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Table of Contents – pages iii Unit 1: What is Biology? Unit 2: Ecology Unit 3: The Life of a Cell Unit 4: Genetics Unit 5: Change Through TimeChange Through Time Unit 6: Viruses, Bacteria, Protists, and Fungi Unit 7: Plants Unit 8: Invertebrates Unit 9: Vertebrates Unit 10: The Human Body
Table of Contents – pages vii-xiii Unit 1: What is Biology? Chapter 1: Biology: The Study of Life Unit 2: Ecology Chapter 2: Principles of Ecology Chapter 3: Communities and Biomes Chapter 4: Population Biology Chapter 5: Biological Diversity and Conservation Unit 3: The Life of a Cell Chapter 6: The Chemistry of Life Chapter 7: A View of the Cell Chapter 8: Cellular Transport and the Cell Cycle Chapter 9: Energy in a Cell
Table of Contents – pages vii-xiii Unit 4: Genetics Chapter 10: Mendel and Meiosis Chapter 11: DNA and Genes Chapter 12: Patterns of Heredity and Human Genetics Chapter 13: Genetic Technology Unit 5: Change Through TimeChange Through Time Chapter 14: The History of Life Chapter 15: The Theory of EvolutionThe Theory of Evolution Chapter 16: Primate Evolution Chapter 17: Organizing Lifes Diversity
Table of Contents – pages vii-xiii Unit 6: Viruses, Bacteria, Protists, and Fungi Chapter 18: Viruses and Bacteria Chapter 19: Protists Chapter 20: Fungi Unit 7: Plants Chapter 21: What Is a Plant? Chapter 22: The Diversity of Plants Chapter 23: Plant Structure and Function Chapter 24: Reproduction in Plants
Table of Contents – pages vii-xiii Unit 8: Invertebrates Chapter 25: What Is an Animal? Chapter 26: Sponges, Cnidarians, Flatworms, and Roundworms Chapter 27: Mollusks and Segmented Worms Chapter 28: Arthropods Chapter 29: Echinoderms and Invertebrate Chordates
Table of Contents – pages vii-xiii Unit 9: Vertebrates Chapter 30: Fishes and Amphibians Chapter 31: Reptiles and Birds Chapter 32: Mammals Chapter 33: Animal Behavior Unit 10: The Human Body Chapter 34: Protection, Support, and Locomotion Chapter 35: The Digestive and Endocrine Systems Chapter 36: The Nervous System Chapter 37: Respiration, Circulation, and Excretion Chapter 38: Reproduction and Development Chapter 39: Immunity from Disease
Unit Overview – pages Change Through Time The History of Life The Theory of Evolution Primate Evolution Organizing Lifes Diversity
Chapter Contents – page ix Chapter 15 The Theory of EvolutionThe Theory of Evolution 15.1: Natural Selection and the Evidence for EvolutionNatural Selection and the Evidence for Evolution 15.1: Section CheckSection Check 15.2: Mechanisms of EvolutionMechanisms of Evolution 15.2: Section CheckSection Check Chapter 15 SummarySummary Chapter 15 AssessmentAssessment
Chapter Intro-page 392 What Youll Learn You will analyze the theory of evolution. You will compare and contrast the processes of evolution.
15.1 Section Objectives – page 393 Summarize Darwins theory of natural selection. Section Objectives: Explain how the structural and physiological adaptations of organisms relate to natural selection. Distinguish among the types of evidence for evolution.
