Forces of Evolutionary Change Giraffe rubberballGetty Images RF

What Is Evolution? Why does this giraffe have a long neck? Why do these bleeding heart flowers have such a strange shape? Section 12. 1 Bleeding heart flowers: © C Squared Studios/Getty Images (RF); giraffe: © rubberball/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

What Is Evolution? Evolution explains the features of all organisms, from microbes to humans. Section 12. 1 Bleeding heart flowers: © C Squared Studios/Getty Images (RF); giraffe: © rubberball/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

What Is Evolution? Evolution is descent with modification —changes in heritable traits from generation to generation. Section 12. 1 Bleeding heart flowers: © C Squared Studios/Getty Images (RF); giraffe: © rubberball/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

What Is Evolution? Recall that a population is a group of interbreeding organisms of the same species. Section 12. 1 Bleeding heart flowers: © C Squared Studios/Getty Images (RF); giraffe: © rubberball/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

What Is Evolution? Evolution occurs in a population when allele frequencies change from one generation to the next. Section 12. 1 Bleeding heart flowers: © C Squared Studios/Getty Images (RF); giraffe: © rubberball/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

What Is Evolution? An allele frequency is calculated by the following equation: # of copies of an allele Total # of alleles for the same gene in the population Section 12. 1 Giraffe: © rubberball/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

What Is Evolution? Evolution is detectable by examining the population’s gene pool—the entire collection of genes and alleles. Section 12. 1 Caucasian: © Stockdisc/Punch. Stock (RF); Asian: © Red Chopsticks/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 1

What Is Evolution? Even for the same species, gene pools differ from population to population. The gene pool for a population of Swedes differs from that of a population of Asians. Section 12. 1 Caucasian: © Stockdisc/Punch. Stock (RF); Asian: © Red Chopsticks/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 1

What Is Evolution? If Swedes migrate to Asia and interbreed with locals, then allele frequencies in the gene pool will change. Evolution has occurred! Section 12. 1 Caucasian: © Stockdisc/Punch. Stock (RF); Asian: © Red Chopsticks/Getty Images (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 1

Clicker Question #1 Which of the following can evolve (according to the biological definition of evolution)? A. a group of fir trees in Oregon B. Earth’s climate C. a single fly as it develops from larva to adult D. a fossilized turtle © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

12. 1 Mastering Concepts Why can evolution act only on populations and not on individuals? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Evolutionary Thought Has Evolved for Centuries Section 12. 2 Aristotle: © Science Source/Photo Researchers; Buffon: © The Print Collector/Imagestate; Lamarck: © Bettmann/Corbis; Lyell: © Corbis; Darwin: © Richard Milner; Wallace: © Hulton Archive/Getty Images Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 2

Fossils Provide Evidence for Slow Change Over Time Fossils of extinct species suggest that living organisms are descended from common ancestors. Section 12. 2 Canyon: © Jeff Greenberg/Peter Arnold/Photolibrary Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 3

Darwin’s Voyage Provided Evidence for Evolution Charles Darwin was the naturalist on the HMS Beagle, a ship that sailed around the world in the 1830 s. Section 12. 2 Galapagos: © David Zurick (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 4

Darwin’s Voyage Provided Evidence for Evolution Darwin’s time on the Galápagos Islands was especially influential to the development of evolutionary thought. Section 12. 2 Galapagos: © David Zurick (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 4

Darwin’s Voyage Provided Evidence for Evolution He described 14 distinct types of finch, each different from the birds on the mainland yet sharing some features. Section 12. 2 Galapagos: © David Zurick (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 4

Darwin’s Voyage Provided Evidence for Evolution In particular, the beak shape of the finches varied depending on the food supply on each island. Section 12. 2 Galapagos: © David Zurick (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 4

Darwin’s Voyage Provided Evidence for Evolution Darwin thought that these 14 finch species had probably descended from a single ancestral type of finch. Section 12. 2 Galapagos: © David Zurick (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 4

