The Princeton Guide to Evolution - Hardcover

Losos, Jonathan B.; Baum, David; Futuyma, Douglas; Hoekstra, Hopi; Lenski, Richard; Moore, Allen; Peichel, Catherine; Schluter, Dolph; Whitlock, Michael; Baum, David A.; Futuyma, Douglas J.; Hoekstra, Hopi E.; Lenski, Richard E.

Hardcover

ISBN 10: 0691149771 ISBN 13: 9780691149776

Publisher: Princeton University Press, 2013

Synopsis

The Princeton Guide to Evolution is a comprehensive, concise, and authoritative reference to the major subjects and key concepts in evolutionary biology, from genes to mass extinctions. Edited by a distinguished team of evolutionary biologists, with contributions from leading researchers, the guide contains some 100 clear, accurate, and up-to-date articles on the most important topics in seven major areas: phylogenetics and the history of life; selection and adaptation; evolutionary processes; genes, genomes, and phenotypes; speciation and macroevolution; evolution of behavior, society, and humans; and evolution and modern society. Complete with more than 100 illustrations (including eight pages in color), glossaries of key terms, suggestions for further reading on each topic, and an index, this is an essential volume for undergraduate and graduate students, scientists in related fields, and anyone else with a serious interest in evolution. * Explains key topics in some 100 concise and authoritative articles written by a team of leading evolutionary biologists * Contains more than 100 illustrations, including eight pages in color * Each article includes an outline, glossary, bibliography, and cross-references * Covers phylogenetics and the history of life; selection and adaptation; evolutionary processes; genes, genomes, and phenotypes; speciation and macroevolution; evolution of behavior, society, and humans; and evolution and modern society

About this title

About the Author

Jonathan B. Losos is the Monique and Philip Lehner Professor for the Study of Latin America and professor of organismic and evolutionary biology at Harvard University.

From the Back Cover

"The marvelous new tools and theoretical approaches that have so greatly deepened our understanding of evolution over the past few decades are clearly and concisely presented in this splendid new guide, which should be of use to everyone involved in the field."--Peter H. Raven, president emeritus of the Missouri Botanical Garden, St. Louis

Excerpt. © Reprinted by permission. All rights reserved.

The Princeton Guide to Evolution

By Jonathan B. Losos

PRINCETON UNIVERSITY PRESS

Copyright © 2014 Princeton University Press
All rights reserved.

ISBN: 978-0-691-14977-6

Contents

Preface....................................................................
vii
Contributors...............................................................
ix
Section I Introduction.....................................................
1
Section II Phylogenetics and the History of Life...........................
47
Section III Natural Selection and Adaptation...............................
189
Section IV Evolutionary Processes..........................................
305
Section V Genes, Genomes, Phenotypes.......................................
363
Section VI Speciation and Macroevolution...................................
483
Section VII Evolution of Behavior, Society, and Humans.....................
605
Section VIII Evolution and Modern Society..................................
727
Index......................................................................
837

CHAPTER 1

Introduction

I.1

What Is Evolution?

Jonathan Losos

OUTLINE

1. What is evolution?

2. Evolution: Pattern versus process

3. Evolution: More than changes in thegene pool

4. In the light of evolution

5. Critiques and the evidence for evolution

6. The pace of evolution

7. Evolution, humans, and society

Evolution refers to change through time as species becomemodified and diverge to produce multiple descendantspecies. Evolution and natural selection are oftenconflated, but evolution is the historical occurrence ofchange, and natural selection is one mechanism—in mostcases the most important—that can cause it. Recentyears have seen a flowering in the field of evolutionarybiology, and much has been learned about the causes andconsequences of evolution. The two main pillars of ourknowledge of evolution come from knowledge of thehistorical record of evolutionary change, deduced directlyfrom the fossil record and inferred from examination ofphylogeny, and from study of the process of evolutionarychange, particularly the effect of natural selection. It isnow apparent that when selection is strong, evolution canproceed considerably more rapidly than was generallyenvisioned by Darwin. As a result, scientists are realizingthat it is possible to conduct evolutionary experiments inreal time. Recent developments in many areas, includingmolecular and developmental biology, have greatly expandedour knowledge and reaffirmed evolution's centralplace in the understanding of biological diversity.

GLOSSARY

Evolution. Descent with modification; transformationof species through time, including both changes thatoccur within species, as well as the origin of newspecies.