Section 15.1 Summary – pages The modern theory of evolution is the fundamental concept in biology. Recall that evolution is the change in populations over time. Charles Darwin and Natural Selection
Section 15.1 Summary – pages When geologists provided evidence indicating that Earth was much older than many people had originally thought, biologists began to suspect that species change over time, or evolve. Many explanations about how species evolve have been proposed, but the ideas first published by Charles Darwin are the basis of modern evolutionary theory. Fossils shape ideas about evolution
Section 15.1 Summary – pages It took Darwin years to develop his theory of evolution. He began in 1831 at age 22 when he took a job as a naturalist on the English ship HMS Beagle, which sailed around the world on a five-year scientific journey. Darwin on HMS Beagle
Section 15.1 Summary – pages Darwin on HMS Beagle
Section 15.1 Summary – pages As the ships naturalist, Darwin studied and collected biological and fossil specimens at every port along the route. His studies provided the foundation for his theory of evolution by natural selection. Darwin on HMS Beagle
Section 15.1 Summary – pages On the Galápagos Islands, Darwin studied many species of animals and plants that are unique to the islands but similar to species elsewhere. These observations led Darwin to consider the possibility that species can change over time. Darwin in the Galápagos
Section 15.1 Summary – pages For the next two decades, Darwin worked to refine his explanation for how species change over time. English economist Thomas Malthus had proposed an idea that Darwin modified and used in his explanation. Darwin continues his studies Malthuss idea was that the human population grows faster than Earths food supply.
Section 15.1 Summary – pages How did this help Darwin? He knew that many species produce large numbers of offspring. Darwin continues his studies He also knew that such species had not overrun Earth.
Section 15.1 Summary – pages Darwin continues his studies He realized that individuals struggle to compete in changing environmental conditions. Only some individuals survive the competition and produce offspring.
Section 15.1 Summary – pages Darwin continues his studies Darwin observed that the traits of individuals vary in populations. Variations are then inherited. Breeding organisms with specific traits in order to produce offspring with identical traits is called artificial selection. Darwin hypothesized that there was a force in nature that worked like artificial selection.
Section 15.1 Summary – pages Darwin explains natural selection Natural selection is a mechanism for change in populations. It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation. Organisms without these variations are less likely to survive and reproduce.
Section 15.1 Summary – pages Darwin explains natural selection As a result, each generation consists largely of offspring from parents with these variations that aid survival. Alfred Russell Wallace, another British naturalist, reached a similar conclusion.
Section 15.1 Summary – pages Darwin explains natural selection Darwin proposed the idea of natural selection to explain how species change over time. In nature, organisms produce more offspring than can survive.
Section 15.1 Summary – pages Darwin explains natural selection In any population, individuals have variations. Fishes, for example, may differ in color, size, and speed.
Section 15.1 Summary – pages Darwin explains natural selection Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation.
Section 15.1 Summary – pages Darwin explains natural selection Over time, offspring with certain variations make up most of the population and may look entirely different from their ancestors.
Section 15.1 Summary – pages Interpreting evidence after Darwin Volumes of scientific data have been gathered as evidence for evolution since Darwins time. Much of this evidence is subject to interpretation by different scientists. One of the issues is that evolutionary processes are difficult for humans to observe directly.
Section 15.1 Summary – pages Interpreting evidence after Darwin The short scale of human life spans makes it difficult to comprehend evolutionary processes that occur over millions of years. Almost all of todays biologists accept the theory of evolution by natural selection.
Section 15.1 Summary – pages Adaptations: Evidence for Evolution Recall that an adaptation is any variation that aids an organisms chances of survival in its environment. Darwins theory of evolution explains how adaptations may develop in species.
Section 15.1 Summary – pages Structural adaptations arise over time According to Darwins theory, adaptations in species develop over many generations. Learning about adaptations in mole-rats can help you understand how natural selection has affected them.
Section 15.1 Summary – pages Structural adaptations arise over time The ancestors of todays common mole-rats probably resembled African rock rats.
Section 15.1 Summary – pages Structural adaptations arise over time Some ancestral rats may have avoided predators better than others because of variations such as the size of teeth and claws.
Section 15.1 Summary – pages Structural adaptations arise over time Ancestral rats that survived passed their variations to offspring. After many generations, most of the populations individuals would have these adaptations.
Section 15.1 Summary – pages Structural adaptations arise over time Over time, natural selection produced modern mole-rats. Their blindness may have evolved because vision had no survival advantage for them.
Section 15.1 Summary – pages Structural adaptations arise over time Some other structural adaptations are subtle. Mimicry is a structural adaptation that enables one species to resemble another species.
Section 15.1 Summary – pages Structural adaptations arise over time In one form of mimicry, a harmless species has adaptations that result in a physical resemblance to a harmful species. Predators that avoid the harmful looking species also avoid the similar-looking harmless species.
