Filling the Cup of AlterationUniformitarianism then and now.

KENNETH WEISS

William Shakespeare (1564–1616)was a remarkable man. Combingthrough his work, one can find almostevery conceivable bit of wisdom, goodidea, or point of view. But until stum-bling across the quote in Box 1, Ihadn’t realized that Shakespeare, atthe turn of the seventeenth century, inaddition to being a poet and play-wright, was also a modern geologist.Though without a university educa-tion, he somehow understood a key as-pect of geology. Those lines in HenryIV were spoken as a geological meta-phor for the winds of political change.But metaphors develop from widelyunderstood notions.Despite Shakespeare’s clear priority

by more than a century, historians ofscience stubbornly credit the foundingof modern geology to James Hutton(1726–1797)1 and the new baby—Charles Lyell (1797–1875), born in theyear of Hutton’s death, to whom thegeological baton was transferred.2 Themajor conceptual insight that ac-counted at a single stroke for muchthat was observed in geology is theidea known as uniformitarianism (Fig. 1),though the term itself was not coineduntil 1840, by William Whewell.3 Theidea of uniformitarianism, that thebasic processes of Nature were thesame in the past as they are today,was largely motivated by the observa-tion that geological changes generally

are very slow, a corollary that becameknown as gradualism. Its importancewas that after long periods of timethese slow, continually acting proc-esses can accumulate large change.

As far as proper priority goes, Hut-ton, like all educated people, musthave read Shakespeare, so it mightmake a juicy, if typically fictional tab-loid story to accuse him of cribbinghis ideas from the Bard. In any case,the way ideas are sometimes just ‘‘inthe air’’ and picked up independentlyby creative contemporaries is illus-trated by the story of a young Ameri-can named James D. Dana (Fig. 2).Dana was America’s leading geologistof the nineteenth century. In 1838,just two years after Darwin’s Beaglevoyage had returned to England,Dana set forth on a voyage of globalexploration designed to put an Ameri-can foot in the door of what hadbeen European domination of mari-time exploration, the grand traditionthat included James Cook (1729–1778), Darwin, and many others.The objectives of the U.S. ExploringExpedition of 1838–1842 were todetermine whether there was anAntarctic continent and to chart the

volcanic island chains in the Pacificthat had proven so dangerous toAmerican whalers and traders.3,4

Lyell had speculated about the pro-cess that formed the many Pacific arcsof islands ringed by coral atolls, withactive volcanoes at one end and noisland inside the atoll at the other end.Essentially, Lyell thought that risingand subsiding volcanoes of differentages were responsible. Dana devel-oped an almost opposite, but stillgradualistic hypothesis, according towhich the islands were built seriallyalong the chain by undersea volca-noes, the cones of which eventuallyemerged from the surface and werecolonized around their edges by coral.Dana noted the linear change in ageof several Pacific island chains and, in1873,5 published his idea that the firstisland was oldest, that it had beenraised and then eroded back beneaththe sea, while later islands in thechain were younger or just building,as spots on the ocean floor move overa volcanic source, forming a kind ofgeosyncline (Fig. 2).6 Many of Dar-win’s earliest publications were ongeology, and he had addressed thisproblem independently, earlier than

Box 1: William Shakespeare, Geologist

O God! that one might read the book of fate,And see the revolution of the timesMake mountains level, and the continent,Weary of solid firmness, melt itselfInto the sea; and other times to seeThe beachy girdle of the oceanToo wide for Neptune’s hips; how chances mock,And changes fill the cup of alterationWith divers liquors!

2 Henry IV, III,i: 44–52, 1600

CROTCHETS & QUIDDITIES

Ken Weiss is Evan Pugh Professor of An-thropology and Genetics at Penn StateUniversity.

VVC 2007 Wiley-Liss, Inc.DOI 10.1002/evan.20123Published online in Wiley InterScience(www.interscience.wiley.com).

Evolutionary Anthropology 16:6–11 (2007)

Dana, and had basically arrived at thesame explanation. Dana was non-plussed when he later read Darwin’saccount. But if uniformitarian gradu-alism was in the air, Darwin took adeeper breath of it and moved the ideaa major step forward, from the pro-cesses of inanimateNature to life itself.

