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How Humans Evolved

INSTRUCTOR’S MANUAL AND TEST BANK

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Full file at http://testbank360.eu/test-bank-how-humans-evolved-5th-edition-boy

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How Humans EvolvedFIFTH EDITION

Robert Boyd and Joan B. Silk

Elizabeth ErhartTEXAS STATE UNIVERSITY

W • W • NORTON & COMPANY • NEW YORK • LONDON

INSTRUCTOR’S MANUAL AND TEST BANK

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Copyright © 2009, 2006, 2003, 2000, 1997 by W. W. Norton & Company, Inc.

All rights reserved

Printed in the United States of America

Composition by Roberta Flechner

Production manager: Eric Pier-Hocking

Fifth Edition

ISBN 978-0-393-93276-8 (pbk.)

W. W. Norton & Company, Inc., 500 Fifth Avenue, New York, N.Y. 10110wwnorton.com

W. W. Norton & Company Ltd., Castle House, 75/76 Wells Street, London W1T 3QT

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v

CONTENTS

Preface ix

Instructor’s Manual

Part One • How Evolution WorksChapter 1 | Adaptation by Natural Selection 3

Chapter 2 | Genetics 9

Chapter 3 | The Modern Synthesis 16

Chapter 4 | Speciation and Phylogeny 26

Part Two • Primate Ecology and BehaviorChapter 5 | Primate Diversity and Ecology 33

Chapter 6 | Primate Mating Systems 42

Chapter 7 | The Evolution of Cooperation 49

Chapter 8 | Primate Life Histories and the Evolution of Intelligence 56

Part Three • The History of the Human LineageChapter 9 | From Tree Shrew to Ape 62

Chapter 10 | From Hominoid to Hominin 67

Chapter 11 | Oldowan Toolmakers and the Origin of Human Life History 75

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vi / Contents

Chapter 12 | From Hominin to Homo 80

Chapter 13 | Homo sapiens and the Evolution of ModernHuman Behavior 89

Part Four • Evolution and Modern HumansChapter 14 | Human Genetic Variation 96

Chapter 15 | Evolution and Human Behavior 102

Chapter 16 | Human Mate Choice and Parenting 107

Appendix | Selected Classroom Films 113

Test Bank

Part One • How Evolution WorksChapter 1 | Adaptation by Natural Selection 121

Chapter 2 | Genetics 141

Chapter 3 | The Modern Synthesis 161

Chapter 4 | Speciation and Phylogeny 181

Part Two • Primate Ecology and BehaviorChapter 5 | Primate Diversity and Ecology 200

Chapter 6 | Primate Mating Systems 232

Chapter 7 | The Evolution of Cooperation 250

Chapter 8 | Primate Life Histories and the Evolution of Intelligence 269

Part Three • The History of the Human LineageChapter 9 | From Tree Shrew to Ape 281

Chapter 10 | From Hominoid to Hominin 299

Chapter 11 | Oldowan Toolmakers and the Origin of Human Life History 318

Chapter 12 | From Hominin to Homo 333

Chapter 13 | Homo sapiens and the Evolution of ModernHuman Behavior 353

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Contents / vii

Part Four • Evolution and Modern HumansChapter 14 | Human Genetic Variation 371

Chapter 15 | Evolution and Human Behavior 391

Chapter 16 | Human Mate Choice and Parenting 409

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ix

PREFACE

This book accompanies Robert Boyd and Joan Silk’s How Humans Evolved, FifthEdition, and comprises two sections, an Instructor’s Manual followed by a TestBank. The Instructor’s Manual is organized by chapter following the table ofcontents in How Humans Evolved. The Test Bank is also organized by textchapter.

Each chapter in the Instructor’s Manual offers teachers two discussions ofthe content: “Key Concepts” and “Answers to Study Questions.” Key Conceptdiscussions review the chapter’s high points to provide explanatory assistance,especially on topics students may find more challenging. The Answers to StudyQuestions provide concise replies to the end-of-chapter Study Questions foundin the text.