Section 15.1 Summary – pages In another form of mimicry, two or more harmful species resemble each other. For example, yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior. Structural adaptations arise over time
Section 15.1 Summary – pages Structural adaptations arise over time Predators may learn quickly to avoid any organism with their general appearance.
Section 15.1 Summary – pages Structural adaptations arise over time Another subtle adaptation is camouflage, an adaptation that enables species to blend with their surroundings. Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.
Section 15.1 Summary – pages Physiological adaptations can develop rapidly In general, most structural adaptations develop over millions of years. However, there are some adaptations that evolve much more rapidly. For example, do you know that some of the medicines developed during the twentieth century to fight bacterial diseases are no longer effective?
Section 15.1 Summary – pages Non-resistant bacterium Resistant bacterium Antibiotic When the population is exposed to an antibiotic, only the resistant bacteria survive. The bacteria in a population vary in their ability to resist antibiotics. The resistant bacteria live and produce more resistant bacteria. Physiological adaptations can develop rapidly
Section 15.1 Summary – pages Today, penicillin no longer affects as many species of bacteria because some species have evolved physiological adaptations to prevent being killed by penicillin. Non-resistant bacterium Resistant bacterium Antibiotic Physiological adaptations can develop rapidly
Section 15.1 Summary – pages Physiological adaptations are changes in an organisms metabolic processes. In addition to species of bacteria, scientists have observed these adaptations in species of insects and weeds that are pests. Physiological adaptations can develop rapidly
Section 15.1 Summary – pages Other Evidence for Evolution Physiological resistance in species of bacteria, insects, and plants is direct evidence of evolution. However, most of the evidence for evolution is indirect, coming from sources such as fossils and studies of anatomy, embryology, and biochemistry.
Section 15.1 Summary – pages Fossils Fossils are an important source of evolutionary evidence because they provide a record of early life and evolutionary history.
Section 15.1 Summary – pages Fossils Although the fossil record provides evidence that evolution occurred, the record is incomplete. Although paleontologists do not have fossils for all the changes that have occurred, they can still understand the overall picture of how most groups evolved.
Section 15.1 Summary – pages Fossils Fossils are found throughout the world. As the fossil record becomes more complete, the sequences of evolution become clearer. For example, you can see how paleontologists have charted the evolutionary path that led to todays camel after piecing together fossil skulls, teeth, and limb bones.
Section 15.1 Summary – pages Fossils Camel Evolution Age Organism Skull and teeth Paleocene 65 million years ago Eocene 54 million years ago Oligocene 33 million years ago Limb bones Miocene 23 million years ago Present
Section 15.1 Summary – pages Anatomy Structural features with a common evolutionary origin are called homologous structures. Homologous structures can be similar in arrangement, in function, or in both. Whale forelimb Crocodile forelimb Bird wing
Section 15.1 Summary – pages Anatomy The body parts of organisms that do not have a common evolutionary origin but are similar in function are called analogous structures. Although analogous structures dont shed light on evolutionary relationships, they do provide evidence of evolution.
Section 15.1 Summary – pages Anatomy For example, insect and bird wings probably evolved separately when their different ancestors adapted independently to similar ways of life.
Section 15.1 Summary – pages Another type of body feature that suggests an evolutionary relationship is a vestigial structurea body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor. A structure becomes vestigial when the species no longer needs the feature for its original function, yet it is still inherited as part of the body plan for the species. Anatomy
Section 15.1 Summary – pages Many organisms have vestigial structures. Vestigial structures, such as pelvic bones in the baleen whale, are evidence of evolution because they show structural change over time. Anatomy
Section 15.1 Summary – pages An embryo is the earliest stage of growth and development of both plants and animals. The embryos of a fish, a reptile, a bird, and a mammal have a tail and pharyngeal pouches. Fish ReptileBirdMammal Pharyngeal pouches Pharyngeal pouches Tail Embryology
Section 15.1 Summary – pages It is the shared features in the young embryos that suggest evolution from a distant, common ancestor. Fish ReptileBirdMammal Pharyngeal pouches Pharyngeal pouches Tail Embryology
Section 15.1 Summary – pages Biochemistry Biochemistry also provides strong evidence for evolution. Nearly all organisms share DNA, ATP, and many enzymes among their biochemical molecules.
