第36章

Theorganizationofeverybusinessismodified。Easeofcommunicationmakes

itbettertododirectlywhatwasbeforedonebyproxy;agenciesareestablished

wherepreviouslytheywouldnothavepaid;goodsareobtainedfromremote

wholesalehousesinsteadofnearretailones;andcommoditiesareusedwhich

distanceoncerenderedinaccessible。Rapidityandeconomyofcarriagetend

tospecializemorethanevertheindustriesofdifferentdistricts——to

confineeachmanufacturetothepartsinwhich，fromlocaladvantages，it

canbebestcarriedon。Cheapdistributionequalizesprices，andalso，on

theaverage，lowersprices:thusbringingdiversarticleswithinthereach

ofthosebeforeunabletobuythem。Atthesametimethepracticeoftravelling

isimmenselyextended。Peoplewhobeforecouldnotaffordit，takeannual

tripstothesea，visittheirdistantrelations，maketours，andsoarebenefited

inbody，feelings，andintellect。Thepromptertransmissionoflettersand

ofnewsproducesfurtherchanges——makesthepulseofthenationfaster。

Yetmore，therearisesawidedisseminationofcheapliteraturethroughrailway

book—stalls，andofadvertisementsinrailwaycarriages:bothofthemaiding

ulteriorprogress。Sothatbeyondimaginationarethechanges，thusbrieflyindicated，consequentontheinventionofthelocomotiveengine。Itshouldbeaddedthatwehereseemoreclearlythan，ever，howinproportion

astheareaoverwhichanyinfluenceextendsbecomesheterogeneous，theresults

areinayethigherdegreemultipliedinnumberandkind。Whileamongthe

uncivilizedmentowhomitwasfirstknown，caoutchouccausedbutfewchanges，

amongourselvesthechangeshavebeensomanyandvariedthatthehistory

ofthemoccupiesavolume。Uponthesmall，homogeneouscommunityinhabiting

oneoftheHebrides，theelectrictelegraphwouldproduce，wereitused，scarcelyanyresults;butinEnglandtheresultsitproducesaremultitudinous。Spacepermitting，thesynthesismightherebepursuedinrelationtoall

thesubtlerproductsofsociallife。Itmightbeshownhow，inScience，an

advanceofonedivisionpresentlyadvancesotherdivisions——howAstronomy

hasbeenimmenselyforwardedbydiscoveriesinOptics，whileotheroptical

discoverieshaveinitiatedMicroscopicAnatomy，andgreatlyaidedthegrowth

ofPhysiology——howChemistryhasindirectlyincreasedourknowledgeof

Electricity，Magnetism，Biology，Geology——howElectricityhasreactedon

ChemistryandMagnetism，developedourviewsofLightandHeat，anddisclosed

sundrylawsofnervousaction。Butitwouldneedlesslytaxthereader\'spatience

todetail，intheirmanyramifications，thesevariouschanges;soinvolvedandsubtleastobefollowedwithdifficulty。§162。Aftertheargumentwhichclosedthelastchapter，aparallel

onehereseemsscarcelyrequired。Forsymmetry\'ssake，however，itwillbe

properbrieflytopointouthowthemultiplicationofeffects，liketheinstabilityofthehomogeneous，isacorollaryfromthepersistenceofforce。Thingswhichwecalldifferentarethingswhichreactindifferentways;

andwecanknowthemasdifferentonlybythedifferencesintheirreactions。

Whenwedistinguishbodiesashardorsoft，roughorsmooth，wemeanthat

certainlikemuscularforcesexpendedonthemarefollowedbyunlikereactive

forces，causingunlikesetsofsensations。Objectsclassedasred，blue，

yellowetc。，areobjectswhichdecomposelightincontrastedways;thatis，

weknowcontrastsofcolourascontrastsinthechangesproducedinauniform

incidentforce。Thepropositionthatthedifferentpartsofanywholemust

reactdifferentlyonauniformincidentforce，andmustthusreduceitto

agroupofmultiformforces，isinessenceatruism。Supposewereducethistruismtoitslowestterms。When，fromunlikenessbetweentheeffectstheyproduceonconsciousness，