Each chapter in the Test Bank offers teachers multiple-choice ques tions,true/false questions, and essay questions. Three items accompany eachmultiple-choice or true/false question: the correct answer, the level of relativedifficulty, and the topic. The “Level of Difficulty” is a relative scale from “1” to“3,” with 3 indicating the highest degree of difficulty. Most questions offer amedium difficulty level of “2.” The “Topic” given for each question is the head -ing for the chapter section in which the question’s answer may be found. TheTest Bank is also available in computer file format for faculty who prefer adigital form.

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Instructor’s Manual

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3

Key Concepts

The purpose of this chapter is to introduce and develop Darwin’s theory of nat -ural selection, the concept which underlies the rest of the textbook. We presentcomplex adaptations as a phenomenon requiring special explanation, returningto the example of the eye throughout the chapter.

1. Before Darwin, there was no adequate biological explanation for the existence ofadaptations; such designs in nature were used as proofs of the existence of God onthe argument that something with the hallmarks of design must have a creator.

2. Darwin’s theory of natural selection states that adaptation will result when thesethree postulates hold: (1) there is a struggle for existence among organisms, (2) thereis variation among organisms in their ability to survive and reproduce, and (3) thisvariation is transmissible from parents to offspring.

The beauty of Darwin’s theory of natural selection in explaining adaptationlies in its simplicity. Nevertheless, there are several problem areas for students.One is “population thinking.” We use Peter and Rosemary Grant’s extensivework on Darwin’s finches as an empirical demonstration of natural selection at work in living populations. Emphasize how Darwin’s three postulates areexemplified by the events the Grants recorded, leading to directed, adaptivechange in the population of finches. Contrast for students essentialist thinkingand population thinking: species are not fixed categories, but populations of vari -able individuals. Natural selection is responsible for both stability (stabilizingselection) and change (directional selection) within species.

Adaptation by Natural SelectionCHAPTER 1

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4 / CHAPTER 1

A second problem area for students is understanding the biological level atwhich adaptations occur. We emphasize that natural selection acts on individ -uals and therefore leads to adaptations at the level of the individual organism. Itis very important to emphasize that natural selection can and does lead to adap -tations that simultaneously benefit individuals but decrease the competitiveability of groups—that is, traits that are beneficial for the individual but deleteri -ous for the group or species as a whole. Merely memorizing Darwin’s postulatesdoes not usually allow students to come naturally to this conclusion.

3. Natural selection produces complex adaptations through a series of incrementalsteps, each of which is an adaptive improvement over its immediate predecessor.

Having given empirical evidence of natural selection in the wild, we returnto the problem of the evolution of complex adaptations. Some still find it in -credible that natural selection can produce complex, functionally integrateddesigns like the eye. The basic problem is that an eye could not be produced bynatural selection in a single jump because the probability of such an occurrenceis astronomically low. To illustrate this, we use Richard Dawkins’ analogy ofmonkeys typing randomly and producing the sentence, “Methinks it is a weasel.”The essential point to make is that natural selection cannot produce complexadaptations in a single generation, but natural selection can be very powerfulin producing complex adaptations if successive approximations are retained.

This insight, however, leaves us with the dilemma that each intermediatestep must be favored by selection. The eyes of living mollusks are used toillustrate potential benefits of each small step in the evolution of the eye, froma single light-sensitive cell to the fully functional eye.

4. Several lines of evidence suggest that natural selection can produce even complexchanges in remarkably short periods of time. First, using artificial selection peoplecan intentionally and unintentionally create dozens of different forms of a speciesin just a few hundred or a few thousand years (e.g., domesticated dogs and pigeons).Second, a recent study of fish from the genus Poeciliopsis shows that three differ -ent types of placenta evolved in this genus in less than 2.4 million years. Third,theoretical studies of the evolution of the eye in an aquatic organism have shownthat the complete structure of the eye can evolve from 1829 changes of 1% each.Therefore, in an organism with a short generation time, a complex eye could evolvein less than a million years.

5. Natural selection requires variation. Darwin’s difficulty with his theory of naturalselection occurred because the blending theory of inheritance prevalent at the timewas incompatible with the maintenance of variation.