Darwin’s Voyage Provided Evidence for Evolution Pondering the great variety of organisms in South America and their relationships to fossils and geology, he began to think that these were clues to how new species originate. Section 12. 2 Galapagos: © David Zurick (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 4

Humans Artificially Alter Allele Frequencies Artificial selection, or selective breeding, also helped Darwin form theory of evolution by natural selection. Section 12. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 5

Humans Artificially Alter Allele Frequencies In artificial selection, a human chooses desired features, then allows only the individuals that best express those qualities to reproduce. Section 12. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 5

Nature Selects for Reproductive Success In natural selection, environmental factors cause the differential reproductive success of individuals with particular genotypes. Section 12. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Nature Selects for Reproductive Success Section 12. 2 Copyright © The Mc. Graw-Hill Companies,

Evolutionary Theory Continues to Expand Much subsequent research has corroborated and expanded on Darwin’s findings. Section 12. 2 Darwin: © Richard Milner Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 6

Clicker Question #2 Which of the following statements supports the concept of natural selection? A. Individuals with the traits best suited to the prevailing conditions tend to leave more surviving, fertile offspring. B. Traits that increase survival and reproduction in the current generation will be more common in the next generation. C. Both A and B are correct. D. None of the choices is correct. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

12. 2 Mastering Concepts How is artificial selection different from natural selection? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Natural Selection Molds Evolution This organism blends almost perfectly into a leafy background. How could an organism like this arise? Section 12. 3 Leaf insect: © IT Stock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Natural Selection Molds Evolution Each generation, the best camouflaged individuals survive to reproduce. The alleles conferring camouflage become more common in each generation. Section 12. 3 Leaf insect: © IT Stock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Natural Selection Molds Evolution But natural selection does not create camouflage alleles. Instead, it strongly selects for camouflage alleles that arise by chance. Section 12. 3 Leaf insect: © IT Stock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Natural Selection Molds Evolution Natural selection operates on the variation present in a population. Since more individuals are born than resources can support, the struggle to survive is inevitable. Section 12. 3 a: © Garrett W. Ellwood/NBAE via Getty Images; b: © Perennou Nuridsany/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 7

Natural Selection Molds Evolution Some individuals in a population are better than others at surviving and reproducing. Section 12. 3 a: © Garrett W. Ellwood/NBAE via Getty Images; b: © Perennou Nuridsany/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 7

Natural Selection Molds Evolution The heritable traits conferring these advantages are adaptations —features that provide a selective advantage because they improve an organism’s ability to survive and reproduce. Section 12. 3 a: © Garrett W. Ellwood/NBAE via Getty Images; b: © Perennou Nuridsany/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 7

Natural Selection Molds Evolution Bacteria that are resistant to antibiotics have an adaptive trait that non-resistant bacteria lack. When antibiotics are administered, resistant bacteria are strongly selected for. Section 12. 3 a: © Dennis Kunkel Microscopy, Inc. ; inset: © Ron Occalea/The Medical File/Peter Arnold/Photolibrary Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 8

Natural Selection Molds Evolution Antibiotics can not create a resistance allele. The variation in resistance was already present in the population; the presence of antibiotics caused the resistance allele frequency to shift. Section 12. 3 a: © Dennis Kunkel Microscopy, Inc. ; inset: © Ron Occalea/The Medical File/Peter Arnold/Photolibrary Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 8

Evolution Never Stops As environmental conditions change, the phenotypes that natural selection favors will also change. Adaptations that seem “perfect” in one environment would be completely wrong in another. Section 12. 3 Cockroach: © Creatas/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Evolution Never Stops This orchid and its wasp pollinator have evolved alongside one another for long enough that no other animal can pollinate the flower. Section 12. 3 Orchid and wasp: © Dr. John Alcock/Visuals Unlimited Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 10

Evolution Does Not Have a Goal But the orchid does not evolve in order to be better-pollinated by the wasp. Neither the orchid nor natural selection has foresight. Section 12. 3 Orchid and wasp: © Dr. John Alcock/Visuals Unlimited Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 10