wepredicateunlikenessbetweentwoobjects，whatisourwarrant？andwhat

dowemeanbytheunlikeness，objectivelyconsidered？Ourwarrantisthe

persistenceofforce。Somekindoramountofchangehasbeenwroughtinus

bytheonewhichhasnotbeenwroughtbytheother。Thischangeweascribe

tosomeforceexercisedbytheonewhichtheotherhasnotexercised。And

wehavenoalternativebuttodothis，ortoassertthatthechangehadno

antecedent，whichistodenythepersistenceofforce。Whenceitisfurther

manifestthatwhatweregardastheobjectiveunlikenessisthepresence

intheoneofsomeforce，orsetofforces，notpresentintheother——something

inthekindsoramountsordirectionsoftheconstituentforcesoftheone，

whichthoseoftheotherdonotparallel。Butnowifthingsorpartsofthings

whichwecalldifferent，arethoseofwhichtheconstituentforcesdiffer

inoneormorerespects，whatmusthappentoanylikeforces，oranyuniform

force，fallingonthem？Suchlikeforces，orpartsofauniformforce，must

bedifferentlymodified。Theforcewhichispresentintheoneandnotin

theother，mustbeanelementintheconflict——mustproduceitsequivalent

reaction;andmustsoaffectthetotalreaction。Tosayotherwiseistosay

thatthisdifferentialforcewillproducenoeffect，whichistosaythatforceisnotpersistent。Ineednotdevelopthiscorollaryfurther。Itmanifestlyfollowsthat

auniformforcefallingonauniformaggregate，mustundergodispersion;

thatfallingonanaggregatemadeupofunlikeparts，itmustundergodispersion

fromeachpart，aswellasqualitativedifferentiations;thatinproportion

asthepartsareunlike，thesequalitativedifferentiationsmustbemarked;

thatinproportiontothenumberoftheparts，theymustbenumerous;that

thesecondaryforcessoproducedmustundergofurthertransformationswhile

workingequivalenttransformationsinthepartsthatchangethem;andsimilarly

withtheforcestheygenerate。Thustheconclusionsthatapart—causeof

Evolutionisthemultiplicationofeffects，andthatthisincreasesingeometrical

progressionastheheterogeneitybecomesgreater，arenotonlytobeestablished

inductively，butarededuciblefromthedeepestofalltruths。

Chapter21Segregation§163。ThegeneralinterpretationofEvolutionisfarfrombeingcompleted

intheprecedingchapters。Wemustcontemplateitschangesunderyetanother

aspect，beforewecanformadefiniteconceptionoftheprocessconstituted

bythem。Thoughthelawsalreadysetforthfurnishakeytothere—arrangement

ofpartswhichEvolutionexhibits，insofarasitisanadvancefromthe

uniformtothemultiform，theyfurnishnokeytothisrearrangementinso

farasitisanadvancefromtheindefinitetothedefinite。Onstudying

theactionsandreactionseverywheregoingon，wehavefoundittofollow

fromacertainprimordialtruth，thatthehomogeneousmustlapseintothe

heterogeneous，andthattheheterogeneousmustbecomemoreheterogeneous;

butwehavenotdiscoveredwhythedifferently—affectedpartsofanysimple

whole，becomeclearlymarkedofffromoneanother，atthesametimethat

theybecomeunlike。Thusfarnoreasonhasbeengivenwhythereshouldnot

ordinarilyariseavaguechaoticheterogeneity，inplaceofthatorderly

heterogeneitydisplayedinEvolution。Itstillremainstofindoutthecause

ofthatlocalintegrationwhichaccompaniedlocaldifferentiation——that

gradually—completedsegregationoflikeunitsintoagroup，distinctlyseparated

fromneighbouringgroupswhichareseverallymadeupofotherkindsofunits。

Therationalewillbeconvenientlyintroducedbyafewinstancesinwhichwemaywatchthissegregativeprocesstakingplace。When，lateinSeptember，thetreesaregainingtheirautumncolours，and

