evolution - gbv

EVOLUTION

THIRD EDITION

MARK RIDLEY

BlackwellPublishing

Brief Contents

Full Contents

Preface

VII

xxii

PART1. INTRODUCTION

1. The Rise of Evolutionary Biology

2. Molecular and Mendelian Genetics

3. The Evidence for Evolution

4. Natural Selection and Variation

3

21

43

71

PART 2. EVOLUTIONARY GENETICS 93

5. The Theory of Natural Selection

6. Random Events in Population Genetics

7. Natural Selection and Random Drift in Molecular Evolution

8. . Two-locus and Multilocus Population Genetics

9. Quantitative Genetics

95137155194222

PART 3. ADAPTATION AND NATURAL SELECTION 253

10. Adaptive Explanation

11. The Units of Selection

12. Adaptations in Sexual Reproduction

255292313

PART 4. EVOLUTION AND DIVERSITY 345

13. Species Concepts and Intraspecific Variation

14. Speciation

15. The Reconstruction of Phylogeny

16. Classification and Evolution

17. Evolutionary Biogeography

347

381

423

471

492

vi | Brief Contents

PART 5. MACROEVOLUTION 521

18. The History of Life 523

19. Evolutionary Genomics 556

20. Evolutionary Developmental Biology 572

21. Rates of Evolution 590

22. Coevolution 613

23. Extinction and Radiation 643

Glossary 682

Answers to Study and Review Questions 690

References 699

Index 733

Color plate section between pp. 70 and 71

Full Contents

Preface xxii

PART1. INTRODUCTION 1

1. The Rise of Evolutionary Biology 3

1.1 Evolution means change in living things by descent with modification 41.2 Living things show adaptations 51.3 A short history of evolutionary biology 6

1.3.1 Evolution before Darwin 71.3.2 Charles Darwin 91.3.3 Darwin's reception 101.3.4 The modern synthesis 14

Summary Further reading Study and review questions

2. Molecular and Mendelian Genetics 21

2.1 Inheritance is caused by DNA molecules, which are physicallypassed from parent to offspring 22

2.2 DNA structurally encodes information used to buildthe body's proteins 23

2.3 Information in DNA is decoded by transcription and translation 252.4 Large amounts of non-coding DNA exist in some species 272.5 Mutational errors may occur during DNA replication 272.6 Rates of mutation can be measured 312.7 Diploid organisms inherit a double set of genes 332.8 Genes are inherited in characteristic Mendelian ratios 342.9 Darwin's theory would probably not work if there was a

non-Mendelian blending mechanism of heredity 37Summary Further reading Study and review questions

3. The Evidence for Evolution 43

3.1 We distinguish three possible theories of the history of life 443.2 On a small scale, evolution can be observed in action 453.3 Evolution can also be produced experimentally 473.4 Interbreeding and phenotypic similarity provide two concepts of

species 48

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3.5 Ring "species" show that the variation within a species can beextensive enough to produce a new species 50

3.6 New, reproductively distinct species can be produced experimentally 53• 3.7 Small-scale observations can be extrapolated over the long term 543.8 Groups of living things have homologous similarities 553.9 Different homologies are correlated, and can be hierarchically classified 613.10 Fossil evidence exists for the transformation of species 643.11 The order of the main groups in the fossil record suggests they have

evolutionary relationships 653.12 Summary of the evidence for evolution 663.13 Creationism offers no explanation of adaptation 673.14 Modern "scientific creationism" is scientifically untenable 67Summary Further reading Study and review questions

4. Natural Selection and Variation 71

4.1 In nature, there is a struggle for existence 724.2 Natural selection operates if some conditions are met 744.3 Natural selection explains both evolution and adaptation 754.4 Natural selection can be directional, stabilizing, or disruptive 764.5 Variation in natural populations is widespread 814.6 Organisms in a population vary in reproductive success 854.7 New variation is generated by mutation and recombination 874.8 Variation created by recombination and mutation is random

with respect to the direction of adaptation 88Summary Further reading Study and review questions

PART 2. EVOLUTIONARY GENETICS 93

5. The Theory of Natural Selection 95

5.1 Population genetics is concerned with genotype and gene frequencies 965.2 An elementary population genetic model has four main steps 975.3 Genotype frequencies in the absence of selection go to the Hardy-

