Tracing Evolutionary History

Tracing Evolutionary History
Chapter 15 Tracing Evolutionary History Lecture by Joan Sharp

EARLY EARTH AND THE ORIGIN OF LIFE
EARLY EARTH AND THE ORIGIN OF LIFE Copyright © 2009 Pearson Education, Inc.

15.1 Conditions on early Earth made the origin of life possible
A recipe for life Raw materials + Suitable environment Energy sources Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Students who have studied cell theory might wonder how the first cells formed. Furthermore, they might wonder if spontaneous generation of cells could occur today. Module 15.1 describes how conditions on the surface of Earth when life first formed were dramatically different from today. Furthermore, if new life were evolving on Earth today, it would face competition from the vast amount of life already present. 2. Consider pointing out the logic of the theory of spontaneous generation, given the state of scientific knowledge during that period in history. Piles of manure and rotting flesh left in the open would apparently produce flies out of nowhere. At that time, so little was understood about eggs, sperm, and fertilization that spontaneous generation was a logical conclusion. 3. The four-stage hypothesis for the origin of life is a little like a recipe for building cells from the bottom up. If your students do not remember details about biological molecules and basic cell structure, you may need to review them before addressing these stages. 4. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be encouraged to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life. Copyright © 2009 Pearson Education, Inc.

The possible composition of Earth’s early atmosphere H2O vapor and compounds released from volcanic eruptions, including N2 and its oxides, CO2, CH4, NH3, H2, and H2S As the Earth cooled, water vapor condensed into oceans, and most of the hydrogen escaped into space Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Students who have studied cell theory might wonder how the first cells formed. Furthermore, they might wonder if spontaneous generation of cells could occur today. Module 15.1 describes how conditions on the surface of Earth when life first formed were dramatically different from today. Furthermore, if new life were evolving on Earth today, it would face competition from the vast amount of life already present. 2. Consider pointing out the logic of the theory of spontaneous generation, given the state of scientific knowledge during that period in history. Piles of manure and rotting flesh left in the open would apparently produce flies out of nowhere. At that time, so little was understood about eggs, sperm, and fertilization that spontaneous generation was a logical conclusion. 3. The four-stage hypothesis for the origin of life is a little like a recipe for building cells from the bottom up. If your students do not remember details about biological molecules and basic cell structure, you may need to review them before addressing these stages. 4. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be encouraged to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life. Copyright © 2009 Pearson Education, Inc.

Many energy sources existed on the early Earth Intense volcanic activity, lightning, and UV radiation Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Students who have studied cell theory might wonder how the first cells formed. Furthermore, they might wonder if spontaneous generation of cells could occur today. Module 15.1 describes how conditions on the surface of Earth when life first formed were dramatically different from today. Furthermore, if new life were evolving on Earth today, it would face competition from the vast amount of life already present. 2. Consider pointing out the logic of the theory of spontaneous generation, given the state of scientific knowledge during that period in history. Piles of manure and rotting flesh left in the open would apparently produce flies out of nowhere. At that time, so little was understood about eggs, sperm, and fertilization that spontaneous generation was a logical conclusion. 3. The four-stage hypothesis for the origin of life is a little like a recipe for building cells from the bottom up. If your students do not remember details about biological molecules and basic cell structure, you may need to review them before addressing these stages. 4. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be encouraged to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life. Copyright © 2009 Pearson Education, Inc.

Earth formed 4.6 billion years ago By 3.5 billion years ago, photosynthetic bacteria formed sandy stromatolite mats The first living things were much simpler and arose much earlier Clarify to students that the first living things must have been very simple. Cyanobacteria are far too complex to be the first cells. Students might not appreciate the challenges of finding fossils of early life. These early life forms were likely microscopic and free of hard parts such as shells and bone. Over time, geological heat, pressure, and friction may destroy fossils. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Students who have studied cell theory might wonder how the first cells formed. Furthermore, they might wonder if spontaneous generation of cells could occur today. Module 15.1 describes how conditions on the surface of Earth when life first formed were dramatically different from today. Furthermore, if new life were evolving on Earth today, it would face competition from the vast amount of life already present. 2. Consider pointing out the logic of the theory of spontaneous generation, given the state of scientific knowledge during that period in history. Piles of manure and rotting flesh left in the open would apparently produce flies out of nowhere. At that time, so little was understood about eggs, sperm, and fertilization that spontaneous generation was a logical conclusion. 3. The four-stage hypothesis for the origin of life is a little like a recipe for building cells from the bottom up. If your students do not remember details about biological molecules and basic cell structure, you may need to review them before addressing these stages. 4. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be encouraged to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life. Copyright © 2009 Pearson Education, Inc.

Figure 15.1 A cross-section of a fossilized stromatolite.

Chemical conditions Physical conditions Abiotic synthesis of monomers Stage 1 Stage 2 Formation of polymers Define protobionts: droplets surrounded by membranes that maintained an internal chemistry different from their surroundings. When presenting the four-stage hypothesis for the origin of life, encourage your students to consider at what point life actually arose. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps students better understand the difficulties in arriving at a simple definition of life. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Students who have studied cell theory might wonder how the first cells formed. Furthermore, they might wonder if spontaneous generation of cells could occur today. Module 15.1 describes how conditions on the surface of Earth when life first formed were dramatically different from today. Furthermore, if new life were evolving on Earth today, it would face competition from the vast amount of life already present. 2. Consider pointing out the logic of the theory of spontaneous generation, given the state of scientific knowledge during that period in history. Piles of manure and rotting flesh left in the open would apparently produce flies out of nowhere. At that time, so little was understood about eggs, sperm, and fertilization that spontaneous generation was a logical conclusion. 3. The four-stage hypothesis for the origin of life is a little like a recipe for building cells from the bottom up. If your students do not remember details about biological molecules and basic cell structure, you may need to review them before addressing these stages. 4. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be encouraged to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life. Stage 3 Packaging of polymers into protobionts Stage 4 Self-replication Copyright © 2009 Pearson Education, Inc.

15.2 TALKING ABOUT SCIENCE: Stanley Miller’s experiments showed that the abiotic synthesis of organic molecules is possible In the 1920s, two scientists—the Russian A. I. Oparin and the British J. B. S. Haldane—independently proposed that organic molecules could have formed on the early Earth Modern atmosphere is rich in O2, which oxidizes and disrupts chemical bonds The early Earth likely had a reducing atmosphere Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Some scientists distinguish between biological evolution and chemical evolution. Biological evolution addresses changes in life once it existed on Earth. Chemical evolution includes the origin of the first forms of life. The word evolution, if strictly defined as a change over time, also applies to changes in the universe. 2. The experiments and hypotheses discussed in Module 15.2 demonstrate the tentative nature of science. As evidence is collected, old hypotheses are tested and new hypotheses arise. Copyright © 2009 Pearson Education, Inc.