wearehopingsoontoseeafurtherchangeincreasingthebeautyofthelandscape，

wearesometimesdisappointedbytheoccurrenceofanequinoctialgale。Out

ofthemixedmassoffoliageoneachbranch，thestrongcurrentofaircarries

awaythedecayingandbrightly—tintedleaves，butfailstodetachthosewhich

arestillgreen。Andwhiletheselast，frayedandsearedbylong—continued

beatingsagainstoneanother，giveasombrecolourtothewoods，thered

andyellowandorangeleavesarecollectedtogetherinditchesandbehind

wallsandincornerswhereeddiesallowthemtosettle。Thatistosay，

bythatuniformforcewhichthewindexertsonbothkinds，thedyingleaves

arepickedoutfromamongtheirstill—livingcompanionsandgatheredinplaces

bythemselves。Again，theseparationofparticlesofdifferentsizes，as

dustandsandfrompebbles，maybesimilarlyeffected，asweseeonevery

roadinMarch。AndfromthedaysofHomerdownwards，thepowerofcurrents

ofair，naturalandartificial，topartfromoneanotherunitsofunlike

characters，hasbeenhabituallyutilizedinthewinnowingofchafffromwheat。

Ineverybrookweseehowthemixedmaterialscarrieddownareseparately

deposited——howinrapidsthebottomgivesresttonothingbutboulders

andpebbles;howwherethecurrentisnotsostrong，sandisletfall;and

how，instillplaces，thereisasedimentofmud。Thisselectiveaction

ofmovingwateriscommonlyappliedintheartstoobtainmassesofparticles

ofdifferentdegreesoffineness。Emery，forexample，afterbeingground，

iscarriedbyaslowcurrentthroughsuccessivecompartments;inthefirst

ofwhichthelargestgrainssubside;inthesecondofwhichthegrainsthat

settlebeforethewaterhasescaped，aresomewhatsmaller;inthethirdsmaller

still;untilinthelasttherearedepositedthosefinestparticleswhich

havenotpreviouslybeenabletoreachthebottom。Andinawaythatisdifferent

thoughequallysignificant，thissegregativeeffectofwaterinmotion，is

exemplifiedinthecarryingawayofsolublefrominsolublematters——an

applicationofithourlymadeineverylaboratory。Theeffectsoftheuniform

forceswhichaerialandaqueouscurrentsexercise，areparalleledbythose

ofuniformforcesofotherorders。Electricattractionwillseparatesmall

bodiesfromlarge，orlightbodiesfromheavy。Bymagnetism，grainsofiron

maybeselectedfromothergrains;asbytheSheffieldgrinder，whosemagnetized

gauze—maskfiltersoutthesteel—dusthiswheelgivesoff，fromthestone—dust

whichaccompaniesit。Andhowtheaffinityofanyagentactingdifferently

onthemixedcomponentsofabody，enablesustotakeawaysomecomponentandleavetherestbehind，isperpetuallyshowninchemicalexperiments。What，now，isthegeneraltruthherevariouslypresented？Howarethese

facts，andcountlesssimilarones，tobeexpressedintermsthatembrace

themall？Ineachcaseweseeinactionaforcewhichmayberegardedas

simpleoruniform—fluidmotioninacertaindirectionatacertainvelocity;

electricormagneticattractionofagivenamount;chemicalaffinityofa

particularkind;orrather，instrictness，theactingforceiscompounded

ofoneofthesewithsomeotheruniformforce，asgravitation，etc。Ineach

casewehaveanaggregatemadeupofunlikeunits——eitheratomsofdifferent

substancescombinedorintimatelymingled，orfragmentsofthesamesubstance

ofdifferentsizes，orotherconstituentpartsthatareunlikeintheirspecific

gravities，shapes，orotherattributes。Andineachcasetheseunlikeunits，

orgroupsofunits，ofwhichtheaggregateconsists，are，undertheinfluence

ofsomeresultantforceactingindiscriminatelyonthemall，separatedfrom

oneanother——segregatedintominoraggregates，eachconsistingofunits

thatareseverallylikeoneanotherandunlikethoseoftheotherminoraggregates。

Suchbeingthecommonaspectofthesechanges，letuslookforthecommoninterpretationofthem。Inthechapteron"TheInstabilityoftheHomogeneous，"itwas