DARWIN HAD HIS REASONS

Darwin is credited with applyingLyell’s notion to biology, but actuallythe idea had long been waftingaround.7 Alfred Wallace was makinggeological observations of his own inIndonesia when he sniffed out thesame extension to biology as didDarwin. But you might be surprisedto learn that back in 1809 the idea wasat the heart of Jean Baptiste deLamarck’s (1744–1829) evolutionarytheory of the inheritance of acquiredcharacteristics. Lamarck wrote that‘‘With regard to living bodies, it is nolonger possible to doubt that naturehas done everything little by littleand successively’’ and ‘‘Throughout thechanges which nature is incessantlyproducing in every part without ex-ception, she still remains always thesame in her totality and her laws. . .’’8

A scantly remembered British physi-cian, Joseph Adams (1756–1818), alsowrote, in 1814: ‘‘By these means a raceis gradually reared with constitutions

best calculated for the climate: a lawwhich, I suspect, has been too muchoverlooked, in our inquires after thecauses of the more marked varieties inthe human species.’’9 Because Adams’book was about the evolution of he-redity disease, historians of biologyseem to have missed the fact that he isone of those who clearly anticipatedthe core ideas of evolution.

Like the steady drip, drip, drip thatslowly but ineluctably erodes Shake-speare’s mountain one micron at atime, incremental biological forcescan also produce major changes overlong time periods.10 Uniformitariangradualism provided a consistentrather than an ad hoc interpretation oflife that did not require the specialpleadings that various catastrophistviews, including multiple creationismand periodic cataclysmic extinctionssuggested. The power of extrapolatingfrom directly observable, if slow, proc-esses of change across the eons of geo-logic time justified the theory of speci-ation by gradual natural selection.

We can observe short-term changedirectly and play with it experimen-tally. In that sense, every processinvoked by evolutionary theory canbe tested in one way or another byobservation or in model systems Therace for success that Darwin andother naturalists observed in the wildtypically seemed to involve small dif-ferences among competitors. Darwin

relied heavily on his knowledge ofagricultural and recreational breed-ing of plants and animals, where itwas clear that you could use differ-ential reproduction to select gradu-ally for woollier wool, hoggier hogs,or poutier pigeons. However, no mat-ter how persuasive these kinds ofdata are, experimental work cannotdirectly make observations over count-less thousands of years. And ofcourse the particular thorn in Dar-win’s side was not just the need toaccount for changing variation, butto explain the origin of distinct spe-cies by means other than instantane-ous creation.It is one of many ironies that agri-

cultural breeding does not producespecies either. But if we’re willing tomake the uniformitarian assumptionthat there were no forces operating inthe past that are not still operatingtoday, we can convince ourselves thatthe evolutionary intuition we reach byextrapolating across deep time fromobservations on the here and now isactually correct. This was the strikingconceptual key to the legerdemain bywhich Darwin explained how some-thing you couldn’t see because it wastoo slow was responsible for every-thing you could see about biologicaldiversity. Darwin’s rapture is reflectedin the quote in Box 2.Another irony is that Darwinism

today still has to fight rear-guardaction against creationistic worldviews. A centerpiece of that resist-ance movement is that since youcan’t observe species forming inNature, uniformitarianism doesn’thelp; hence, evolution can’t be true.How that false syllogism is taken toimply creationism is puzzling, sincethe purported creation events arealso tucked safely and unobservablyaway in the prehistoric past.The persistence of this resistance to

evolution is interesting but derives nosupport from science. From the earlytwentieth century, the uniformitariangradualism assumption is how Dar-win’s world view became formalizedby the mathematical theory of popula-tion genetics, which is the formal wayto extrapolate the process to showhow it could work. An important rea-son was the still-current concept ofpolygenic control of quantitative traits

Figure 1. Readers of the book of fate. A. James Hutton (by Sir Henry Raeborn, in ScottishNat. Port. Gallery). B. Charles Lyell (engraved by G. J. Stodart from a photograph frompages.britishlibrary.net).

CROTCHETS & QUIDDITIES Uniformitarianism Then and Now 7

by countless individual genes varyingin the ordinary Mendelian way butwith individually infinitesimal effects.Population genetics theory couldn’tdemonstrate evolution directly, butprovided a quantitative basis for test-ing it indirectly, for example by pre-dicting the pattern of DNA sequencedivergence among species that wouldbe expected on the basis of observedmorphological differences and the ge-ological dating of fossils. The testshave added exceedingly powerful sup-port to the idea.Darwin’s famous belief was that

natura non facit saltum, as he put it—a creeping if not creepy view ofNature (not to be confused with theBible’s ‘‘every thing that creepethupon the earth’’) that does not allowfor discrete jumps, or saltations, inevolution. In Descent of Man (1871),Darwin clearly stated that he stressedgradualistic natural selection to show

that there was a mechanism for theproduction of new, adapted species, aprocess that did not require divineintervention: Nature works by unifor-mitarian, Lyellian gradualism ratherthan by creationistic or catastrophis-tic discontinuities. In Darwin’s worldview, things do not just arise suddenlyde novo. Leaps of Nature, unlike leapsof faith, were prohibited. The evolu-tionary teapot simmers along, slowlygenerating new species, but you’ll neversee it boil.