Natural Selection. The process in which individuals witha particular trait tend to leave more offspring in thenext generation than do individuals with a differenttrait.

Approximately 375 million years ago, a large and vaguelysalamander-like creature plodded from its aquatichome and began the vertebrate invasion of land, settingforth the chain of evolutionary events that led to the birdsthat fill our skies, the beasts that walk our soil, me writingthis chapter, and you reading it. This was, of course, justone episode in life's saga: millions of years earlier, plantshad come ashore, followed soon thereafter—or perhapssimultaneously—by arthropods. We could go back muchearlier, 4 billion years or so, to that fateful day when thefirst molecule replicated itself, an important milestone inthe origin of life and the beginning of the evolutionarypageant. Moving forward, the last few hundred millionyears have also had their highs and lows: the origins offrogs and trees, the end-Permian extinction when 90percent of all species perished, and the rise and fall of thedinosaurs.

These vignettes are a few of many waypoints in theevolutionary chronicle of life on earth. Evolutionarybiologists try to understand this history, explaining howand why life has taken its particular path. But the studyof evolution involves more than looking backward to tryto understand the past. Evolution is an ongoing process,one possibly operating at a faster rate now than in timespast in this human-dominated world. Consequently,evolutionary biology is also forward looking: it includesthe study of evolutionary processes in action today—howthey operate, what they produce—as well as investigationof how evolution is likely to proceed in thefuture. Moreover, evolutionary biology is not solely anacademic matter; evolution affects humans in manyways, from coping with the emergence of agriculturalpests and disease-causing organisms to understandingthe workings of our own genome. Indeed, evolutionaryscience has broad relevance, playing an important role inadvances in many areas, from computer programmingto medicine to engineering.

1. WHAT IS EVOLUTION?

Lookup the word "evolution" in the online version of theOxford English Dictionary, and you will find 11 definitionsand numerous subdefinitions, ranging from mathematical("the successive transformation of a curve bythe alteration of the conditions which define it") to chemical("the emission or release of gas, heat, light, etc.") tomilitary ("a manoeuvre executed by troops or ships toadopt a different tactical formation"). Even with referenceto biology, there are several definitions, including"emergence or release from an envelope or enclosingstructure; (also) protrusion, evagination," not to mention"rare" and "historical" usage related to the conceptof preformation of embryos. Even among evolutionarybiologists, evolution is defined in different ways. Forexample, one widely read textbook refers to evolution as"changes in the properties of groups of organisms overthe course of generations" (Futuyma 2005), whereasanother defines it as "changes in allele frequencies overtime" (Freeman and Herron 2007).

One might think that—as in so many other areas ofevolutionary biology—we could look to Darwin forclarity. But in the first edition of On the Origin of Species,the term "evolution" never appears (though the lastword of the book is "evolved"); not until the sixth editiondoes Darwin use "evolution." Rather, Darwin'sterm of choice is "descent with modification," a simplephrase that captures the essence of what evolutionarybiology is all about: the study of the transformation ofspecies through time, including both changes that occurwithin species, as well as the origin of new species.

2. EVOLUTION: PATTERN VERSUS PROCESS

Many people—sometimes even biologists—equate evolutionwith natural selection, but the two are not thesame. Natural selection is one process that can causeevolutionary change, but natural selection can occurwithout producing evolutionary change. Conversely,processes other than natural selection can lead toevolution.

Natural selection within populations refers to the situationin which individuals with one variant of a trait(say, blue eyes) tend to leave more offspring that arehealthy and fertile in the next generation than do individualswith an alternative variant of the trait. Suchselection can occur in many ways, for example, if thevariant leads to greater longevity, greater attractiveness tomembers of the other sex, or greater number of offspringper breeding event. The logic behind natural selection isunassailable. If some trait variant is causally related togreater reproductive success, then more members of thepopulation will have that variant in the next generation;continued over many generations, such selection cangreatly change the constitution of a population.

But there is a catch. Natural selection can occur withoutleading to evolution if differences among individualsare not genetically based. For natural selection to causeevolutionary change, trait variants must be transmittedfrom parent to offspring; if that is the case, then offspringwill resemble their parents and the trait variants possessedby the parents that produce the most offspring will increasein frequency in the next generation.