Section 15.1 Summary – pages Biochemistry One enzyme, cytochrome c, occurs in organisms as diverse as bacteria and bison. Biologists compared the differences that exist among species in the amino acid sequence of cytochrome c.
Section 15.1 Summary – pages The data show the number of amino acid substitutions in the amino acid sequences for the different organisms. Biochemical Similarities of Organisms Comparison of Organisms Percent Substitutions of Amino Acids in Cytochrome c Residues Two orders of mammals Birds vs. mammals Amphibians vs. birds Fish vs. land vertebrates Insects vs. vertebrates Algae vs. animals 5 and Biochemistry
Section 15.1 Summary – pages Organisms that are biochemically similar have fewer differences in their amino acid sequences. Biochemical Similarities of Organisms Comparison of Organisms Percent Substitutions of Amino Acids in Cytochrome c Residues Two orders of mammals Birds vs. mammals Amphibians vs. birds Fish vs. land vertebrates Insects vs. vertebrates Algae vs. animals 5 and Biochemistry
Section 15.1 Summary – pages Since Darwins time, scientists have constructed evolutionary diagrams that show levels of relationships among species. In the 1970s, some biologists began to use RNA and DNA nucleotide sequences to construct evolutionary diagrams. Biochemistry
Section 15.1 Summary – pages Biochemistry Today, scientists combine data from fossils, comparative anatomy, embryology, and biochemistry in order to interpret the evolutionary relationships among species.
Section 1 Check Question 1 _______ is considered to be the fundamental concept of biology. D. structural adaptation C. artificial selection B. the modern theory of evolution A. genetics The answer is B.
Section 1 Check Question 2 Breeding organisms with specific traits in order to produce offspring with identical traits is called _______. D. artificial selection C. mutation B. adaptation A. natural selection The answer is D.
Section 1 Check Question 3 What is the difference between artificial selection and natural selection? Answer Artificial selection is the intentional breeding of organisms with specific traits in order to produce offspring with identical traits. Natural selection occurs when organisms with favorable variations of traits survive in nature, reproduce, and pass these favorable variations to offspring.
Section 1 Check Question 4 Mimicry and camouflage are NOT examples of _________. D. artificial selection C. evolution B. natural selection A. adaptation The answer is D.
Section 1 Check Question 5 How does mimicry differ from camouflage? Answer Mimicry is an adaptation that allows one species to resemble another species. Camouflage is an adaptation that allows one species to resemble its surroundings.
15.2 Section Objectives – page 404 Section Objectives Relate changes in genetic equilibrium to mechanisms of speciation. Summarize the effects of the different types of natural selections on gene pools. Explain the role of natural selection in convergent and divergent evolution.
Section 15.2 Summary– pages Since Darwins time, scientists have learned a great deal about genes and modified Darwins ideas accordingly. Population Genetics and Evolution The principles of todays modern theory of evolution are rooted in population genetics and other related fields of study and are expressed in genetic terms.
Section 15.2 Summary– pages Genes determine most of an individuals features, such as tooth shape or flower color. If an organism has a featurecalled a phenotype in genetic termsthat is poorly adapted to its environment, the organism may be unable to survive and reproduce. However, within its lifetime, it cannot evolve a new phenotype by natural selection in response to its environment. Populations, not individuals, evolve
Section 15.2 Summary– pages Natural selection acts on the range of phenotypes in a population. Populations, not individuals, evolve Each member has the genes that characterize the traits of the species, and these genes exist as pairs of alleles. Evolution occurs as a populations genes and their frequencies change over time.
Section 15.2 Summary– pages How can a populations genes change over time? Populations, not individuals, evolve Picture all of the alleles of the populations genes as being together in a large pool called a gene pool. The percentage of any specific allele in the gene pool is called the allelic frequency.