Once Darwinism was establishedas the formal theory of life, ‘‘sal-tation’’ became a flash-word to berooted out and purged by the ever-vigilant Darwin Police. But any kindof Prohibition leads to speakeasies,and in this case they are the insur-gents who occasionally appear withclaims of having discovered somenew violation of uniformitarianism.It’s not new but, in some new

clothes, biology seems to be gettingjumpy again.

A WATCHED TEAPOT THATSOMETIMES BOILS

Some of today’s saltation rum-run-ners even seem to be coyly revivingRichard Goldschmidt’s famous argu-ment that occasional mutational‘‘hopeful monsters’’ might accountfor major biological adaptive advan-ces.11 Goldschmidt was not as super-ficial as the ridicule leveled at himsuggests.12 Furthermore, modern ge-netic research has shown that unifor-mitarian gradualism isn’t quite asabsolute as classical Darwinian fun-damentalism insists: Not all geneticeffects are created equal and infini-tesimal. However, when we lookcarefully at the inequality, we find nojustification for theoretical atavisms.Among events that opened the door

first was the remarkable finding of thegenetic basis of homeotic mutants inflies. Homeotic changes are changesin count or segment identity of meris-tic traits; that is, traits characterizedby multiple similar units. Exampleshad long been known empirically.However, a couple of decades ago de-velopmental genetic work in experi-mental fruit flies showed that changesin single genes, now known as Hoxgenes, could cause variation in thenumber of segments in structures con-trolled by those genes, like an extra setof wings or ectopic antennae. Home-otic changes in the number or regionalidentity of vertebrae have been experi-mentally induced by modifying thesesame (homologous) Hox genes inmice, resulting in lower cervical verte-brae with ribs or lumbar vertebraemorphologically like thoracic ones.Strikingly similar variation is rou-tinely seen in modern collections ofnormal skeletons, including humanskeletons. Many of these variants areharmless, but could be the fuel ofadaptive evolution. Among numerousexamples are variable numbers of nip-ples, cusps, or teeth—or differences inthe number of neck vertebrae betweengeese and whales. They are discretechanges, but they aren’t monsters,even if they have generated hopefulideas for jump-seekers.In 1972, Eldredge and Gould coined

the phrase ‘‘punctuated equilibria’’ in

Figure 2. A. James Dwight Dana (1813–1895), from W. M. Davis, 1928, The Coral Reef Prob-lem: American Geographical Society Special Publication 9, Fig. 1. B. The linear array ofPacific island chains. C. The process of volcanic island-coral reef formation. B and C fromDana’s 1873 Manual of Geology.5

8 Weiss CROTCHETS & QUIDDITIES

reference to evidence from the fossil re-cord that traits remained rather similarfor long time periods, then manifestrapid change (see Eldredge and Gould13

and Wikipedia3.) I thank John Fleaglefor pointing out to me that this claimoriginated by observations of meristicvariation in fossil arthropods—trilo-bites. The evolutionary questions raisedby such traits were noted much earlierby William Bateson, and largely in con-nection with vertebrate evolution.14,15

From a modern point of view, we knowthat change in meristic traits is easilyaccounted for in a perfectly straightfor-ward genetic way by the quantitativenature of the signaling and combinato-rial gene expression processes that pro-duce those traits.16,17 These are not newevolutionary principles.A second source of potentially dis-

crete evolutionary change is geneduplication. Indeed, if we accept therather modest proposal that genomesare part of life, they evolve mainly oreven only through discrete events.When DNA is replicated, chemicalmistakes occasionally occur in whichwhole segments can be copied morethan once and transmitted to thenext generation. This can producetwo copies of a gene when, in theformer generation, there was butone. The second copy is then free tovary and evolve new functions if itaffects the organism in ways that itsenvironment favors. If genomes areanything, they are the product of ahistory of duplication events. Even amutation changing a single nucleo-

tide is, of course, a discrete eventthat can have major effects.18 Varia-tion in vertebrate segmental struc-tures like limbs, teeth, craniofacialfeatures, and vertebrae are examplesof traits that seem to arise some timeafter enabling gene duplicationevents.19–21 This is true not just ofthe skeleton, but also the brain, aswell as other soft-tissue and physio-logical systems; it is generally howevolution works. But while duplica-tions are discrete events and, as faras we know, novel traits, they andtheir effects still have to evolve grad-ually, the old-fashioned way.