Video: Hydrothermal Vent
15.2 TALKING ABOUT SCIENCE: Stanley Miller’s experiments showed that the abiotic synthesis of organic molecules is possible In 1953, graduate student Stanley Miller tested the Oparin-Haldane hypothesis Miller set up an airtight apparatus with gases circulating past an electrical discharge, to simulate conditions on the early Earth He also set up a control with no electrical discharge Why? Discuss the importance of the control to eliminate the possibility that contamination produced the observed results. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Some scientists distinguish between biological evolution and chemical evolution. Biological evolution addresses changes in life once it existed on Earth. Chemical evolution includes the origin of the first forms of life. The word evolution, if strictly defined as a change over time, also applies to changes in the universe. 2. The experiments and hypotheses discussed in Module 15.2 demonstrate the tentative nature of science. As evidence is collected, old hypotheses are tested and new hypotheses arise. Video: Hydrothermal Vent Video: Tubeworms Copyright © 2009 Pearson Education, Inc.

Figure 15.2 Stanley Miller re-creating his 1953 experiment.

15.2 TALKING ABOUT SCIENCE: Stanley Miller’s experiments showed that the abiotic synthesis of organic molecules is possible After a week, Miller’s setup produced abundant amino acids and other organic molecules Similar experiments used other atmospheres and other energy sources, with similar results Miller-Urey experiments demonstrate that Stage 1, abiotic synthesis of organic molecules, was possible on the early Earth These experiments and hypotheses exhibit the tentative nature of science. As evidence is collected, old hypotheses are tested and new hypotheses arise. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Some scientists distinguish between biological evolution and chemical evolution. Biological evolution addresses changes in life once it existed on Earth. Chemical evolution includes the origin of the first forms of life. The word evolution, if strictly defined as a change over time, also applies to changes in the universe. 2. The experiments and hypotheses discussed in Module 15.2 demonstrate the tentative nature of science. As evidence is collected, old hypotheses are tested and new hypotheses arise. Copyright © 2009 Pearson Education, Inc.

15.2 TALKING ABOUT SCIENCE: Stanley Miller’s experiments showed that the abiotic synthesis of organic molecules is possible An alternative hypothesis Submerged volcanoes and deep-sea hydrothermal vents may have provided the chemical resources for the first life Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Some scientists distinguish between biological evolution and chemical evolution. Biological evolution addresses changes in life once it existed on Earth. Chemical evolution includes the origin of the first forms of life. The word evolution, if strictly defined as a change over time, also applies to changes in the universe. 2. The experiments and hypotheses discussed in Module 15.2 demonstrate the tentative nature of science. As evidence is collected, old hypotheses are tested and new hypotheses arise. Copyright © 2009 Pearson Education, Inc.

15.3 The formation of polymers, membranes, and self-replicating molecules represent stages in the origin of the first cells Stage 2: The formation of polymers Monomers could have combined to form organic polymers Same energy sources Clay as substratum for polymerization? Polymers are synthesized by enzyme-catalyzed reactions that add monomers to a growing chain. Organic polymers such as proteins and nucleic acids may have polymerized on hot sand, rocks, or clay. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes heal naturally as the hydrophobic phospholipid tails and polar heads align together. 2. As you discuss the conditions on early Earth and the pathways through which life might have first evolved, you might challenge your class to identify a set of defining traits for something to be considered alive. What are the essential properties of life? Copyright © 2009 Pearson Education, Inc.

15.3 The formation of polymers, membranes, and self-replicating molecules represent stages in the origin of the first cells Stage 2: Packaging of polymers into protobionts Polymers could have aggregated into complex, organized, cell-like structures Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes heal naturally as the hydrophobic phospholipid tails and polar heads align together. 2. As you discuss the conditions on early Earth and the pathways through which life might have first evolved, you might challenge your class to identify a set of defining traits for something to be considered alive. What are the essential properties of life? Copyright © 2009 Pearson Education, Inc.

Figure 15.3A Microscopic spheres with membranes made of lipids.
Protobionts form spontaneously, bounded by lipids. Explain to your students the inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles.

15.3 The formation of polymers, membranes, and self-replicating molecules represent stages in the origin of the first cells What characteristics do cells and protobionts share? Structural organization Simple reproduction Simple metabolism Simple homeostasis A protobiont is a collection of molecules within a membrane, with an internal environment that differs from its surroundings. Protobionts can split into two smaller entities in a simple form of reproduction. Protobionts can carry out simple metabolic reactions if enzymes are included. Protobionts and living cells share a selectively permeable membrane that allows some materials but not others to cross. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes heal naturally as the hydrophobic phospholipid tails and polar heads align together. 2. As you discuss the conditions on early Earth and the pathways through which life might have first evolved, you might challenge your class to identify a set of defining traits for something to be considered alive. What are the essential properties of life? Copyright © 2009 Pearson Education, Inc.

(a) Simple reproduction by liposomes
Campbell, Neil, and Jane Reece, Biology, 8th ed., Figure 25.3 Laboratory versions of protobionts; Simple reproduction. A protobiont is a collection of molecules within a membrane, with an internal environment that differs from its surroundings. Protobionts can split into two smaller entities in a simple form of reproduction. Protobionts can carry out simple metabolic reactions if enzymes are included. Protobionts and living cells share a selectively permeable membrane that allows some materials but not others to cross. (a) Simple reproduction by liposomes

15.3 The formation of polymers, membranes, and self-replicating molecules represent stages in the origin of the first cells Which came first? Life requires the maintenance of a complex, stable, internal environment What provides this in modern cells? Life requires accurate self replication Question students, who should suggest that (1) protein enzymes and (2) DNA provide these in modern cells. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes heal naturally as the hydrophobic phospholipid tails and polar heads align together. 2. As you discuss the conditions on early Earth and the pathways through which life might have first evolved, you might challenge your class to identify a set of defining traits for something to be considered alive. What are the essential properties of life? Copyright © 2009 Pearson Education, Inc.

polymers: simple “genes”
Figure 15.3B A hypothesis for the origin of the first genes. Monomers 1 Formation of short RNA polymers: simple “genes”

polymers: simple “genes”
2 Assembly of a complementary RNA chain, the first step in replication of the original “gene” Figure 15.3B A hypothesis for the origin of the first genes. Monomers 1 Formation of short RNA polymers: simple “genes”

15.3 The formation of polymers, membranes, and self-replicating molecules represent stages in the origin of the first cells Stage 4: Self-replication RNA may have served both as the first genetic material and as the first enzymes The first genes may have been short strands of RNA that replicated without protein support RNA catalysts or ribozymes may have assisted in this process. RNA world! Describe the function of ribozymes and the key role of rRNA ribozymes in protein synthesis in living cells. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes heal naturally as the hydrophobic phospholipid tails and polar heads align together. 2. As you discuss the conditions on early Earth and the pathways through which life might have first evolved, you might challenge your class to identify a set of defining traits for something to be considered alive. What are the essential properties of life? Copyright © 2009 Pearson Education, Inc.