Evolution Does Not Have a Goal Instead, the orchids bestsuited to wasp pollination are the most likely to reproduce, so their alleles get passed to the next generation most often. Section 12. 3 Orchid and wasp: © Dr. John Alcock/Visuals Unlimited Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 10

Clicker Question #3 Ferns require moisture to reproduce. What will happen to a fern population during a prolonged drought? A. To save the species, some of the ferns will acquire the ability to reproduce without water. B. If none of the ferns already have the ability to reproduce without water, the ferns might go extinct. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

12. 3 Mastering Concepts How can natural selection favor different phenotypes at different times? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Allele Frequencies Always Change Scientists test evolution against a null hypothesis, which states that allele frequencies do not change from one generation to the next. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Hardy-Weinberg equilibrium is the unlikely situation in which allele frequencies do not change between generations. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Hardy-Weinberg equilibrium occurs if a population meets all of the following assumptions: (1) natural selection does not occur (2) no mutations (3) the population is large enough to eliminate random changes in allele frequencies (4) individuals mate at random (5) no migration Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Assuming the assumptions of Hardy-Weinberg equilibrium are met, two equations represent the relationship between allele frequencies and genotype frequencies. p+q=1 p 2 + 2 pq + q 2 = 1 p is the frequency of the dominant allele and q is the frequency of the recessive allele. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Since the D gene has two alleles, the frequency of the dominant allele plus the frequency of the recessive allele must equal 1. p+q=1 p 2 + 2 pq + q 2 = 1 p is the frequency of the dominant allele and q is the frequency of the recessive allele. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Multiplying the frequency of the dominant allele by itself gives the frequency of homozygous dominant individuals in the next generation. p+q=1 p 2 + 2 pq + q 2 = 1 p is the frequency of the dominant allele and q is the frequency of the recessive allele. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Multiplying the frequency of the recessive allele by itself gives the frequency of homozygous recessive individuals in the next generation. p+q=1 p 2 + 2 pq + q 2 = 1 p is the frequency of the dominant allele and q is the frequency of the recessive allele. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change The frequency of the dominant allele times the frequency of the recessive allele times 2 gives the frequency of heterozygous individuals in the next generation. p+q=1 p 2 + 2 pq + q 2 = 1 p is the frequency of the dominant allele and q is the frequency of the recessive allele. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Allele Frequencies Always Change Hardy-Weinberg equilibrium is a useful model for converting known allele frequencies to genotype frequencies (or vice versa), but in real populations, the assumptions of Hardy-Weinberg are always violated. Section 12. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 12

Clicker Question #4 A population of 100 starfish is in Hardy. Weinberg equilibrium. The trait for long arms is completely dominant to the trait for short arms. In this population, 40% of alleles for this trait are recessive, and 60% of alleles for this trait are dominant. How many individuals would you expect to be homozygous dominant? A. 80 B. 60 C. 36 © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. D. 16

12. 4 Mastering Concepts What five conditions are required for Hardy–Weinberg equilibrium? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Natural Selection Can Shape Populations in Many Ways Three modes of natural selection—directional, disruptive, and stabilizing—are distinguished by their effects on the phenotypes in a population. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 13

Natural Selection Can Shape Populations in Many Ways In directional selection, one phenotype is favored over another. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 13

Natural Selection Can Shape Populations in Many Ways In disruptive selection, extreme phenotypes are favored over an intermediate phenotype. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 13

Natural Selection Can Shape Populations in Many Ways In stabilizing selection, an intermediate phenotype is favored over the extreme phenotypes. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 13

Natural Selection Can Shape Populations in Many Ways However, these three models do not explain why natural selection maintains some harmful alleles in the population. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 13

Natural Selection Can Shape Populations in Many Ways One explanation for why some harmful alleles persist in the population is heterozygote advantage, in which a heterozygote is favored over homozygotes. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 14

Natural Selection Can Shape Populations in Many Ways For example, heterozygotes for the sickle cell allele do not have sickle cell disease and are protected against malaria. But if two heterozygotes mate, their child might have sickle cell disease. Section 12. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 14

