1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 25 The History of Life on Earth

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Lost Worlds Past organisms were very different from those now alive The fossil record shows macroevolutionary changes over large time scales including – The emergence of terrestrial vertebrates – The origin of photosynthesis – Long-term impacts of mass extinctions

3. Fig. 25-1

4. Fig 25-UN1 Cryolophosaurus

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 25.1: Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into macromolecules 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Synthesis of Organic Compounds on Early Earth Earth formed about 4.6 billion years ago, along with the rest of the solar system Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

7. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings However, the evidence is not yet convincing that the early atmosphere was in fact reducing Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents Video: Hydrothermal Vent Video: Hydrothermal Vent Video: Tubeworms Video: Tubeworms

9. Fig. 25-2

10. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Amino acids have also been found in meteorites

11. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Abiotic Synthesis of Macromolecules Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Protobionts Replication and metabolism are key properties of life Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

14. Fig. 25-3 (a) Simple reproduction by liposomes (b) Simple metabolism Phosphate Maltose Phosphatase Maltose Amylase Starch Glucose-phosphate 20 µm

15. Fig. 25-3a (a) Simple reproduction by liposomes 20 µm

16. Fig. 25-3b (b) Simple metabolism Phosphate Maltose Phosphatase Maltose Amylase Starch Glucose-phosphate

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Self-Replicating RNA and the Dawn of Natural Selection The first genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions – For example, ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection The early genetic material might have formed an “RNA world”

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 25.2: The fossil record documents the history of life The fossil record reveals changes in the history of life on earth

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Fossil Record Sedimentary rocks are deposited into layers called strata and are the richest source of fossils Video: Grand Canyon Video: Grand Canyon

21. Fig. 25-4 Present Dimetrodon Coccosteus cuspidatus Fossilized stromatolite Stromatolites Tappania, a unicellular eukaryote Dickinsonia costata Hallucigenia Casts of ammonites Rhomaleosaurus victor, a plesiosaur 100 million years ago 200 175 300 270 400 375 500 525 565 600 3,500 1,500 2.5 cm 4.5 cm 1 cm

22. Fig. 25-4-1 Fossilized stromatolite Stromatolites Tappania, a unicellular eukaryote Dickinsonia costata Hallucigenia 500 525 565 600 3,500 1,500 2.5 cm 4.5 cm 1 cm

23. Fig. 25-4a-2 Present Dimetrodon Coccosteus cuspidatus Casts of ammonites Rhomaleosaurus victor, a plesiosaur 100 million years ago 200 175 300 270 400 375 4.5 cm

24. Fig. 25-4b Rhomaleosaurus victor, a plesiosaur

25. Fig. 25-4c Dimetrodon

26. Fig. 25-4d Casts of ammonites

27. Fig. 25-4e Coccosteus cuspidatus 4.5 cm

28. Fig. 25-4f Hallucigenia 1 cm

29. Fig. 25-4g Dickinsonia costata 2.5 cm

30. Fig. 25-4j Fossilized stromatolite

31. Fig. 25-4i Stromatolites

32. Fig. 25-4h Tappania, a unicellular eukaryote

33. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Few individuals have fossilized, and even fewer have been discovered The fossil record is biased in favor of species that – Existed for a long time – Were abundant and widespread – Had hard parts Animation: The Geologic Record Animation: The Geologic Record

34. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils The absolute ages of fossils can be determined by radiometric dating A “parent” isotope decays to a “daughter” isotope at a constant rate Each isotope has a known half-life, the time required for half the parent isotope to decay

35. Fig. 25-5 Time (half-lives) Accumulating “daughter” isotope Remaining “parent” isotope Fraction of parent isotope remaining 1 2 3 4 1/21/2 1/41/4 1/81/8 1 / 16

36. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Radiocarbon dating can be used to date fossils up to 75,000 years old For older fossils, some isotopes can be used to date sedimentary rock layers above and below the fossil

37. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The magnetism of rocks can provide dating information Reversals of the magnetic poles leave their record on rocks throughout the world

38. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Origin of New Groups of Organisms Mammals belong to the group of animals called tetrapods The evolution of unique mammalian features through gradual modifications can be traced from ancestral synapsids through the present