Section 15.2 Summary– pages They refer to a population in which the frequency of alleles remains the same over generations as being in genetic equilibrium. Populations, not individuals, evolve
Section 15.2 Summary– pages Look at the population of snapdragons. RR Phenotype frequency Allele frequency First generation Second generation White = 0 R = 0.75 Pink = 0.5 Red = 0.5 R = 0.25 Phenotype frequency Allele frequency White = Pink = 0.25 Red = R = 0.75 R = 0.25 RR R Populations, not individuals, evolve
Section 15.2 Summary– pages Populations, not individuals, evolve A pattern of heredity called incomplete dominance governs flower color in snapdragons. The population of snapdragons is in genetic equilibrium when the frequency of its alleles for flower color is the same in all its generations.
Section 15.2 Summary– pages A population that is in genetic equilibrium is not evolving. Changes in genetic equilibrium Any factor that affects the genes in the gene pool can change allelic frequencies, disrupting a populations genetic equilibrium, which results in the process of evolution.
Section 15.2 Summary– pages One mechanism for genetic change is mutation. Changes in genetic equilibrium Environmental factors, such as radiation or chemicals, cause many mutations, but other mutations occur by chance.
Section 15.2 Summary– pages However, occasionally, a mutation results in a useful variation, and the new gene becomes part of the populations gene pool by the process of natural selection. Changes in genetic equilibrium Many are lethal.
Section 15.2 Summary– pages Genetic drift can greatly affect small populations that include the descendants of a small number of organisms. Changes in genetic equilibrium Another mechanism that disrupts a populations genetic equilibrium is genetic driftthe alteration of allelic frequencies by chance events.
Section 15.2 Summary– pages Genetic equilibrium is also disrupted by the movement of individuals in and out of a population. Changes in genetic equilibrium Genetic drift has been observed in some small human populations that have become isolated due to reasons such as religious practices and belief systems.
Section 15.2 Summary– pages When an individual leaves a population, its genes are lost from the gene pool. Changes in genetic equilibrium The transport of genes by migrating individuals is called gene flow. When individuals enter a population, their genes are added to the pool.
Section 15.2 Summary– pages There are three different types of natural selection that act on variation: stabilizing, directional, and disruptive. Natural selection acts on variations Some variations increase or decrease an organisms chance of survival in an environment.
Section 15.2 Summary– pages Stabilizing selection is a natural selection that favors average individuals in a population. Selection for average size spiders Normal variation Natural selection acts on variations
Section 15.2 Summary– pages Natural selection acts on variations Directional selection occurs when natural selection favors one of the extreme variations of a trait. Normal variation Selection for longer beaks
Section 15.2 Summary– pages Natural selection acts on variations In disruptive selection, individuals with either extreme of a traits variation are selected for. Selection for light limpets Normal variation Selection for dark limpets
Section 15.2 Summary– pages Natural selection acts on variations Natural selection can significantly alter the genetic equilibrium of a populations gene pool over time. Significant changes in the gene pool could lead to the evolution of a new species over time.
Section 15.2 Summary– pages Recall that a species is defined as a group of organisms that look alike and can interbreed to produce fertile offspring in nature. The evolution of new species, a process called speciation (spee shee AY shun), occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment. The Evolution of Species
Section 15.2 Summary– pages Physical barriers can prevent interbreeding In nature, physical barriers can break large populations into smaller ones. Geographic isolation occurs whenever a physical barrier divides a population. A new species can evolve when a population has been geographically isolated.
Section 15.2 Summary– pages The Evolution of Species When geographic isolation divides a population of tree frogs, the individuals no longer mate across populations. Tree frogs are a single population.
Section 15.2 Summary– pages The Evolution of Species The formation of a river may divide the frogs into two populations.
Section 15.2 Summary– pages The Evolution of Species Over time, the divided populations may become two species that may no longer interbreed, even if reunited.
Section 15.2 Summary– pages Reproductive isolation can result in speciation As populations become increasingly distinct, reproductive isolation can arise. Reproductive isolation occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring.
Section 15.2 Summary– pages Reproductive isolation can result in speciation There are different types of reproductive isolation. One type occurs when the genetic material of the populations becomes so different that fertilization cannot occur. Another type of reproductive isolation is behavioral.
