atkinsongray2006a how old is ie lang fam

8/7/2019 AtkinsonGray2006a How old is IE lang Fam

1/20

91

HowOldistheIndoEuropeanLanguageFamily?

Chapter8

HowOldistheIndoEuropeanLanguageFamily?IlluminationorMoreMothstotheFlame?

QuentinD.Atkinson&RussellD.Gray

European(thehypothesizedancestralIndoEuropeantongue)withtheKurgancultureofsouthernRussiaandtheUkraine.TheKurganswereagroupofseminomadic,pastoralist,warriorhorsemenwhoexpandedfromtheirhomelandintheRussiansteppesduring

thefiPhandsixthmillennia,conqueringDanubianEurope,CentralAsiaandIndia,andlatertheBalkansandAnatolia.Thisexpansionis thoughttoroughlymatchtheacceptedancestralrangeofIndoEuropean(Trask1996).As well as the apparent geographicalcongruencebetweenKurganandIndoEuropeanterritories,thereislinguisticevidenceforanassociation

betweenthetwocultures.WordsforsupposedKurgantechnologicalinnovationsarenotablyconsistentacrosswidelydivergentIndoEuropeansubfamilies.Theseincludetermsforwheel(*rotho,*kW(e)kWlo),axle(*akslo),yoke(*jugo),horse(*ekwo)andtogo,transportinavehicle( *wegh:Mallory1989;Campbell2004).Itisarguedthatthesewordsandas

sociatedtechnologiesmusthavebeenpresentintherotoIndoEuropeancultureandthattheywerelikelytohavebeenKurganinorigin.Hence,theargumentgoes,theIndoEuropeanlanguagefamilyisnoolderthan50006000.Mallory(1989)arguesforasimilartimeandplaceofIndoEuropeanoriginaregionaroundtheBlackSeaabout50006000 (althoughhe is more cautious and refrains from identifyingrotoIndoEuropeanwithaspecificculturesuchastheKurgans).

The second theory, proposed by archaeologistColin Renfrew (1987), holds that IndoEuropeanlanguagesspread,notwithmaraudingRussianhorsemen,butwiththeexpansionofagriculturefromAna

toliabetween8000and9500yearsago.RadiocarbonanalysisoftheearliestNeolithicsitesacrossEuropeprovidesafairlydetailedchronologyofagriculturaldispersal.ThisarchaeologicalevidenceindicatesthatagriculturespreadfromAnatolia,arrivinginGreeceatsometimeduringtheninthmillenniumandreachingasfarastheBritishIslesby5500(Gkiastaetal.2003).Renfrewmaintainsthatthelinguisticargument

1.Anelectriclightonasummernight

TheoriginofIndoEuropeanhasrecentlybeendescribedasoneofthemostintensivelystudied,yetstillmostrecalcitrantproblemsofhistoricallinguistics

(Diamond&Bellwood2003,601).Despiteover200yearsofscrutiny,scholarshavebeenunabletolocatetheoriginofIndoEuropeandefinitivelyintimeorplace.Theorieshavebeenputforwardadvocatingagesrangingfrom4000to23,000years(Oe1997),withhypothesized homelandsincluding Central Europe(Devoto1962),theBalkans(Diakonov1984),andevenIndia(Kumar1999).Mallory(1989)acknowledges14distincthomelandhypothesessince1960alone.Herathercolourfullyremarksthat

thequestfortheoriginsoftheIndoEuropeanshasallthefascinationofanelectriclightintheopenaironasummernight:ittendstoaracteveryspeciesofscholarorwouldbesavantwhocantakepento

hand(Mallory1989,143).Unfortunately,archaeological,geneticandlinguisticresearchonIndoEuropeanoriginshassofarprovedinconclusive. Whilst numerous theories of IndoEuropean origin have been proposed, they haveprovendifficulttotest.Inthischapter,weoutlinehowtechniquesderivedfromevolutionarybiologycanbeadaptedtotestbetweencompetinghypothesesaboutthe age of the IndoEuropeanlanguage family. Wearguethatthesetechniquesareausefulsupplementtotraditional methodsin historicallinguistics.Thischapterisadevelopmentandextensionofpreviousworkontheapplicationofphylogeneticmethodstothestudy of language evolution (Gray &Atkinson

2003;Atkinson&Gray2006;Atkinsonetal.2005).

2.Twotheories

TherearecurrentlytwomaintheoriesabouttheoriginofIndoEuropean.Thefirsttheory,putforwardbyMaraGimbutas(1973a,b)onthe basisof linguisticand archaeological evidence, links rotoIndo


2/20

92

Chapter8

fortheKurgantheoryisbasedononlylimitedevidenceforafewenigmaticrotoIndoEuropeanwordforms.HepointsoutthatparallelsemanticshiPsorwidespreadborrowingcanproducesimilarwordforms

acrossdifferentlanguageswithoutrequiringthatanancestral term was present in the protolanguage.RenfrewalsochallengestheideathatKurgansocialstructureandtechnologywassufficientlyadvancedtoallowthemtoconquerwholecontinentsinatimewhenevensmallcitiesdidnotexist.Farmorecredible, heargues,isthat rotoIndoEuropean spreadwiththespreadofagricultureascenariothatisalsothoughttohaveoccurredacrosstheacific(Bellwood1991;1994),SoutheastAsia(Glover&Higham1996)andsubSaharanAfrica(Holden2002).Onthebasisoflinguisticevidence,Diakonov(1984)alsoarguesforanearlyIndoEuropeanspreadwithagriculturebutplacesthehomelandintheBalkansapositionthat

maybereconcilablewithRenfrewstheory.The debate about IndoEuropeanorigins thuscentresonarchaeologicalevidencefortwopopulationexpansions,bothimplyingverydifferenttimescales the Kurgan theory with a dateof 50006000 ,andtheAnatoliantheorywithadateof80009500.Onewayofpotentiallyresolvingthedebateistolookoutside the archaeological record for independentevidencethatallowsustotestbetweenthesetwotimedepths.Geneticstudiesofferonepotentialsourceofevidence.Unfortunately,duetoproblemsassociatedwithadmixture,slowratesofgeneticchangeandtherelativelyrecenttimescalesinvolved,geneticanalyseshavebeenunabletoresolvethedebate(CavalliSforza

etal.1994;Rosser etal.2000).Anotherpotentiallineofevidenceiscontainedinthelanguagesthemselves,anditisthelinguisticevidenceweshallturntonow.

3.ThedemiseofgloDochronologyandtheriseofcomputationalbiology

Languages, likegenes, chronicle their evolutionaryhistory.Languages,however,changemuchfasterthangenesandsocontainmoreinformationatshallowertimedepths.Conventionalmeansoflinguisticinquiry,likethecomparativemethod,areabletoinferancestralrelationshipsbetweenlanguagesbutcannotprovideanabsoluteestimateoftimedepth.Analternativeap

proachisMorrisSwadeshs(1952;1955)lexicostatisticsanditsderivativegloochronology.Thesemethodsuselexicaldatatodeterminelanguagerelationshipsand to estimate absolute divergence times. Lexicostatisticalmethodsinferlanguagetreesonthebasisofthepercentageofsharedcognatesbetweenlanguagesthemoresimilarthelanguages,themorecloselytheyarerelated.Wordsarejudgedtobecognateifthey

canbeshowntoberelatedviaapaernofsystematicsound correspondences andhavesimilar meanings(see Fig. 8.1 for some examples). This informationcanbeusedtoconstructevolutionarylanguagetrees.

Gloochronologyisanextensionofthisapproachtoestimatedivergence times under theassumptionofaglooclock,orconstantrateoflanguagechange.Thefollowingformulaecanbeusedtorelatelanguagesimilaritytotimealonganexponentialdecaycurve:

t logC

2logr

wheretistimedepthinmillennia,Cisthepercentageofcognatessharedandristheuniversalconstantorrateofretention(theexpectedproportionofcognatesremaining aPer 1000 years of separation: Swadesh1955).Usually,analysesarerestrictedtotheSwadeshwordlist,acollectionof100200basicmeaningsthat

arethoughttoberelativelyculturallyuniversal,stableand resistant to borrowing. These include kinshipterms(e.g.mother,father),termsforbodyparts(e.g.hand,mouth,hair),numeralsandbasicverbs(e.g.todrink,tosleep,toburn).FortheSwadesh200wordlist,avalueof81percentisoPenusedforr.

Linguistshave identified a number of seriousproblemswiththegloochronologicalapproach:1. Muchoftheinformationinthelexicaldataislost

whenwordinformationisreducedtopercentagesimilarity scores between languages (Steel etal.1988).

2. Themethodsusedtoconstructevolutionarytreesfromlanguagedistancematriceshavebeenshown

toproduceinaccurateresults,particularlywhereratesofchangevary(Blust2000).3. Languagesdonotalwaysevolveataconstantrate.

Bergsland& Vogt (1962) compared presentdaylanguages with their archaic forms and foundevidence for significant rate variation betweenlanguages.Forexample,IcelandicandNorwegianwere compared to their common ancestor, OldNorse,spokenroughly1000yearsago.Norwegianhasretained81percentofthevocabularyofOldNorse,correctlysuggestinganageofapproximately1000years.However,Icelandichasretainedover95percentoftheOldNorsevocabulary,falselysuggestingthatIcelandicsplitfromOldNorseless

than200yearsago.4. Languages do not always evolve in a treelikemanner(Batemanetal.1990;Hjelmslev1958).Borrowingbetweenlanguagescanproduceerroneous(or,inextremecases,meaningless)languagetrees.Also,widespreadborrowingcanbiasdivergencetimeestimatesbymakinglanguagesseemmoresimilar(andhenceyounger)thantheyreallyare.