shownthatauniformforcefallingonanyaggregate，producesunlikemodifications

initsdifferentparts——turnstheuniformintothemultiformandthemultiform

intothemoremultiform。Thetransformationthuswrought，consistsofeither

insensibleorsensiblechangesofrelativepositionamongtheunits，orof

both。Suchportionofthepermanentlyeffectiveforceasreacheseachdifferent

part，ordifferently—conditionedpart，maybeexpendedinmodifyingthemutual

relationsofitsconstituents;oritmaybeexpendedinmovingthepartto

anotherplace;oritmaybeexpendedpartiallyinthefirstandpartially

inthesecond。Andiflittleornoneisabsorbedinre—arrangingthecomponents

ofacompoundunit，muchorthewholemustshowitselfinmotionofsuch

compoundunittosomeotherplaceintheaggregate。andconversely。What

mustfollowfromthis，incaseswherenoneoronlypartoftheforcegenerates

chemicalre—distributions，whatphysicalre—distributionsmustbegenerated？

Partsthataresimilartoeachotherwillbesimilarlyactedonbytheforce，

whilepartsthataredissimilarwillbedissimilarlyactedon。Hencethe

permanentlyeffectiveincidentforce，whenwhollyorpartiallytransformed

intomechanicalmotionoftheunits，willproducelikemotionsinunitsthat

arealike，andunlikemotionsinunitsthatareunlike。Ifthen，inanaggregate

containingtwoormoreordersofmixedunits，thoseofthesameorderwill

bemovedinthesameway，andinawaythatdiffersfromthatinwhichunits

ofotherordersaremoved，therespectiveordersmustsegregate。Agroup

oflikethingsonwhichareimpressedmotionsthatarealikeinamountand

direction，mustbetransferredasagrouptoanotherplace，andiftheyare

mingledwithsomegroupofotherthings，onwhichthemotionsimpressedare

likeoneanother，butunlikethoseofthefirstgroupinamountordirection

orboth，theseotherthingsmustbetransferredasagrouptosomeotherplace——themixedunitsmustundergoasimultaneousselectionandseparation。Furthertoelucidatethisprocess，letmesetdownafewinstancesin

whichwemayseethatthedefinitenessoftheseparationisinproportion

tothedefinitenessofthedifferencesamongtheunits。Takeahandfulof

poundedsubstance，containingfragmentsofallsizes，andletitfallgradually

whileagentlebreezeisblowing。Thelargefragmentswillbecollectedon

thegroundalmostimmediatelyunderthehand;somewhatsmallerfragments

willbecarriedalittletotheleeward;stillsmalleronesfurtheraway;

andthoseminuteparticleswecalldust，willbedriftedfarbeforethey

reachtheearth:thatis，thesegregationisindefinitewherethedifferences

amongthefragmentsareindefinite，thoughthedivergencesaregreatestwhere

thedifferencesaregreatest。If，again，thehandfulbemadeupofdistinct

ordersofunits——aspebbles，coarsesand，anddust——thesewill，under

likeconditions，besegregatedwithgreaterdefiniteness。Thepebbleswill

dropalmostvertically;thesand，fallingobliquely，willdeposititself

withinatolerablycircumscribedspacebeyondthepebbles;whilethedust

willbeblownalmosthorizontallytoagreatdistance。Acaseinwhichanother

kindofforcecomesintoplay，willstillbetterillustratethistruth。Through

amixedaggregateofsolubleandinsolublesubstances，letwaterslowlypercolate。

Therewillinthefirstplacebeadistinctpartingofthesubstancesthat

arethemostwidelyunlike:thesolublewillbecarriedaway;theinsoluble

willremainbehind。Further，someseparation，thoughalessdefiniteone，

willbeeffectedamongthesolublesubstances;sincethefirstpartofthe

currentwillremovethemostsolubleinthelargestamounts，andafterthese

havebeendissolved，itwillcontinuetobringouttheremaininglesssoluble。

Eventheundissolvedmatterswillhavesimultaneouslyundergonesomesegregation;