Weinberg equilibrium . 985.4 We can test, by simple observation, whether genotypes in a population

are at the Hardy-Weinberg equilibrium 1025.5 The Hardy-Weinberg theorem is important conceptually,

historically, in practical research, and in the workings oftheoretical models 103

5.6 The simplest model of selection is for one favored allele at one locus 1045.7 The model of selection can be applied to the peppered moth 108

5.7.1 Industrial melanism in moths evolved by natural selection 1085.7.2 One estimate of the fitnesses is made using the rate of change

in gene frequencies 109

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5.7.3 A second estimate of the fitnesses is made from the survivorship1 of the different genotypes in mark-recapture experiments 111

5.7.4 The selective factor at work is controversial, but bird predationwas probably influential 112

5.8 Pesticide resistance in insects is an example of natural selection 1155.9 Fitnesses are important numbers in evolutionary theory and can be

estimated by three main methods 1185.10 Natural selection operating on a favored allele at a single locus is not

meant to be a general model of evolution 1205.11 A recurrent disadvantageous mutation will evolve to a calculable

equilibrial frequency 1215.12 Heterozygous advantage 123

5.12.1 Selection can maintain a polymorphism when theheterozygote is fitter than either homozygote 123

5.12.2 Sickle cell anemia is a polymorphism with heterozygousadvantage 124

5.13 The fitness ofa genotype may depend on its frequency 1275.14 Subdivided populations require special population genetic principles 129

5.14.1 A subdivided set of populations have a higher proportion ofhomozygotes than an equivalent fused population: this is theWahlund effect 129

5.14.2 Migration acts to unify gene frequencies between populations 1305.14.3 Convergence of gene frequencies by gene flow is illustrated

by the human population of the USA 1325.14.4 A balance of selection and migration can maintain genetic

differences between subpopulations 132Summary Further reading Study and review questions

6. Random Events in Population Genetics 137

6.1 The frequency of alleles can change at random through time in aprocess called genetic drift 138

6.2 A small founder population may have a non-representative sampleof the ancestral population's genes 140

6.3 One gene can be substituted for another by random drift 1426.4 Hardy-Weinberg "equilibrium" assumes the absence of genetic drift 1456.5 Neutral drift over time produces a march to homozygosity 1456.6 A calculable amount of polymorphism will exist in a population

because of neutral mutation 1506.7 Population size and effective population size 151Summary Further reading Study and review questions

7. Natural Selection and Random Drift inMolecular Evolution 155

7.1 Random drift and natural selection can both hypothetically explainmolecular evolution 156

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7.2 Rates of molecular evolution and amounts of genetic variation canbe measured 159

7.3 Rates of molecular evolution are arguably too constant for a processcontrolled by natural selection 164

7.4 The molecular clock shows a generation time effect 1677.5 The nearly neutral theory 170

7.5.1 The "purely" neutral theory faces several empirical problems 1707.5.2 The nearly neutral theory of molecular evolution posits a class

of nearly neutral mutations 1717.5.3 The nearly neutral theory can explain the observed facts better

than the purely neutral theory 1737.5.4 The nearly neutral theory is conceptually closely related to the

original, purely neutral theory 1747.6 Evolutionary rate and functional constraint 175

7.6.1 More functionally constrained parts of proteins evolve atslower rates 175

7.6.2 Both natural selection and neutral drift can explain the trendfor proteins, but only drift is plausible for DNA 177

7.7 Conclusion and comment: the neutralist paradigm shift 1787.8 Genomic sequences have led to new ways of studying molecular

evolution 1797.8.1 DNA sequences provide strong evidence for natural selection

on protein structure 1807.8.2 A high ratio of non-synonymous to synonymous changes

provides evidence of selection 1817.8.3 Selection can be detected by comparisons of the dN/dS ratio

within and between species 1847.8.4 The gene for lysozyme has evolved convergently in cellulose-

digesting mammals 1867.8.5 Codon usages are biased 1877.8.6 Positive and negative selection leave their signatures in

DNA sequences 1897.9 Conclusion: 35 years of research on molecular evolution 190Summary Further reading Study and review questions