39. Fig. 25-6 Very late cynodont (195 mya) Later cynodont (220 mya) Early cynodont (260 mya) Therapsid (280 mya) Synapsid (300 mya) Temporal fenestra Temporal fenestra Temporal fenestra EARLY TETRAPODS Articular Key Quadrate Dentary Squamosal Reptiles (including dinosaurs and birds) Dimetrodon Very late cynodonts Mammals Synapsids Therapsids Earlier cynodonts

40. Fig. 25-6-1 Therapsid (280 mya) Synapsid (300 mya) Temporal fenestra Temporal fenestra Articular Key Quadrate Dentary Squamosal

41. Fig. 25-6-2 Very late cynodont (195 mya) Later cynodont (220 mya) Early cynodont (260 mya) Temporal fenestra Articular Key Quadrate Dentary Squamosal

42. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons Concept 25.3: Key events in life’s history include the origins of single-celled and multicelled organisms and the colonization of land

43. Table 25-1

44. Table 25-1a

45. Table 25-1b

46. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Phanerozoic encompasses multicellular eukaryotic life The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic Major boundaries between geological divisions correspond to extinction events in the fossil record

47. Fig. 25-7 Animals Colonization of land Paleozoic Meso- zoic Humans Ceno- zoic Origin of solar system and Earth Prokaryotes Proterozoic Archaean Billions of years ago 1 4 3 2 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen

48. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The First Single-Celled Organisms The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago

49. Fig 25-UN2 Prokaryotes Billions of years ago 4 3 2 1

50. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Photosynthesis and the Oxygen Revolution Most atmospheric oxygen (O 2 ) is of biological origin O 2 produced by oxygenic photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations The source of O 2 was likely bacteria similar to modern cyanobacteria

51. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings By about 2.7 billion years ago, O 2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks This “oxygen revolution” from 2.7 to 2.2 billion years ago – Posed a challenge for life – Provided opportunity to gain energy from light – Allowed organisms to exploit new ecosystems

52. Fig 25-UN3 Atmospheric oxygen Billions of years ago 4 3 2 1

53. Fig. 25-8

54. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The First Eukaryotes The oldest fossils of eukaryotic cells date back 2.1 billion years The hypothesis of endosymbiosis proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells An endosymbiont is a cell that lives within a host cell

55. Fig 25-UN4 Single- celled eukaryotes Billions of years ago 4 3 2 1

56. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites In the process of becoming more interdependent, the host and endosymbionts would have become a single organism Serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events

57. Fig. 25-9-1 Nucleus Cytoplasm DNA Plasma membrane Endoplasmic reticulum Nuclear envelope Ancestral prokaryote

58. Fig. 25-9-2 Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote

59. Fig. 25-9-3 Ancestral photosynthetic eukaryote Photosynthetic prokaryote Mitochondrion Plastid

60. Fig. 25-9-4 Ancestral photosynthetic eukaryote Photosynthetic prokaryote Mitochondrion Plastid Nucleus Cytoplasm DNA Plasma membrane Endoplasmic reticulum Nuclear envelope Ancestral prokaryote Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote

61. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Key evidence supporting an endosymbiotic origin of mitochondria and plastids: – Similarities in inner membrane structures and functions – Division is similar in these organelles and some prokaryotes – These organelles transcribe and translate their own DNA – Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

62. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Origin of Multicellularity The evolution of eukaryotic cells allowed for a greater range of unicellular forms A second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals

63. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Earliest Multicellular Eukaryotes Comparisons of DNA sequences date the common ancestor of multicellular eukaryotes to 1.5 billion years ago The oldest known fossils of multicellular eukaryotes are of small algae that lived about 1.2 billion years ago

64. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The “snowball Earth” hypothesis suggests that periods of extreme glaciation confined life to the equatorial region or deep-sea vents from 750 to 580 million years ago The Ediacaran biota were an assemblage of larger and more diverse soft-bodied organisms that lived from 565 to 535 million years ago

65. Fig 25-UN5 Multicellular eukaryotes Billions of years ago 4 3 2 1

66. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Cambrian Explosion The Cambrian explosion refers to the sudden appearance of fossils resembling modern phyla in the Cambrian period (535 to 525 million years ago) The Cambrian explosion provides the first evidence of predator-prey interactions

67. Fig 25-UN6 Animals Billions of years ago 4 3 2 1

68. Fig. 25-10 Sponges Late Proterozoic eon Early Paleozoic era (Cambrian period) Cnidarians Annelids Brachiopods Echinoderms Chordates Millions of years ago 500 542 Arthropods Molluscs

69. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings DNA analyses suggest that many animal phyla diverged before the Cambrian explosion, perhaps as early as 700 million to 1 billion years ago Fossils in China provide evidence of modern animal phyla tens of millions of years before the Cambrian explosion The Chinese fossils suggest that “the Cambrian explosion had a long fuse”

70. Fig. 25-11 (a) Two-cell stage 150 µm 200 µm (b) Later stage

71. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Colonization of Land Fungi, plants, and animals began to colonize land about 500 million years ago Plants and fungi likely colonized land together by 420 million years ago Arthropods and tetrapods are the most widespread and diverse land animals Tetrapods evolved from lobe-finned fishes around 365 million years ago

72. Fig 25-UN7 Colonization of land Billions of years ago 4 3 2 1

73. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The history of life on Earth has seen the rise and fall of many groups of organisms Concept 25.4: The rise and fall of dominant groups reflect continental drift, mass extinctions, and adaptive radiations Video: Lava Flow Video: Lava Flow Video: Volcanic Eruption Video: Volcanic Eruption

74. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Continental Drift At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago Earth’s continents move slowly over the underlying hot mantle through the process of continental drift Oceanic and continental plates can collide, separate, or slide past each other Interactions between plates cause the formation of mountains and islands, and earthquakes

75. Fig. 25-12 (a) Cutaway view of Earth (b) Major continental plates Inner core Outer core Crust Mantle Pacific Plate Nazca Plate Juan de Fuca Plate Cocos Plate Caribbean Plate Arabian Plate African Plate Scotia Plate North American Plate South American Plate Antarctic Plate Australian Plate Philippine Plate Indian Plate Eurasian Plate

76. Fig. 25-12a (a) Cutaway view of Earth Inner core Outer core Crust Mantle

77. Fig. 25-12b (b) Major continental plates Pacific Plate Nazca Plate Juan de Fuca Plate Cocos Plate Caribbean Plate Arabian Plate African Plate Scotia Plate North American Plate South American Plate Antarctic Plate Australian Plate Philippine Plate Indian Plate Eurasian Plate

78. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Consequences of Continental Drift Formation of the supercontinent Pangaea about 250 million years ago had many effects – A reduction in shallow water habitat – A colder and drier climate inland – Changes in climate as continents moved toward and away from the poles – Changes in ocean circulation patterns leading to global cooling

79. Fig. 25-13 South America Pangaea Millions of years ago 65.5 135 Mesozoic 251 Paleozoic Gondwana Laurasia Eurasia India Africa Antarctica Australia North America Madagascar Cenozoic Present

80. Fig. 25-13a South America Millions of years ago 65.5 Eurasia India Africa Antarctica Australia North America Madagascar Cenozoic Present

81. Fig. 25-13b Pangaea Millions of years ago 135 Mesozoic 251 Paleozoic Gondwana Laurasia

82. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The break-up of Pangaea lead to allopatric speciation The current distribution of fossils reflects the movement of continental drift For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached

83. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mass Extinctions The fossil record shows that most species that have ever lived are now extinct At times, the rate of extinction has increased dramatically and caused a mass extinction

84. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The “Big Five” Mass Extinction Events In each of the five mass extinction events, more than 50% of Earth’s species became extinct

85. Fig. 25-14 Total extinction rate (families per million years): Time (millions of years ago) Number of families: Cenozoic Mesozoic Paleozoic E OS D C P Tr J 542 0 488444416359299251 200 145 Era Period 5 C P N 65.5 0 0 200 100 300 400 500 600 700 800 15 10 20

86. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras This mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species This event might have been caused by volcanism, which lead to global warming, and a decrease in oceanic oxygen

87. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs

88. Fig. 25-15 NORTH AMERICA Chicxulub crater Yucatán Peninsula

89. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The presence of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time

90. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Is a Sixth Mass Extinction Under Way? Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate Data suggest that a sixth human-caused mass extinction is likely to occur unless dramatic action is taken

91. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Consequences of Mass Extinctions Mass extinction can alter ecological communities and the niches available to organisms It can take from 5 to 100 million years for diversity to recover following a mass extinction Mass extinction can pave the way for adaptive radiations