forthepercolatingfluidwillcarrydowntheminutefragmentsfromamong

thelargeones，andwilloftendepositthoseofsmallspecificgravityin

oneplace，andthoseofgreatspecificgravityinanother。Tocompletethe

elucidationwemustglanceattheobversefact;namelythatmixedunitswhich

differbutslightly，aremovedinbutslightlydifferentwaysbyincident

forces，andcanthereforebeseparatedonlybysuchadjustmentsoftheincident

forcesasallowslightdifferencestobecomeappreciablefactorsintheresult。

Thepartingofalcoholfromwaterbydistillationisagoodexample。Here

wehavemoleculesconsistingofoxygenandhydrogen，mingledwithmolecules

consistingofoxygen，hydrogen，andcarbon。Thetwoordersofmoleculeshave

aconsiderablelikenessofnature:theysimilarlymaintainafluidformat

ordinarytemperatures;theysimilarlybecomegaseousmoreandmorerapidly

asthetemperatureisraised;andtheyboilatpointsnotveryfarapart。

Nowthiscomparativelikenessofthemoleculesisaccompaniedbydifficulty

insegregatingthem。Ifthemixedfluidisundulyheated，muchwaterdistils

overwiththealcohol:itisonlywithinanarrowrangeoftemperaturethat

moleculesoftheonekindaredrivenoffratherthantheothers;andeven

thennotafewoftheothersaccompanythem。Themostinterestingandinstructive

example，however，isfurnishedbycertainphenomenaofcrystallization。When

severalsaltsthathavelittleanalogyofconstitution，aredissolvedin

thesamebodyofwater，theyareseparatedwithoutmuchtrouble，bycrystallization:

subjectastheyaretouniformforces，theysegregate。Thecrystalsofeach

saltdo，indeed，usuallycontaincertainsmallamountsoftheothersalts

presentinthesolution;butfromthesetheyareseverallyfreedbyrepeated

re—solutionsandcrystallizations。Marknow，however，thatthereverseis

thecasewhenthesaltscontainedinthesamebodyofwaterarechemically

homologous。Thenitratesofbarytaandlead，orthesulphatesofzinc，soda，

andmagnesia，uniteinthesamecrystals;norwilltheycrystallizeseparately

ifthesecrystalsbedissolvedafresh，andafreshcrystallized。Onseeking

thecauseofthisanomaly，chemistsfoundthatsuchsaltswereisomorphous—that

theirmolecules，thoughnotchemicallyidentical，areidenticalintheproportions

ofacid，base，andwater，composingthem，andinthecrystallineformsthey

assumewhenuniting。Here，then，weseeclearlythatunitsofunlikekinds

areselectedoutandseparatedwithareadinessproportionatetothedegreeoftheirunlikeness。Thereisaconversecauseofsegregationwhichitisneedlesshereto

treatofwithequalfullness。Ifdifferentunitsactedonbythesameforce，

mustbedifferentlymoved;so，converselyunitsofthesamekindmustbe

differentlymovedbydifferentforces。Supposingsomegroupofunitsforming

partofahomogeneousaggregate，areunitedlyexposedtoaforcewhichis

unlikeinamountordirectiontotheforceactingontherestoftheaggregate，

thenthisgroupofunitswillseparatefromtherest，providedthat，ofthe

forcesoactingonit，thereremainsanyportionnotdissipatedinmolecular

vibrationsorabsorbedinproducingmolecularrearrangements。Afterallthathasbeensaidabove，thispropositionneedsnodefence。Beforeendingourpreliminaryexposition，acomplementarytruthmustbe

specified;namelythatmixedforcesaresegregatedbythereactionofuniform

matters，justasmixedmattersaresegregatedbytheactionofuniformforces。

Ofthistruthacompleteandsufficientillustrationisfurnishedbythe

dispersionofrefractedlight。Abeamoflight，madeupofetherealundulations

ofdifferentorders，isnotuniformlydeflectedbyahomogeneousrefracting

body;butthedifferentordersofundulationsitcontainsaredeflectedat

differentangles:theresultbeingthatthesedifferentordersofundulations

areseparatedandintegrated，andsoproducethecoloursofthespectrum。

Asegregationofanotherkindoccurswhenraysoflighttraverseanobstructing

medium。Thosewhichconsistofcomparativelyshortundulationsareabsorbed

beforethosewhichconsistofcomparativelylongones;andtheredrays，

whichconsistofthelongestundulations，alonepenetratewhentheobstruction

isverygreat。How，conversely，thereisproducedaseparationoflikeforces

bythereactionofunlikematters，isalsomademanifestbythephenomena

ofrefraction;sinceadjacentandparallelbeamsoflight，fallingon，andpassingthrough，unlikesubstances，aremadetodiverge。§164。Invaguewaystheheavenlybodiesexemplifythatcauseofmaterialsegregationlastassigned——theactionofunlikeforcesonlikeunits。IsayinvaguewaysbecauseourSiderealSystemdisplaysmoreofaggregation