Clicker Question #5 As humans migrated out of Africa and towards northern Europe, reduced exposure to ultraviolet radiation selected for lighter skin color. What type of natural selection does this example illustrate? A. stabilizing selection B. disruptive selection C. directional selection © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

12. 5 Mastering Concepts Distinguish among directional, disruptive, and stabilizing selection. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Sexual Selection Directly Influences Reproductive Success At face value, building complex nests, flashing showy plumage, and butting heads with rival males all appear to waste energy. How can natural selection allow for traits that apparently reduce survival? Section 12. 6 a: © James Warwick/Getty Images; b: © Michael S. Yamashita/Corbis; c: © Sumio Harada/Minden Pictures Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 15

Sexual Selection Directly Influences Reproductive Success Sexual selection is a type of natural selection resulting from variation in the ability to obtain mates. Section 12. 6 a: © James Warwick/Getty Images; b: © Michael S. Yamashita/Corbis; c: © Sumio Harada/Minden Pictures Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 15

Sexual Selection Directly Influences Reproductive Success Sexual selection results either from competition for access to the other sex (e. g. , these rams) or from one sex choosing attractive mates of the other sex. Section 12. 6 a: © James Warwick/Getty Images; b: © Michael S. Yamashita/Corbis; c: © Sumio Harada/Minden Pictures Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 15

Sexual Selection Directly Influences Reproductive Success Generations of choosy females have selected for males with nest-building traits or elaborate ornamentation. Section 12. 6 a: © James Warwick/Getty Images; b: © Michael S. Yamashita/Corbis; c: © Sumio Harada/Minden Pictures Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 15

Sexual Selection Directly Influences Reproductive Success Though the yellow weaver bird uses time and energy making nests for females, this behavior might secure a mating opportunity. Section 12. 6 a: © James Warwick/Getty Images; b: © Michael S. Yamashita/Corbis; c: © Sumio Harada/Minden Pictures Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 15

12. 6 Mastering Concepts Describe two ways that competition for access to mates can lead to sexual selection. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Evolution Occurs in Several Other Ways Other factors change allele frequencies over time: - Mutation - Genetic drift - Migration Section 12. 7 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Evolution Occurs in Several Other Ways Genetic drift occurs purely by chance. It is most common in small populations. Section 12. 7 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 16

Evolution Occurs in Several Other Ways When only a few individuals establish a new population, the allele frequency might change. This process illustrates the founder effect. Section 12. 7 b: Courtesy of Dr. Victor A. Mc. Kusick/Johns Hopkins Hospital Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 17

Evolution Occurs in Several Other Ways A population bottleneck occurs if a disaster drastically reduces the size of a population. Section 12. 7 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 18

Evolution Occurs in Several Other Ways Migration moves alleles between populations. This might affect the allele frequencies in both populations. Section 12. 7 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 19

12. 7 Mastering Concepts How does sampling error cause genetic drift? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Size Matters in Fishing Frenzy Evolution by means of natural selection has practical applications, such as establishing fishing regulations. Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Size Matters in Fishing Frenzy If the largest fish were always removed from a lake, what might you predict about the size of fish in future generations? What if the smallest fish were always removed? Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Size Matters in Fishing Frenzy Researchers conducted studies of fish size over several generations to find out how fish harvesting affects average fish size. Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Section 12. 20

Investigating Life: Size Matters in Fishing Frenzy They established three populations and applied the following treatments: • Removing large fish • Removing random fish • Removing small fish Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 20

Investigating Life: Size Matters in Fishing Frenzy Predictably, the average weight of harvested fish was highest for the large harvested population at the start of the study. Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 20

Investigating Life: Size Matters in Fishing Frenzy However, after just four generations, the small harvested population had a much higher average size than the large harvested population. Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 20

Investigating Life: Size Matters in Fishing Frenzy Also, fish in the small harvested population developed more quickly than those in the large harvested population. Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 20

Investigating Life: Size Matters in Fishing Frenzy These results are not surprising, which is a testament to the predictive power of natural selection. Section 12. 8 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 20