3/20

93


These problems have led many linguists tocompletelyabandonanyaempttoderivedatesfromlexicaldata.Forexample,Clackson(2000,451)claimsthatthedataandmethodsdonotallowthequestion

WhenwasrotoIndoEuropeanspoken?tobeansweredinanyreallymeaningfulorhelpfulway.

Fortunately,noneoftheseproblemsareuniquetolinguistics.It isironicthat whilst computationalmethods in historical linguistics have fallen out offavouroverthelasthalfcentury,computationalbiologyhasthrived.Inmuchthesamewayaslinguistsuseinformationaboutcurrentandhistoricallyaestedlanguagestoinfertheirhistory,evolutionarybiologistsuse DNA sequence, morphological and sometimes

behavioural data to construct evolutionary treesof biological species. Questions of relatedness anddivergencedatesareofinteresttobiologistsjustastheyaretolinguists.Asaresultbiologistsmustalso

dealwith the problems outlinedabove:nucleotidesequenceinformationis lostwhendataisanalyzedasdistancematrices(Steeletal.1988);distancebasedtreebuildingmethodsmaynotaccuratelyreconstructphylogeny (Kuhner & Felsenstein 1994); differentgenes(andnucleotides)evolveatdifferentratesandtheseratescanvarythroughtime(Excoffier&Yang1999);andfinally,evolutionisnotalwaystreelikeduetophenomenasuchashybridizationandhorizontalgenetransfer(Faguy&Doolile2000).

Despitetheseobstacles,computationalmethodshaverevolutionizedevolutionarybiology.Ratherthangiving up and declaringthat timedepth estimatesareintractable,biologistshavedevelopedtechniques

toovercomeeachproblem.Here,wedescribehowthesebiologicalmethodscanbeadaptedandappliedtolexicaldatatoanswerthequestionHowoldistheIndoEuropeanlanguagefamily?

4.Fromwordliststobinarymatrices

Inordertoestimatephylogeniesaccuratelyweneedtoovercometheproblemofinformationlossencounteredinlexicostatisticsandgloochronology.Thisrequiresalargedatasetwithindividualcharacterstateinformationforeachlanguage.Lexicaldataareidealbecausethereare alargenumber ofwellstudiedcharactersavailableandthesecanbe dividedintomeaningful

evolutionaryunitsknownascognatesets(asdescribedabove,wordsarejudgedtobecognateiftheycanbeshowntoberelatedviaapaernofsystematicsoundcorrespondencesandhavesimilarmeaning).Cognatewordsfromdifferentlanguagescanbegroupedintocognatesetsthatreflectpaernsofinheritance.Owingtothepossibilityofunintuitiveormisleadingsimilaritiesbetweenwordsfromdifferentlanguages,expert

knowledgeofthesoundchangesinvolvedisrequiredinordertomakecognacyjudgementsaccurately.Forexample, knowledge of regular sound correspondencesbetweenthelanguagesisrequiredtoascertain

thattheEnglishwordwheniscognatewithGreekpoteofthesamemeaning.Conversely,EnglishhaveisnotcognatewithLatinhaberedespitesimilarwordformandmeaning.

Toestimatetreetopologyandbranchlengthsaccuratelyrequiresalargeamountofdata.OurdatawastakenfromtheDyen etal.(1992)IndoEuropeanlexicaldatabase,whichcontainsexpertcognacyjudgementsfor200Swadeshlisttermsin95languages.Dyenetal.(1997)identifiedelevenlanguagesaslessreliableandhencetheywerenotincludedintheanalysispresentedhere.Threeextinctlanguages(Hiite,TocharianAandTocharianB)wereaddedtothedatabaseinanaempttoimprovetheresolutionofbasalrelationshipsinthe

inferredphylogeny.Multiplereferenceswereusedtocorroboratecognacyjudgements(Adams1999;Gamkrelidze&Ivanov1995;Guterbock&Hoffner1986;Hoffner1967;Tischler1973;1997).Foreachmeaninginthedatabase,languagesweregroupedintocognatesets.SomeexamplesareshowninFigure8.1.

ByrestrictinganalysestobasicvocabularysuchastheSwadeshwordlisttheinfluenceofborrowingcanbeminimized.Forexample,althoughEnglishisaGermaniclanguage,ithasborrowedaround60percentofitstotallexiconfromFrenchandLatin.However,onlyabout6percentofEnglishentriesintheSwadesh200wordlistareclearRomancelanguage

borrowings(Embleton1986).Knownborrowingswere

notcodedascognateintheDyenetal.database.Forexample,theEnglishwordmountainwasnotcodedascognatewithFrenchmontagne,sinceitwasobviously

borrowedfromFrenchintoEnglishaPertheNormaninvasion.Anyremainingreticulationcanbedetectedusingbiologicalmethodssuchassplitdecomposition,which can identify conflicting signal. The issue of

borrowinginlexicaldataisdiscussedinmoredetailbyHolden&Gray(Chapter2thisvolume;seealsoBryantetal.2005).

WecanrepresenttheinformationinFigure8.1mostsimplyasbinarycharactersinamatrix,wherethepresenceorabsenceofaparticularcognatesetinaparticularlanguageisdenotedbya1 or0respec

tively.Figure8.2showsabinaryrepresentationofthecognateinformationfromFigure8.1.Usingthiscodingprocedureweproducedamatrixof2449cognacy

judgementsacross87languages.Alternativecodingmethodsarealsopossible, suchasrepresentingthedata as 200meaning categories eachwith multiplecharacter states. It has been argued that semanticcategoriesarethefundamentalobjectsoflinguistic


4/20

94

Chapter8

change(seeEvans etal.Chapter9thisvolume)andthatbinarycodingofthepresenceorabsenceofcognatesetsisthusinappropriate.However,cognatesetsconstitutediscrete,relativelyunambiguousheritableevolutionaryunitswithabirthanddeath(seeNicholls&Gray,Chapter14thisvolume)andthereisnoreasontosupposetheyareanymoreorlessfundamentaltolanguage evolution than semantic categories. Further, coding thedata as semantic categories makes

itdifficulttodealwithpolymorphisms(i.e.whenalanguagehasmorethanonewordforagivenmeaninge.g.forthemeaningseaGermanhasbothSeeandMeer).Italsosignificantlyincreasesthenumberofparametersrequiredtomodeltheprocessofevolution.agel(2000)pointsoutthat,ifeachwordrequiresa differentset of rateparameters,then forjust 200wordsin40languagesthereare1278parameterstoestimate.Wethususedabinarycodingofcognatepresence/absenceinformationtorepresentlinguistic

changeinouranalysis.Aswellasavoidingtheproblemofinformationloss,analyzingcognatepresence/absenceinformationallowsustoexplicitlymodeltheevolutionaryprocess.UnlikelexicostatisticsandgloAochronology,wedonotcountthenumberofcognatessharedbetweenlanguages,nordowecalculatepairwisedistancesbetweenlanguages. Instead,thedistributionofcognatesismappedontoanevolutionarylanguagetree(seeFig.8.3),andlikelycharacterstatechangesareinferredacrossthewholetree.

5.Modelsareliesthatleadustothetruth

Whenbiologists model evolution, theylie: theylieabout the independence of character state changesacrosssites;theylieaboutthehomogeneityofsubstitutionmechanisms;andtheylieabouttheimportanceofselectionpressureonsubstitutionrates.Buttheseareliesthatleadustothetruth.Biologicalresearchis

basedonastrategyofmodelbuildingandstatisticalinference that has proved highly successful (Hillis

English here1 sea5 water9 when12

German hier1 See5,Meer6 Wasser9 wann12

French ici2 mer6 eau10 quand12

Italian qui2,qua2 mare6 acqua10 quando12

ModernGreek edo3 thalassa7 nero11 pote12

Hiite ka4 aruna8 watar9 kuwapi12

Figure8.1.SelectionoflanguagesandSwadeshlistterms.Cognacyisindicatedbythenumbersinsuperscript.

Meaning here sea water when

Cognateset 1 2 3 4 5 6 7 8 9 10 11 12

English 1 0 0 0 1 0 0 0 1 0 0 1

German 1 0 0 0 1 1 0 0 1 0 0 1

French 0 1 0 0 0 1 0 0 0 1 0 1

Italian 0 1 0 0 0 1 0 0 0 1 0 1

Greek 0 0 1 0 0 0 1 0 0 0 1 1

Hiite 0 0 0 1 0 0 0 1 1 0 0 1

Figure8.2.CognatesetsfromFigure8.1expressedinabinarymatrixshowingcognatepresence(1)orabsence(0).

Figure8.3.Characterstatesforcognatesets5(black)and6(grey)fromFigure8.1areshownmappedontoahypotheticaltree.Impliedcharacterstatechangescanthenbereconstructedonthetree.Theblackandgreybandsshowalikelypointatwhichcognatesets5and6weregained.Wecanusethisinformationtoevaluatepossibleevolutionaryscenarios.


5/20

95


1992;Hillisetal.1996;agel1999).Thegoalforbiologistsisnottoconstructamodelsocomplexthatitcaptureseverynuanceandvagaryoftheevolutionaryprocess,butrathertofindthesimplestmodelavailablethatcanreliablyestimatetheparametersofinterest.