How could natural selection have acted on these protobionts?
15.3 The formation of polymers, membranes, and self-replicating molecules represent stages in the origin of the first cells A variety of protobionts existed on the early Earth Some of these protobionts contained self-replicating RNA molecules How could natural selection have acted on these protobionts? Membranes may have separated various aggregates of self-replicating molecules, which could be acted on by natural selection. Those that were especially stable and capable of growing and replicating more efficiently than others would increase in number, passing on their characteristics to next generations. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24   31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. The inherent property of bipolar molecules such as phospholipids to naturally form double membranes or micelles is worth discussing with your class. Because of these properties, membranes heal naturally as the hydrophobic phospholipid tails and polar heads align together. 2. As you discuss the conditions on early Earth and the pathways through which life might have first evolved, you might challenge your class to identify a set of defining traits for something to be considered alive. What are the essential properties of life? Copyright © 2009 Pearson Education, Inc.

MAJOR EVENTS IN THE HISTORY OF LIFE
MAJOR EVENTS IN THE HISTORY OF LIFE Copyright © 2009 Pearson Education, Inc.

15.4 The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Three eons Archaean and Proterozoic lasted 4 billion years Phanerozoic is the last ½ billion years Divided into Paleozoic era, Mesozoic era, Cenozoic era Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. For the Discovery Video Early Life, go to Animation and Video Files. Copyright © 2009 Pearson Education, Inc.

Phanerozoic eon Meso- zoic
Cenozoic Meso- zoic Humans Paleozoic Colonization of land Origin of solar system and Earth Animals 1 4 Proterozoic eon Archaean eon Figure 15.4 A clock analogy for some key events in the history of Earth and its life. Billions of years ago 2 3 Multicellular eukaryotes Prokaryotes Single-celled eukaryotes Atmospheric oxygen

15.4 The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Prokaryotes lived alone on Earth for 1.5 billion years They created our atmosphere and transformed Earth’s biosphere Virtually all metabolic pathways evolved within prokaryotes Atmospheric oxygen appeared 2.7 billion years ago due to prokaryotic photosynthesis Cellular respiration arose in prokaryotes, using oxygen to harvest energy from organic molecules Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

15.4 The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history The eukaryotic cell probably originated as a community of prokaryotes, when small prokaryotes capable of aerobic respiration or photosynthesis began living in larger cells Oldest fossils of eukaryotes are 2.1 billion years old Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

15.4 The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Multicellular forms arose about 1.5 billion years ago The descendents of these forms include a variety of algae, plants, fungi, animals The oldest known fossils of multicellular organisms were small algae, living 1.2 billion years ago Comprehending the length of time of the major phases of life’s history is problematic for most students. Point out to your students that multicellular life represents only about 13% of Earth’s history (0.6 of 4.6 billion years). The period in which all life on Earth was prokaryotic lasted more than twice the period of time since multicellular life evolved. Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

15.4 The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history The diversity of animal forms increased suddenly and dramatically about 535–525 million years ago in the Cambrian explosion Fungi and plants colonized land together 500 million years ago Roots of most plants have fungal associates that exchange water and minerals for nutrients Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

15.4 The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Arthropods and tetrapods are the most widespread and diverse land animals Human lineage diverged from apes 7–6 million years ago Our species originated 160,000 years ago Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

15.5 The actual ages of rocks and fossils mark geologic time
Radiometric dating measures the decay of radioactive isotopes “Young” fossils may contain isotopes of elements that accumulated when the organisms were alive Carbon-14 can date fossils up to 75,000 years old Potassium-40, with a half-life of 1.3 billion years, can be used to date volcanic rocks that are hundreds of millions of years old A fossil’s age can be inferred from the ages of the rock layers above and below the strata in which the fossil is found Teaching Tips 1. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. 2. With a half-life of 5,730 years, carbon-14 is an inappropriate measure of large periods of time, such as the dinosaur bones that are 100 million years old. This is like trying to measure the distance across a state with a tape measure. 3. The sequence of layers, but not their absolute age, are revealed by the stratifications in sedimentary rocks. Imagine peeling the layers of wallpaper from the walls of a very old house that has been inhabited by many owners. We can tell which layers are older than others, but not the exact age of each. Copyright © 2009 Pearson Education, Inc.

Fraction of Carbon-14 remaining
– 2 1 – 4 1 – 8 –– 1 16 –– 1 32 Figure 15.5 Radiometric dating. 5.7 11.4 17.1 22.8 28.5 Time (thousands of years)

15.6 The fossil record documents the history of life
The fossil record documents the main events in the history of life The geologic record is defined by major transitions in life on Earth Student Misconceptions and Concerns 1. Table 15.6 includes a timeline of the entire history of Earth, with a large section focused on the most recent 13% of Earth’s history. Students might not notice that this enlarged section is an expansion of this proportionately small, but significant, period. Furthermore, the bottom of the enlarged portion is not scaled to the top portion. These clarifications may be needed for proper appreciation of this table. Teaching Tips 1. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. 2. The sequence of layers, but not their absolute age, are revealed by the stratifications in sedimentary rocks. Imagine peeling the layers of wallpaper from the walls of a very old house that has been inhabited by many owners. We can tell which layers are older than others, but not the exact age of each. 3. Students might not appreciate the difficulty of finding fossils of early life. Early life forms were likely microscopic and lacked hard parts such as shells and bone. Furthermore, over time, heat, pressure, and friction may destroy what fossils were formed or render them difficult to detect. Animation: The Geologic Record Copyright © 2009 Pearson Education, Inc.

Table 15.6 The Geologic Record.

MECHANISMS OF MACROEVOLUTION
MECHANISMS OF MACROEVOLUTION Copyright © 2009 Pearson Education, Inc.

15.7 Continental drift has played a major role in macroevolution
Continental drift is the slow, continuous movement of Earth’s crustal plates on the hot mantle Crustal plates carrying continents and seafloors float on a liquid mantle Important geologic processes occur at plate boundaries Sliding plates are earthquake zones Colliding plates form mountains Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Consider this analogy to help students understand the biological consequences of speciation as continents drifted apart. As your students left high school and entered the workforce or continued their education, their high school social groups drifted apart. Your students, in their new circumstances, adapted and changed in different ways, separate from the members of their old social groups. A note of caution: This analogy to individual social changes is not an example of biological evolution, which occurs over generations. Video: Lava Flow Copyright © 2009 Pearson Education, Inc.

