CHAPTER 13: Evidence of Evolution BIO 121 Clues to Evolution Lie in the Earth, Body Structures, and Molecules 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. Section 13.1 Figure 13.2 Clues to Evolution Lie in the Earth, Body Structures, and Molecules 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. Section 13.1 Figure 13.2 1
Clues to Evolution Lie in the Earth, Body Structures, and Molecules 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. Section 13.1 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. 1601-1772. 1998 AAAS. All rights reserved. Used with permission. Clues to Evolution Lie in the Earth, Body Structures, and Molecules Researchers analyze fossils, anatomy, and molecular sequences to learn how species are related to one another. Section 13.1 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. 1601-1772. 1998 AAAS. All rights reserved. Used with permission Clues to Evolution Lie in the Earth, Body Structures, and Molecules Paleontology is the study of fossil remains or other clues to past life. Fossils provided the original evidence for evolution. Section 13.1 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. 1601-1772. 1998 AAAS. All rights reserved. Used with permission 2
Clues to Evolution Lie in the Earth, Body Structures, and Molecules Fossils are the remains of ancient organisms. Section 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. 1601-1772. 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 Figure 13.1 Fossils form in many ways. Compression fossil of leaf: William E. Ferguson Human skull and bone fossil: John Reader/Science Source Figure 13.4 Fossils form in many ways. Impression of dinosaur skin: Dr. John D. Cunningham/Visuals Unlimited Horn coral: Robert Gossington/Photoshot Figure 13.4 3
Fossils form in many ways. Mosquito trapped in amber: Natural Visions/Alamy Figure 13.4 Even though fossil evidence is diverse, it is often challenging or impossible to find fossils of transitional forms between groups. Ammonite: Jean-Claude Carton/Photoshot Figure 13.3 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. Ammonite: Jean-Claude Carton/Photoshot Figure 13.3 4
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. Ammonite: Jean-Claude Carton/Photoshot Figure 13.3 Dating fossils yields clues about the timeline of life s history. Canyon: Terry Moore/Stocktrek Images/Getty Images RF Figure 12.3 The simpler, and less precise, method of dating fossils is relative dating, which assumes that lower rock layers have older fossils than newer layers. Canyon: Terry Moore/Stocktrek Images/Getty Images RF Figure 12.3 5
Absolute dating uses chemistry to determine how long ago a fossil formed. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 Radiometric dating is a type of absolute dating that uses radioactive isotopes. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 Throughout life, organisms accumulate carbon 14, a radioactive isotope, along with stable carbon 12. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 6
Living organisms have a constant amount of carbon 14 in their tissues. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 After the organism dies, no more carbon 12 or carbon 14 is added. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 However, carbon 14 decays at a constant rate, leaving the organism as nitrogen. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 7
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. Woolly mammoth skeleton: Ethan Miller/Getty Images Figure 13.6 By determining the amount of carbon 14 in a fossil, scientists can estimate when the organism lived. Woolly mammoth skeleton; Ethan Miller/Getty Images Figure 13.6 Question #1 Which rock layer (A, B, or C) should have fossils with the most carbon 14? A B C 8
ANSWER Which rock layer (A, B, or C) should have fossils with the most carbon 14? A B C Biogeography Considers Species Geographical Locations Earth s geography has changed drastically over the last 200 million years. Section 13.3 Figure 13.7 Biogeography Considers Species Geographical Locations These images represent only about 5% of Earth s history. (Scientists hypothesize that this cycle has occurred several times.) Section 13.3 Figure 13.7 9
Biogeography Considers Species Geographical Locations Why do the continents move? Section 13.3 Figure 13.7 Biogeography Considers Species Geographical Locations 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. Section 13.3 Figure 13.7 Biogeography Considers Species Geographical Locations Earthquakes and volcanoes are evidence that Earth s plates continue to move today. Section 13.3 Figure 13.7 10
Biogeography Considers Species Geographical Locations Fossils help geographers piece together Earth s continents into Pangaea. Section 13.3 Figure 13.8 Biogeography Considers Species Geographical Locations Biogeography sheds light on evolutionary events. Section 13.3 Figure 13.9 Biogeography Considers Species Geographical Locations Animals on either side of Wallace s line have been separated for millions of years, evolving independently. Section 13.3 Figure 13.9 11