Modelchoiceisthusabalancebetweenoverandunderfiingparameters(Burnham&Anderson1998). Adding extra parameters can improve theapparentfitofamodeltodata,however,samplingerroris also increasedbecause thereare moreunknownparameterstoestimate(Swoffordetal.1996).Dependingonthequestionwearetryingtoanswer,thisaddeduncertaintycanpreventusfromestimatingthemodelparametersfromthedatatowithinausefulmarginoferror.Inmanycases,addingjustafewextraparameterscancreateacomputationallyintractableproblem.Conversely,amodelthatistoosimplecanproducebiasedresultsifitfailstocaptureanimportantpartoftheprocess(Burnham&

Anderson1998).Thereisthusacompromisebetweenbiasedestimatesandvarianceinflation.Thestrategythathasprovedsuccessfulinbiol

ogyistostartwithasimplemodelthatcapturessomeof thefundamentalprocessesinvolvedand increasethecomplexityasnecessary.Forexample,nucleotidesubstitutionmodelsrangefromasimpleequalratesmodel(Jukes&Cantor1969),tomorecomplexmodelsthat allow for differences in transition/transversionrates,unequalcharacterstatefrequencies,sitespecificrates,andautocorrelationbetweensites(Swofford etal.1996).Althougheventhemostcomplicatedmodelsaresimplificationsoftheprocessofevolution,oPenthesimplestsubstitutionmodelcapturesenoughofwhat

isgoingontoallowbiologiststoextractameaningfulsignalfromthedata.Levins(1966)givesthreereasonswhyweshoulduseasimplemodel.First,violationsoftheassumptionsofthemodelareexpectedtocanceleachotherout.Second,smallerrorsinthemodelshouldresultinsmallerrorsintheconclusions.Andthird,bycomparingmultiplemodelswithrealitywecandeterminewhichaspectsoftheprocessareimportant.

Likelihoodevolutionarymodellinghasbecomethemethodofchoiceinphylogenetics(Swoffordetal. 1996). The likelihood approach to phylogeneticreconstructionallowsustoexplicitlymodeltheproc

essoflanguageevolution.Themethodisbasedonthepremisethatweshouldfavourthetreetopology/topologiesandbranchlengthsthatmakeourobserveddatamostlikely,giventhedataandassumptionsofourmodeli.e.weshouldfavourthetreewiththehighestlikelihoodscore.Wecanevaluatepossibletreetopologiesforagivenmodelanddatabymodellingthesequenceofcognategainsandlossesacrossthetrees.

Likelihoodmodelshaveanumberofadvantagesoverotherapproaches.First,wecanworkwithexplicitmodelsofevolutionandtestbetweencompetingmodels.Theassumptionsofthemethodarethusovertand easilyverifiable.Second,we canincrease

thecomplexityof themodelas required.Forexample,asexplainedbelow,wewereabletotestfortheinfluenceofratevariationbetweencognatesetsand,asaresult,incorporatethisintotheanalysisusingagamma distribution. And third, model parameterscanbeestimatedfromthedataitself,thusavoidingrestrictiveaprioriassumptionsabouttheevolutionaryprocessesinvolved(agel1997).

Likelihoodmodelsofevolutionareusuallyexpressedasaratematrixrepresentingtherelativeratesofallpossiblecharacterstatechanges.Here,weareinterestedintheprocessesofcognategainandloss,respectivelyrepresentedby0to1changesand1to0changesonthetree(seeFig.8.3).Wecanmodelthis

processeffectivelywitharelativelysimpletwostatetimereversiblemodeloflexicalevolution(showninFig.8.4).Weextendedthissimplemodelbyaddingagammashapeparameter()toallowratesofchangetovarybetweencognatesetsaccordingtoagammadistribution.ThiswasimplementedaPeralikelihoodratio test (Goldman1993) showed that adding thegammashapeparametersignificantlyimprovedtheabilityofthemodeltoexplainthedata(2=108,df=1,p


6/20

96

Chapter8

theprocessof linguistic change,weexplicitlyrejectWarnow etal.s (Chapter7 thisvolume) counselofdespair,thatlanguageevolution is so idiosyncraticand unconstrained that inferring divergence datesisimpossible.Languageevolutionissubjecttoreal

worldconstraints,suchashumanlanguageacquisition, expressiveness, intelligibility, and generationtime.WecannothelpbutquoteRingeetal.(2002,61)onthispoint:

Languagesreplicatethemselves(andthussurvivefromgeneration togeneration) through a processofnativelanguageacquisitionbychildren.Importantlyforhistoricallinguistics,thatprocessistightlyconstrained.

Theseconstraintscreateunderlyingcommonalitiesintheevolutionaryprocessthatwecan,andshould,betryingtomodel.

Evans et al. (Chapter 10 this volume) arguethatourmodelispatentlyinappropriatebecause

it assumes that all charactersare independent. Inbiology,thisisknownastheI.I.D.(identicallyandindependently distributed) assumption. Evans etal.correctlypointoutthattheI.I.D.assumptionisviolatedwhenindividualmeaningsintheSwadeshwordlistarebrokenupintocharactersrepresentingmultiple cognate sets. Specifically, if a particularcognatesetispresentinalanguage,itwillbe less

likelythatothercognatesetsforthesamemeaningwillalsobepresent.However,wedonotthinkthatthislackofindependencebiasesourresults.Theissueofindependencewillbedealtwithindetailin

section10.2.

6.Bayesianinferenceofphylogeny

Itisnotusuallycomputationallyfeasibletoevaluatethelikelihoodofallpossiblelanguagetreesfor87languagesthereareover110155possiblerootedtrees.Further,thevastnumberofpossibilitiescombinedwithfinitedatameansthatinferringasingletreewillbemisleadingtherewillalwaysbeuncertaintyinthetopology and branchlengths. Ifwe are touse ourresults to testhypotheseswe needto useheuristicmethodstosearchthroughtreespaceandquantifythisphylogeneticuncertainty. Bayesianinference is

analternativeapproachtophylogeneticanalysisthatallowsustodrawinferencesfromalargeamountofdata using powerful probabilistic models withoutsearchingfor the optimaltree (Huelsenbeck etal.2001).Inthisapproachtreesaresampledaccordingtotheirposteriorprobabilities.Theposteriorprobabilityofatree(theprobabilityofthetreegiventhepriors,dataandthemodel)isrelatedbyBayesstheoremtoitslikelihoodscore(theprobabilityofthedatagiventhetree)anditspriorprobability(areflectionofanyprior knowledge about tree topology that is to beincludedintheanalysis).Unfortunately,wecannotevaluatethisfunctionanalytically.However,wecanuseaMarkovChainMonteCarlo(MCMC:Metropolis

etal.1953)algorithmtogenerateasampleoftreesinwhichthefrequencydistributionofthesampleisanapproximationoftheposteriorprobabilitydistributionofthetrees(Huelsenbecketal.2001).Todothis,weusedMrBayes,aBayesianphylogeneticinferenceprogramme(Huelsenbeck&Ronquist2001).

MrBayes uses MCMC algorithms to searchthroughtherealmofpossibletrees.Fromarandomstartingtree,changesareproposedtothetreetopology,branchlengthsandmodelparametersaccordingtoaspecifiedpriordistributionoftheparameters.Thechangesareeitheracceptedorrejectedbasedonthe likelihood ofthe resulting evolutionaryreconstructioni.e.reconstructionsthatgivehigher

likelihoodscores tend tobe favoured.Inthiswaythechainquicklygoesfromsamplingrandomtreestosamplingthosetreeswhichbestexplainthedata.APeraninitialburninperiod,treesbegintobesampledinproportiontotheirlikelihoodgiventhedata.Thisproducesadistributionoftrees.Ausefulwaytosummarizethisdistributioniswithaconsensustreeorconsensusnetwork(Holland&Moulton2003)

Figure8.5.Thegammadistribution,usedtomodelratevariationbetweensites.Threepossiblevaluesforareshown.Forsmallvaluesof(e.g.=0.5),mostcognatesetsevolveslowly,butafewcanevolveathigherrates.sincreases,thedistributionbecomesmorepeakedandsymmetricalaroundarateof1i.e.ratesbecomemoreequal(e.g.=50).


7/20

97


depictinguncertaintyinthereconstructedrelationships.Thesegraphsare,however,justusefulpictorialsummariesoftheanalysis.Thefundamentaloutputoftheanalysisisthedistributionoftrees.

TheconsensusnetworkfromaBayesiansample

distributionof100treesisshowninFigure8.6.Thevaluesnexttosplitsgiveanindicationoftheuncertaintyassociatedwitheachsplit(theposteriorprobability,derivedfromthepercentageoftreesintheBayesiandistributionthatcontainthesplit).Forexample,thevalue41nexttotheparallellinesseparatingItalicandCeltic from the of the IndoEuropean subfamiliesindicatesthatthatsplitwaspresentin41percentof

thetreesinthesampledistribution.Similarly,thesplitgroupingItalicandGermaniclanguageswaspresentin46percentofthesampledistribution.

7.Ratevariationandestimatingdates

Thereareatleasttwotypesofratevariationinlexicalevolution.First,ratevariationcanoccurbetweencognates.Forexample,evenintheSwadeshwordlist,theIndoEuropeanwordforfiveishighlyconserved(1 cognate set) whilst the word for dirty is highlyvariable(27cognatesets).Thisisakintositespecificrate variationin biology. Biologists canaccount for

Figure8.6.ConsensusnetworkfromtheBayesianMCMCsampleoftrees.Valuesexpresstheposteriorprobabilityofeachsplit(valuesabove90percentarenotindicated).thresholdof10percentwasusedtodrawthissplitsgraphi.e.onlythosesplitsoccuringinatleast10percentoftheobservedtreesareshowninthegraph.Branchlengthsrepresentthemediannumberofreconstructedsubstitutionspersiteacrossthesampledistribution.


8/20

98

Chapter8

thistypeofratevariationbyallowingadistributionof rates.As mentionedabove, weused a model ofcognateevolutionthatallowedforgammadistributedratevariationbetweencognates.

Second, rates of lexical evolution can varythroughtimeandbetweenlineages.Clearlythiswillcauseproblemsifwearetryingtoestimateabsolutedivergencetimesontheinferredphylogeniessinceinferredbranchlengthsarenotdirectlyproportionaltotime.Again,biologistshavedevelopedanumberofmethodsfordealingwiththistypeofratevariation.Weusedthepenalizedlikelihoodmethodofratesmoothingimplementedinr8s(version1.7;Sanderson2002a),to allow forrate variation across each tree.Sanderson(2002b)hasshownthat,underconditionsofratevariation,thepenalizedlikelihoodratesmoothingalgorithmperformssignificantlybeerthanmethodsthatassumeaconstantrateofevolution.