North American Plate Eurasian Plate Caribbean Plate Juan de Fuca Plate
Philippine Plate Arabian Plate Cocos Plate Indian Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Figure 15.7A Earth’s continental plates. Red arrows indicate direction of movement, red dots are zones of violent geologic activity. Scotia Plate Antarctic Plate

15.7 Continental drift has played a major role in macroevolution
The supercontinent Pangaea, which formed 250 million years ago, altered habitats and triggered the greatest mass extinction in Earth’s history Its breakup led to the modern arrangement of continents Australia’s marsupials became isolated when the continents separated, and placental mammals arose on other continents India’s collision with Eurasia 55 million years ago led to the formation of the Himalayas Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Consider this analogy to help students understand the biological consequences of speciation as continents drifted apart. As your students left high school and entered the workforce or continued their education, their high school social groups drifted apart. Your students, in their new circumstances, adapted and changed in different ways, separate from the members of their old social groups. A note of caution: This analogy to individual social changes is not an example of biological evolution, which occurs over generations. Video: Volcanic Eruption Copyright © 2009 Pearson Education, Inc.

Present Cenozoic 65.5 Millions of years ago 135 Mesozoic 251 Paleozoic
North America Eurasia 65.5 Africa South America India Madagascar Australia Antarctica Laurasia 135 Gondwana Millions of years ago Mesozoic Figure 15.7B Continental drift during the Phanerozoic eon. 251 Pangaea Paleozoic

15.8 CONNECTION: The effects of continental drift may imperil human life
Volcanoes and earthquakes result from the movements of crustal plates The boundaries of plates are hotspots of volcanic and earthquake activity An undersea earthquake caused the 2004 tsunami, when a fault in the Indian Ocean ruptured Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. A Google satellite map of the Atlantic Ocean, available at clearly reveals the mid-Atlantic ridge. Copyright © 2009 Pearson Education, Inc.

San Andreas Fault North American Plate San Francisco Santa Cruz
Pacific Plate Figure 15.8 The San Andreas Fault (an aerial view north of Los Angeles), a boundary between two crustal plates. Los Angeles California

15.9 Mass extinctions destroy large numbers of species
Extinction is the fate of all species and most lineages The history of life on Earth reflects a steady background extinction rate with episodes of mass extinction Over the last 600 million years, five mass extinctions have occurred in which 50% or more of the Earth’s species went extinct Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. 2. The slow speed at which life can evolve in response to human damage of natural systems may not be appreciated by our students. As noted in Module 15.9, it may take 5–10 million years for the planet to recover from the ongoing human-induced loss of biological diversity. Teaching Tips 1. The consequences of an asteroid impact, large or small, reveal the role of random chance in evolution. Like throwing a dart at a spinning globe, where the asteroid hits and what continents and forms of life are most affected can change greatly if the impact occurs even a few hours earlier or later. An asteroid delayed by 12 hours, in what might be a journey of millions or billions of years, will land on the opposite side of the Earth. 2. Students might not realize that entire categories of animals have come and gone. The once abundant Trilobites and nonavian dinosaurs are now extinct. Birds and mammals are relatively recent additions. Such examples of macroevolution are apparent in the fossil record. Copyright © 2009 Pearson Education, Inc.

Permian extinction 96% of shallow water marine species died in the Permian extinction Possible cause? Extreme vulcanism in Siberia released CO2, warmed global climate, slowed mixing of ocean water, and reduced O2 availability in the ocean Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. 2. The slow speed at which life can evolve in response to human damage of natural systems may not be appreciated by our students. As noted in Module 15.9, it may take 5–10 million years for the planet to recover from the ongoing human-induced loss of biological diversity. Teaching Tips 1. The consequences of an asteroid impact, large or small, reveal the role of random chance in evolution. Like throwing a dart at a spinning globe, where the asteroid hits and what continents and forms of life are most affected can change greatly if the impact occurs even a few hours earlier or later. An asteroid delayed by 12 hours, in what might be a journey of millions or billions of years, will land on the opposite side of the Earth. 2. Students might not realize that entire categories of animals have come and gone. The once abundant Trilobites and nonavian dinosaurs are now extinct. Birds and mammals are relatively recent additions. Such examples of macroevolution are apparent in the fossil record. Copyright © 2009 Pearson Education, Inc.

Cretaceous extinction 50% of marine species and many terrestrial lineages went extinct 65 million years ago All dinosaurs (except birds) went extinct Likely cause was a large asteroid that struck the Earth, blocking light and disrupting the global climate Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. 2. The slow speed at which life can evolve in response to human damage of natural systems may not be appreciated by our students. As noted in Module 15.9, it may take 5–10 million years for the planet to recover from the ongoing human-induced loss of biological diversity. Teaching Tips 1. The consequences of an asteroid impact, large or small, reveal the role of random chance in evolution. Like throwing a dart at a spinning globe, where the asteroid hits and what continents and forms of life are most affected can change greatly if the impact occurs even a few hours earlier or later. An asteroid delayed by 12 hours, in what might be a journey of millions or billions of years, will land on the opposite side of the Earth. 2. Students might not realize that entire categories of animals have come and gone. The once abundant Trilobites and nonavian dinosaurs are now extinct. Birds and mammals are relatively recent additions. Such examples of macroevolution are apparent in the fossil record. For the Discovery Video Mass Extinctions, go to Animation and Video Files. Copyright © 2009 Pearson Education, Inc.

North America • Chicxulub crater Yucatán Peninsula Yucatán Peninsula
Figure 15.9 The impact hypothesis for the Cretaceous mass extinction. Yucatán Peninsula

Figure 15.9 The impact hypothesis for the Cretaceous mass extinction.
Yucatán Peninsula

Figure 15.9 The impact hypothesis for the Cretaceous mass extinction.

It took 100 million years for the number of marine families to recover after Permian mass extinction Is a 6th extinction under way? The current extinction rate is 100–1,000 times the normal background rate It may take life on Earth millions of years to recover Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. 2. The slow speed at which life can evolve in response to human damage of natural systems may not be appreciated by our students. As noted in Module 15.9, it may take 5–10 million years for the planet to recover from the ongoing human-induced loss of biological diversity. Teaching Tips 1. The consequences of an asteroid impact, large or small, reveal the role of random chance in evolution. Like throwing a dart at a spinning globe, where the asteroid hits and what continents and forms of life are most affected can change greatly if the impact occurs even a few hours earlier or later. An asteroid delayed by 12 hours, in what might be a journey of millions or billions of years, will land on the opposite side of the Earth. 2. Students might not realize that entire categories of animals have come and gone. The once abundant Trilobites and nonavian dinosaurs are now extinct. Birds and mammals are relatively recent additions. Such examples of macroevolution are apparent in the fossil record. Copyright © 2009 Pearson Education, Inc.

15.10 EVOLUTION CONNECTION: Adaptive radiations have increased the diversity of life
Adaptive radiation: a group of organisms forms new species, whose adaptations allow them to fill new habitats or roles in their communities A rebound in diversity follows mass extinctions as survivors become adapted to vacant ecological niches Mammals underwent a dramatic adaptive radiation after the extinction of nonavian dinosaurs 65 million years ago Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Many business models reveal analogies to adaptive radiations. Personal computers of all types and sizes represent a type of technological radiation. The Internet is an ongoing radiation that has changed the way we communicate with each other and make purchases. Many other analogies can be developed as they relate to culture and commercialism. Challenge your students to suggest their own. Copyright © 2009 Pearson Education, Inc.

