Chapter 13 Evidence of Evolution Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Section 13.1 Life on Earth arose 3.8 billion years ago. Changes in body structures and molecules have slowly accumulated through that time, producing the variety of organisms we see today. Figure 13.2

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Section 13.1 Scientists use the geologic timescale to divide the history of the Earth into eons and eras. These periods are defined by major geological or biological events, like mass extinctions. Figure 13.2

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Section 13.1 Even though the events that led to today’s diversity of life occurred in the past, many clues suggest that all organisms derived from a common ancestor. Ge Sun, et al. "In Search of the First Flower: A Jurassic Angiosperm, Archaefructus, from Northeast China," Science, Vol. 282, no. 5394, November 27, 1998, pp ©1998 AAAS. All rights reserved. Used with permission.

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Section 13.1 Researchers analyze fossils, anatomy, and molecular sequences to learn how species are related to one another. Ge Sun, et al. "In Search of the First Flower: A Jurassic Angiosperm, Archaefructus, from Northeast China," Science, Vol. 282, no. 5394, November 27, 1998, pp ©1998 AAAS. All rights reserved. Used with permission

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Section 13.1 Paleontology is the study of fossil remains or other clues to past life. Fossils provided the original evidence for evolution. Ge Sun, et al. "In Search of the First Flower: A Jurassic Angiosperm, Archaefructus, from Northeast China," Science, Vol. 282, no. 5394, November 27, 1998, pp ©1998 AAAS. All rights reserved. Used with permission

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Section 13.1 Fossils are the remains of ancient organisms. Figure 13.1 Left fossil: Ge Sun, et al. "In Search of the First Flower: A Jurassic Angiosperm, Archaefructus, from Northeast China," Science, Vol. 282, no. 5394, November 27, 1998, pp ©1998 AAAS. All rights reserved. Used with permission; Wood: ©PhotoLink/Getty Images RF; Embryo: ©University of the Witwatersrand/epa/Corbis; Coprolite: ©Sinclair Stammers/Science Source; Trilobite: ©Siede Preis/Getty Images RF; Fish fossil: ©Phil Degginger/Carnegie Museum/Alamy RF; Leaf fossil: ©Biophoto Associates/Science Source; Triceratops: ©Francois Gohier/Science Source

13.1 Mastering Concepts What is the geologic timescale? Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Fossils Record Evolution Section 13.2 Fossils form in many ways. Figure 13.4 Compression fossil of leaf: ©William E. Ferguson Human skull and bone fossil: ©John Reader/Science Source

Fossils Record Evolution Section 13.2 Fossils form in many ways. Figure 13.4 Impression of dinosaur skin: ©Dr. John D. Cunningham/Visuals Unlimited Horn coral: ©Robert Gossington/Photoshot

Fossils Record Evolution Section 13.2 Fossils form in many ways. Figure 13.4 Mosquito trapped in amber: ©Natural Visions/Alamy

Fossils Record Evolution Section 13.2 Even though fossil evidence is diverse, it is often challenging— or impossible—to find fossils of transitional forms between groups. Figure 13.3 Ammonite: ©Jean-Claude Carton/Photoshot

Fossils Record Evolution Section 13.2 The fossil record is incomplete, partly because some organisms (such as those with soft bodies) fail to fossilize. Also, erosion and movement of Earth’s plates might destroy fossils. Figure 13.3 Ammonite: ©Jean-Claude Carton/Photoshot

Fossils Record Evolution Section 13.2 Still, fossils help researchers piece together Earth’s history. For example, these marine fossils from landlocked Oklahoma show that water once covered the central United States. Figure 13.3 Ammonite: ©Jean-Claude Carton/Photoshot

Fossils Record Evolution Dating fossils yields clues about the timeline of life’s history. Figure 12.3Section 13.2 Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF

Fossils Record Evolution The simpler, and less precise, method of dating fossils is relative dating, which assumes that lower rock layers have older fossils than newer layers. Figure 12.3Section 13.2 Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF

Fossils Record Evolution Section 13.2 Absolute dating uses chemistry to determine how long ago a fossil formed. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 Radiometric dating is a type of absolute dating that uses radioactive isotopes. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 Throughout life, organisms accumulate carbon-14, a radioactive isotope, along with stable carbon-12. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 Living organisms have a constant amount of carbon-14 in their tissues. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 After the organism dies, no more carbon-12 or carbon-14 is added. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 However, carbon-14 decays at a constant rate, leaving the organism as nitrogen. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 During any 5730-year period, the amount of carbon-14 in the organism divides in half. In other words, the half-life of carbon-14 is 5730 years. Figure 13.6 Woolly mammoth skeleton: ©Ethan Miller/Getty Images

Fossils Record Evolution Section 13.2 By determining the amount of carbon-14 in a fossil, scientists can estimate when the organism lived. Figure 13.6 Woolly mammoth skeleton; ©Ethan Miller/Getty Images

Clicker Question #1 Which rock layer (A, B, or C) should have fossils with the most carbon-14? A B C Flower: © Doug Sherman/Geofile/RF Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF

Clicker Question #1 Which rock layer (A, B, or C) should have fossils with the most carbon-14? A B C Flower: © Doug Sherman/Geofile/RF Canyon: ©Terry Moore/Stocktrek Images/Getty Images RF

Clicker Question #2 Researchers used a radioactive isotope with a 25,000-year half-life to date a fossil to 100,000 years ago. The fossil contains ____ as much of the isotope as does a living organism. A. 1/2 B. 1/4 C. 1/8 D. 1/16 E. 1/32 Flower: © Doug Sherman/Geofile/RF

Clicker Question #2 Researchers used a radioactive isotope with a 25,000-year half-life to date a fossil to 100,000 years ago. The fossil contains ____ as much of the isotope as does a living organism. A. 1/2 B. 1/4 C. 1/8 D. 1/16 E. 1/32 Flower: © Doug Sherman/Geofile/RF

13.2 Mastering Concepts Distinguish between relative and absolute dating of fossils. Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Biogeography Considers Species’ Geographical Locations Section 13.3 Earth’s geography has changed drastically over the last 200 million years. Figure 13.7

Biogeography Considers Species’ Geographical Locations Section 13.3 These images represent only about 5% of Earth’s history. (Scientists hypothesize that this cycle has occurred several times.) Figure 13.7

Biogeography Considers Species’ Geographical Locations Section 13.3 Why do the continents move? Figure 13.7

Biogeography Considers Species’ Geographical Locations Section 13.3 According to the theory of plate tectonics, Earth’s surface consists of several rigid layers, called tectonic plates, that move in response to forces acting deep within the planet. Figure 13.7

Biogeography Considers Species’ Geographical Locations Section 13.3 Earthquakes and volcanoes are evidence that Earth’s plates continue to move today. Figure 13.7

Biogeography Considers Species’ Geographical Locations Section 13.3 Fossils help geographers piece together Earth’s continents into Pangaea. Figure 13.8

Biogeography Considers Species’ Geographical Locations Section 13.3 Biogeography sheds light on evolutionary events. Figure 13.9

Biogeography Considers Species’ Geographical Locations Section 13.3 Animals on either side of Wallace’s line have been separated for millions of years, evolving independently. Figure 13.9

Biogeography Considers Species’ Geographical Locations Section 13.3 The result is a unique variety of organisms on each side of the line. Figure 13.9

13.3 Mastering Concepts How have the positions of Earth’s continents changed over the past 200 million years? Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Anatomical Relationships Reveal Common Descent Section 13.4Figure Investigators often look for anatomical features to determine the evolutionary relationship of two organisms.