Inordertoinferabsolutedivergencetimes,wefirstneedtocalibrateratesofevolutionbyconstrainingtheageofknownpointsoneachtreeinaccordancewithhistoricallyaesteddates.Forexample,theRomancelanguages(derivedfromLatin)probablybegantodivergepriortothefalloftheRomanEmpire.WecanthusconstraintheageofthenodecorrespondingtothemostrecentcommonancestoroftheRomance

languagestowithintherangeimpliedbyourhistoricalknowledge(seeFig.8.7).Weconstrainedtheageof14suchnodesonthetreeinaccordancewithhistoricalevidence(seeAtkinson&Gray2006).Theseknown

nodeageswerethencombinedwithbranchlengthinformationtoestimateratesofevolutionacrosseachtree.Thepenalizedlikelihoodmodelallowsratestovary across the treewhilstincorporating a roughnesspenaltythatcoststhemodelmoreifratesvaryexcessively frombranchto branch.This procedureallowsustoderiveageestimatesforeachnodeonthetree.Figure8.8showstheconsensustreefortheinitialBayesiansampledistributionof1000trees, 1with

branchlengthsdrawnproportionaltotime.Theposteriorprobabilityvaluesaboveeachinternalbranchgiveanindicationoftheuncertaintyassociatedwitheachcladeontheconsensustree(thepercentageoftreesintheBayesiandistributionthatcontaintheclade).For

example,thevalue67abovethebranchleadingtotheItaloCeltoGermaniccladeindicatesthatthatcladewaspresentin67percentofthetreesinthesampledistribution.We canderive ageestimates fromthistree,includinganageof 8700at the baseof thetreewithintherangepredictedbytheAnatolianfarmingtheoryofIndoEuropeanorigin.

Asingledivergencetime,withnoestimateoftheerrorassociatedwiththecalculation,isoflimitedvalue.To testbetween historical hypotheses weneed somemeasureoftheerrorassociatedwiththedateestimates.Specifically,uncertaintyinthephylogenygivesrisetoacorrespondinguncertaintyinageestimates.Inordertoaccountforphylogeneticuncertaintyweestimatedthe

ageatthebaseofthetreesinthepostburninBayesianMCMC sampletoproducea probabilitydistributionfortheageof IndoEuropean. Oneadvantageof theBayesian framework is that prior knowledge aboutlanguage relationships can be incorporated into theanalysis. Inordertoeliminatetreesthat conflictwithknownIndoEuropeanlanguagegroupings,theoriginal1000treesamplewasfilteredusingaconstrainttreerepresentingtheseknownlanguagegroupings[(Anatolian,Tocharian,(Greek,Armenian,Albanian,(Iranian,Indic),(Slavic,Baltic),((NorthGermanic,WestGermanic),Italic,Celtic)))].ThisconstrainttreewasconsistentwiththemajorityruleconsensustreegeneratedfromtheentireBayesiansampledistribution.Thefiltereddistribution

ofdivergencetimeestimateswasthenusedtocreateaconfidenceintervalfortheageoftheIndoEuropeanlanguagefamily.ThisdistributioncouldthenbecomparedwiththeagerangesimpliedbythetwomaintheoriesofIndoEuropeanorigin(seeFig.8.9).TheresultsareclearlyconsistentwiththeAnatolianhypothesis.

Notallhistoricallyaestedlanguagesplitswereusedin ouranalysis. One means of validating our

Figure8.7.TheRomancelanguages(derivedfromLatin)probablybegantodivergepriortothefalloftheRomanEmpire.Wecanthusconstraintheageofthepointonthetreewhichcorrespondstothisdivergenceevent(2).Usingthisrationale14nodeswereconstrained,includinganIberianFrenchnode(1)andaGermanicnode(3).


9/20

99


Figure8.8.MajorityruleconsensustreefromtheinitialBayesianMCMCsampleof1000trees(Gray&tkinson

2003).Valuesaboveeachbranchindicateuncertainty(posteriorprobability)inthetreeasapercentage.Branchlengthsareproportionaltotime.Shadedbarsrepresenttheagerangeproposedbythetwomaintheoriesthenatoliantheory(greybar)andtheKurgantheory(hatchedbar).Thebasalage(8700`)supportsthenatoliantheory.

methodology is to produce divergence timedistributions fornodes thatwere notconstrainedin theanalysisandcomparethistothehistoricallyaested

timeofdivergence.Forexample,Figure8.10showstheinferreddivergencetimedistributionsfortheNorthand West Germanic subgroups. The grey band in


10/20

100

Chapter8

thesefiguresindicatesthelikelyageofeachsubgroupbasedonthehistoricalrecord.TheageestimatesfortheNorthGermaniccladecorrespondwithwrienevidenceforthebreakupoftheselanguagesbetween|}900and|}1250.Similarly,estimatedagesoftheWest Germanic clade are consistentwith historical

evidence dating the AngloSaxon migration to theBritishIslesabout1500yearsago.

8.Testingrobustness

AkeypartofanyBayesianphylogeneticanalysisisanassessmentoftherobustnessoftheinferences.Todothiswetestedtheeffectofalteringanumberofdifferentparametersandassumptionsofthemethod.

8.1.BayesianpriorsInitializingeachBayesianMCMCchainrequiredthespecification of a starting treeand prior parameters(priors)fortheanalysis.ThesampleBayesiandistribu

tionwastheproductoftenseparaterunsfromdifferentrandomstartingtrees.Divergencetimeandtopologyresultsforeachoftheseparaterunswereconsistent.Othertestanalyseswererunusingarangeofpriorsforparameterscontrollingtheratematrix,branchlengths,gammadistribution and characterstatefrequencies.Theinferredtreephylogenyandbranchlengthsdidnotnoticeablychangewhenpriorswerealtered.

8.2.CognacyjudgementsTheDyenetal.(1992)databasecontainedinformationaboutthecertaintyofcognacyjudgements.Wordswerecodedascognateordoubtfulcognates.Intheinitialanalysisweincludedallcognateinformationinanefforttomaximizeanyphylogeneticsignal.However,wewantedtotesttherobustnessofourresultstochangesinthestringencyofcognacydecisions.Forthisreason,theanalysiswasrepeatedwithdoubtfulcognatesexcluded.Thisproducedasimilaragerangetotheinitialanalysis,indicatingthatourresultswererobusttoerrorsincognacyjudgements(seeFig.8.11).

Figure8.9.FrequencydistributionofbasalageestimatesfromfilteredBayesianMCMCsampleoftreesfortheinitialassumptionset(n=435).Themajorityruleconsensustreefortheentire(unfiltered)sampleisshownintheupperle.

Figure8.10.FrequencydistributionofageestimatesfortheNorthandWestGermanicsubgroupsacrossfilteredBayesianMCMCsampleoftrees(n=433).ThegreybandsindicatethehistoricallyaAestedtimeofdivergence.

Figure8.11.FrequencydistributionofbasalageestimatesfromfilteredBayesianMCMCsampleoftreesforanalysiswithdoubtfulcognatesexcluded(n=433).Themajorityruleconsensustreefortheentiresampleisshownintheupperle.


11/20

101


8.3.CalibrationsandconstrainttreesAttheconferenceonwhichthisvolumeisbased,aquestionwasraisedabouttheageconstraintusedforInsularCeltic.Itwassuggestedthatwhilst weusedamaximumageconstraintof2750,anageconstraintof between2200 and 1800 wouldhavebeenmoresuitable.WedonotwishtoengageindebatesaboutthecorrectageoftheInsularCelticdivergence,however,areanalysisofthedatausingthesuggestedagesservestodemonstratetherobustnessofourresultstovariationsinageconstraints.Figure 8.12 shows the distribution of divergencetimes using themuch later Celticage constraints.Clearly,ourresultsarerobusttoalterationsinthisageconstraint.Infact,thestepbystepremovalofeachofthe14ageconstraintsontheconsensustreerevealedthatdivergencetimeestimateswererobusttocalibrationerrors acrossthe tree. For13 nodes,thereconstructedagewaswithin390yearsoftheoriginalconstraintrange.OnlythereconstructedageforHiiteshowedanappreciablevariationfromtheconstraintrange.Thismaybeaributabletotheeffectofmissingdataassociatedwithextinctlanguages.Reconstructed ages atthe base ofthe tree rangedfrom10,400 with theremovalof theHiiteage

constraint,to8500withtheremovaloftheIraniangroupageconstraint.Theresultsarehighlyrobustcalibration errors because of the large number ofageconstraintsweusedtocalibrateratesoflexicalevolutionacrossthetree.

WealsowantedtobesurethattheconstrainttreeusedtofiltertheBayesiandistributionoftreeshadnotsystematicallybiasedourresults.Figure8.13showsthedivergencetimedistributionfortheinitialdatasetaPerfilteringusingaminimumsetoftopologicalconstraints[(Anatolian,Tocharian,(Greek,Armenian,Albanian, (Iranian, Indic), (Slavic, Baltic), (NorthGermanic,WestGermanic),Italic,Celtic))].Again,thedivergencetimedistributionwasconsistentwiththeAnatolianfarmingtheory.

8.4.MissingdataAnotherpossiblebiaswastheeffectofmissingdata.SomeofthelanguagesintheDyen etal.(1992)data

base may have contained fewer cognates becauseinformationabouttheselanguageswasmissing.Forexample,thethreeextinctlanguages(Hiite,TocharianA&TocharianB)arederivedfromalimitedrangeofsourcetextsanditispossiblethatsomecognatesweremissedbecausethetermswerenotreferredtoin

Figure8.12.Frequencydistributionofbasalageestimatesfromfiltered

BayesianMCMCsampleoftreesusingrevisedCelticageconstraintofbetween1800`and2200`.Themajorityruleconsensustreefortheentiresampleisshownintheupperle.