Ancestral mammal Monotremes (5 species) Reptilian Ancestor Marsupials
(324 species) Eutherians (placental mammals; 5,010 species) Figure Adaptive radiation of mammals (width of line reflects numbers of species). Where on this time line did the dinosaurs become extinct? 250 200 150 100 50 Millions of years ago

15.10 EVOLUTION CONNECTION: Adaptive radiations have increased the diversity of life
Adaptive radiations may follow the evolution of new adaptations, such as wings Radiations of land plants were associated with many novel features, including waxy coat, vascular tissue, seeds, and flowers Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Many business models reveal analogies to adaptive radiations. Personal computers of all types and sizes represent a type of technological radiation. The Internet is an ongoing radiation that has changed the way we communicate with each other and make purchases. Many other analogies can be developed as they relate to culture and commercialism. Challenge your students to suggest their own. Copyright © 2009 Pearson Education, Inc.

Plant Reproductive structures (flowers) contain spores and gametes Leaf performs photosynthesis Cuticle reduces water loss; stomata allow gas exchange Stem supports plant and may perform photosynthesis Surrounding water supports alga Alga Whole alga performs photosynthesis; absorbs water, CO2, and minerals from the water Campbell, Neil A., Jane B. Reece, Martha R Taylor, Eric J. Simon, Biology: Concepts & Connections, 5th ed. Figure 17.2A Comparing a plant and a multicellular green alga. Roots anchor plant; absorb water and minerals from the soil Holdfast anchors alga

15.11 Genes that control development play a major role in evolution
“Evo-devo” is a field that combines evolutionary and developmental biology Slight genetic changes can lead to major morphological differences between species Changes in genes that alter the timing, rate, and spatial pattern of growth alter the adult form of an organism Many developmental genes have been conserved throughout evolutionary history Changes in these genes have led to the huge diversity in body forms Changes may include alteration in number, nucleotide sequence, and regulation of developmental genes. Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Students may not be familiar enough with salamander life histories to appreciate the similarity of a larval salamander to the axolotl form. By analogy, students might be asked to imagine what would result if a caterpillar reproduced and never turned into a winged adult butterfly. The caterpillar stage can then be related to the early larval form of salamanders. Furthermore, students might wonder why paedomorphosis occurs in salamanders but not frogs or butterflies. Animation: Allometric Growth Copyright © 2009 Pearson Education, Inc.

Gills Figure 15.11A An axolotl, a paedomorphic salamander.
Changes may include alteration in number, nucleotide sequence, and regulation of developmental genes.

Human development is paedomorphic, retaining juvenile traits into adulthood Adult chimps have massive, projecting jaws; large teeth; and a low forehead with a small braincase Human adults—and both human and chimpanzee fetuses—lack these features Humans and chimpanzees are more alike as fetuses than as adults The human brain continues to grow at the fetal rate for the first year of life Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Students may not be familiar enough with salamander life histories to appreciate the similarity of a larval salamander to the axolotl form. By analogy, students might be asked to imagine what would result if a caterpillar reproduced and never turned into a winged adult butterfly. The caterpillar stage can then be related to the early larval form of salamanders. Furthermore, students might wonder why paedomorphosis occurs in salamanders but not frogs or butterflies. Copyright © 2009 Pearson Education, Inc.

Chimpanzee fetus Chimpanzee adult Human fetus Human adult
Figure 15.11B Chimpanzee and human skulls compared. Human fetus Human adult

Homeotic genes are master control genes that determine basic features, such as where pairs of wings or legs develop on a fruit fly Developing fish and tetrapod limbs express certain homeotic genes A second region of expression in the developing tetrapod limb produces the extra skeletal elements that form feet, turning fins into walking legs Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Students may not be familiar enough with salamander life histories to appreciate the similarity of a larval salamander to the axolotl form. By analogy, students might be asked to imagine what would result if a caterpillar reproduced and never turned into a winged adult butterfly. The caterpillar stage can then be related to the early larval form of salamanders. Furthermore, students might wonder why paedomorphosis occurs in salamanders but not frogs or butterflies. Copyright © 2009 Pearson Education, Inc.

Duplication of developmental genes can be important in the formation of new morphological features A fruit fly has a single cluster of homeotic genes; a mouse has four Two duplications of these gene clusters in evolution from invertebrates into vertebrates Mutations in these duplicated genes may have led to the origin of novel vertebrate characteristics, including backbone, jaws, and limbs Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Students may not be familiar enough with salamander life histories to appreciate the similarity of a larval salamander to the axolotl form. By analogy, students might be asked to imagine what would result if a caterpillar reproduced and never turned into a winged adult butterfly. The caterpillar stage can then be related to the early larval form of salamanders. Furthermore, students might wonder why paedomorphosis occurs in salamanders but not frogs or butterflies. Copyright © 2009 Pearson Education, Inc.

Figure 15.11C Stickleback fish from ocean (top) and lake (bottom) stained to show bony plates and spines. (Arrow indicates the absence of the pelvic spine in the lake fish.) Missing pelvic spine

15.12 Evolutionary novelties may arise in several ways
In the evolution of an eye or any other complex structure, behavior, or biochemical pathway, each step must bring a selective advantage to the organism possessing it and must increase the organism’s fitness Mollusc eyes evolved from an ancestral patch of photoreceptor cells through series of incremental modifications that were adaptive at each stage A range of complexity can be seen in the eyes of living molluscs Cephalopod eyes are as complex as vertebrate eyes, but arose separately Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Clear examples of evolutionary remodeling include the many variations of the pattern of bones in the vertebrate forelimb. Bat wings, bird wings, penguin flippers, the arms of apes, and the digging forelimbs of moles all show how the ancestral pattern evolved in response to various selective pressures. Descent with modification is a powerful explanation of such diversity. 2. Another way to think about evolutionary remodeling is to make an analogy to remodeling a home. A remodeled home retains many of the “ancestral” traits perhaps the same plumbing and electrical system. However, the place where there was once a wall might now be an opening into an enlarged family room or a window to the outside. Evolution can work like the TV show This Old House! 3. When discussing exaptations, have students consider the many new uses for common household items if they were to have them in a survival situation, stranded on an island, or lost in the woods. A handkerchief, a screwdriver, and a pair of pliers might take on new functions in this different context. Copyright © 2009 Pearson Education, Inc.