8. Two-locus and Multilocus Population Genetics 194

8.1 Mimicry in Papilio is controlled by more than one genetic locus 1958.2 Genotypes at different loci in Papilio memnon axe coadapted 1978.3 Mimicry in Heliconius is controlled by more than one gene, but

they are not tightly linked 1978.4 Two-locus genetics is concerned with haplotype frequencies 1998.5 Frequencies ofhaplotypes may or may not be in linkage equilibrium 1998.6 Human HLA genes are a multilocus gene system 2038.7 Linkage disequilibrium can exist for several reasons 2048.8 Two-locus models of natural selection can be built 206

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8.9 Hitch-hiking occurs in two-locus selection models 2108.10 Selective sweeps can provide evidence of selection in DNA sequences 2108.11 Linkage disequilibrium can be advantageous, neutral, or

disadvantageous 2128.12 Wright invented the influential concept of an adaptive topography 2148.13 The shifting balance theory of evolution 216Summary Further reading Study and review questions

9. Quantitative Genetics 222

9.1 Climatic changes have driven the evolution of beak size in one ofDarwin's finches 223

9.2 Quantitative genetics is concerned with characters controlled bylarge numbers of genes 226

9.3 Variation is first divided into genetic and environmental effects 2289.4 Variance of a character is divided into genetic and environmental effects 2319.5 Relatives have similar genotypes, producing the correlation between

relatives 2349.6 Heritability is the proportion of phenotypic variance that is additive 2359.7 A character's heritability determines its response to artificial selection 2369.8 Strength of selection has been estimated in many studies of natural

populations 2409.9 Relations between genotype and phenotype may be non-linear,

producing remarkable responses to selection 2429.10 Stabilizing selection reduces the genetic variability of a character 2459.11 Characters in natural populations subject to stabilizing selection

show genetic variation 2469.12 Levels of genetic variation in natural populations are imperfectly

understood 2479.13 Conclusion 249Summary Further reading Study and review questions

PART 3. ADAPTATION AND NATURAL SELECTION 253

10. Adaptive Explanation 255

10.1 Natural selection is the only known explanation for adaptation 25610.2 Pluralism is appropriate in the study of evolution, not of adaptation 25910.3 Natural selection can in principle explain all known adaptations 25910.4 New adaptations evolve in continuous stages from pre-existing

adaptations, but the continuity takes various forms 26310.4.1 In Darwin's theory, no special process produces

evolutionary novelties 26310.4.2 The function of an adaptation may change with little

change in its form 26410.4.3 A new adaptation may evolve by combining unrelated parts 265

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10.5 Genetics of adaptation 26610.5.1 Fisher proposed a model, and microscope analogy, to

explain why the genetic changes in adaptive evolutionwill be small 266

10.5.2 An expanded theory is needed when an organism is not nearan adaptive peak 268

10.5.3 The genetics of adaptation is being studied experimentally 26810.5.4 Conclusion: the genetics of adaptation 270

10.6 Three main methods are used to study adaptation 27010.7 Adaptations in nature are not perfect 272

10.7.1 Adaptations maybe imperfect because of time lags 27210.7.2 Genetic constraints may cause imperfect adaptation 27410.7.3 Developmental constraints may cause adaptive imperfection 27510.7.4 Historic constraints may cause adaptive imperfection 28110.7.5 An organism's design may be a trade-off between different

adaptive needs 28410.7.6 Conclusion: constraints on adaptation 284

10.8 How can we recognize adaptations? 28610.8.1 The function of an organ should be distinguished from

the effects it may have 28610.8.2 Adaptations can be defined by engineering design or

reproductive fitness 287Summary Further reading Study and review questions

11. The Units of Selection 292

11.1 What entities benefit from the adaptations produced by selection? 29311.2 Natural selection has produced adaptations that benefit various

levels of organization 29411.2.1 Segregation distortion benefits one gene at the expense of

its allele 29411.2.2 Selection may sometimes favor some cell lines relative to

other cell lines in the same body 29511.2.3 Natural selection has produced many adaptations to

benefit organisms 29611.2.4 Natural selection working on groups of close genetic

relatives is called kin selection 29811.2.5 Whether group selection ever produces adaptations for the

benefit of groups has been controversial, though mostbiologists now think it is only a weak force in evolution 301