Darwin’s difficulties concerning the maintenance of variation are solvedwith a modern understanding of inheritance, which is dealt with in the next



Adaptation by Natural Selection / 5

chapter. Once students have a basic understanding of genetics, natural selectionand modern genetics are wed in Chapter 3.

Answers to Study Questions

1. It is sometimes observed that offspring do not resemble their parents for somecharacter, even though the character varies in the population. Suppose that thiswere the case for beak depth in the medium ground finch. (a) What would the plotof offspring beak depth against parental beak depth look like? (b) Plot the meandepth in the population among (i) adults before a drought, (ii) adults after a year ofdrought, and (iii) offspring.

(a) Plot parents and offspring on the x- and y-axes of a graph. It may beuseful to first show students graphic examples of positive and negative correla -tions. Then show the hypothetical case with the scatter plot spread out randomlyover the graph, indicating no correlation between parents and offspring.

Offs

prin

g

Parents

Positive Correlation

Offs

prin

g

Parents

Negative Correlation



6 / CHAPTER 1

(b) This part requires a different type of graph than part (a), which throwssome students off. Several graphic representations are capable of conveyingthe meaning. Before a drought the mean beak depth is at some arbitrary value.After selection, the mean rises. Offspring have the same mean as before selectionbecause there is no heritability.

To make the results clear, refer back to the graph showing no correlation inpart (a). That is, demonstrate that parents with any size beak produce offspringwith beaks of all sizes, so that the average is the same even though the parentshave the largest beaks. The lesson is that if there is no heritability (postulate 3),then there is no selection.

Mea

n B

eak

Dep

th

BeforeSelection

AfterSelection

Offspring

Offs

prin

g

Parents

No Correlation



Adaptation by Natural Selection / 7

2. Many species of animals are engage in cannibalism. This practice certainly reducesthe ability of the species to survive. Is it possible that cannibalism could arise bynatural selection? If so, with what adaptive advantage?

Yes, it is possible for cannibalism to arise by natural selection because itmay confer nutritive advantages to the cannibal. This is true even though itmay lead to the extinction of the species. First, it is often a good idea to definecannibalism (the act of eating a conspecific, not just humans eating humans).A discussion of cannibalism in humans and other animals can be entertaining.Adaptive examples of cannibalism in the animal kingdom include mantids(female eats male during copulation), Jerusalem crickets (female eats male aftercopulation), and perhaps humans, for example, under conditions of starvation(for example, the Donner party) or during ritualized cannibalism (for example,among some indigenous New Guinea peoples).

The key phrases for students to understand in this question are “the abilityof the species to survive” and “adaptive advantage.” Ability of the species to sur -vive is a reference to adaptation at the group level, which requires selection atthat level. Selection among individuals results in adaptations at the individuallevel, which may or may not result in group adaptation. For adaptations tooccur at the level of the group or species (which is not just the by-product ofindividual adaptations), there must be selection among groups or species, aprocess considered unlikely by evolutionary biologists. Therefore, adaptiveadvantage will normally refer to individual advantage. The primary difficultyfor students is the tendency to think about humans and other animals from agroup or species point of view.

3. Some insects mimic dung. Ever since Darwin, biologists have explained this as aform of camouflage: selection favors individuals who most resemble dung becausethey are less likely to be eaten. Recently, Harvard paleontologist Stephen J. Gouldhas objected to this explanation. He argues that while selection could perfect suchmimicry once it evolved, it could not cause the resemblance to arise in the first place.“Can there be any edge,” Gould asks, “to looking 5% like a turd?” (quoted on p. 81in R. Dawkins, 1986, The Blind Watchmaker, W. W. Norton). Can you think of a reason why looking 5% like a turd would be better than not looking at all likea turd?

Looking 5% like a turd can be better than nothing at all. In a population ofother individuals who look nothing like a turd, resembling a turd a little bitmay decrease the probability of being spotted and eaten by a predator. Any slightblending into the background or slight increase in resemblance to somethinginedible may increase the probability that a predator who is flying by quickly,or from some distance, or searching at twilight will miss the food item. If this isthe case, then selection will favor those individuals because, on average, theyhave slightly better survival chances than other individuals in the population.