Transparent protective
Light-sensitive cells Light-sensitive cells Transparent protective tissue (cornea) Fluid-filled cavity Cornea Lens Eye cup Layer of light-sensitive cells (retina) Nerve fibers Nerve fibers Retina Optic nerve Optic nerve Optic nerve Patch of light- sensitive cells Eye cup Simple pinhole camera-type eye Eye with primitive lens Complex camera-type eye Figure A range of eye complexity among molluscs. Limpet Abalone Nautilus Marine snail Squid

15.12 Evolutionary novelties may arise in several ways
Other novel structures result from exaptation, the gradual adaptation of existing structures to new functions Natural selection does not anticipate the novel use; each intermediate stage must be adaptive and functional The modification of the vertebrate forelimb into a wing in pterosaurs, bats, and birds provides a familiar example Clear examples of evolutionary remodeling include the many variations of the 1-2-many pattern of bones in the vertebrate forelimb. Bat wings, bird wings, penguin flippers, the arms of apes, and the digging forelimbs of moles all show how the ancestral pattern was revised as new functions evolved. Descent with modification is a powerful explanation of such diversity. Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Clear examples of evolutionary remodeling include the many variations of the pattern of bones in the vertebrate forelimb. Bat wings, bird wings, penguin flippers, the arms of apes, and the digging forelimbs of moles all show how the ancestral pattern evolved in response to various selective pressures. Descent with modification is a powerful explanation of such diversity. 2. Another way to think about evolutionary remodeling is to make an analogy to remodeling a home. A remodeled home retains many of the “ancestral” traits perhaps the same plumbing and electrical system. However, the place where there was once a wall might now be an opening into an enlarged family room or a window to the outside. Evolution can work like the TV show This Old House! 3. When discussing exaptations, have students consider the many new uses for common household items if they were to have them in a survival situation, stranded on an island, or lost in the woods. A handkerchief, a screwdriver, and a pair of pliers might take on new functions in this different context. Copyright © 2009 Pearson Education, Inc.

Pterosaur.

Flying bat.

Flying eagle.

15.13 Evolutionary trends do not mean that evolution is goal directed
Species selection is the unequal speciation or unequal survival of species on a branching evolutionary tree Species that generate many new species may drive major evolutionary change Natural selection can also lead to macroevolutionary trends, such as evolutionary arms races between predators and prey Predators and prey act on each other as significant agents of natural selection Over time, predators evolve better weaponry while prey evolve better defenses Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Consider challenging your students to explain why the evolution of a group is not driven in any particular direction, or directed towards any ideal form or function. As a hint, you can ask them to describe the mechanisms by which variety arises in a species. Copyright © 2009 Pearson Education, Inc.

15.13 Evolutionary trends do not mean that evolution is goal directed
Evolution is not goal directed Natural selection results from the interactions between organisms and their environment If the environment changes, apparent evolutionary trends may cease or reverse Student Misconceptions and Concerns 1. Student backgrounds in earth sciences may be uneven based upon their specific college prep coursework. Emphasis on chemistry, physics, and biology may leave large gaps in basic content regarding geology and Earth’s history. Teaching Tips 1. Consider challenging your students to explain why the evolution of a group is not driven in any particular direction, or directed towards any ideal form or function. As a hint, you can ask them to describe the mechanisms by which variety arises in a species. Copyright © 2009 Pearson Education, Inc.

Figure 15.13 The branched evolution of horses.
RECENT Equus Hippidion and other genera PLEISTOCENE Nannippus Pliohippus Neohipparion PLIOCENE Hipparion Sinohippus Megahippus Callippus Archaeohippus Merychippus MIOCENE Anchitherium Hypohippus Parahippus Miohippus OLIGOCENE Figure The branched evolution of horses. Mesohippus Paleotherium Epihippus Propalaeotherium Pachynolophus Orohippus EOCENE Grazers Browsers Hyracotherium

15.14 Phylogenies are based on homologies in fossils and living organisms
Phylogeny is the evolutionary history of a species or group of species Hypotheses about phylogenetic relationships can be developed from various lines of evidence The fossil record provides information about the timing of evolutionary divergences Homologous morphological traits, behaviors, and molecular sequences also provide evidence of common ancestry Homologous and analogous relationships can be confusing for students. Simple explanations and concrete examples can serve as guides to understanding each process. Homologous relationships reflect modifications of “one form” to many “functions.” Analogous relationships reflect modifications of many “forms” for “one function.” Student Misconceptions and Concerns 1. Homologous and analogous relationships can be confusing for students. Simple explanations and concrete examples can serve as guides to understanding each process. Homologous relationships reflect modifications of one form for many functions. Analogous relationships reflect modifications of many forms for one function. Teaching Tips 1. Our hierarchical classification system is analogous to sorting mail first by zip code, then by street, house number, and finally individual name. Such a system of classification based upon hierarchical categories is also common in the military and many other places in our lives. Copyright © 2009 Pearson Education, Inc.

15.14 Phylogenies are based on homologies in fossils and living organisms
Analogous similarities result from convergent evolution in similar environments These similarities do not provide information about evolutionary relationships Marsupial and eutherian moles are very similar due to adaptation to similar burrowing life style, but are not closely related. Their last common ancestor lived 170 million years ago and was not mole-like. Both moles have enlarged front paws for digging, small eyes, and a pad of protective thickened skin on the nose. Student Misconceptions and Concerns 1. Homologous and analogous relationships can be confusing for students. Simple explanations and concrete examples can serve as guides to understanding each process. Homologous relationships reflect modifications of one form for many functions. Analogous relationships reflect modifications of many forms for one function. Teaching Tips 1. Our hierarchical classification system is analogous to sorting mail first by zip code, then by street, house number, and finally individual name. Such a system of classification based upon hierarchical categories is also common in the military and many other places in our lives. Copyright © 2009 Pearson Education, Inc.

Figure Convergent evolution of burrowing adaptations in Australian “mole” (top) and North American mole (bottom).

15.15 Systematics connects classification with evolutionary history
Systematics classifies organisms and determines their evolutionary relationship Taxonomists assign each species a binomial consisting of a genus and species name Genera are grouped into progressively larger categories. Each taxonomic unit is a taxon Although Linnaeus recognized a hierarchical structure in the natural world, he had no natural explanation for the occurrence of such groups. One of Darwin’s greatest insights was to understand that these clusters reflect similarities due to shared ancestry and to propose a natural mechanism for the formation of new species and the generation of this diversity. Student Misconceptions and Concerns 1. Students can be frustrated by the changing state of systematics. Some comfort can be offered by noting that this is true about many active areas of science. For example, scientists continue to learn more and revise advice regarding the causes, treatment, and prevention of heart disease and cancer. 2. Students might express concern over the need to learn scientific names, when common names already seem sufficient. Depending upon where you live, find some examples of common organisms with more than one common name. Fishermen are famous for the various names they assign to the same species, depending upon the geographic region where they fish. Have your students imagine the problems of using common names when communicating with someone in another language. Clearly, there are advantages to scientific names! Teaching Tips 1. Although Linnaeus recognized a hierarchical structure in the natural world, he had no natural explanation for the occurrence of such groups. One might wonder why all life does not blend evenly from one form to another. One of Darwin’s greatest insights was to understand that these clusters reflect similarities due to shared ancestry, i.e., life itself is grouped into family trees. Furthermore, Darwin proposed a natural mechanism for the formation of new species and the generation of this diversity. Animation: Classification Schemes Copyright © 2009 Pearson Education, Inc.