However, offspring do not always resemble theirparents. In some cases, individuals vary phenotypicallynot because they are different genetically, but becausethey experienced different environments during growth(this is the "nurture" part of the nature versus nurturedebate; see chapters III.10 and VII.1). If, in fact, variationin a population is not genetically based, then selectionwill have no evolutionary consequence; individualssurviving and producing many offspring willnot differ genetically fromthose that fail to prosper, andas a result, the gene pool of the population will notchange. Nonetheless, much of the phenotypic variationwithin a population is, in fact, genetically based; consequently,natural selection often does lead to evolutionarychange.

But that does not mean that the occurrence of evolutionarychange necessarily implies the action of naturalselection. Other processes—especially mutation,genetic drift, and immigration of individuals with differentgenetic constitutions—also can cause a change inthe genetic makeup of a population from one generationto the next (see Section IV: Evolutionary Processes). Inother words, natural selection can cause adaptive evolutionarychange, but not all evolution is adaptive.

These caveats notwithstanding, 150 years of researchhave made clear that natural selection is a powerful forceresponsible for much of the significant evolutionarychange that has occurred over the history of life. As thechapters in Section II: Phylogenetics and the History ofLife, and Section III: Natural Selection and Adaptation,demonstrate, natural selection can operate in manyways, and scientists have correspondingly devised manymethods to detect it, both through studies of the phenotypeand of DNA itself (see also chapter V.14).

3. EVOLUTION: MORE THAN CHANGES IN THEGENE POOL

During the heyday of population genetics in the middledecades of the last century, many biologists equatedevolution with changes from one generation to the nextin gene frequencies (gene frequency refers to the frequenciesof different alleles of a gene; for backgroundon genetic variation, see chapter I.4). The "ModernSynthesis" of the 1930s and 1940s led to several decadesin which the field was primarily concerned with the geneticsof populations with an emphasis on natural selection(see chapter I.2). This focus was sharpened by theadvent of molecular approaches to studying evolution.Starting in 1960 with the application of enzyme electrophoresistechniques, biologists could, for the firsttime, directly assess the extent of genetic variation withinpopulations. To everyone's surprise, populations werefound to contain much more variation than expected.This finding both challenged the view that natural selectionwas the dominant force guiding evolutionarychange (see discussion of "neutralists" in chapters I.2and V.1), yet further directed attention to the genetics ofpopulations. With more advanced molecular techniquesavailable today, the situation has not changed. There ismuch more variation than we first suspected.

The last 35 years have seen a broadening of evolutionaryinquiry as the field has recognized that there ismore to understanding evolutionary change than studyingwhat happens to genes within populations—thoughthis area remains a critically important part of evolutionaryinquiry. Three aspects of expansion in evolutionarythinking are particularly important.

First, phenotypic evolution results from evolutionarychange in the developmental process that transforms asingle-celled fertilized egg into an adult organism. Althoughunder genetic control, development is an intricateprocess that cannot be understood by examinationof DNA sequences alone. Rather, understandinghow phenotypes evolve, and the extent to which developmentalsystems constrain and direct evolutionarychange, requires detailed molecular and embryologicalknowledge (see chapters V.10 and V.11).

Second, history is integral to understanding evolution(see introduction to Section II: Phylogenetics and theHistory of Life). The study of fossils—paleontology—providesthe primary, almost exclusive, direct evidenceof life in the past. Somewhat moribund in the middle ofthe last century, paleontology has experienced a resurgencein recent decades owing to both dramatic new discoveriesstemming from an upsurge in paleontologicalexploration, and new ideas about evolution inspired byand primarily testable with fossil data, such as theoriesconcerning punctuated equilibrium and stasis, speciesselection, and mass extinction. Initially critical in thedevelopment and acceptance of evolutionary theory,paleontology has once again become an important andvibrant part of evolutionary biology (see chapter II.9 andothers in Section II).

Concurrently, a more fundamental revolution emphasizingthe historical perspective has taken place overthe last 30 years with the realization that information onphylogenetic relationships—that is, the tree of life, thepattern of descent and relationship among species—iscritical in interpreting all aspects of evolution above thepopulation level. Beginning with a transformation in thefield of systematics concerning how phylogenetic relationshipsare inferred, this "tree-thinking" approachnow guides study not only of all aspects of macroevolutionbut also of many population-level phenomena.