8 / CHAPTER 1

Over time, the population will come to be characterized by such individuals.The key element is that although looking 5% like a turd is far worse than look -ing 100% like one, looking 5% like a turd is an improvement in a populationlooking nothing at all like turds.

4. In the late 1800s an American biologist named Hermon Bumpus collected a largenumber of sparrows that had been killed in a severe ice storm. He found that birdswhose wings were about average length were rare among the dead birds. Whatkind of selection is this? What effect would this episode of selection have on themean wing length in the population?

The question states that birds with average wing length were rare amongdead birds, that is, birds with average wing length survived the storm whilebirds with extreme wing lengths (either short or long) died. This is a form ofstabilizing selection. At this time, contrasting stabilizing with directionalselection can be helpful. Stabilizing selection would have no effect on themean because it only culls away at the tails of the distribution.

Stabilizing Selection

Directional Selection



9

GeneticsCHAPTER 2

Key Concepts

In this chapter we introduce the mechanics of genetic inheritance, beginningwith Mendel’s experiments and continuing to cell division and the role ofchromosomes as a way of providing additional evidence for Mendel’s laws, andfinishing with molecular genetics. This should prepare students for Chapter 3,in which Darwinian evolutionary theory is wedded to modern genetic theory(the “modern synthesis”).

1. Mendel’s law of segregation states that inheritance is particulate. The law of inde -pendent assortment states that the probability of inheriting one trait does not affectthe probability of inheriting another trait.

Here we provide Mendel’s basic experimental design and the laws hederived from his results. We return to Mendel again after knowledge of themechanics of inheritance will provide students with a mechanical understandingof Mendel’s laws.

2. In mitosis, a diploid mother cell divides into two identical haploid daughter cells.Chromosomes are linear bodies that occur in pairs inside the cell nucleus. Theycontain the hereditary material, are replicated during mitosis, and are passed on todaughter cells. Thus, every cell of a living body contains the same chromosomes.

3. Gametes are produced through meiosis. A diploid mother cell gives rise to four hap -loid daughter cells, each containing only one chromosome from each homologouspair. Haploid sperm meet haploid ova and produce diploid zygotes. A zygote dividesmitotically, producing another individual.



10 / CHAPTER 2

The modern model of cell division and the role of chromosomes provide amaterial explanation for Mendel’s laws. True breeding lines consist of homozy -gous individuals. A cross betweenhomozygous lines produces an F1 gen erationof heterozygotes. However, if one allele is dominant, only one phenotype isobserved. In the F2 generation, however, the recessive trait appears again inrecessive homozygotes. Thus, inheritance is particulate, not blending (Mendel’sfirst law).

Mendel’s second law states that different traits are inherited independentlyof one another. This is true if the loci for each trait are on different chromo -somes. However, if two loci are tightly linked on the same chromosome theymay segregate into gametes as a unit. Crossing over in meiosis causes theexchange of material between homologous chromosomes and can break uplinkage units.

4. DNA is an unusually stable molecule in which hereditary information is encoded.The stability of DNA results in messages that are preserved and transmittedfaithfully.

DNA structure is that of a double helix, consisting of a series of four bases,adenine, thymine, cytosine, and guanine. Replication of DNA during theproduction of daughter cells is possible due to base pair complementarity. Thesequence of the four bases along DNA molecules constitutes a code thatprovides for an infinite number of messages.

5. DNA affects phenotypes in a number of ways, including (1) DNA in codingsequences specifies the structure of proteins, (2) DNA in regulatory sequencesdetermines the conditions under which the message in the coding sequence will beexpressed, and (3) DNA specifies the structure of several kinds of RNA moleculesthat are critical to protein synthesis and gene regulation.

Proteins regulate the biochemical processes of organisms. Proteins consistof a series of amino acids (the primary structure) that specifies the folded,tertiary structure and its function. DNA specifies the primary structure andthus the function of proteins. A sequence of triplet base sequences, or codons,codes for the sequence of amino acids in a protein. The genetic code isredundant, with 64 codons and 20 amino acids, from which it follows thatmany mutations have no effect on the structure and function of proteins.