Species: Felis catus Genus: Felis Family: Felidae Order: Carnivora
Class: Mammalia Figure 15.15A Hierarchical classification of the domestic cat. Phylum: Chordata Kingdom: Animalia Bacteria Domain: Eukarya Archaea

Order Family Genus Species Felis catus (domestic cat) Felidae Felis
Mephitis mephitis (striped skunk) Mephitis Carnivora Mustelidae Lutra lutra (European otter) Lutra Figure 15.15B The relationship between classification and phylogeny. Canis latrans (coyote) Canidae Canis Canis lupus (wolf)

15.16 Shared characters are used to construct phylogenetic trees
A phylogenetic tree is a hypothesis of evolutionary relationships within a group Cladistics uses shared derived characters to group organisms into clades, including an ancestral species and all its descendents An inclusive clade is monophyletic Shared ancestral characters were present in ancestral groups Consider that you are building a phylogenetic tree for tetrapods. The first tetrapod had a backbone, so the presence of a backbone is not useful in constructing a phylogenetic tree for tetrapods. By contrast, the amniotic egg and hair are traits that arose within the tetrapods. Both traits are useful in sorting out evolutionary relationships within tetrapods. Student Misconceptions and Concerns 1. Students may struggle with many aspects of phylogenetic trees, including: (a) Students may not realize that each node/branch can be rotated to rearrange the groups without changing the nature of the relationships. For example, in Figure 15.16A, the position of the beaver and kangaroo can be reversed without changing any relationships represented in the phylogenetic tree. (b) The length of each branch is not meaningful and is not intended to be proportional to time. (c) The spacing between groups is not meaningful and does not denote the degree of divergence between them. Whether the tree is compressed or expanded in size, the information communicated in it remains the same. Teaching Tips 1. Emphasize to students that phylogenetic trees are tentative hypotheses. As new data are collected, the hypotheses are modified or rejected outright. Copyright © 2009 Pearson Education, Inc.

An important step in cladistics is the comparison of the ingroup (the taxa whose phylogeny is being investigated) and the outgroup (a taxon that diverged before the lineage leading to the members of the ingroup) The tree is constructed from a series of branch points, represented by the emergence of a lineage with a new set of derived traits The simplest (most parsimonious) hypothesis is the most likely phylogenetic tree Remind students that many kinds of evidence are used to construct phylogenetic trees, including structural features, developmental features, molecular data, behavioral traits, and so on. As new data are acquired, hypotheses are revised and new trees are drawn. Student Misconceptions and Concerns 1. Students may struggle with many aspects of phylogenetic trees, including: (a) Students may not realize that each node/branch can be rotated to rearrange the groups without changing the nature of the relationships. For example, in Figure 15.16A, the position of the beaver and kangaroo can be reversed without changing any relationships represented in the phylogenetic tree. (b) The length of each branch is not meaningful and is not intended to be proportional to time. (c) The spacing between groups is not meaningful and does not denote the degree of divergence between them. Whether the tree is compressed or expanded in size, the information communicated in it remains the same. Teaching Tips 1. Emphasize to students that phylogenetic trees are tentative hypotheses. As new data are collected, the hypotheses are modified or rejected outright. Animation: Geologic Record Copyright © 2009 Pearson Education, Inc.

Figure 15.16A Constructing a phylogenetic tree using cladistics.
TAXA Iguana Duck-billed platypus Iguana Kangaroo Beaver Duck-billed platypus Long gestation 1 Hair, mammary glands Kangaroo CHARACTERS Gestation 1 1 Gestation Hair, mammary glands 1 1 1 Beaver Figure 15.16A Constructing a phylogenetic tree using cladistics. Long gestation Character Table Phylogenetic Tree

The phylogenetic tree of reptiles shows that crocodilians are the closest living relatives of birds They share numerous features, including four-chambered hearts, singing to defend territories, and parental care of eggs within nests These traits were likely present in the common ancestor of birds and crocodiles Point out to your students a number of key features of phylogenetic trees. (1) Each node/branch can be rotated to rearrange the groups, without changing the nature of the relationships. (2) The length of each branch is not meaningful and is not intended to be proportional to time. (3) The spacing between groups is not meaningful. The same phylogenetic tree squeezed onto a page or stretched wide does not denote some degree of divergence between the groups. Remind your students that phylogenetic trees are tentative hypotheses. As new data is collected, the hypotheses are modified or outright rejected. Student Misconceptions and Concerns 1. Students may struggle with many aspects of phylogenetic trees, including: (a) Students may not realize that each node/branch can be rotated to rearrange the groups without changing the nature of the relationships. For example, in Figure 15.16A, the position of the beaver and kangaroo can be reversed without changing any relationships represented in the phylogenetic tree. (b) The length of each branch is not meaningful and is not intended to be proportional to time. (c) The spacing between groups is not meaningful and does not denote the degree of divergence between them. Whether the tree is compressed or expanded in size, the information communicated in it remains the same. Teaching Tips 1. Emphasize to students that phylogenetic trees are tentative hypotheses. As new data are collected, the hypotheses are modified or rejected outright. Copyright © 2009 Pearson Education, Inc.

Lizards and snakes Crocodilians Pterosaurs Common ancestor of
dinosaurs, and birds Ornithischian dinosaurs Figure 15.16B A phylogenetic tree of reptiles. Saurischian dinosaurs Birds

Front limb Hind limb Eggs
Figure Fossil remains of Oviraptor and eggs. The orientation of the bones, which surround the eggs, suggests that the dinosaur died while incubating or protecting its eggs. Eggs

15.17 An organism’s evolutionary history is documented in its genome
Molecular systematics compares nucleic acids or other molecules to infer relatedness of taxa Scientists have sequenced more than 100 billion bases of nucleotides from thousands of species The more recently two species have branched from a common ancestor, the more similar their DNA sequences should be The longer two species have been on separate evolutionary paths, the more their DNA should have diverged Teaching Tips 1. Genetic relationships provide one strong line of evidence for the ancestral relationships of life. Fossils, anatomy, embryology, and biogeography can also be used to test these same relationships. Remind students that scientists prefer to use multiple lines of evidence to test hypotheses such as phylogenies. For the BLAST Animation DNA and RNA Compared, go to Animation and Video Files. Copyright © 2009 Pearson Education, Inc.