Biogeography Considers Species Geographical Locations The result is a unique variety of organisms on each side of the line. Section 13.3 Figure 13.9 Investigators often look for anatomical features to determine the evolutionary relationship of two organisms. Section 13.4 Figure 13.10 Two structures are homologous if the similarities between them reflect common ancestry. Section 13.4 Figure 13.10 12
All of these animals, for example, have similar bones in their forelimbs. Section 13.4 Figure 13.10 These similarities suggests that their common ancestor had this bone configuration. Section 13.4 Figure 13.10 Homologous structures need not have the same function or look exactly alike. Section 13.4 Figure 13.10 13
Different selective pressures in each animal s evolutionary line have led to small changes from their ancestor s bone structure. Section 13.4 Figure 13.10 Homologous Structures A vestigial structure has lost its function but is homologous to a functional structure in another species. Section 13.4 Mexican-boa-constrictor: Pascal Goetgheluck/Science Source Python skeleton: Science VU/Visuals Unlimited Figure 13.11 14
Vestigial hind limbs in some snake species and pelvises in whales are evidence of these organisms ancestors. Section 13.4 Mexican-boa-constrictor: Pascal Goetgheluck/Science Source Python skeleton: Science VU/Visuals Unlimited Figure 13.11 Anatomical structures are analogous if they are superficially similar but did not derive from a common ancestor. Section 13.4 Salamander: Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: Dante Fenolio/Science Source Figure 13.13 None of these cave animals has pigment or eyes. Section 13.4 Salamander: Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: Dante Fenolio/Science Source Figure 13.13 15
These similarities arose by convergent evolution, which produces similar structures in organisms that don t share the same lineage. Section 13.4 Salamander: Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: Dante Fenolio/Science Source Figure 13.13 Lack of pigment arose independently in each of these cave animals. Section 13.4 Salamander: Francesco Tomasinelli/The Lighthouse/Visuals Unlimited Crayfish: Dante Fenolio/Science Source Figure 13.13 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. 16
ANSWER 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 Embryonic Development Patterns Provide Evolutionary Clues 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. Section 13.5 Figure 13.14 Embryonic Development Patterns Provide Evolutionary Clues Adult fish, mice, and alligators have very different bodies. Their evolutionary relationships are more obvious in embryos. Section 13.5 Fish: Dr. Richard Kessel/Visuals Unlimited; Mouse: Steve Gschmeissner/Science Source; Alligator: USGS/Southeast Ecological Science Center Figure 13.15 17
Embryonic Development Patterns Provide Evolutionary Clues How do similar embryos develop into such different organisms? Homeotic genes provide a clue. Section 13.5 Fish: Dr. Richard Kessel/Visuals Unlimited; Mouse: Steve Gschmeissner/Science Source; Alligator: USGS/Southeast Ecological Science Center Figure 13.15 Embryonic Development Patterns Provide Evolutionary Clues Homeotic genes control an organism s development. Small differences in gene expression might make the difference between a limbed and limbless organism. Section 13.5 Figure 13.16 Embryonic Development Patterns Provide Evolutionary Clues Homeotic genes therefore help explain how a few key mutations might produce new species. Section 13.5 Figure 13.16 18
Embryonic Development Patterns Provide Evolutionary Clues Mutations in segments of DNA that do not encode proteins also produce new phenotypes. Section 13.5 Figure 13.17 Molecules Reveal Relatedness Comparing DNA and protein sequences determines evolutionary relationships in unprecedented detail. Section 13.6 Molecules Reveal Relatedness It is highly unlikely that two unrelated species would evolve precisely the same DNA and protein sequences by chance. Section 13.6 19
Molecules Reveal Relatedness 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. Section 13.6 Molecules Reveal Relatedness Cytochrome c is a mitochondrial protein that is often used in molecular comparisons. Section 13.6 Figure 13.19 Molecules Reveal Relatedness The more amino acid differences between species, the more distant the common ancestor. Section 13.6 Figure 13.19 20
Molecules Reveal Relatedness Molecular clocks assign dates to evolutionary events. Section 13.6 Figure 13.20 Molecules Reveal Relatedness If a gene is estimated to mutate once every 25 million years, then two differences from an ancestor might arise in 50 million years. Section 13.6 Figure 13.20 Molecules Reveal Relatedness If a gene is estimated to mutate once every 25 million years, then two differences from an ancestor might arise in 50 million years. Section 13.6 Figure 13.20 21
Molecules Reveal Relatedness If a gene is estimated to mutate once every 25 million years, then two differences from an ancestor might arise in 50 million years. Section 13.6 Figure 13.20 Molecules Reveal Relatedness Therefore, two species that derived from the same common ancestor 50 MYA might have four differences in the nucleotide sequence of the gene. Section 13.6 Figure 13.20 22