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1、PERFECTPHYLOGENETICNETWORKS:ANEWMETHODOLOGYFORRECONSTRUCTINGTHEEVOLUTIONARYHISTORYOFNATURALLANGUAGESLUAYNAKHLEHDONRINGETANDYWARNOWRiceUniversityUniversityofUniversityofTexasPennsylvaniaInthisarticleweextendthemodeloflanguageevolutionexemplifiedinRingeetal.2002,whichr
2、ecoversphylogenetictreesoptimizedaccordingtoacriterionofweightedmaximumcom-patibility,toincludecasesinwhichlanguagesremainincontactandtradelinguisticmaterialastheyevolve.WedescribeouranalysisofanIndo-European(IE)dataset(originallyassembledbyRingeandTaylor)basedonthis
3、newmodel.OurstudyshowsthatthisnewmodelfitstheIEfamilywellandsuggeststhattheearlyevolutionofIEinvolvedonlylimitedcontactbetweendistinctlineages.Furthermore,thecandidatehistoriesweobtainappeartobeconsistentwitharchaeologicalfindings,whichsuggeststhatthismethodmaybeofpr
4、acticaluse.Thecaseathandprovidesnoopportunitytoexploretheproblemofconflictbetweennetworkoptimizationcriteria;thatproblemmustbelefttofutureresearch.*1.INTRODUCTION.Languagesdifferentiateanddivideintonewlanguagesbyapro-cessroughlysimilartobiologicalspeciation:1communit
5、iesseparate(typicallygeo-graphically),thelanguagechangesdifferentlyineachofthenewcommunities,andintimepeoplefromseparatecommunitiescannolongerunderstandeachother.2Whilethisisnottheonlywayinwhichlanguageschange,itisthisprocessthatisreferredtowhenwesay,forexample,‘Fren
6、chandItalianarebothdescendantsofLatin’.Theevolutionoffamiliesofrelatedlanguagescanbemodeledmathematicallyasarootedtreeinwhichinternalnodesrepresentancestrallanguagesatthepointsintimeatwhichtheybegantodiversifyandtheleavesrepresentattestedlanguages.Reconstructingthisp
7、rocessforvariouslanguagefamiliesisamajorendeavorwithinhistoricallinguistics,butitisalsoofinteresttoarchaeologists,humangeneticists,andphysicalanthropolo-gists,forexample,becauseanaccuratereconstructionofhowparticularfamiliesoflanguageshaveevolvedcanhelpanswerquestion
8、sabouthumanmigrations,thetimesatwhichnewtechnologieswerefirstdeveloped,whenancientpeoplebegantouse*ThisworkwassupportedinpartbytheD