6. DNA specifies the primary structure of a protein.

It is at the ribosomes that protein synthesis takes place. DNA is transcribedinto messenger RNA (mRNA), which leaves the nucleus and migrates into the



Genetics / 11

cytoplasm to the ribosomes. At the ribosomes, mRNA passes through a bindingsite one codon at a time. As codons of mRNA enter the binding site, transferRNA (tRNA) with complementary anticodons is bound to the mRNA. Aminoacids are detached from the tRNA and form the chain of amino acids thatmakes up the protein.

7. In eukaryotes, the same DNA sequence can produce many different mRNAs andcode for many different proteins. This happens through the process of alternativesplicing.

Recombinant DNA technology has revealed that within a DNA sequencethat codes for a protein there are coding sequences, or exons, that are interruptednoncoding sequences, or introns. The introns are snipped out as a DNA sequenceis copied to make an mRNA molecule, leaving the exons behind. However, whenthe exons are spliced together by organelles called “splice somes,” not all of theexons may be in place. Thus, a mature strand of mRNA may not contain all of itsoriginal exons; this means that the same DNA sequence can produce manydifferent mRNAs and code for many different proteins.

8. The expression of structural genes is often affected by regulatory genes.

For example, glucose is the primary source of energy for E. coli. Wheneverglucose is absent, a regulatory gene called an activator switches on theproduction of lactose, as well as a number of other genes needed to metabolizelactose. However, whenever glucose is present, a regulatory gene called arepressor inhibits the production of lactose. This multiple regulatory sequenceallows for combinatorial control of the expression of lactose in E. coli.

9. Not all DNA carries a message.

Until recently, it was thought that the majority of the 98% of the genomethat lies outside of exons was “junk” DNA. However, we now think that at leasthalf of the genome is expressed as noncoding RNA ((ncRNA). Although thefunction of ncRNA is unknown, one form of ncRNA, called microRNA(miRNA), helps to regulate the transition of mRNA into a protein. This isaccomplished when miRNA binds to complementary mRNA molecules andprevents them from being translated into protein, thus providing analternative means for gene regulation.



12 / CHAPTER 2

Answers to Study Questions

1. Explain why Mendel’s laws follow from the mechanics of meiosis.

Following alleles across a single generation will illustrate the law of parti -culate inheritance: in meiosis, haploid gametes are formed in which only oneof each pair of alleles is present. In zygote formation, two gametes come togetherand a new combination of two alleles—one from each parent—is created. Oneor both of them may contribute to the phenotype of the organism, but they donot blend together in any way. Furthermore, they segregate as separate, distinctunits once again during the production of new gametes.

Going through meiosis with two pairs of chromosomes will illustrate thelaw of independent assortment: during meiosis, when one pair of homologouschromosomes lines up in the center of the cell, which of the pair goes intowhich daughter cell is not influenced by the other pair of homologous chro -mo somes. Only when alleles are at different loci on the same chromosome isthere dependent assortment into gametes. The degree to which they segregateinto different gametes is a function of their distance from each other along thechromosome, that is, of the probability of a crossing-over event between them.The closer together are two loci, the lower the probability of a crossing-overevent between them.

2. Mendel did experiments in which he kept track of the inheritance of seed texture(wrinkled or smooth). First, he created true-breeding lines: parents with smoothseeds produced offspring with smooth seeds, and parents with wrinkled seeds pro -duced offspring with wrinkled seeds. When he crossed wrinkled and smooth seedsfrom these true-breeding lines, all of the offspring were smooth. Which trait is dom -inant? What happened when he crossed members of the F1? What would havehappened if he backcrossed members of the F1 generation with individuals from atrue-breeding line (like their parents) with smooth seeds? What about crossesbetween the F1 generation and the wrinkled true-breeding line?