Anatomical Relationships Reveal Common Descent Section 13.4 Two structures are homologous if the similarities between them reflect common ancestry. Figure 13.10

Anatomical Relationships Reveal Common Descent Section 13.4 All of these animals, for example, have similar bones in their forelimbs. Figure 13.10

Anatomical Relationships Reveal Common Descent Section 13.4 These similarities suggests that their common ancestor had this bone configuration. Figure 13.10

Anatomical Relationships Reveal Common Descent Section 13.4 Homologous structures need not have the same function or look exactly alike. Figure 13.10

Anatomical Relationships Reveal Common Descent Section 13.4 Different selective pressures in each animal’s evolutionary line have led to small changes from their ancestor’s bone structure. Figure 13.10

Anatomical Relationships Reveal Common Descent Section 13.4 A vestigial structure has lost its function but is homologous to a functional structure in another species. Figure Mexican-boa-constrictor: ©Pascal Goetgheluck/Science Source Python skeleton: ©Science VU/Visuals Unlimited

Anatomical Relationships Reveal Common Descent Section 13.4 Vestigial hind limbs in some snake species and pelvises in whales are evidence of these organisms’ ancestors. Figure Mexican-boa-constrictor: ©Pascal Goetgheluck/Science Source Python skeleton: ©Science VU/Visuals Unlimited

Anatomical Relationships Reveal Common Descent Section 13.4 Anatomical structures are analogous if they are superficially similar but did not derive from a common ancestor. Figure Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: ©Dante Fenolio/Science Source

Anatomical Relationships Reveal Common Descent Section 13.4 None of these cave animals has pigment or eyes. Figure Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: ©Dante Fenolio/Science Source

Anatomical Relationships Reveal Common Descent Section 13.4 These similarities arose by convergent evolution, which produces similar structures in organisms that don’t share the same lineage. Figure Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: ©Dante Fenolio/Science Source

Anatomical Relationships Reveal Common Descent Section 13.4 Lack of pigment arose independently in each of these cave animals. Figure Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: ©Dante Fenolio/Science Source

Clicker Question #3 The streamlined shapes of dolphins and sharks evolved independently. The body plan of these two animals are A. homologous. B. vestigial. C. analogous. D. a product of convergent evolution. E. Both C and D are correct. Flower: © Doug Sherman/Geofile/RF

Clicker Question #3 The streamlined shapes of dolphins and sharks evolved independently. The body plan of these two animals are A. homologous. B. vestigial. C. analogous. D. a product of convergent evolution. E. Both C and D are correct. Flower: © Doug Sherman/Geofile/RF

13.4 Mastering Concepts What can homologies reveal about evolution? Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Embryonic Development Patterns Provide Evolutionary Clues Section 13.5 Anatomical similarities are often most obvious in embryos. Notice how much more similar human and chimpanzee skull structure is in fetuses compared to in adults. Figure 13.14

Embryonic Development Patterns Provide Evolutionary Clues Section 13.5 Adult fish, mice, and alligators have very different bodies. Their evolutionary relationships are more obvious in embryos. Figure Fish: ©Dr. Richard Kessel/Visuals Unlimited; Mouse: ©Steve Gschmeissner/Science Source; Alligator: USGS/Southeast Ecological Science Center

Embryonic Development Patterns Provide Evolutionary Clues Section 13.5 How do similar embryos develop into such different organisms? Homeotic genes provide a clue. Figure Fish: ©Dr. Richard Kessel/Visuals Unlimited; Mouse: ©Steve Gschmeissner/Science Source; Alligator: USGS/Southeast Ecological Science Center

Embryonic Development Patterns Provide Evolutionary Clues Section 13.5 Homeotic genes control an organism’s development. Small differences in gene expression might make the difference between a limbed and limbless organism. Figure 13.16

Embryonic Development Patterns Provide Evolutionary Clues Section 13.5 Homeotic genes therefore help explain how a few key mutations might produce new species. Figure 13.16

Embryonic Development Patterns Provide Evolutionary Clues Section 13.5 Mutations in segments of DNA that do not encode proteins also produce new phenotypes. Figure 13.17

13.5 Mastering Concepts How does the study of embryonic development reveal clues to a shared evolutionary history? Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Molecules Reveal Relatedness Section 13.6 Comparing DNA and protein sequences determines evolutionary relationships in unprecedented detail.