BayesianMCMCsampleoftreesusingminimumsetoftopologicalconstraints[(natolian,Tocharian,(Greek,rmenian,lbanian,(Iranian,Indic),(Slavic,Baltic),(NorthGermanic,WestGermanic),Italic,Celtic))](n=670).Themajorityruleconsensustreefortheentiresampleisshownintheupperle.


BayesianMCMCsampleoftreeswithinformationaboutmissingcognatesincluded(n=620).Themajorityruleconsensustreefortheentiresampleisshownintheupperle.


12/20

102

Chapter8

thesourcetext.Thismayhavebiaseddivergencetimeestimatesbyfalselyincreasingbasalbranchlengths.Nicholls&Gray(Chapter14thisvolume)pointoutthatweshouldexpectfewercognatestobepresent

inthelanguagesatthebaseofthetreeanywaythefactthatHiitehas94cognateswhilstmostlanguageshavearound200,doesnotnecessarilyimplythatdatais missing. Nonetheless, wetested forthe effect ofmissingdatabyincludinginformationaboutwhetherornotthewordforaparticulartermwasmissingfromthedatabase.Ifwecouldnotruleoutthepossibilitythatacognatewasabsentfromalanguagebecauseithadnotbeenfoundorrecorded,thenthatcognatewascodedasmissing(representedbya?inthematrix).Encodingmissingcognateinformationinthiswaymeansthatwecanaccountforuncertaintyinthedataitselfusingthelikelihoodmodeltheunknownstatesbecomeparameterstobeestimated.Analyzing

thisrecodeddataalsoproducedanagerangeconsistentwiththeAnatoliantheory(seeFig.8.14).

8.5.RootofIndoEuropeanFinally,wetestedtheeffectoftherootingpointforthetrees.Inthepreviousanalyses,treeswererootedwithHiite.Although this is consistentwith independentlinguisticanalyses(Gamkrelidze&Ivanov1995;Rexov et al. 2003), otherpotential root points arepossible.ItcouldbeclaimedthataHiiterootbiasesageestimatesinfavouroftheAnatolianhypothesis.WethusrerantheratesmoothinganalysisrootingtheconsensustreeinFigure8.8withBaltoSlavic,Greek,TocharianandIndoIraniangroups.Inallfourcases

theestimated divergence timeincreasedtobetween9500and10,700.

9.iscussion

Thetimedepthestimatesreportedhereareconsistentwiththetimespredictedbyaspreadoflanguagewith the expansion of agriculture from Anatolia.The branching paern and dates of internal nodesarebroadlyconsistentwitharchaeologicalevidenceindicatingthatbetweenthetenthandsixthmillenniaaculturebasedoncerealcultivationandanimalhusbandryspreadfromAnatoliaintoGreeceandtheBalkansandthenoutacrossEuropeandtheNearEast

(Gkiastaetal.2003;Renfrew1987).Hiiteappearstohave divergedfromthe mainrotoIndoEuropeanstockaround8700yearsago,perhapsreflectingtheinitial migration out of Anatolia. Indeed, this dateexactlymatchesestimatesfortheageofEuropesfirstagriculturalselementsinsouthernGreece(Renfrew1987). Followingthe initialsplit, the language treeshowsthe formationof separate Tocharian, Greek,

andthenArmenianlineages,allbefore6000,withall of the remaining language families formed by4000.Wenotethatthereceivedlinguisticorthodoxy (IndoEuropean is only 6000 years old) does

approximatelyfitthedivergencedatesweobtainedformostofthebranchesofthetree.Onlythebasal

branches leading to Hiite, Tocharian, Greek andArmenianarewellbeyondthisage.Interestingly,thedaterangehypothesizedfortheKurganexpansiondoescorrespondtoarapidperiodofdivergenceontheconsensustree.AccordingtothedivergencetimeestimatesshowninFigure8.8,manyofthemajorIndoEuropeansubfamiliesIndoIranian,BaltoSlavic,Germanic,ItalicandCelticdivergedbetweensixandseventhousandyearsagointriguinglyclosetothehypothesizedtimeoftheKurganexpansion.ThusitseemspossiblethatthereweretwodistinctphasesinthespreadofIndoEuropean:aninitialphase,involv

ingthemovementofIndoEuropeanwithagriculture,outofAnatoliaintoGreeceandtheBalkanssome8500yearsago;andasecondphase(perhapstheKurganexpansion)whichsawthesubsequentspreadofIndoEuropeanlanguagesacrosstherestofEuropeandeast,intoersiaandCentralAsia.

10.Responsetoourcritics

10.1.ThepotentialpitfallsoflinguisticpalaeontologyA number of linguists have claimed that linguisticpalaeontology offers a compelling reason why theargumentswehavepresentedmustbewrong:rotoIndoEuropeansareclaimedtohavehadawordfor

wheel(*kW(e)kWlo)butwheelsdidnotexistinEurope9000yearsago.Thecaseisbasedonawidespreaddistributionof apparently related words forwheelinIndoEuropeanlanguages.ThisisoPenpresentedasaknockdownargumentagainstanyageofIndoEuropeanolderthan5000to6000years(whenwheelsfirstappearinthearchaeologicalrecord).However,there are at least two alternative explanations forthedistributionoftermsassociatedwithwheelandwheeledtransport.

First,independent semanticinnovationsfromacommonrootarealikelymechanismbywhichwecanaccountforthesupposedrotoIndoEuropeanreconstructionsassociated withwheeled transport

(Trask1996;Watkins1969).Linguistscanreconstructwordformswithmuchgreatercertaintythantheirmeanings. Forexample,uponthe developmentofwheeledtransport,wordsderivedfromtherotoIndoEuropeanterm*kwel(meaningtoturn,rotate)mayhavebeenindependentlycooptedtodescribethewheel.On thebasisof thereconstructedagesshowninFigure8.8,asfewasthreesuchsemantic


13/20

103


innovationsaroundthesixthmillenniumcouldhaveaccountedfortheaesteddistributionoftermsrelatedto*kW(e)kWlowheel(oneshiPjustbeforethe break up of the ItalicCelticGermanicBalto

SlavicIndoIranianlineage,oneshiPintheGreekArmenianlineage,andoneshiP[orborrowing]intheTocharianlineage).

The second possible explanation for the distributionof termspertainingto wheeledvehiclesiswidespread borrowing. Good ideas spread. TermsassociatedwithanewtechnologyareoPenborrowedalong with the technology. The spread of wheeledtransportacrossEuropeandtheNearEast50006000yearsagoseemsalikelycandidateforborrowingofthissort.Linguistsareabletoidentifymanyborrowings(particularlymorerecentones)onthebasisofthepresenceorabsenceofcertainsystematicsoundcorrespondences.However,ourdateestimatessuggest

thatmostofthemajorIndoEuropeangroupswerejustbeginningtodivergewhenthewheelwasintroduced.WewouldthusexpectthecurrentlyaestedformsofanyborrowedtermstolookasiftheywereinheritedfromrotoIndoEuropeantheymaythusbeimpossibletoreliablyidentify.

Bothoftheseargumentsarediscussedinmoredetail elsewhere (Watkins 1969; Renfrew 1987; Atkinson&Gray2006).Itsufficestosaythatboththepowerandthepitfallsoflinguisticpalaeontologyarewellknown.Wearedisappointedthatintheirrushtodismissourpaperinthemedia,otherwisescholarlyandresponsiblelinguistshaveclaimedmuchgreatercertainty for their semantic reconstructions thanis

justifiable.Thisdoesnotmeanthatwethinkthereisnoissuehere.Ideally,weshouldaimtosynthesizealllinesofevidencerelatingtotheageofIndoEuropean.Ringe (unpublished manuscript) presents a carefulsummary of the terms related to wheeled vehiclesinIndoEuropean.Hearguesthatwordsforthill(apolethatconnectsayokeorharnesstoavehicle)andyokecanconfidentlybereconstructedforrotoIndoEuropean.Henotesthatreflexesof *kW(e)kWlowheelhavenotbeenfoundinAnatolianlanguagesbutexistin TocharianA andB andother IndoEuropeanlanguages, and hence can be reconstructed for thecommonancestorofallnonAnatolianIndoEuropeanlanguages. Ringe claims that the specific forms of

thesewordsmakeparallelsemanticchangesorborrowingextremelyimplausible.Itwouldbeextremelyusefultoaempttoquantifyjusthowunlikelysuchalternativescenariosare.Untilalltheassumptionsoftheseargumentsareformalized,andtheprobabilityofalternativescenariosquantified,itwillremaindifficulttosynthesizeallthedifferentlinesofevidenceontheageofIndoEuropean.