11.2.6 Which level in the hierarchy of organization levels willevolve adaptations is controlled by which level showsheritability 305

11.3 Another sense of "unit of selection" is the entity whose frequency isadjusted directly by natural selection 306

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11.4 The two senses of "unit of selection" are compatible: onespecifies the entity that generally shows phenotypic adaptations,the other the entity whose frequency is generally adjusted bynatural selection 310


12. Adaptations in Sexual Reproduction 313

12.1 The existence of sex is an outstanding, unsolved problem inevolutionary biology 31412.1.1 Sex has a 50% cost 31412.1.2 Sex is unlikely to be explained by genetic constraint 31512.1.3 Sex can accelerate the rate of evolution 31612.1.4 Is sex maintained by group selection? 318

12.2 There are two main theories in which sex may have a short-termadvantage 32012.2.1 Sexual reproduction can enable females to reduce the

number of deleterious mutations in their offspring 32012.2.2 The mutational theory predicts U >1 32112.2.3 Coevolution of parasites and hosts may produce rapid

environmental change 32312.3 Conclusion: it is uncertain how sex is adaptive 32712.4 The theory of sexual selection explains many differences between

males and females 32712.4.1 Sexual characters are often apparently deleterious 32712.4.2 Sexual selection acts by male competition and

female choice 32812.4.3 Females may choose to pair with particular males 32912.4.4 Females may prefer to pair with handicapped males,

because the male's survival indicates his high quality 33112.4.5 Female choice in most models of Fisher's and Zahavi's

theories is open ended, and this condition can be tested 33212.4.6 Fisher's theory requires heritable variation in the male

character, and Zahavi's theory requires heritable variationin fitness 333

12.4.7 Natural selection may work in conflicting ways on malesand females 335

12.4.8 Conclusion: the theory of sex differences is well worked outbut incompletely tested 336

12.5 The sex ratio is a well understood adaptation 33712.5.1 Natural selection usually favors a 50 : 50 sex ratio 33712.5.2 Sex ratios may be biased when either sons or daughters

disproportionately act as "helpers at the nest" 33912.6 Different adaptations are understood in different levels of detail 341Summary Further reading Study and review questions

xiv | Full Contents

PART 4. EVOLUTION AND DIVERSITY 345

13. Species Concepts and Intraspecific Variation 347

13.1 In practice species are recognized and defined by phenetic characters 34813.2 Several closely related species concepts exist 350

13.2.1 The biological species concept 35113.2.2 The ecological species concept 35313.2.3 The phenetic species concept 354

13.3 Isolating barriers 35513.3.1 Isolating barriers prevent interbreeding between species 35513.3.2 Sperm or pollen competition can produce subtle

prezygotic isolation 35613.3.3 Closely related African cichlid fish species are prezygotically

isolated by their color patterns, but are not postzygoticallyisolated 357

13.4 Geographic variation within a species can be understood in termsof population genetic and ecological processes 35913.4.1 Geographic variation exists in all species and can be caused

by adaptation to local conditions 35913.4.2 Geographic variation may also be caused by genetic drift 36013.4.3 Geographic variation may take the form of a cline 362

13.5 "Population thinking" and "typological thinking" are two ways ofthinking about biological diversity 363

13.6 Ecological influences on the form of a species are shown by thephenomenon of character displacement 366

13.7 Some controversial issues exist between the phenetic, biological,and ecological species concepts 36713.7.1 The phenetic species concept suffers from serious

theoretical defects 36813.7.2 Ecological adaptation and gene flow can provide

complementary, or in some cases competing, theories ofthe integrity of species 369

13.7.3 Both selection and genetic incompatibility provideexplanations of reduced hybrid fitness 373

13.8 Taxonomic concepts may be nominalist or realist 37413.8.1 The species category 37413.8.2 Categories below the species level 37513.8.3 Categories above the species level 376

13.9 Conclusion 377Summary Further reading Study and review questions

14. Speciation 381

14.1 How can one species split into two reproductively isolated groupsoforganisms? 382

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14.2 A newly evolving species could theoretically have an allopatric,parapatric, or sympatric geographic relation with its ancestor 382