92. Fig. 25-16 Predator genera (percentage of marine genera) Time (millions of years ago) Cenozoic Mesozoic Paleozoic E O S DCP Tr J 542 0 488444 416 359 299251 200145 Era Period C P N 65.50 10 20 30 40 50

93. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Adaptive Radiations Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

94. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Worldwide Adaptive Radiations Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

95. Fig. 25-17 Millions of years ago Monotremes (5 species) 250 150 100 200 50 ANCESTRAL CYNODONT 0 Marsupials (324 species) Eutherians (placental mammals; 5,010 species) Ancestral mammal

96. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Regional Adaptive Radiations Adaptive radiations can occur when organisms colonize new environments with little competition The Hawaiian Islands are one of the world’s great showcases of adaptive radiation

97. Fig. 25-18 Close North American relative, the tarweed Carlquistia muirii Argyroxiphium sandwicense Dubautia linearis Dubautia scabra Dubautia waialealae Dubautia laxa HAWAII 0.4 million years OAHU 3.7 million years KAUAI 5.1 million years 1.3 million years MOLOKAI MAUI LANAI

98. Fig. 25-18a HAWAII 0.4 million years OAHU 3.7 million years KAUAI 5.1 million years 1.3 million years MOLOKAI MAUI LANAI

99. Fig. 25-18b Close North American relative, the tarweed Carlquistia muirii

100. Fig. 25-18c Dubautia waialealae

101. Fig. 25-18d Dubautia laxa

102. Fig. 25-18e Dubautia scabra

103. Fig. 25-18f Argyroxiphium sandwicense

104. Fig. 25-18g Dubautia linearis

105. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Studying genetic mechanisms of change can provide insight into large-scale evolutionary change Concept 25.5: Major changes in body form can result from changes in the sequences and regulation of developmental genes

106. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolutionary Effects of Development Genes Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult

107. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Changes in Rate and Timing Heterochrony is an evolutionary change in the rate or timing of developmental events It can have a significant impact on body shape The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates Animation: Allometric Growth Animation: Allometric Growth

108. Fig. 25-19 (a) Differential growth rates in a human (b) Comparison of chimpanzee and human skull growth Newborn Age (years) Adult 15 5 2 Chimpanzee fetus Chimpanzee adult Human fetus Human adult

109. Fig. 25-19a (a) Differential growth rates in a human Newborn Age (years) Adult 15 5 2

110. Fig. 25-19b (b) Comparison of chimpanzee and human skull growth Chimpanzee fetus Chimpanzee adult Human fetus Human adult

111. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Heterochrony can alter the timing of reproductive development relative to the development of nonreproductive organs In paedomorphosis, the rate of reproductive development accelerates compared with somatic development The sexually mature species may retain body features that were juvenile structures in an ancestral species

112. Fig. 25-20 Gills

113. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Changes in Spatial Pattern Substantial evolutionary change can also result from alterations in genes that control the placement and organization of body parts Homeotic genes determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged

114. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hox genes are a class of homeotic genes that provide positional information during development If Hox genes are expressed in the wrong location, body parts can be produced in the wrong location For example, in crustaceans, a swimming appendage can be produced instead of a feeding appendage

115. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes Two duplications of Hox genes have occurred in the vertebrate lineage These duplications may have been important in the evolution of new vertebrate characteristics

116. Fig. 25-21 Vertebrates (with jaws) with four Hox clusters Hypothetical early vertebrates (jawless) with two Hox clusters Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster Second Hox duplication First Hox duplication

117. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Evolution of Development The tremendous increase in diversity during the Cambrian explosion is a puzzle Developmental genes may play an especially important role Changes in developmental genes can result in new morphological forms

118. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Changes in Genes New morphological forms likely come from gene duplication events that produce new developmental genes A possible mechanism for the evolution of six- legged insects from a many-legged crustacean ancestor has been demonstrated in lab experiments Specific changes in the Ubx gene have been identified that can “turn off” leg development

119. Fig. 25-22 Hox gene 6 Hox gene 7 Hox gene 8 About 400 mya Drosophila Artemia Ubx

120. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Changes in Gene Regulation Changes in the form of organisms may be caused more often by changes in the regulation of developmental genes instead of changes in their sequence For example three-spine sticklebacks in lakes have fewer spines than their marine relatives The gene sequence remains the same, but the regulation of gene expression is different in the two groups of fish