12. 8 Mastering Concepts The heritability of a trait is the extent to which it is genetically determined. Heritability ranges from 0 (entirely under environmental control) to 1. 0 (100% controlled by genes). In these fish, the heritability of body size is about 0. 2. How would the results of this experiment differ if heritability of body size were higher? What if it approached zero? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Evidence of Evolution Dinosaur Protoarchaeopteyx: © O. Louis Mazzatenta/NGS Image Collection Copyright © The

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 2

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 Plant fossils: © Mc. Graw-Hill Higher Education/Carlyn Iverson, photographer Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 Plant fossils: © Mc. Graw-Hill Higher Education/Carlyn Iverson, photographer Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 Plant fossils: © Mc. Graw-Hill Higher Education/Carlyn Iverson, photographer Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Clues to Evolution Lie in the Earth, Body Structures, and Molecules Fossils form in many ways and preserve evidence of many types of organisms. Section 13. 1 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 1

13. 1 Mastering Concepts What is the geologic timescale? © 1996 Photo. Disc, Inc.

Fossils Record Evolution Even though fossil evidence is diverse, it is often challenging— or impossible—to find fossils of transitional forms between groups. Section 13. 2 Ammonite: © Jean-Claude Carton/Bruce Coleman/Photoshot Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 3

Fossils Record Evolution 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. Section 13. 2 Ammonite: © Jean-Claude Carton/Bruce Coleman/Photoshot Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 3

Fossils Record Evolution 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. Section 13. 2 Ammonite: © Jean-Claude Carton/Bruce Coleman/Photoshot Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 3

Fossils Record Evolution Dating fossils yields clues about the timeline of life’s history. Section 13. 2 Canyon: © Jeff Greenberg/Peter Arnold/Photolibrary Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 3

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. Section 13. 2 Canyon: © Jeff Greenberg/Peter Arnold/Photolibrary Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 12. 3

Fossils Record Evolution Absolute dating uses chemistry to determine how long ago a fossil formed. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution Radiometric dating is a type of absolute dating that uses radioactive isotopes. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution Throughout life, organisms accumulate carbon-14, a radioactive isotope, along with stable carbon-12. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution Living organisms have a constant amount of carbon-14 in their tissues. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution After the organism dies, no more carbon-12 or carbon-14 is added. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution However, carbon-14 decays at a constant rate, leaving the organism as nitrogen. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution 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. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Fossils Record Evolution By determining the amount of carbon-14 in a fossil, scientists can estimate when the organism lived. Section 13. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 4

Clicker Question #1 Which rock layer (A, B, or C) should have fossils with the most carbon-14? A B C Woodpecker: © 1996 Photo. Disc, Inc. /Getty Images/RF Canyon: © Jeff Greenberg/Peter Arnold/Photolibrary Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

13. 2 Mastering Concepts Distinguish between relative and absolute dating of fossils. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Biogeography Considers Species’ Geographical Locations Earth’s geography has changed drastically over the last 200 million years. Section 13. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 5

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 5

Biogeography Considers Species’ Geographical Locations Why do the continents move? Section 13. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 5

Biogeography Considers Species’ Geographical Locations According to 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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 5

Biogeography Considers Species’ Geographical Locations Earthquakes and volcanoes are evidence that Earth’s plates continue to move today. Section 13. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 5

Biogeography Considers Species’ Geographical Locations Fossils help geographers piece together Earth’s continents into Pangaea. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Section 13. 3 Figure 13. 6

Biogeography Considers Species’ Geographical Locations Biogeographical studies shed light on evolutionary events. Section 13. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 7

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 7

Biogeography Considers Species’ Geographical Locations The result is a unique variety of organisms on each side of the line. Section 13. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 7

13. 3 Mastering Concepts How have the positions of Earth’s continents changed over the past 200 million years? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Anatomical Relationships Reveal Common Descent Investigators often look for anatomical features to determine the evolutionary relationship of two organisms. Section 13. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 8

Anatomical Relationships Reveal Common Descent Two structures are homologous if the similarities between them reflect common ancestry. Section 13. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 8