14.3 Reproductive isolation can evolve as a by-product of divergencein allopatric populations 38314.3.1 Laboratory experiments illustrate how separately evolving

populations of a species tend incidentally to evolvereproductive isolation 384

14.3.2 Prezygotic isolation evolves because it is genetically correlatedwith the characters undergoing divergence 386

14.3.3 Reproductive isolation is often observed when members ofgeographically distant populations are crossed 387

14.3.4 Speciation as a by-product of divergence is well documented 38914.4 The Dobzhansky-Muller theory of postzygotic isolation 389

14.4.1 The Dobzhansky-Muller theory is a genetic theory ofpostzygotic isolation, explaining it by interactions amongmany gene loci 389

14.4.2 The Dobzhansky-Muller theory is supported by extensivegenetic evidence 391

14.4.3 The Dobzhansky-Muller theory has broad biologicalplausibility 392

14.4.4 The Dobzhansky-Muller theory solves a general problemof "valley crossing" during speciation 394

14.4.5 Postzygotic isolation may have ecological as well as geneticcauses 395

14.4.6 Postzygotic isolation usually follows Haldane's rule 39614.5 An interim conclusion: two solid generalizations about speciation 39914.6 Reinforcement 399

14.6.1 Reproductive isolation may be reinforced by natural selection 39914.6.2 Preconditions for reinforcement maybe short lived 40114.6.3 Empirical tests of reinforcement are inconclusive or fail to

support the theory 40214.7 Some plant species have originated by hybridization 40514.8 Speciation may occur in non-allopatric populations, either

parapatrically or sympatrically 40814.9 Parapatric speciation 409

14.9.1 Parapatric speciation begins with the evolution of astepped cline 409

14.9.2 Evidence for the theory of parapatric speciation isrelatively weak 411

14.10 Sympatric speciation 41114.10.1 Sympatric speciation is theoretically possible 41114.10.2 Phytophagous insects may split sympatrically by host shifts 41214.10.3 Phylogenies can be used to test whether speciation has been

sympatric or allopatric 41314.11 The influence of sexual selection in speciation is one current trend

in research 413

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14.12 Identification of genes that cause reproductive isolation is anothercurrent trend in research 415


15. The Reconstruction of Phylogeny 423

15.1 Phylogenies express the ancestral relations between species 42415.2 Phylogenies are inferred from morphological characters using

cladistic techniques 42515.3 Homologies provide reliable evidence for phylogenetic inference,

and homoplasies provide unreliable evidence 42715.4 Homologies can be distinguished from homoplasies by

several criteria 43015.5 Derived homologies are more reliable indicators of phylogenetic

relations than are ancestral homologies 43115.6 The polarity of character states can be inferred by several techniques 433

15.6.1 Outgroup comparison 43415.6.2 The fossil record 43515.6.3 Other methods 436

15.7 Some character conflict may remain after cladistic characteranalysis is complete 436

15.8 Molecular sequences are becoming increasingly important inphylogenetic inference, and they have distinct properties 43 7

15.9 Several statistical techniques exist to infer phylogenies frommolecular sequences 43915.9.1 An unrooted tree is a phylogeny in which the common

ancestor is unspecified 43915.9.2 One class of molecular phylogenetic techniques uses

molecular distances 44015.9.3 Molecular evidence may need to be adjusted for the

problem of multiple hits 44215.9.4 A second class of phylogenetic techniques uses the

principle of parsimony 44515.9.5 A third class of phylogenetic techniques uses the principle

ofmaximumlikelihood 44715.9.6 Distance, parsimony, and maximum likelihood methods

are all used, but their popularity has changed over time 44915.10 Molecular phylogenetics in action 449

15.10.1 Different molecules evolve at different rates and molecularevidence can be tuned to solve particular phylogeneticproblems 449

15.10.2 Molecular phylogenies can now be produced rapidly, andare used in medical research 451

15.11 Several problems have been encountered in molecular phylogenetics 45115.11.1 Molecular sequences can be difficult to align 452

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15.11.2 The number of possible trees may be too large for themall to be analyzed 452

15.11.3 Species in a phylogeny may have diverged too little ortoo much 455

15.11.4 Different lineages may evolve at different rates 45615.11.5 Paralogous genes may be confused with orthologous genes 45715.11.6 Conclusion: problems in molecular phylogenetics 458