Section 15.2 Summary– pages A change in chromosome numbers and speciation Chromosomes can also play a role in speciation. Many new species of plants and some species of animals have evolved in the same geographic area as a result of polyploidy. Any individual or species with a multiple of the normal set of chromosomes is known as a polyploid.
Section 15.2 Summary– pages Mistakes during mitosis or meiosis can result in polyploid individuals. Parent plant (2n) Meiosis begins Nondisjunction Normal meiosis Normal gametes (n) Fertilization Zygote (3n) Abnormal gametes (2n) Fertilization Zygote (4n) Sterile plant New polyploid species A change in chromosome numbers and speciation
Section 15.2 Summary– pages A change in chromosome numbers and speciation Polyploidy may result in immediate reproductive isolation. When a polyploid mates with an individual of the normal species, the resulting zygotes may not develop normally because of the difference in chromosome numbers.
Section 15.2 Summary– pages A change in chromosome numbers and speciation However, polyploids within a population may interbreed and form a separate species. Many flowering plant species and many important crop plants, such as wheat, cotton, and apples, originated by polyploidy. Polyploids can arise from within a species or from hybridization between species.
Section 15.2 Summary– pages Speciation rates Scientists once argued that evolution occurs at a slow, steady rate, with small, adaptive changes gradually accumulating over time in populations. Gradualism is the idea that species originate through a gradual change of adaptations. Some evidence from the fossil record supports gradualism.
Section 15.2 Summary– pages Speciation rates In 1972, Niles Eldredge and Stephen J. Gould proposed a different hypothesis known as punctuated equilibrium. This hypothesis argues that speciation occurs relatively quickly, in rapid bursts, with long periods of genetic equilibrium in between.
Section 15.2 Summary– pages Speciation rates Loxodonta africana Elephas maximus Mammuthus primigenius Mammuthus Elephas Loxodonta Primelephas about 55 million years ago Ancestral species Millions of Years Ago
Section 15.2 Summary– pages Speciation rates According to this hypothesis, environmental changes, such as higher temperatures or the introduction of a competitive species, lead to rapid changes in a small populations gene pool that is reproductively isolated from the main population. Speciation happens quicklyin about 10,000 years or less.
Section 15.2 Summary– pages Speciation rates Biologists generally agree that both gradualism and punctuated equilibrium can result in speciation, depending on the circumstances.
Section 15.2 Summary– pages Patterns of Evolution Biologists have observed different patterns of evolution that occur throughout the world in different natural environments. These patterns support the idea that natural selection is an important agent for evolution.
Section 15.2 Summary– pages Diversity in new environments When an ancestral species evolves into an array of species to fit a number of diverse habitats, the result is called adaptive radiation.
Section 15.2 Summary– pages Adaptive radiation in both plants and animals has occurred and continues to occur throughout the world and is common on islands. Adaptive radiation is a type of divergent evolution, the pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly distinct. Diversity in new environments
Section 15.2 Summary– pages Possible Ancestral Lasan finch Amakihi Extinct mamo Crested honeycreeper Akialoa Akepa Akiapolaau Liwi Maui parrotbill Apapane Ou Grosbeak finch Palila Akikiki Niihau Kauai Oahu Lanai Molokai Maui Kahoolawe Hawaii Diversity in new environments
Section 15.2 Summary– pages Diversity in new environments Divergent evolution occurs when populations change as they adapt to different environmental conditions, eventually resulting in new species.
Section 15.2 Summary– pages Different species can look alike A pattern of evolution in which distantly related organisms evolve similar traits is called convergent evolution. Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world.
Section 2 Check The fur of an Arctic fox turns white in the winter. Is this an example of natural selection? Why or why not? Question 1
Section 2 Check The answer is no. An individual cannot evolve a new phenotype (in this case, changing the color of its fur) within its lifetime in response to its environment.
Section 2 Check Which type of natural selection does NOT favor the evolution of new species? Question 2 D. directional C. stabilizing B. disruptive A. divergent
Section 2 Check The answer is C. Stabilizing selection reduces variation in a population.