thanofsegregation。Thattheirregularswarmsofstarsconstitutingthe

MilkyWaywithitsbranchesandgapsanddenserregions，havebeengathered

togetherfromamorewidelydiffusedstate，maybereasonablyinferred;though

asweknownothingoftheprecedingdistributionsuchachangecannotbeproved:stilllesscantherebeprovedasegregativeprocess。Itistruethatinclustersofstars，beginningwiththosehavingmembers

considerablydispersedandendingwiththosehavingmemberscloselyconcentrated—globular

clusters——weseestrongevidenceofaggregation;anditmaybecontended

thatsincethemutualgravitationsofthestarsformingacluster，differ

intheirdegreesanddirectionsfromthoseofthestarsfromwhichtheyhave

separated，thereisakindofsegregation。Butitmustbeadmittedthattheconformitytotheabove—namedprincipleisbutanindefiniteone。Thereare，however，twoclassesoffactswhichexhibitsegregation，though

theyleaveusignorantofitscauses。Thefirstisthatstar—clustersare

abundantalongthecourseoftheMilkyWay:byfarthelargernumberofthem

lyingintheneighbourhoodofitsplaneandrelativelyfewinregionson

eitherside。Thesecondisthat，contrariwise，thenebulaearesparselyscattered

inandaboutthegalacticcircleandarerelativelynumerousinthespaces

remotefromit。Thoughtherearethuspresentedtwocasesofsegregation

thereisnoevidencethatthesedifferentclassesofbodieshavebeenseparated

fromamixedassemblage，noristhereanyindicationoftheforcesbywhich

thiscontrastindistributionhasbeenproduced。Wecanonlysaythatthe

factsarecongruouswiththebeliefthatsegregation，probablyindirectratherthandirectinitscause，hasbeengoingon。Theformationanddetachmentofanebulousring，illustratesthesame

generalprinciple。Toconclude，asLaplacedid，thattheequatorialportion

ofarotatingnebulousspheroidwill，duringconcentration，acquireacentrifugal

forcesufficienttopreventitfromfollowingtherestofthecontracting

mass，istoconcludethatsuchportionswillremainbehindasareincommon

subjecttoacertaindifferentialforce。Thelineofdivisionbetweenthe

ringandthespheroid，mustbealineinsideofwhichtheaggregativeforce

isgreaterthantheforceresistingaggregation;andoutsideofwhichthe

forceresistingaggregationisgreaterthantheaggregativeforce。Hence

theallegedprocessconformstothelawthatamonglikeunits，exposedtounlikeforces，thesimilarlyconditionedseparatefromthedissimilarlyconditioned。###第37章§165。Thosegeologicchangesusuallyclassedasaqueous，display