A third line of evidence that not allin life is infinitesimally uniform hasbecome available with advances ingene-mapping technology. Scans ofentire genomes can find variation ingenes in families of humans or ex-perimental animals or plants that isassociated with variation in quantita-tive traits, like the various shape andsize of components of the skull, jaws,and limbs. Most variation in suchtraits is due to genes having contri-butions that individually are so smallthat the genes can’t be identified.These are the polygenes of classicalgradualism. However, mapping stud-ies also consistently find that a fewgenes have alleles, or sequence var-iants, that do have substantial indi-vidual effects on the trait. Thesegenes are called Quantitative Trait Loci(QTL). Alleles at these loci show thesense in which not all genes are cre-ated equal.

The uneven distribution of theeffects of alleles at different genescontributes to quantitative variationin a trait at any given time, and isconsistent with the necessarily indi-rect evidence of what has happenedover evolutionary time. There is stillmuch to be learned and much debateabout the genetic ‘‘architecture’’ ofcomplex traits, but there is no doubtthat variation with more than trivialeffects routinely exists.22–24 Alleles atQTL might be favored by selectionand, when that happens, phenotypesmight evolve relatively rapidly. QTLalleles have more than infinitesimaleffects on the trait and arise as dis-crete mutational events, so that,almost by definition, they constitute‘‘saltations.’’ But while QTL show

that not everything genetic is grad-ual, there are no monsters involved.A fourth kind of evidence is being

cited these days as well. Essentially,it has to do with ways that variationcan build up (or sneak up?), accumu-lating unnoticed until an environ-mental stressor of some sort comesalong. That stress can release thepent-up variation, leading to rapid, ifnot exactly saltational evolution.That would be a discontinuous phe-nomenon in the sense that the pent-up variation is suddenly released.A well-studied example involves a

class of genes called chaperonins.Genes code for strings of aminoacids called polypeptides, but poly-peptides are not by themselvesmature, functioning proteins. Theymust first fold up on themselves inways determined by their specificamino acid arrangement, then befurther processed and modified. Buta polypeptide is born into a cellularsoup of chemicals that might harm itbefore it can mature, so the proteinscoded by chaperonin genes bind tonewly hatched polypeptides and helpthem gently fold into functional shape.A famous group of chaperonins arethe genes that code for heat shockproteins or Hsps. Clearly, chapero-nins have long been of fundamentalimportance because they are foundin all branches of life. Hsps are acti-vated to protect against the poten-tially degrading effect of unusualtemperature changes in the environ-ment, among other things. However,under various kinds of stress thechaperonins may fail and fall off of thepolypeptides they have been hired byevolution to protect.One would think that if protection

falls away it’s curtains for the cell.But that seems not necessarily to beso. Experiments have shown thatHsps cover for a considerable amountof variation in proteins that is nevernoticed until it is released by stress-induced failure of the Hsps.25 This isa sudden burst of variation, but itmust be screened by selection in theusual way if it is to serve as anadaptive mechanism in a new stress-ful environment.The hidden protein variation is not

designed in advance specifically forany particular stress. Some interpret

Box 2:

‘‘I had brought with me the firstvolume of Lyell’s ‘‘Principles ofGeology,’’ which I studied atten-tively; and the book was of thehighest service to me in manyways. . . . [It] showed me clearlythe wonderful superiority of Lyell’smanner of treating geology, com-pared with that of any otherauthor, whose works I had withme or ever afterwards read.’’

Life and letters of CharlesDarwin, 1887 (his private autobiog-raphy)

CROTCHETS & QUIDDITIES Uniformitarianism Then and Now 9

this mechanism as a strategy to im-prove one’s chances under unspeci-fied stress, seeing it as a kind of‘‘evolvability’’ system. Several othersuch mechanisms not involving chap-eronins have also been suggested.26–28

What these mechanisms seem to dois produce hopeful molecular mon-sters rather than morphological ones.A molecule is not an organized, com-plex new trait suddenly popping up.It is interesting, however, that manyof the genes normally protected bychaperonins are related to the devel-opmental pathways that would haveto go awry to produce major morpho-logical monsters.