15.12 Paralogous genes can be used to root unrooted trees 45915.13 Molecular evidence successfully challenged paleontological

evidence in the analysis of human phylogenetic relations 46015.14 Unrooted trees can be inferred from other kinds of evidence,

such as chromosomal inversions in Hawaiian fruitflies 46315.15 Conclusion 466Summary Further reading Study and review questions

16. Classification and Evolution 47116.1 Biologists classify species into a hierarchy of groups 47216.2 There are phenetic and phylogenetic principles of classification 47216.3 There are phenetic, cladistic, and evolutionary schools of

classification 47416.4 A method is needed to judge the merit of a school of classification 47516.5 Phenetic classification uses distance measures and cluster statistics 47616.6 Phylogenetic classification uses inferred phylogenetic relations 479

16.6.1 Hennig's cladism classifies species by their phylogeneticbranching relations 479

16.6.2 Cladists distinguish monophyletic, paraphyletic, andpolyphyletic groups 481

16.6.3 A knowledge of phylogeny does not simply tell us the ranklevels in Linnaean classification - 483

16.7 Evolutionary classification is a synthesis of phenetic andphylogenetic principles 485

16.8 The principle of divergence explains why phylogeny is hierarchical 48716.9 Conclusion 489Summary Further reading Study and review questions

17. Evolutionary Biogeography 49217.1 Species have defined geographic distributions 49317.2 Ecological characteristics of a species limit its geographic distribution 49617.3 Geographic distributions are influenced by dispersal 49617.4 Geographic distributions are influenced by climate, such as in

the ice ages 49717.5 Local adaptive radiations occur on island archipelagos 50017.6 Species of large geographic areas tend to be more closely related to

other local species than to ecologically similar species elsewhere inthe globe 503

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17.7 Geographic distributions are influenced by vicariance events, someof which are caused by plate tectonic movements 505

17.8 The Great American Interchange 51217.9 Conclusion 517Summary Further reading Study and review questions

PART 5. MACROEVOLUTION 521

18. The History of Life 52318.1 Fossils are remains of organisms from the past and are preserved in

sedimentary rocks 52418.2 Geological time is conventionally divided into a series of eras,

periods, and epochs 52518.2.1 Successive geological ages were first recognized by

characteristic fossil faunas 52518.2.2 Geological time is measured in both absolute and

relative terms 52618.3 The history of life: the Precambrian 529

18.3.1 The origin of life 52918.3.2 The origin of cells 53118.3.3 The origin of multicellular life 533

18.4 The Cambrian explosion 53518.5 Evolution of land plants 53818.6 Vertebrate evolution 540

18.6.1 Colonization of the land 54018.6.2 Mammals evolved from the reptiles in a long series of

small changes 54218.7 Human evolution . 545

18.7.1 Four main classes of change occurred during homininevolution 545

18.7.2 Fossil records show something of our ancestors for thepast 4 million years 547

18.8 Macroevolution may or may not be an extrapolated form ofmicroevolution 550


19. Evolutionary Genomics 55619.1 Our expanding knowledge of genome sequences is making it

possible to ask, and answer, questions about the evolutionofgenomes 557

19.2 The human genome documents the history of the human geneset since early life 558

19.3 The history of duplications can be inferred in a genomic sequence 55919.4 Genome size can shrink by gene loss 561

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19.5 Symbiotic mergers, and horizontal gene transfer, between speciesinfluence genome evolution 563

19.6 The X/Y sex chromosomes provide an example of evolutionarygenomic research at the chromosomal level 565

19.7 Genome sequences can be used to study the history ofnon-coding DNA 567


20. Evolutionary Developmental Biology 572

20.1 Changes in development, and the genes controlling development,underlie morphological evolution 573

20.2 The theory of recapitulation is a classic idea (largely discredited)about the relation between development and evolution 573

20.3 Humans may have evolved from ancestral apes by changes inregulatory genes 578

20.4 Many genes that regulate development have been identified recently 57920.5 Modern developmental genetic discoveries have challenged and

clarified the meaning of homology 58020.6 The Hox gene complex has expanded at two points in the evolution

ofanimals 58220.7 Changes in the embryonic expression of genes are associated with

evolutionary changes in morphology 58320.8 Evolution of genetic switches enables evolutionary innovation,

making the system more "evolvable" 58520.9 Conclusion 587Summary Further reading Study and review questions