undernumerousformsthesegregationofunlikeunitsbyauniformincident

force。Onseashoresthewavesareeversorting—outandseparatingthemixed

materialsagainstwhichtheybreak。Fromeachmassoffallencliff，thetide

carriesawayallthoseparticleswhicharesosmallastoremainlongsuspended

inthewater;and，atsomedistancefromshore，depositsthemintheshape

offinesediment。Largeparticles，sinkingwithcomparativerapidity，are

accumulatedintobedsofsandnearlowwater—mark。Thesmallpebblescollect

togetheratthebottomoftheinclineupwhichthebreakersrush;andon

thetopliethelargerstonesandboulders。Stillmorespecificsegregations

mayoccasionallybeobserved。Flatpebbles，producedbythebreakingdown

oflaminatedrock，aresometimesseparatelycollectedinonepartofashingle

bank。Onthisshorethedepositiswhollyofmud;onthatitiswhollyof

sand。Herewefindashelteredcovefilledwithsmallpebblesalmostofone

size;andthere，inacurvedbayoneendofwhichismoreexposedthanthe

otherweseeaprogressiveincreaseinthemassivenessofthestonesaswe

walkfromthelessexposedtothemoreexposedend。Tracethehistoryof

eachgeologicdeposit，andwearequicklyleddowntothefactthatmixed

fragmentsofmatter，differingintheirsizesorweights，are，whenexposed

tothemomentumandfrictionofwater，joinedwiththeattractionofthe

Earth，selectedfromoneanother，andunitedintogroupsofcomparatively

likefragments。Andweseethat，otherthingsequal，theseparationisdefinite

inproportionasthedifferencesoftheunitsaremarked。Aftertheyhave

beenformed，sedimentarystrataexhibitsegregationsofanotherkind。The

flintsandthenodulesofironpyritesthatarefoundinchalk，aswellas

thesiliciousconcretionswhichsometimesoccurinlimestone，areinterpreted

asaggregationsofmoleculesofsilexorsulphuretofiron，originallydiffused

throughthedeposit，butgraduallycollectedroundcentres，notwithstanding

thesolidorsemi—solidstateofthesurroundingmatter。Bogiron—oresuppliestheconditionsandtheresultinstillmoreobviouscorrelation。Amongigneouschangeswedonotfindsomanyexamplesoftheprocessdescribed。

Nevertheless，geologicalphenomenaofthisorderarenotbarrenofillustrations。

WherethemixedmatterscomposingtheEarth\'scrusthavebeenraisedtoa

veryhightemperature，segregationcommonlytakesplaceasthetemperature

falls。Sundryofthesubstancesthatescapeinagaseousformfromvolcanoes，

sublimeintocrystalsoncomingagainstcoolsurfaces;andsolidifying，as

thesesubstancesdo，atdifferenttemperatures，theyaredepositedatdifferent

partsofthecrevicesthroughwhichtheyareemittedtogether。Thebestillustration，

however，isfurnishedbythechangesthatoccurduringtheslowcoolingof

igneousrock。When，throughoneofthefracturesfromtimetotimemadein

theEarth\'scrust，aportionofthemoltennucleusisextruded，andwhen

thisiscooledwithcomparativerapidity，thereresultstraporbasalt——

asubstancethatisuniformintexture，thoughmadeupofvariousingredients。

Butwhen，notescapingthroughthesuperficialstrata，suchaportionof

themoltennucleusisslowlycooled，graniteistheresult:themingledparticles

ofquartz，feldspar，andmica，beingkeptforalongtimeinafluidand

semi—fluidstate——astateofcomparativemobility—undergothosechanges

ofpositionwhichtheforcesimpressedonthembytheirfellowunitsnecessitate。

Thedifferentialforcesarisingfrommutualpolarity，segregatethequartz，

feldspar，andmica，intocrystals。Howcompletelythisisdependentonthe

long—continuedagitationofthemixedparticles，andconsequentlong—continued

movablenessbysmalldifferentialforces，isprovedbythefactthatina

granitedykethecrystalsinthecentre，wherethefluidityorsemi—fluidity

continuedforalongertime，aremuchlargerthanthoseatthesides，wherecontactwiththeneighbouringrockcausedmorerapidcoolingandsolidification。§166。Theactionsgoingonthroughoutanorganismaresoinvolved，

thatwecannotexpecttoidentifytheforcesbywhichparticularsegregations

areeffected。Amongthefewinstancesadmitting。ofinterpretation，thebest

arethoseinwhichmechanicalpressuresandtensionsaretheagenciesatwork。Thespineofavertebrateanimalissubjectedtocertaingeneralstrains

——theweightofthebody，togetherwiththereactionsinvolvedbyallconsiderable

muscularefforts;andundertheseconditionsithasbecomesegregatedas

awhole。Atthesametimebeingexposedtodifferentforcesduringthose

lateralbendingswhichthemovementsnecessitate，itspartsretainacertain

separateness。Ifwetraceupthedevelopmentofthevertebralcolumnfrom

itsprimitiveformofacartilaginouscordinthelowestfishes，weseethat，

throughout，itmaintainsanintegrationcorrespondingtotheunityofthe

incidentforces，joinedwithadivisionintosegmentscorrespondingtothe

varietyoftheincidentforces。Eachsegment，consideredapart，exemplifies

thetruthmoresimply。Avertebraisnotasinglebone，butconsistsofa

centralmasswithsundryappendagesorprocesses，andinunfinishedtypes

ofvertebratheseappendagesareseparatefromthecentralmass，and，indeed，

existbeforeitmakesitsappearance。Buttheseseveralindependentbones

constitutingaprimitivespinalsegment，aresubjectedtoacertainaggregate

offorceswhichagreemorethantheydiffer:asthefulcrumtoagroupof

muscleshabituallyactingtogether，theyperpetuallyundergocertainreactions

incommon。Andaccordingly，inthecourseofdevelopment，theygradually

coalesce。Stillcleareristheillustrationfurnishedbyspinalsegments

thatbecomefusedtogetherwheretheyaretogetherexposedtosomepredominant

strain。Thesacrumconsistsofagroupofvertebrafirmlyunited。Inthe

ostrichanditscongenerstherearefromseventeentotwentysacralvertebra;