10.2.IndependenceofcharactersAsmentionedinsection5,Evansetal.(Chapter10thisvolume)claimourevolutionarymodelofbinarycharacterevolutionispatentlyinappropriatebecause

it assumes independence betweencharacters whenourcharactersareclearlynotindependent.However,wedonotbelievethatanyviolationofindependencenecessarilybiasesourtimedepthestimates.Wenotethattheassumptionofindependencedoesnotholdfornucleotideoraminoacidsequencedataeither.Forexample,compensatingsubstitutionsinribosomalRNAsequencesresultincorrelationbetweenpairedsitesinstemregions(Felsenstein2004).However,biologistsstillgetreasonablyaccurateestimatesofphylogenydespiteviolationsofthisassumption.Infact,nothingintheEvansetal.paperdemonstratesthatcodingthedataasbinarycharacters,ratherthanthemultistatecharacters,willproducebiasedresults.agel&Mead(Chapter15this

volume)demonstratedthat,onthecontrary,binaryandmultistatecodeddataproducetreesthatdifferinlengthbyaconstantofproportionality.Inotherwords,thebinaryandmultistatetreesarejustscaledversionsofoneanother.Sinceweestimateratesofevolutionforeachtreeusingthebranchlengthsofthattree,scalingthebranchlengthsdoesnotaffectourresults.agel&Meade(Chapter15thisvolume)alsoapproximatedtheeffectofviolationsoftheindependenceassumptionontheMCMCanalysisbyheatingthelikelihoodscores.Theyinferredthatviolationsofindependencewouldproducehigherposteriorprobabilityvaluesbutwouldhavelileeffectontheconsensustreetopology.Thismeansthatwemayhaveunderestimatedtheer

rorduetophylogeneticuncertaintybutourestimateswillnotbebiasedtowardsanyparticulardate.Finally,treatingcognatesetsasthefundamen

talunitof lexicalevolutiondoesnot,asEvansetal.(Chapter10thisvolume)argue,constituteanextremeviolation of theindependenceassumption.AlmostallofthelanguagesintheDyen etal.(1992)databasecontain polymorphisms, meaning that for a givenlanguagethereexistmultiplewordsofthesamemeaning.Thepolymorphismsinourdataareareflectionof thenature of lexicalevolution.Specifically, theydemonstrate a lack of strict dependence betweencognatesetswithinmeaningcategoriesi.e.awordwitha given meaning canarise in a languagethat

alreadyhasawordofthatmeaning.Modelsoflexicalevolutionthatdonotallowpolymorphisms(e.g.Ringeetal.2002)couldalsobelabelledas patentlyinappropriatebecausetheyassumethatforawordtoariseinalanguageanyexistingwordswiththatmeaning mustbe concomitantlylost fromthe language.Thisisnotalwaysthecase.Ringeetal.(2002)notethatalthoughthewordssmallandlilehave


14/20

104

Chapter8

verysimilarmeanings,theyhavepersistedtogetherinEnglishforoverathousandyears.Ourbinarycodingprocedureallowsustorepresentsuchpolymorphisms withease. Thepresenceof polymorphismsmeansthat dependencies betweencognatesets arenotasstrongasEvans etal. claim.Afurtherfactorthatweakensthedependenciesbetweenthecognatesetsarisesfromthethinningprocessthatoccursinlexicalevolution.Theobservedcognatesetsdonot

representthefullcomplimentofactualcognatesthataroseinIndoEuropean(seeNicholls&GrayChapter14thisvolume).Somecognatesthatexistedinthepastwill nothave persistedinto presentday languagesandanyuniquecognateswerenotincludedintheanalysis.Thisthinning ofthecognatesalsoacts toreducedependenciesbetweencharactersintheanalysisandthusfurtherweakensanyeffectofviolationsofindependence.FurtherresearchbyAtkinsonetal.(2005)usingsyntheticdatahasshownthatviolationsoftheindependenceassumptiondonotsignificantlyaffectdateestimates.

10.3.Confidenceinlexicaldata

Fromaphylogeneticviewpointthelexiconisatremendouslyaractivesourceofdatabecauseofthelargenumberofpossiblecharactersitaffords.However,weareawarethatmanyhistoricallinguistsarescepticalofinferencesbasedpurelyonlexicaldata.Garre(Chapter12thisvolume)arguesthatborrowingoflexicalterms,oradvergence,withinthemajorIndoEuropean

subgroupscouldhavedistortedourresults.Heidentifiesanumberofcaseswhereanancestraltermhas

beenreplacedbyadifferentterminallorsomeofthedaughterlanguages,presumablyviaborrowing:

ThusLatinignisfirehasbeenreplacedbyreflexesofLatinfocushearththroughoutRomance,andarchaicSanskrithanti kills hasbeen replacedby reflexesof a younger Sanskrit form marayati throughoutIndoAryan.

Garret argues correctly that, where a word hasbeen borrowed across a subgroup aPer the initialdivergenceofthe group,ourmethodwillinferthattheword evolvedin thebranchleadingup tothatsubgroup(seeLatinfocusexample:Fig.8.15a).Thiswill falsely inflate the branch lengths below thesubgroups and deflate branch lengths within eachgroup. Since we estimaterates of evolution on the

basis of withingroup branch lengths, it is arguedthatwewillunderestimateratesofchangeandhenceoverestimatedivergencelowerinthetree.However,thisargumentrequiresthattwospecialassumptionshold.First,anyborrowingmustoccuracrossawholesubgroupandonlyacrossawholesubgroup.When

termsarenotborrowedacrossthewholegroupthereisnosystematicbiastoinferchangesinthebranchleadingtothegroup.Dependingonthedistributionofborrowedterms,advergencecanevenproducetheoppositeeffect,falselyinflatingbranchlengthswithinsubgroups and hence causing us to underestimatedivergencetimes.Itseemsunlikelythatalloreven

Figure8.15.a)ParsimonycharactertraceforreflexesofLatinfocus(originallyhearthbutborrowedasfire)ontheRomanceconsensustree.Blackindicatespresenceofthecharacter,greyindicatesabsenceanddashedindicates

uncertainty.ThisshowsborrowingacrossthewholeRomancesubgroupevolutionarychangeisinferredatthebaseofthesubgroupwithnochangewithinthesubgroup,falselyinflatingdivergencetimeestimates.b)aswith(a)butforreflexesofLatintesta(originallycup,jar,shellbutborrowedashead).HeretheborrowingisnotacrossthewholeRomancesubgroupevolutionarychangeisinferredwithinthesubgroup.

a b


15/20

105


mostborrowedtermswereborrowedacrossanentiresubgroup.Garrehighlighted16instancesofborrowing within IndoEuropeansubgroups.2 These werepresumably selected because theywere thought to

reflectthesortofadvergencepaernthatwouldbiasourresults.Ofthese,atleast6areunlikelytofavourinferredlanguagechangeatthebaseofasubgroup.3Figure8.15bshowstheexampleoftheRomancetermforhead.

Second,evenifweacceptthefirstassumption,wemustassume that the proposedprocess ofadvergenceis unique to contemporarylanguages.AsGarre(Chapter12thisvolume)putsit,thisrequirestheunscientificassumptionthatlinguisticchangeintheperiodforwhichwehavenodirectevidencewasradicallydifferentfromchangewecanstudydirectly.Ratherthanarguingthatborrowingwasrareatonestageandthensuddenlybecamecommonacrossall

ofthemajorlineagesataboutthesametime,itseemsmoreplausibletosuggestthatborrowinghasalwaysoccurred.IfthesameprocessofadvergenceinrelatedlanguageshasalwaysoccurredthentheeffectofshiPingimpliedchangestomoreancestralbrancheswill

bepropagateddownthetreesuchthatthereshouldbenonet effecton divergencetimecalculation.Forexample,borrowingwithinItalicmayshiPinferredchangesfromthemoremodernbranchestothebranchleadingtoItalic,butborrowingbetweenrotoItalicanditscontemporarieswillalsoshiPinferredchangesfromthisbranchtoancestralbranches.ThismeansthatwhilstwemayincorrectlyreconstructsomeprotoIndoEuropean roots, our divergence time calcula

tionwillnotbeaffected.Wemaintainthatalthoughadvergence has undoubtedly occurred throughoutthehistoryofIndoEuropean,andthatthismayhaveaffectedourtrees,thiseffectislikelytoberandomandthereisnoreasontothinkitwillhavesignificantly

biased our results. Atkinson et al. (2005) analyzedsyntheticdatawithsimulatedborrowing,andfoundthatdateestimateswerehighlyrobusttoevenhighlevelsofborrowing.

Ringeetal.(2002)arguethatnonlexicalcharacterssuchasgrammaticalandphonologicalfeaturesarelesslikelytobeborrowed(althoughtheyalsonotethatparallelchangesinphonologicalandmorphologicalcharactersarepossible).Toavoidpotentialproblems

duetolexicalborrowingtheycoded15phonologicaland22morphologicalcharactersasstrictconstraintsintheiranalyses(theydidnotthrowouttheremaining333lexicalcharacters).Whileweagreethatphonologicalandmorphologicalcharacterswouldbeveryuseful,webelievetherearegoodreasonstotrusttheinferencesbasedonthelexicaldatainourcase.TheDyenetal.(1992)datahashadmuchoftheknown

borrowingfilteredfromit.Further,therelationshipsweinfer betweenIndoEuropean languagesare remarkablysimilartothoseinferredbylinguistsusingthe comparative method. Our results are not onlyconsistentwithacceptedlanguagerelationships,butalsoreflectacknowledgeduncertainties,suchasthepositionof Albanian. Ourtimedepth estimatesforinternalnodesoftheIndoEuropeantreearealsocongruentwithknownhistoricalevents(i.e.whenconstraintswereremovedstepbystepfromeachofthe13internalconstraintpoints,thereconstructedages

werewithin390yearsoftheoriginalconstraintrange:Gray&Atkinson2003).Significantly,ifweconstrainourtreestofittheRingeetal.(2002)typologywegetverysimilardateestimatestoourinitialconsensustreetopology.Inshort,thereisnothingtoindicatethateitherourtreetypologiesordateestimateshavebeenseriouslydistortedbytheuseofjustlexicaldata.