There are two true-breeding lines, smooth seeds (BB) and wrinkled seeds(bb). When they are crossed, offspring (Bb) are smooth, so the smooth trait isdominant. If members of the F1 generation are crossed with each other (Bb × Bb),offspring would appear in a 1:2:1 (BB:Bb:bb) genotypic ratio, and a 3:1 (smooth:wrinkled) phenotypic ratio.

A backcross of F1 with true-breeding smooth line (Bb × BB) would producea 1:1 (BB:Bb) genotypic ratio, but all offspring would be smooth. A backcrossbetween F1 and a true breeding wrinkled line (Bb × bb) would produce a 1:1(Bb:bb) genotypic ratio and a 1:1 (smooth:wrinkled) phenotypic ratio. Manystudents solve these problems best by using Punnet squares:



Genetics / 13

3. Mendel also did experiments in which he kept track of two traits. For example, hecreated true-breeding lines of smooth-green and wrinkled-yellow, and then crossedthese lines to produce an F1 generation. What were the F1 individuals like? He thencrossed the members of the F1 generation to form an F2 generation. Assuming thatthe seed color locus and the seed texture locus are on different chromosomes, calcu -late the ratio of each of the four phenotypes among the F2 generation. Calculate theratios (approximately) assuming that the two loci were very close together on thesame chromosome.

There are true-breeding lines of smooth-green (BBaa) and wrinkled-yellow(bbAA). The F1 generation are all smooth-yellow (BbAa). If seed color and textureloci are on different chromosomes, then F2 (BbAa × BbAa) consists of 9 smooth-yellow: 3 smooth-green: 3 wrinkled-yellow: 1 wrinkled-yellow. The gen eralratio rule is 9 dominant-dominant combinations: 3 of each dominant-recessivecombination: 1 recessive-recessive combination.

If there is very tight linkage with no crossing-over between the two loci, F2would consist of 3 smooth-green, and 1 wrinkled-yellow. Here are the Punnetsquares:

Bbb

B

Bb

B

Bbb Bb

BBB

B

Bb

b

Bbb bb

BBB

B

BB

B

Bbb Bb

BbB

b

Bb

b

bbb bb



14 / CHAPTER 2

4. Many organisms, like birds and mammals, maintain their body temperatureswell above the air temperature. Such organisms, called homeotherms, accomplishthis task with specific physiological mechanisms. Other organisms, called poikilo -therms, regulate their body temperatures by moving closer to or further away fromsources of heat. Use what you learned about chemical reactions to develop ahypothesis that explains why animals do this.

Organisms can regulate body temperature through physiological or be -havioral means. In each case, the probable function is to maintain the optimaltemperature for the biochemical reactions of living systems, such as those that enzymes perform. For instance, too much heat can destroy the tertiarystructure of proteins, which they cannot regain, and cold slows down chemicalreactions.

5. Why is DNA so well suited for carrying information?

DNA is so well suited for carrying information because (1) it can carry aninfinite number of messages (encoded by different base sequences) each with

AABBAB

AB

AaBB

aB

AaBBaB aaBB

AABb

Ab

AaBb

ab

AaBb aaBb

AABbAb AaBb

AaBbab aaBb

AAbb Aabb

Aabb aabb

BBAABA

BA

BbAa

ba

BbAaba bbaa



Genetics / 15

equal stability, (2) due to base pair complementarity, information is faithfullycopied and passed on to daughter cells, and (3) even when there is mutation,redundancy in the genetic code means that many “silent” mutations will notaffect function.

6. Recall the discussion about crossing over to explain why introns might increase therate of recombination between surrounding exons.

Introns are noncoding regions of DNA within a gene. Exons are the codingregions. Various explanations for introns have been proposed. Two mentionedin the text are (1) introns are selfish DNA, and (2) introns divide a gene intoseparate functional parts. If introns are the locations where crossing-overevents occur, then the probability of crossing-over within a gene would be afunction of the number of crossing-over spots, or the number of introns. This isconsistent with the idea that introns separate functional units that might beinterchanged—if introns were distributed randomly throughout a gene, thenexchange of parts might be too destructive to sequences capable of producingfunctional proteins. If, however, exons constitute functional subunits of a gene,then exchange of these functional subunits to create novel recombinationswould not be destructive.



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