121. Fig. 25-23 Test of Hypothesis A: Differences in the coding sequence of the Pitx1 gene? Result: No Marine stickleback embryo Close-up of ventral surface Test of Hypothesis B: Differences in the regulation of expression of Pitx1 ? Pitx1 is expressed in the ventral spine and mouth regions of developing marine sticklebacks but only in the mouth region of developing lake stickbacks. The 283 amino acids of the Pitx1 protein are identical. Result: Yes Lake stickleback embryo Close-up of mouth RESULTS

122. Fig. 25-23a Marine stickleback embryo Close-up of ventral surface Lake stickleback embryo Close-up of mouth

123. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 25.6: Evolution is not goal oriented Evolution is like tinkering—it is a process in which new forms arise by the slight modification of existing forms

124. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolutionary Novelties Most novel biological structures evolve in many stages from previously existing structures Complex eyes have evolved from simple photosensitive cells independently many times Exaptations are structures that evolve in one context but become co-opted for a different function Natural selection can only improve a structure in the context of its current utility

125. Fig. 25-24 (a) Patch of pigmented cells Optic nerve Pigmented layer (retina) Pigmented cells (photoreceptors) Fluid-filled cavity Epithelium (c) Pinhole camera-type eye Optic nerve Cornea Retina Lens (e) Complex camera-type eye (d) Eye with primitive lens Optic nerve Cornea Cellular mass (lens) (b) Eyecup Pigmented cells Nerve fibers

126. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolutionary Trends Extracting a single evolutionary progression from the fossil record can be misleading Apparent trends should be examined in a broader context

127. Fig. 25-25 Recent (11,500 ya) Neohipparion Pliocene (5.3 mya) Pleistocene (1.8 mya) Hipparion Nannippus Equus Pliohippus Hippidion and other genera Callippus Merychippus Archaeohippus Megahippus Hypohippus Parahippus Anchitherium Sinohippus Miocene (23 mya) Oligocene (33.9 mya) Eocene (55.8 mya) Miohippus Paleotherium Propalaeotherium Pachynolophus Hyracotherium Orohippus Mesohippus Epihippus Browsers Grazers Key

128. Fig. 25-25a Oligocene (33.9 mya) Eocene (55.8 mya) Miohippus Paleotherium Propalaeotherium Pachynolophus Hyracotherium Orohippus Mesohippus Epihippus Browsers Grazers Key

129. Fig. 25-25b Recent (11,500 ya) Neohipparion Pliocene (5.3 mya) Pleistocene (1.8 mya) Hipparion Nannippus Equus Pliohippus Hippidion and other genera Callippus Merychippus Archaeohippus Megahippus Hypohippus Parahippus Anchitherium Sinohippus Miocene (23 mya)

130. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings According to the species selection model, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics The appearance of an evolutionary trend does not imply that there is some intrinsic drive toward a particular phenotype

131. Fig 25-UN8 Millions of years ago (mya) 1.2 bya: First multicellular eukaryotes 2.1 bya: First eukaryotes (single-celled) 3.5 billion years ago (bya): First prokaryotes (single-celled) 535–525 mya: Cambrian explosion (great increase in diversity of animal forms) 500 mya: Colonization of land by fungi, plants and animals Present 500 2,000 1,500 1,000 3,000 2,500 3,500 4,000

132. Fig 25-UN9 Origin of solar system and Earth 4 3 2 1 Paleozoic Meso- zoic Ceno- zoic Proterozoic Archaean Billions of years ago

133. Fig 25-UN10 Flies and fleas Moths and butterflies Caddisflies Herbivory

134. Fig 25-UN11 Origin of solar system and Earth 4 3 2 1 Paleozoic Meso- zoic Ceno- zoic Proterozoic Archaean Billions of years ago

135. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1.Define radiometric dating, serial endosymbiosis, Pangaea, snowball Earth, exaptation, heterochrony, and paedomorphosis 2.Describe the contributions made by Oparin, Haldane, Miller, and Urey toward understanding the origin of organic molecules 3.Explain why RNA, not DNA, was likely the first genetic material

136. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 4.Describe and suggest evidence for the major events in the history of life on Earth from Earth’s origin to 2 billion years ago 5.Briefly describe the Cambrian explosion 6.Explain how continental drift led to Australia’s unique flora and fauna 7.Describe the mass extinctions that ended the Permian and Cretaceous periods 8.Explain the function of Hox genes