Finally, life is hierarchically organized. Genes are locatedwithin individuals, individuals within populations,populations within species, and species within clades(a clade consists of an ancestral species and all its descendants).Population genetics concerns what happensamong individuals within a population, but evolutionarychange can occur at all levels. For example, why are theremore than 2000 species of rodents but only 3 species ofmonotremes (the platypus and echidnas), a much olderclade of mammals? One cannot look at questions concerningnatural selection within a population to answerthis question. Rather, one must inquire about propertiesof entire species. Is there some attribute of rodents thatmakes them particularly prone to speciate or to avoidextinction? Similarly, why is there so much seeminglyuseless noncoding DNA in the genomes of many species(see chapter V.2)? One possibility is that some genes areparticularly adept at mutating to multiply the number ofcopies of that gene within a genome; such DNA mightincrease in frequency in the genome even if such multiplicationhas no benefit to the individual in whose bodythe DNA resides. Just as selection among individual organismson heritable traits can lead to evolutionarychange within populations, selection among entities atother levels (species, genes) can also lead to evolutionarychange, as long as those entities have traits that aretransmitted to their offspring (be they descendant speciesor genes) and affect the number of descendants they produce.The upshot is that evolution occurs at multiple levelsof the hierarchy of life; to understand its rich complexitywe must study evolution at these distinct levels as well asthe interactions among them. What happens, for example,when a trait that benefits an individual within a population(perhaps cannibalism—more food, fewer competitors!)has detrimental effects at the level of species?

Although evolutionary biology has expanded inscope, genetic change is still its fundamental foundation.Nonetheless, in recent years attention has focused onvariation that is not genetically based. Phenotypic plasticity—theability of a single genotype to produce differentphenotypes when exposed to different environments—mayitself be adaptive (see chapter III.10). Ifindividuals in a population are likely to experiencedifferent conditions as they develop, then the evolution ofa genotype that could produce appropriate phenotypesdepending on circumstances would be advantageous.Although selection on these different phenotypes wouldnot lead to evolutionary change, the degree of plasticityitself can evolve if differences in extent of plasticity leadto differences in the number of surviving offspring. Indeed,an open question is, why don't populations evolveto become infinitely malleable, capable of producing theappropriate phenotype for any environment? Presumably,plasticity has an associated cost such that adaptation todifferent environments often occurs by genetic differentiationrather than by the evolution of a single genotypethat can produce different phenotypes. Such costs, however,have proven difficult to demonstrate.

Differences observed among populations may alsoreflect plastic responses to different environmental conditionsand thus may not reflect genetic differentiation.However, if consistently transmitted from one generationto the next, such nongenetic differences may lead todivergent selective pressures on traits that are geneticallydetermined, thus promoting evolutionary divergencebetween the populations. One particular example concernsbehavior, which is highly variable in response tothe environment—an extreme manifestation of plasticity(see chapter VIII.10). Learned behaviors that aretransmitted from one generation to the next—oftencalled traditions or culture—occur not only in humansbut in other animals, not only our near relatives the apesbut also cetaceans, birds, and others. Such behavioraldifferences among populations would not reflect geneticdifferentiation, but they might set the stage for geneticdivergence in traits relating to the behaviors. One caneasily envision, for example, how chimpanzee populationsthat use different tools—such as delicate twigs toprobe termite mounds, or heavy stones to pound nuts—mightevolve different morphological features to enhancethe effectiveness of these behaviors. A concreteexample involves human populations that tend cattle—surelya nongenetically based behavior—and haveevolved genetic changes to permit the digestion of milkin adults.

4. IN THE LIGHT OF EVOLUTION

In a 1964 address to the American Society of Zoologists,the distinguished Russian-born biologist TheodosiusDobzhansky proclaimed "nothing makes sense in biologyexcept in the light of evolution." Ever since, evolutionarybiologists have trotted out this phrase (or somepermutation of it) to emphasize the centrality of evolutionin understanding the biological world. Nonetheless,for much of the twentieth century, the pervasive importanceof an evolutionary perspective was not at allobvious to many biologists, some of whom consideredDobzhansky's claim to be self-serving hype. One couldargue, for example, that the enormous growth in ourunderstanding of molecular biology from 1950 to 2000was made with little involvement or insight from evolutionarybiology. Indeed, to the practicing molecularbiologist in the 1980s and 1990s, evolutionary biologywas mostly irrelevant.

(Continues...)

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Edition details

• Publisher: Princeton University Press
• Publication date: 2013
• ISBN 10: 0691149771
• ISBN 13: 9780691149776
• Binding: Hardcover
• Language: English
• Number of pages: 872