Molecules Reveal Relatedness Section 13.6 It is highly unlikely that two unrelated species would evolve precisely the same DNA and protein sequences by chance.

Molecules Reveal Relatedness Section 13.6 It is more likely that the similarities were inherited from a common ancestor and that differences arose by mutation after the species diverged from the ancestral type.

Molecules Reveal Relatedness Section 13.6 Cytochrome c is a mitochondrial protein that is often used in molecular comparisons. Figure 13.19

Molecules Reveal Relatedness Section 13.6 The more amino acid differences between species, the more distant the common ancestor. Figure 13.19

Molecules Reveal Relatedness Section 13.6 Molecular clocks assign dates to evolutionary events. Figure 13.20

Molecules Reveal Relatedness Section 13.6Figure If a gene is estimated to mutate once every 25 million years, then two differences from an ancestor might arise in 50 million years.

Molecules Reveal Relatedness Section 13.6 If a gene is estimated to mutate once every 25 million years, then two differences from an ancestor might arise in 50 million years. Figure 13.20

Molecules Reveal Relatedness Section 13.6Figure If a gene is estimated to mutate once every 25 million years, then two differences from an ancestor might arise in 50 million years.

Molecules Reveal Relatedness Section 13.6 Therefore, two species that derived from the same common ancestor 50 MYA might have four differences in the nucleotide sequence of the gene. Figure 13.20

Clicker Question #4 Mutations in a gene occur at a rate of one nucleotide every 10 million years. The gene sequence differs by 6 nucleotides between two related organisms. How long ago did these organisms split from a common ancestor? A. about 2 million years ago B. about 30 million years ago C. about 60 million years ago D. about 120 million years ago E. None of the choices is correct. Flower: © Doug Sherman/Geofile/RF

Clicker Question #4 Mutations in a gene occur at a rate of one nucleotide every 10 million years. The gene sequence differs by 6 nucleotides between two related organisms. How long ago did these organisms split from a common ancestor? A. about 2 million years ago B. about 30 million years ago C. about 60 million years ago D. about 120 million years ago E. None of the choices is correct. Flower: © Doug Sherman/Geofile/RF

13.6 Mastering Concepts How does analysis of DNA and proteins support other evidence for evolution? Fossil: ©Lou Mazzatenta/National Geographic Stock Protoarchaeopteryx: ©O. Louis Mazzatenta/National Geographic Stock

Investigating Life: Limbs Gained and Limbs Lost Section 13.7 In 2006, researchers discovered fossils of an intermediate form between fish and terrestrial vertebrates. Figure Fossil: ©Ted Daeschler/VIREO/Academy of Natural Sciences

Investigating Life: Limbs Gained and Limbs Lost Section 13.7 Transitional fossils, like those of Tiktaalik, are evidence for gradual evolutionary change. Figure Fossil: ©Ted Daeschler/VIREO/Academy of Natural Sciences

Investigating Life: Limbs Gained and Limbs Lost Section 13.7 As we’ve already seen, evolution does not always lead to greater complexity. Sometimes, features are lost. Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/PunchStock RF

Section 13.7 This cave salamander, for example, has no eyes or pigment. Investigating Life: Limbs Gained and Limbs Lost Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/PunchStock RF

Section 13.7 Snakes lost their limbs as they adapted to a burrowing lifestyle. Investigating Life: Limbs Gained and Limbs Lost Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/PunchStock RF

Section 13.7 Snakes without limbs burrow more easily than those with limbs. In snakes, natural selection favors the alleles that confer limblessness. Investigating Life: Limbs Gained and Limbs Lost Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/PunchStock RF

Section 13.7 The case of the salamander is slightly different from the snake. Investigating Life: Limbs Gained and Limbs Lost Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/PunchStock RF

Section 13.7 In an environment without light, pigment provides no selective advantage. Since producing pigment costs energy, alleles conferring colorlessness are favored. Investigating Life: Limbs Gained and Limbs Lost Salamander: ©Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/PunchStock RF