Lesser panda Procyonidae Raccoon Giant panda Spectacled bear Ursidae
Sloth bear Sun bear American black bear Asian black bear Figure A phylogenetic tree based on molecular data. Polar bear Brown bear 35 30 25 20 15 10 Pleistocene Oligocene Miocene Pliocene Millions of years ago

Different genes evolve at different rates DNA coding for conservative sequences (like rRNA genes) is useful for investigating relationships between taxa that diverged hundreds of millions of years ago This comparison has shown that animals are more closely related to fungi than to plants mtDNA evolves rapidly and has been used to study the relationships between different groups of Native Americans, who have diverged since they crossed the Bering Land Bridge 13,000 years ago Genetic relationships provide one strong line of evidence for the ancestral relationships of life. Fossils, anatomy, embryology, and biogeography can also be used to test these same relationships. Remind students that scientists prefer to use multiple lines of evidence to test hypotheses such as phylogenies. Teaching Tips 1. Genetic relationships provide one strong line of evidence for the ancestral relationships of life. Fossils, anatomy, embryology, and biogeography can also be used to test these same relationships. Remind students that scientists prefer to use multiple lines of evidence to test hypotheses such as phylogenies. Copyright © 2009 Pearson Education, Inc.

Homologous genes have been found in organisms separated by huge evolutionary distances 50% of human genes are homologous with the genes of yeast Gene duplication has increased the number of genes in many genomes The number of genes has not increased at the same rate as the complexity of organisms Humans have only four times as many genes as yeast Teaching Tips 1. Genetic relationships provide one strong line of evidence for the ancestral relationships of life. Fossils, anatomy, embryology, and biogeography can also be used to test these same relationships. Remind students that scientists prefer to use multiple lines of evidence to test hypotheses such as phylogenies. Copyright © 2009 Pearson Education, Inc.

15.18 Molecular clocks help track evolutionary time
Some regions of the genome appear to accumulate changes at constant rates Molecular clocks can be calibrated in real time by graphing the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record Molecular clocks are used to estimate dates of divergences without a good fossil record For example, a molecular clock has been used to estimate the date that HIV jumped from apes to humans Teaching Tips 1. Genetic relationships provide one strong line of evidence for the ancestral relationships of life. Fossils, anatomy, embryology, and biogeography can also be used to test these same relationships. Remind students that scientists prefer to use multiple lines of evidence to test hypotheses such as phylogenies. 2. Molecular clocks reveal the usefulness of corroborative data, since they can be made more precise through calibration against the fossil record or other evidence. This is not much different from the accuracy of a watch set to a time standard every week, every year, or every ten years. Copyright © 2009 Pearson Education, Inc.

Differences between HIV sequences
0.20 0.15 Differences between HIV sequences 0.10 Computer model of HIV 0.05 Figure Dating the origin of HIV-1 M with a molecular clock. The data points in the upper-right corner represent different HIV samples taken at known times. Explain that Figure shows how a molecular clock has been used to date the 1930s origin of HIV infection in humans. Samples of virus from different points in the epidemic were collected and compared. 1900 1920 1940 1960 1980 2000 Year

15.19 Constructing the tree of life is a work in progress
An evolutionary tree for living things has been developed, using rRNA genes Life is divided into three domains: the prokaryotic domains Bacteria and Archaea and the eukaryote domain Eukarya (including the kingdoms Fungi, Plantae, and Animalia) Molecular and cellular evidence indicates that Bacteria and Archaea diverged very early in the evolutionary history of life The first major split was divergence of Bacteria from other two lineages, followed by the divergence of the Archaea and Eukarya For some students, the discussion of the ambiguous relationships of early life and the three domains can be unsettling. Students who expect clear answers and sharp definitions may be uncomfortable with such ambiguity. Teaching Tips 1. The authors reference Module for information on horizontal gene transfer. If this module was not previously addressed, consider covering it in your final discussion of the early evolution of life. 2. For some students, the discussion of the ambiguous relationships of early life and the three domains can be unsettling. Students who expect clear answers and sharp definitions from science may be uncomfortable with such ambiguity. 3. The National Center for Science Education is an organization working to support the teaching of evolution and defend it against sectarian attack. Its website, contains a great deal of useful information Copyright © 2009 Pearson Education, Inc.

Most recent common ancestor of all living things
1 Most recent common ancestor of all living things 2 Gene transfer between mitochondrial ancestor and ancestor of eukaryotes 3 Gene transfer between chloroplast ancestor and ancestor of green plants Bacteria 3 2 1 Eukarya Figure 15.19A A phylogenetic tree depicting the origin of the three domains of life. Archaea 4 3 2 1 Billions of years ago

Eukarya Bacteria Archaea
Figure 15.19B Is the tree of life really a ring?

15.19 Constructing the tree of life is a work in progress
There have been two major episodes of horizontal gene transfer over time, with transfer of genes between genomes by plasmid exchange, viral infection, and fusion of organisms: Gene transfer between a mitochondrial ancestor and the ancestor of eukaryotes, Gene transfer between a chloroplast ancestor and the ancestor of green plants We are the descendents of Bacteria and Archaea Teaching Tips 1. The authors reference Module for information on horizontal gene transfer. If this module was not previously addressed, consider covering it in your final discussion of the early evolution of life. 2. For some students, the discussion of the ambiguous relationships of early life and the three domains can be unsettling. Students who expect clear answers and sharp definitions from science may be uncomfortable with such ambiguity. 3. The National Center for Science Education is an organization working to support the teaching of evolution and defend it against sectarian attack. Its website, contains a great deal of useful information Copyright © 2009 Pearson Education, Inc.

2.1 bya: First eukaryotes (single-celled) 1.2 bya: First multicellular eukaryotes 500 mya: Colonization of land by fungi, plants, and animals 3.5 bya: First prokaryotes (single-celled) 4 3.5 3 2.5 2 1.5 1 .5 Billions of years ago (bya)

(a) (b) (c) (d)

Systematics evolutionary relationships (a) (b) cladistics nucleotide
traces generates hypotheses for constructing evolutionary relationships shown in (a) based on using (b) cladistics seen in analysis identifies nucleotide sequences must distinguish from shared ancestral characters (f) using determine sequence of branch points (c) (d) (e)

Outgroup

You should now be able to
Compare the structure of the wings of pterosaurs, birds, and bats and explain how the wings are based upon a similar pattern Describe the four stages that might have produced the first cells on Earth Describe the experiments of Dr. Stanley Miller and their significance in understanding how life might have first evolved on Earth Describe the significance of protobionts and ribozymes in the origin of the first cells Copyright © 2009 Pearson Education, Inc.

Explain how and why mass extinctions and adaptive radiations may occur Explain how genes that program development are important in the evolution of life Define an exaptation, with a suitable example Distinguish between homologous and analogous structures and describe examples of each; describe the process of convergent evolution Copyright © 2009 Pearson Education, Inc.

Describe the goals of phylogenetic systematics; define the terms clade, monophyletic groups, shared derived characters, shared ancestral characters, ingroup, outgroup, phylogenetic tree, and parsimony Explain how molecular comparisons are used as a tool in systematics, and explain why some studies compare ribosomal RNA (rRNA) genes and other studies compare mitochondrial DNA (mtDNA) Copyright © 2009 Pearson Education, Inc.

Tracing Evolutionary History

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