Section 2 Check Which of the following rarely affects a populations genetic equilibrium? Question 3 D. disruptive selection C. gene flow B. lethal mutations A. genetic drift
Section 2 Check The answer is B. Organisms with lethal mutations do not survive. Therefore, organisms with lethal mutations cannot produce enough offspring to affect a populations genetic equilibrium.
Section 2 Check Why are the Galapagos Islands rich in unique species of organisms? Question 4 D. The island species have been subjected to stabilizing selection. C. The island species have been subjected to increased gene flow. B. The islands are geographically isolated. A. The islands are an area exhibiting an abnormal number of mutations.
Section 2 Check The answer is B. Geographic isolation has helped to keep the islands species unique.
Chapter Summary – 15.1 After many years of experimentation and observation, Charles Darwin proposed the idea that species originated through the process of natural selection. Natural Selection and the Evidence for Evolution Natural selection is a mechanism of change in populations. In a specific environment, individuals with certain variations are likely to survive, reproduce, and pass these variations to future generations.
Chapter Summary – 15.1 Evolution has been observed in the lab and field, but much of the evidence for evolution has come from studies of fossils, anatomy, and biochemistry. Natural Selection and the Evidence for Evolution
Chapter Summary – 15.2 Evolution can occur only when a populations genetic equilibrium changes. Mutation, genetic drift, and gene flow can change a populations genetic equilibrium, especially in a small, isolated population. Natural selection is usually a factor that causes change in established gene poolsboth large and small. Mechanisms of Evolution
Chapter Summary – 15.2 There are many patterns of evolution in nature. These patterns support the idea that natural selection is an important mechanism of evolution. Mechanisms of Evolution The separation of populations by physical barriers can lead to speciation.
Chapter Summary – 15.2 Mechanisms of Evolution Gradualism is the hypothesis that species originate through a gradual change in adaptations. The alternative hypothesis, punctuated equilibrium, argues that speciation occurs in relatively rapid bursts, followed by long periods of genetic equilibrium. Evidence for both evolutionary rates can be found in the fossil record.
Chapter Assessment Question 1 Why does disruptive selection favor speciation? Answer Disruptive selection favors extreme variations of a trait. Over time, it is less likely that species with extreme variations will mate, therefore giving rise to new species.
Chapter Assessment Question 2 Are the physical similarities between a dolphin and a shark evidence of convergent or divergent evolution?
The answer is convergent evolution. Dolphins and sharks are unrelated organisms that have evolved similar traits because they share similar environmental pressures. Chapter Assessment
Question 3 Niles Eldredge and Stephen J. Gould proposed _______. D. directional selection C. punctuated equilibrium B. reproductive isolation A. gradualism The answer is C.
Chapter Assessment Question 4 Which of the following pairs of terms is NOT related? D. polyploid – gene flow C. gene pool – allelic frequency B. natural selection – disruptive selection A. gradualism – speciation The answer is D.
Chapter Assessment Question 5 Why do some insects and bacteria evolve adaptations more rapidly than other species?
Insects and bacteria are examples of species that reproduce in large numbers and many times in a relatively short span of time, allowing adaptations to be more easily observed. Chapter Assessment
Question 6 Why is most of the evidence for evolution indirect rather than direct evidence? Answer Evolutionary processes are difficult for humans to observe directly. The short scale of human life spans makes it difficult to comprehend evolutionary processes that occur over millions of years.
Chapter Assessment Question 7 Are the fangs of a rattlesnake and the fangs of a spider homologous structures or analogous structures, and why?
The fangs of these organisms are analogous structures. They share the same function in each organism, to deliver venom, but the organisms do not share a common evolutionary origin. Chapter Assessment
Question 8 How do bird bones show an adaptation to flying that the bones of the flightless organisms, though homologous, do not?
Bird bones have evolved to be delicate, lightweight, and elongated. Chapter Assessment
Question 9 How do analogous structures provide evidence of evolution? Answer Analogous structures show the way dissimilar organisms adapted independently to similar ways of life by developing functionally similar structures.
Chapter Assessment Question 10 Why is the presence of pelvic bones in the baleen whale considered to be evidence of evolution?
Pelvic bones are evidence that whales once possessed hind limbs. Since whales now have no hind limbs, their loss must be the result of an evolutionary change. Chapter Assessment
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