21. Rates of Evolution 590

21.1 Rates of evolution can be expressed in "darwins," as illustrated by astudy of horse evolution 59121.1.1 How do population genetic, and fossil, evolutionary

rates compare? 59321.1.2 Rates of evolution observed in the short term can explain

speciation over longer time periods in Darwin's finches 59521.2 Why do evolutionary rates vary? 59621.3 The theory of punctuated equilibrium applies the theory of allopatric

speciation to predict the pattern of change in the fossil record 59921.4 What is the evidence for punctuated equilibrium and for phyletic

gradualism? 60221.4.1 A satisfactory test requires a complete stratigraphic record

and biometrical evidence 60221.4.2 Caribbean bryozoans from the Upper Miocene and Lower

Pliocene show a punctuated equilibrial pattern of evolution 603

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21.4.3 Ordovician trilobites show gradual evolutionary change 60521.4.4 Conclusion 605

21.5 Evolutionary rates can be measured for non-continuous characterchanges, as illustrated by a study of "living fossil" lungfish 606

21.6 Taxonomic data can be used to describe the rate of evolution ofhigher taxonomic groups 609


22. Coevolution 613

22.1 Coevolution can give rise to coadaptations between species 61422.2 Coadaptation suggests, but is not conclusive evidence of, coevolution 61622.3 Insect-plant coevolution 616

22.3.1 Coevolution between insects and plants may have driven thediversification of both taxa 616

22.3.2 Two taxa may show mirror-image phylogenies, butcoevolution is only one of several explanations for this pattern 618

22.3.3 Cophylogenies are not found when phytophagous insectsundergo host shifts to exploit phylogenetically unrelatedbut chemically similar plants 620

22.3.4 Coevolution between plants and insects may explain thegrand pattern of diversification in the two taxa 622

22.4 Coevolutionary relations will often be diffuse 62322.5 Parasite-host coevolution 623

22.5.1 Evolution of parasitic virulence 62522.5.2 Parasites and their hosts may have cophylogenies 630

22.6 Coevolution can proceed in an "arms race" 63222.6.1 Coevolutionary arms races can result in evolutionary

escalation . 63422.7 The probability that a species will go extinct is approximately

independent of how long it has existed 63722.8 Antagonistic coevolution can have various forms, including

the Red Queen mode 63822.9 Both biological and physical hypotheses should be tested on

macroevolutionary observations 640Summary Further reading Study and review questions

23. Extinction and Radiation 643

23.1 The number of species in a taxon increases during phases ofadaptive radiation 644

23.2 Causes and consequences of extinctions can be studied in thefossil record 646

23.3 Mass extinctions 64823.3.1 The fossil record of extinction rates shows recurrent

rounds of mass extinctions 648

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23.3.2 The best studied mass extinction occurred atthe Cretaceous-Tertiary boundary 651

23.3.3 Several factors can contribute to mass extinctions 65323.4 Distributions of extinction rates may fit a power law 65523.5 Changes in the quality of the sedimentary record through time are

associated with changes in the observed extinction rate 65723.6 Species selection 658

23.6.1. Characters that evolve within taxa may influence extinctionand speciation rates, as is illustrated by snails withplanktonic and direct development 658

23.6.2 Differences in the persistence of ecological niches willinfluence macroevolutionary patterns 664

23.6.3 When species selection operates, the factors that controlmacroevolution differ from the factors that controlmicroevolution 665

23.6.4 Forms of species selection may change during massextinctions 666

23.7 One higher taxon may replace another, because of chance,environmental change, or competitive replacement 66923.7.1 Taxonomic patters through time can provide evidence

about the cause of replacements 66923.7.2 Two bryozoan groups are a possible example of

a competitive replacement 67023.7.3 Mammals and dinosaurs are a classic example of

independent replacement, but recent molecularevidence has complicated the interpretation 671

23.8 Species diversity may have increased logistically or exponentiallysince the Cambrian, or it may have increased little at all 674

23.9 Conclusion: biologists and paleontologists have held a range ofviews about the importance of mass extinctions in the history of life 677


Glossary 682Answers to Study and Review Questions 690References 699Index • 733

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evolution - gbv

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