Anatomical Relationships Reveal Common Descent All of these animals, for example, have similar bones in their forelimbs. Section 13. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 8

Anatomical Relationships Reveal Common Descent These similarities suggests that their common ancestor had this bone configuration. Section 13. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 8

Anatomical Relationships Reveal Common Descent Homologous structures need not have the same function or look exactly alike. Section 13. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 8

Anatomical Relationships Reveal Common Descent Different selective pressures in each animal’s evolutionary line have led to small changes from their ancestor’s bone structure. Section 13. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 8

Anatomical Relationships Reveal Common Descent A vestigial structure has lost its function but is homologous to a functional structure in another species. Section 13. 4 a: © E. R. Degginger/Animals - Earth Scenes; b: © Science Vu/Visuals Unlimited Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 9

Anatomical Relationships Reveal Common Descent Vestigial hind limbs in some snake species and pelvises in whales are evidence of these organisms’ ancestors. Section 13. 4 a: © E. R. Degginger/Animals - Earth Scenes; b: © Science Vu/Visuals Unlimited Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 9

Anatomical Relationships Reveal Common Descent Anatomical structures are analogous if they are superficially similar but did not derive from a common ancestor. Section 13. 4 a/b: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; c: © Dante Fenolio/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 10

Anatomical Relationships Reveal Common Descent None of these cave animals has pigment or eyes. Section 13. 4 a/b: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; c: © Dante Fenolio/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 10

Anatomical Relationships Reveal Common Descent These similarities arose by convergent evolution, which produces similar structures in organisms that don’t share the same lineage. Section 13. 4 a/b: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; c: © Dante Fenolio/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 10

Anatomical Relationships Reveal Common Descent Lack of pigment arose independently in each of these cave animals. Section 13. 4 a/b: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; c: © Dante Fenolio/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 10

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. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

13. 4 Mastering Concepts What can homologies reveal about evolution? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 11

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/Photo Researchers; alligator: USGS/Southeast Ecological Science Center Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 12

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/Photo Researchers; alligator: USGS/Southeast Ecological Science Center Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 12

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 13

Embryonic Development Patterns Provide Evolutionary Clues Homeotic genes therefore help explain how a few key mutations might produce new species. Section 13. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 13

13. 5 Mastering Concepts How does the study of embryonic development reveal clues to a shared evolutionary history? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Molecules Reveal Relatedness Comparing DNA and protein sequences determines evolutionary relationships in unprecedented detail. Section 13. 6 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Molecules Reveal Relatedness Cytochrome c is a mitochondrial protein that is often used in molecular comparisons. Section 13. 6 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 14

Molecules Reveal Relatedness The more amino acid differences between species, the more distant the common ancestor. Section 13. 6 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 14

Molecules Reveal Relatedness Molecular clocks assign dates to evolutionary events. Section 13. 6 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 15

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 15

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 13. 15

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. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

13. 6 Mastering Concepts How does analysis of DNA and proteins support other evidence for evolution? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Evolving Backwards As we’ve already seen, evolution does not always lead to greater complexity. Sometimes, features are lost. Section 13. 7 a: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Evolving Backwards This cave salamander, for example, has no eyes or pigment. Section 13. 7 a: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Evolving Backwards Snakes lost their limbs as they adapted to a burrowing lifestyle. Section 13. 7 a: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Evolving Backwards Snakes without limbs burrow more easily than those with limbs. In snakes, natural selection favors the alleles that confer limblessness. Section 13. 7 a: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Evolving Backwards The case of the salamander is slightly different from the snake. Section 13. 7 a: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Evolving Backwards In an environment without light, pigment provides no selective advantage. Since producing pigment costs energy, alleles conferring colorlessness are favored. Section 13. 7 a: © Francesco Tomasinelli/The Lighthouse/Visuals Unlimited; snake: © Comstock/Punch. Stock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

13. 7 Mastering Concepts How might the loss of limbs enhance the fitness of a burrowing animal such as a snake? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.