lasted until ~200,000 years ago </li></ul><ul><li>Taller than H. habilis </li></ul><ul><li>Apparently survived cold climates </li></ul><ul><li>Wore clothing, made fire, lived in caves or built shelters </li></ul><ul><li>Had advanced weapons (spears) </li></ul><ul><li>Homo egaster might be original stock with H. erectus derived from it, possibly an evolutionary dead-end </li></ul>Homo Egaster
  58. 66. Homo sapiens <ul><li>Also called H. heidelbergensis , the archaic form seems to have arisen ~800,000 years ago, in Africa, Asia and Europe. </li></ul><ul><li>Fundamentally modern, with tools, weapons, clothing, fire, simple houses or caves </li></ul><ul><li>Might include Neanderthal Man, H. neanderthalensis , who lived ~250,000-300,000 years ago in Europe </li></ul><ul><ul><li>Heavy, strong, </li></ul></ul><ul><ul><li>Broad featured face </li></ul></ul><ul><ul><ul><li>Large nasal cavities, </li></ul></ul></ul><ul><ul><ul><li>Receding cheekbones </li></ul></ul></ul><ul><ul><ul><li>More sophisticated tools than archaic H. erectus </li></ul></ul></ul><ul><ul><ul><li>Cared for the dead </li></ul></ul></ul><ul><ul><ul><li>Apparently cared for the sick and injured </li></ul></ul></ul><ul><ul><ul><li>Disappeared ~30,000 years ago; possibly due to competition with H. sapiens </li></ul></ul></ul><ul><ul><ul><li>Might have interbred </li></ul></ul></ul>Limits on brain size * * *
  59. 67. Classification: Homo sapiens <ul><li>Kingdom: Animalia </li></ul><ul><li>Phylum: Chordata </li></ul><ul><li>Class: Mammalia </li></ul><ul><li>Order: Primates </li></ul><ul><li>Family: Hominidae </li></ul><ul><li>Genus: Homo </li></ul><ul><li>Species: sapiens </li></ul>A unt C lara M ake P eople H appy. H ow, S he’s S weet
  60. 68. Origin of Homo sapiens <ul><li>Two alternative hypotheses have been proposed for the origin of anatomically modern humans . </li></ul><ul><li>In the multiregional hypothesis , fully modern humans evolved in parallel from the local populations of H . erectus . </li></ul><ul><ul><li>In this view, the great genetic similarity of all modern people is the product of occasional interbreeding between neighboring populations. </li></ul></ul>
  61. 69. Origin of Homo sapiens <ul><li>The other hypothesis, the “Out of Africa” or replacement hypothesis , argues that all Homo sapiens throughout the world evolved from a second major migration out of Africa that occurred about 100,000 years ago. </li></ul><ul><ul><li>This migration completely replaced all the regional populations of Homo derived from the first hominid migrations. </li></ul></ul>
  62. 70. Two Models of Human Evolution
  63. 71. Origin of Homo sapiens <ul><li>Both hypotheses recognize the fossil evidence for humanity’s African origin. </li></ul><ul><ul><li>The multiregional hypothesis places the last common ancestor in Africa over 1.5 million years ago, when H . erectus began migrating to other parts of the world about 100,000 years ago. </li></ul></ul><ul><ul><li>According to the replacement hypothesis, all of the world’s populations diverged from anatomically modern Homo sapiens that evolved from an African H . erectus population and then migrated throughout the world. </li></ul></ul><ul><ul><ul><li>All of the regional descendents of H . erectus are therefore evolutionary dead ends. </li></ul></ul></ul>
  64. 72. Origin of Homo sapiens <ul><li>A compromise alternative to these extremes suggests that Homo sapiens originated and then dispersed from Africa 100,000 years ago. </li></ul><ul><ul><ul><li>These individuals then interbred with the regional descendents of the earlier H . erectus migration. </li></ul></ul></ul><ul><ul><ul><li>This hypothesis predicts that the genomes of indigenous people from around the world today should reflect a complex mix of ancestries. </li></ul></ul></ul>
  65. 73. Homo sapiens Out of Africa <ul><li>So far, the genetic data have mostly supported the replacement hypothesis. </li></ul><ul><ul><li>Using changes in mitochondrial DNA (mtDNA) among human populations as a molecular clock, research have reported a time of genetic divergence of about 100,000 years ago. </li></ul></ul><ul><ul><ul><li>This is supported by nuclear genetic markers. </li></ul></ul></ul><ul><ul><li>The mtDNA extracted from Neanderthal bones fall completely outside the range of mtDNA for modern Europeans. </li></ul></ul><ul><ul><ul><li>These data suggest that Neanderthals contributed nothing to the ancestry of anatomically modern humans in Europe. </li></ul></ul></ul>
  66. 74. <ul><li>To choose among these competing hypotheses, comparisons of Y chromosomes in 2001 provide perhaps the most important genetic data so far. </li></ul><ul><ul><li>The Y chromosome is passed from male to male through the generations of a family with a minimum of crossing over with the X chromosome. </li></ul></ul><ul><ul><li>The diversity among Y chromosomes is limited to mutations. </li></ul></ul><ul><ul><li>By comparing the Y chromosomes of males from various geographic regions, researchers were able to infer divergence from a common African ancestor less than 100,000 years ago. </li></ul></ul><ul><li>So far, the fossil evidence has been less one-sided than the genetic data in testing the alternative hypotheses. </li></ul><ul><ul><li>The western European fossil evidence is consistent with total replacement of Neanderthals about 40,000 years ago by anatomically modern humans, known as Cro-Magnons. </li></ul></ul><ul><ul><ul><li>There were no intermediates suggesting interbreeding between Neanderthals and the later arrivals. </li></ul></ul></ul><ul><ul><li>However, fossil evidence from outside Europe is more ambiguous, with some paleoanthropologists interpreting some Asian fossils as intermediates between older fossils of H . erectus and the skeletal features of modern Asians . </li></ul></ul>
  67. 75. Language and Cultural Evolution <ul><li>With the development of language a new type of evolution was possible, Cultural Evolution . This is the passing of information (behaviors, customs, religions, etc.) from generation to generation through syntax and not genetic transmission such as instinctive behaviors. This is done through language and is passed on from old to young of our species. This characteristic is unique to humans and is one of the major contributors to our success as a species! This contributed to the shift from a hunter gathering life style to the domestication of plants and animals and the formation of civilizations. </li></ul>