A TEMPEST IN THE TEAPOT?

These are interesting findings thatget press ink, but are they telling usmore about hopeful monsters orhopeful scientists wanting monstrousinsights that overthrow Darwin’s ba-sic ideas? The answer is that Darwincan rest easy. And the reason is aconfusing of product with process.It’s true enough that homeotic and

other segmental changes are discreterather than continuous. However,they involve differences in the num-ber of similar already-existing struc-tures, and hence variation in thesame well-established process, not adiscontinuity of process nor a sud-den new process, and hence no realdeparture from classical evolutionaryideas. Mutations in QTL are part ofthe normal, perfectly mainstream na-ture of mutation and genomic change.Given that mutations can strike anypart of a gene, it is not any sort ofsurprise that their effects will not beuniformly small. The same is true ofgene duplication. Likewise, the Hspstory is about the release of existingvariation that must be screened byordinary drift and selection, notmonsters arising ready-made in timesof stress. There is no violation of or-dinary day-to-day biology.If one wants to be a contrarian,

given what we know about genes andgenomes, we could argue that genet-ics has shown that discrete change—saltation—is the only way heritablechange happens. In that sense, Dar-win would have been totally wrong,but only as a rather minor technical-

Figure 3. Hopeful monsters. A. Passage from Hell? (from Dana5). B. In the confines of Hell.From Gustave Dore illustrations from Milton’s Paradise Lost, 1866.

10 Weiss CROTCHETS & QUIDDITIES

ity, because most mutational change,even if discrete, is either devastatingand we rarely see it, or has minisculeDarwin-like effects.In the end, without any revolution-

ary thinking, we can see that Naturedoesn’t always just inch along with in-finitesimal creep. Darwin would haveno problem accommodating his viewsof Nature these new facts. Althoughgradualism was key to the views ofevolutionary thinking in both geologyand biology, growing out of the uni-formitarian assumption, the key factwas not that everything had to begradual, but that slow, gradual changewas very difficult to observe directly.Nevertheless, such change was a majorway in which large changes happenedin Nature without catastrophic events.The key aspect of uniformitarianismis that the same processes have beentaking place throughout the history oflife. But uniformitarianism does notimply gradualism.The real exceptions that would be

needed to give Darwin’s ghost theshakes would be entirely new kindsof traits arising instantly, ready-made, and properly wired into therest of the body. We know of few, ifany, such instances. Indeed, weknow enough about the hierarchicalnature of developmental genetics toknow why that is so. Organized traitshave to develop in proper develop-mental context with what’s going onin the rest of the embryo. We knowexamples of what seem to be simpleand hence, possibly rapid change ofsubstantial sorts, such as related spe-cies of sea urchin or amphibian thatdo or don’t undergo separate tadpolestages, or repeated evolution of blind-ness in cave fish that can be restoredby interbreeding. But these changesarise as understandable switches indevelopmental processes, and someexamples caught in the act are poly-morphic within species. These eventsdon’t suddenly generate whole newtraits.Uniformitarianism is the belief

that the cosmos is basically a univer-sal, continuous, Newtonian (law-like)river of causation. In fact, the samebelief is consistent with probabilistic

causation, so long as its behavior islaw-like as, for example, Mendeliansegregation and genetic drift. Unifor-mitarianism provides a workableframework for research because itdoes not require ad hoc invocation ofexceptions and special cases or crea-tion events. No matter how jumpyNature may occasionally turn out tobe, none of the apparent exceptionsto continuity or gradualism suspendthe basic ways that Nature fills life’scup of alteration, as Shakespearemight put it. These exceptions reflectthe ability of genetic change undersome circumstances to produce newvariations on existing themes. On thebasis of present evidence, the hopeof scientists to escape from obscurityin the shadows of Darwin seems tobe as vain as the hope of monsters toescape from the shadows of Hell(Fig. 3). Nonetheless, the way unifor-mitarianism actually works from dayto day need not be uniform, even ifthe rules of life work uniformly. Anda sudden burst like Mount St. Helensdoesn’t change the rules of geology,either.

NOTES

I welcome comments on this col-umn: kenweiss@psu.edu. I have afeedback and supplemental materialpage at http://www.anthro.psu.edu/weiss_lab/index.html. I thank AnneBuchanan, Jeff Kurland, and espe-cially John Fleagle for critically read-ing this manuscript.

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