DeterminedcriticsmightstillclaimthattheremainingundetectedlexicalborrowingthatundoubtedlyexistsintheDyenetal.data(seeNicholls&GrayChapter14thisvolume)hasledustomakeerroneoustimedepthinferencesattherootoftheIndoEuropeantree. The Swadesh 100word list is expected to bemoreresistanttochangeandlesspronetoborrowing

thanthe200wordlist(Embleton1991;McMahon&McMahon2003).Ifundetectedborrowinghasbiasedourtreetopologyanddivergencetimeestimatesthenthe100wordlistmightbeexpectedtoproducedifferentestimates.Toassessthispossibilitywerepeatedthe analysis using only the Swadesh 100word listitems.Figure8.16showstheresultsofthisanalysis.redictably,withasmallerdatasetvarianceintheage

Figure8.16.Frequencydistributionofbasalage

estimatesfromfilteredBayesianMCMCsampleoftreesusingSwadesh100wordlistitemsonly(n=97).


16/20

106

Chapter8

estimatesincreased.However,theresultingagerangewasstillconsistentwiththeAnatoliantheoryofIndoEuropeanorigin.Interestingly,themajorityruleconsensustree(showninFig.8.17)isslightlydifferenttothatobtainedfromthefulldataset.ItcontainsaBaltoSlavicIndoIraniangroupandanItaloCelticgroup.Ringeetal.s(2002)compatibilityanalysisalsofound

theseclades.Thelowposterior probability valuesforthesegroupsmeanthatweshouldnotoverinter

pretthecertaintyofthesedeeper relationships, butclearlythepossibilitythatundetectedlexicalborrowing is obscuring some ofthe deeper relationshipswouldrepayfurtheraention. We emphasize thatthis possible borrowingdoesnotappear,however,to affect our timedepthestimates for the root ofthetree.

It is interesting to

notethatwhilstourmethodology produced consistent results using theSwadesh 100 and 200wordlist,Tischlers(1973)gloochronologicalanalysis was affected by thechoiceofwordlist.Tischlergenerated IndoEuropeandivergence times usingpairwisedistancecomparisons between languagesunder the assumption ofconstant rates of lexical

replacement. Using theSwadesh 200word list,hecalculatedthatthecoreIndoEuropean languages(Greek,Italic,BaltoSlavic,G e rm an ic a nd I nd oIranian) diverged around5500 whilst Hiite divergedfromthecommonstockaround8400.Thisis in striking agreementwiththetimingdepictedin Figure 8.8. However,thesamecalculationusing

theSwadesh100wordlist,producedaHiitedivergencetimeofalmost11,000.Otherinferreddivergencetimeswerealsoolder.Tischlerfavouredthe200wordlistresultsbecausetheytendedtobemoreconsistentandwerebasedonalargersamplesize.However,thedisparate100wordlistagesledTischlertoconcludethatthedivergencetimesforHiite(andanumberofotherperipheralIndo

Figure8.17.Majorityruleconsensustree(unfiltered)forSwadesh100wordlistitemsonly.Valuesaboveeachbranchexpressuncertainty(posteriorprobability)inthetreeasapercentage.


17/20

107


Europeanlanguages,includingAlbanian,ArmenianandOldIrish)wereinfactanomalousandheinsteadfavouredanageforIndoEuropeanofbetween5000and6000 years, reflecting the breakup of thecore

languages.HeexplainedtheapparentearlierdivergenceofHiite,Albanian,OldIrishandArmenianasanartefactofborrowingwithnonIndoEuropeanlanguagesorincreasedratesofchange.

11.Conclusion

TheanalyseswehavepresentedherearefarfromthelastwordonthevexedissueofIndoEuropeanorigins.WeexpectthateveryspeciesofscholarandwouldbesavantwhocantakepentohandwillstillbedrawntothequestionofIndoEuropeanorigins.However,incontrasttosomeofthemorepessimisticclaimsofourcritics,wedonotthinkthatestimatingtheageof

theIndoEuropeanlanguagefamilyisanintractableproblem.Someofthesecriticshavearguedthatitishardenoughtogetthetreetypologycorrect,letalone

branchlengthsordivergencetimes.Fromthispointofviewalleffortstoestimatedatesshouldbeabandoneduntilwecangetthetreeexactlyright.Wethinkthatwouldbeabigmistake.Itwouldprematurelycloseofflegitimatescientificinquiry.Theprobabilityofgeingtheoneperfectphylogenyfromthe6.6610152possibleunrootedtreesfor87languagesisrathersmall.Fortunatelywedonotneedtogetthetreeexactlycorrectinordertomakeaccuratedateestimates.UsingtheBayesianphylogeneticapproachwecancalculatedivergencedatesoveradistributionofmostprobable

trees, integrating outuncertaintyin thephylogeny.Weacknowledgethatestimatinglanguagedivergencedatesisdifficult,butmaintainitispossibleifthefollowingconditionsaresatisfied:a) adatasetofsufficientsizeandqualitycanbeas

sembledtoenablethetreeanditsassociatedbranchlengthstobeestimatedwithsufficientaccuracy;

b) mostoftheborrowingisremovedfromthedata;c) anappropriatestatisticalmodelofcharacterevolu

tionisused(itshouldcontainsufficientparameterstogiveaccurateestimatesbutnotbeoverparameterized);

d) multiplenodesonthetreearecalibratedwithreliableageranges;

e) uncertaintyintheestimationoftreetopologyandbranchlengthsareincorporatedintotheanalysis;f) variationintherateof linguisticevolutionisac

commodatedintheanalysis.TheanalysesofIndoEuropeandivergencedateswehaveoutlinedabovegoalongwaytomeetingtheserequirements.TheDyenetal.(1997)datasetweusedinouranalysescontainsovertwothousandcarefully

codedcognatesets(conditiona).Dyen etal.excludedknownborrowingsfromthesesets(conditionb).Thetwostate,timereversiblemodelofcognategainsandlosseswithgammadistributedrateheterogeneitypro

ducedaccuratetrees(i.e.congruentwiththeresultsofthecomparativemethodandknownhistoricalrelationships)4(conditionc).Whenthebranchlengthswerecombinedwiththelargenumberofwellcali

bratednodes(conditiond),theestimateddivergencedateswerealsoinlinewithknownhistoricalevents.TheBayesianMCMCapproachallowedustoincorporate phylogenetic uncertainty into our analyses(conditione),andtoinvestigatetheconsequencesofvariationsinthepriors,treerooting,andstringencyincognatejudgements.Finally,ratesmoothingallowedustoestimatedivergencedateswithouttheassumptionofastrictglooclock(conditionf). Wechallengeourcriticstofindanypaperonmoleculardivergencedatesthat

usesasmanycalibrationpoints,investigatestheimpactofsomanydifferentassumptions,orgoestothesamelengthstovalidateitsresults.

InthewordsofW.S.Holt,historyisadamndimcandle overa damn dark abyss.Although weseereasonforcarefulscholarshipwhenaemptingtoestimatelanguagedivergencedates,weseenojustificationforpessimismhere.FarfromdancingaroundthequestionofIndoEuropeanoriginslikemothsaroundaflame,withthelightofcomputationalphylogeneticmethodswecanilluminatethepast.

Notes1. Tenmillion postburnintreesweregeneratedusing

theMrBayes(Huelsenbeck&Ronquist2001).Toensurethatconsecutivesampleswereindependent,onlyevery10,000thtreewassampledfromthisdistribution,producingasamplesizeof1000.

2. Theproposedborrowingswere:inRomanceear,fire,liver,count,eat,headandnarrow;inGermanicleaf,sharpandthink;andinIndickill,night,play,suck,flowerandliver.WenotethatthislistwasnotintendedbyGarretobeacomprehensiveaccountofallpossibleborrowings.

3. Borrowings that are unlikelyto favour inferredlanguagechangeatthebaseofasubgrouporthatwouldfavourinferredlanguagechangewithinasubgroupare:inRomanceear,head,narrow;inGermanicleaf;andinIndicflowerandliver.

4. Wedo,however,agreethatthequestionofmodelspeci

ficationwouldrepayfurtherinvestigation(seeNicholls&GrayChapter14thisvolume;agelChapter15thisvolume;Atkinsonetal.2005).

References

Adams,D.Q.,1999.DictionaryofTocharianB.(LeidenStudiesinIndoEuropean10.)Amsterdam:Rodopi.Avail


18/20

108

Chapter8

ableviaonlinedatabaseatS.Starostin&A.Lubotsky(eds.),DatabaseQuerytodictionaryofTocharianB.hp://iiasnt.leidenuniv.nl/ied/index2.html.

Atkinson,Q.D.&R.D.Gray,2006.Areaccuratedatesanintractableproblemforhistoricallinguistics?inMappingourncestry:PhylogeneticMethodsinnthropologyandPrehistory,eds.C.Lipo,M.OBrien,S.Shennan&M.Collard.Chicago(IL):Aldine,26996.

Atkinson,Q.D.,G. Nicholls,D. Welch&R.D.Gray,2005.Fromwordstodates:waterintowine,mathemagicorphylogeneticinference?TransactionsofthePhilologicalSociety103(2),193219.

Bateman,R.,I.Goddard,R.OGrady,V.Funk,R.Mooi,W.Kress&.Cannell,1990.Speakingofforkedtongues:Thefeasibilityofreconcilinghumanphylogenyandthehistoryoflanguage.Currentnthropology31,124.

Bellwood,.,1991.TheAustronesiandispersalandtheoriginoflanguages.Scientificmerican265,8893.

Bellwood, ., 1994.An archaeologists view of languagemacrofamily relationships. Oceanic Linguistics 33,

391406.Bergsland,K.&H.Vogt,1962.Onthevalidityofgloochronology.Currentnthropology3,11553.

Blust,R.,2000.Whylexicostatisticsdoesntwork:theUniversal Constant hypothesis and the Austronesianlanguages,inTimeDepthinHistoricalLinguistics,eds.C.Renfrew,A.McMahon&L.Trask.(apersintherehistory of Languages.) Cambridge: McDonaldInstituteforArchaeologicalResearch,31132.

Bryant,D.,F.Filimon& R.D.Gray,2005.Untanglingourpast:acificselement,phylogenetictreesandAustronesianlanguages,inTheEvolutionofCulturalDiversity:Phylogeneticpproaches,eds.R.Mace,C.Holden&S.Shennan.London:UCLress,6985.

Burnham,K..&D.R.Anderson,1998.ModelSelectionandInference: a Practical InformationTheoretic pproach.

NewYork(NY):Springer.Campbell,L.,2004.HistoricalLinguistics:anIntroduction.2nd

edition.Edinburgh:EdinburghUniversityress.CavalliSforza,L.L.,.Menozzi&A.iazza,1994.TheHis

toryandGeographyofHumanGenes.rinceton(NJ):rincetonUniversityress.

Clackson,J.,2000.TimedepthinIndoEuropean,inTimeDepth in Historical Linguistics, eds. C. Renfrew, A.McMahon & L. Trask. (apers in therehistory ofLanguages.)Cambridge:McDonaldInstituteforArchaeologicalResearch,44154.

Devoto,G.,1962.OriginiIndeuropeo.Florence:InstitutoItalianodireistoriaItaliana.

Diakonov,I.M.,1984.OntheoriginalhomeofthespeakersofIndoEuropean. Sovietnthropologyandrchaeology23,587.

Diamond,J. & . Bellwood, 2003.Farmers andtheirlanguages:thefirstexpansions.Science300,597.

Dyen,I.,J.B.Kruskal&.Black,1992.nIndoeuropeanClassification:aLexicostatisticalExperiment. (Transactions82(5).)hiladelphia(A):AmericanhilosophicalSociety.

Dyen, I., J.B. Kruskal & . Black, 1997. FILE IEDATA1.Availableathp://www.ntu.edu.au/education/langs/ielex/IEDATA1.

Embleton,S.,1986.StatisticsinHistoricalLinguistics.Bochum:Brockmeyer.

Embleton, S.M., 1991. Mathematical methods of geneticclassification,inSprungfromSomeCommonSource,eds.S.L.Lamb&E.D.Mitchell.Stanford(CA):StanfordUniversityress,36588

Excoffier,L. & Z. Yang,1999. Substitution ratevariationamong sites inmitochondrialhypervariableregionIofhumansandchimpanzees.MolecularBiologyandEvolution16,135768.

Faguy,D.M.&W.F.Doolile,2000.Horizontaltransferofcatalaseperoxidasegenesbetweenarchaeaandpathogenicbacteria.TrendsinGenetics16,1967.

Felsenstein,J.,2004.InferringPhylogenies .Sunderland(MA):Sinauer.

Gamkrelidze,T.V.&V.V.Ivanov,1995. IndoEuropeanandtheIndoEuropeans:aReconstructionandHistoricalnalysisofaProtoLanguageandProtoCulture.Berlin:MoutondeGruyter.

Gimbutas, M., 1973a. Old Europe c. 70003500 , the

earliestEuropeanculturesbeforetheinfiltrationoftheIndoEuropeanpeoples.JournalofIndoEuropeanStudies1,120.

Gimbutas,M.,1973b.ThebeginningoftheBronzeAgeinEuropeandtheIndoEuropeans35002500.JournalofIndoEuropeanStudies1,163214.

Gkiasta,M.,T.Russell,S.Shennan&J.Steele,2003.NeolithictransitioninEurope:theradiocarbonrecordrevisited.ntiquity77,4562.

Glover,I.&C.Higham,1996.NewevidenceforricecultivationinS.,S.E.andE.Asia,in TheOriginsandSpreadofgricultureandPastoralisminEurasia,ed.D.Harris.Cambridge:Blackwell,41342.

Goldman,N.,1993.StatisticaltestsofmodelsofDNAsubstitution.JournalofMolecularEvolution36,18298.

Gray,R.D.&Q.D.Atkinson,2003.Languagetreedivergence

timessupporttheAnatoliantheoryofIndoEuropeanorigin.Nature426,4359.

Guterbock,H.G.&H.A.Hoffner,1986. TheHiAiteDictionaryoftheOrientalInstituteoftheUniversityofChicago.Chicago(IL):TheInstitute.

Hillis,D.M.,1992.Experimentalphylogeneticsgenerationofaknownphylogeny.Science255,58992.

Hillis,D.M.,C.Moritz&B.K.Marble,1996.MolecularSystematics.2ndedition.Sunderland(MA):Sinauer.

Hjelmslev,L.,1958. EssaiduneCritiquede laMethodediteGloAochronologique.ProceedingsoftheThirtysecondInternationalCongressofmericanists,Copenhagen,1956.Copenhagen:Munksgaard.

Hoffner, H.A., 1967.n EnglishHiAite Dictionary. NewHaven(CT):AmericanOrientalSociety.

Holden,C.J.,2002.BantulanguagetreesreflectthespreadoffarmingacrossSubSaharanAfrica:amaximumparsimonyanalysis.ProceedingsoftheRoyalSocietyofLondonSeriesB269,7939.

Holland, B. & V. Moulton, 2003.Consensus networks:amethodforvisualisingincompatibilitiesincollectionsoftrees,inlgorithmsinBioinformatics,WBI2003 ,eds.G. Benson & R. age. Berlin: SpringerVerlag,16576.


19/20

109


Huelsenbeck,J..&F.Ronquist,2001.MRBAYES:Bayesianinferenceofphylogeny. Bioinformatics17,7545.

Huelsenbeck,J..,F.Ronquist,R.Nielsen&J..Bollback,2001.Bayesianinferenceofphylogenyanditsimpactonevolutionarybiology. Science294,231014.

Jukes, T.H. & C.R. Cantor, 1969. Evolution of proteinmolecules,inMammalianProteinMetabolism,vol.3,ed.M.N.Munro.NewYork(NY):Academicress,21132.

Kuhner,M.K.&J.Felsenstein,1994.Asimulationcomparisonofphylogenyalgorithmsunderequalandunequalevolutionaryrates.MolecularBiologyandEvolution 11,45968.

Kumar, V.K., 1999.Discovery ofDravidian as theCommonSourceofIndoEuropean.RetrievedSept.27th2002fromhp://www.datanumeric.com/dravidian/.

Levins,R.,1966.Thestrategyofmodelbuildinginpopulationbiology,mericanScientist54,42131.

Mallory,J..,1989.InSearchoftheIndoEuropeans:Languages,rchaeologyandMyth.London:Thames&Hudson.

McMahon,A.&R.McMahon,2003.Findingfamilies:quantitativemethodsinlanguageclassification.TransactionsofthePhilologicalSociety101,755.

Metropolis,N., A.W. Rosenbluth, M.N.Rosenbluth,A.H.Teller&E.Teller,1953.Equationsofstatecalculationsbyfastcomputingmachines.JournalofChemicalPhysics21,108791.

Oe,M.,1997.ThediffusionofmodernlanguagesinprehistoricEurasia,inrchaeologyandLanguage,eds.R.Blench&M.Spriggs.London:Routledge,7481.

agel,M.,1997.Inferringevolutionaryprocessesfromphylogenies.ZoologicaScripta26,33148.

agel,M.,1999.Inferringthehistoricalpaernsofbiologicalevolution.Nature401,87784.

agel, M., 2000. Maximumlikelihood models for glottochronologyandforreconstructinglinguisticphy

logenies,inTimeDepthinHistoricalLinguistics, eds.C.Renfrew,A.McMahon&L.Trask.(apersintherehistoryofLanguages.)Cambridge:TheMcDonaldInstituteforArchaeologicalResearch,41339.

Renfrew,C.,1987.rchaeologyandLanguage:thePuzzleofIndoEuropeanOrigins.London:Cape.

Rexov,K.,D.Frynta&J.Zrzavy,2003.Cladisticanalysisoflanguages:IndoEuropeanclassificationbasedonlexicostatisticaldata.Cladistics19,12027.

Ringe,D.,n.d.rotoIndoEuropeanWheeledVehicleTerminology.Unpublishedmanuscript.

Ringe,D.,T.Warnow&A.Taylor,2002.IndoEuropeanandcomputationalcladistics.TransactionsofthePhilologicalSociety100,59129.

Rosser,Z.H.,T.Zerjal,M.E.Hurles etal.,2000.Ychromosomal diversity in Europe is clinal and influencedprimarily by geography, rather than by language.mericanJournalofHumanGenetics67,152643.

Sanderson,M.,2002a.R8s,nalysisofRatesofEvolution,version1.50.hp://ginger.ucdavis.edu/r8s/

Sanderson,M.,2002b.Estimatingabsoluteratesofevolution and divergence times: a penalized likelihoodapproach.MolecularBiologyandEvolution19,1019.

Steel,M.,M.Hendy&D.enny,1988.Lossofinformation

ingeneticdistances.Nature333,4945.Swadesh, M., 1952. Lexicostatistic dating of prehistoricethniccontacts.ProceedingsofthemericanPhilosophicalSociety96,45363.

Swadesh,M.,1955.Towardsgreateraccuracyinlexicostatisticdating.InternationalJournalofmericanLinguistics21,12137.

Swofford,D.L.,G.J.Olsen,.J.Waddell&D.M.Hillis,1996.hylogeneticInference,inMolecularSystematics,eds.D.M.Hillis, C. Moritz & B.K.Marble.2nd edition.Sunderland(MA):Sinauer,407514.

Tischler,J.,1973.GloAochronologieundLexicostatistik.Innsbruck:InnsbruckerVerlag.

Tischler, J., 1997. HethitischDeutschesWorterverzeichnis.Dresden:robedruck.

Trask, R.L., 1996.Historical Linguistics. New York (NY):

Arnold.Watkins,C.,1969.IndogermanischeGrammatikIII/1.Geschich

tederIndogermanischenVerbalflexion. Heidelberg:Carl

WinterVerlag.


20/20

atkinsongray2006a how old is ie lang fam

Documents