and，besidesbeingconfluentwithoneanother，theseareconfluentwith

theiliacbones，whichrunoneachsideofthem。If，now，weassumethese

vertebratohavebeenoriginallyseparate，astheystillareintheembryo

bird，andifweconsidertheforcestowhichtheymustinsuchcasehave

beenexposed，weshallseethattheirunionresultsintheallegedway。For

throughthesevertebratheentireweightofthebodyistransferredtothe

legs:thelegssupportthepelvicarch;thepelvicarchsupportsthesacrum;

andtothesacrumisarticulatedtherestofthespine，withalltheorgans

attachedtoitandupheldbyit。Hence，ifseparate，thesacralvertebra

mustbeheldfirmlytogetherbystrongly—contractedmuscles，andmust，by

implication，bepreventedfrompartakinginthoselateralmovementswhich

theothervertebraundergo——theymustbesubjectedtoacommonstrain，

whiletheyarepreservedfromstrainswhichwouldaffectthemdifferently;

andsotheyfulfiltheconditionsunderwhichsegregationoccurs。Butthe

casesinwhichcauseandeffectarebroughtintothemostobviousrelation，

aresuppliedbythelimbs。Themetacarpalbones（thosewhichinmansupport

thepalmofthehand）areseparatefromoneanotherinmostmammals:the

separateactionsofthetoesentailingonthemslightamountsofseparate

movements。Thisisnotsohoweverintheox—tribeandthehorse—tribe。In

theox—tribe，onlythemiddlemetacarpals（thirdandfourth）aredeveloped;

andthese，attainingmassiveproportions，coalescetoformthecannonbone。

Inthehorse—tribe，thesegregationiswhatwemaydistinguishasindirect:

thesecondandfourthmetacarpalsarepresentonlyasrudimentsunitedto

thesidesofthethird，whilethethirdisimmenselydeveloped;thusforming

acannonbonewhichdiffersfromthatoftheoxinbeingasinglecylinder，

insteadoftwocylindersfusedtogether。Themetatarsusinthesequadrupeds

exhibitsparallelchanges。Noweachofthesemetamorphosesoccurswherethe

differentbonesgroupedtogetherhavenolongeranydifferentfunctions，

butretainonlyacommonfunction。Thefeetofoxenandhorsesareusedsolely

forlocomotion——arenotput，likethoseofunguiculatemammals，topurposes

whichinvolvesomerelativemovementsofthemetacarpals。Thustheredirectly

orindirectlyresultsasinglemassofbonewheretheincidentforceissingle。

Andfortheinferencethatthesefactshaveacausalconnexion，wefindconfirmation

throughouttheentireclassofbirds，inthewingsandlegsofwhich，like

segregationsarefoundunderlikeconditions。Whilethissheetispassing

throughthepress（1862），afactillustratingthisgeneraltruthinayet

moreremarkablemanner，hasbeenmentionedtomebyProf。Huxleywhokindly

allowsmetomakeuseofitwhilestillunpublishedbyhim。TheGlyptodon，

anextinctmammalfoundfossilizedinSouthAmerica，haslongbeenknown

asalargeuncouthcreaturealliedtotheArmadillo，buthavingamassive

dermalarmourconsistingofpolygonalplatescloselyfittedtogethersoas

tomakeavastbox，inclosingthebodyinsuchwayaseffectuallytoprevent

itfrombeingbent，laterallyorvertically，intheslightestdegree。This

box，whichmusthaveweighedseveralhundredweight，wassupportedonthe

spinousprocessesofthevertebrae，andontheadjacentbonesofthepelvic

andthoracicarches。Andthesignificantfactisthathere，wherethetrunk

vertebraeweretogetherexposedtothepressureofthisheavydermalarmour，

atthesametimethat，byitsrigidity，theywerepreservedfromallrelativemovements，theywereunitedintoonesolid，continuousbone。Theformationandmaintenanceofaspecies，consideredasanassemblage

ofsimilarorganisms，isinterpretableinananalogousway。Alreadywehave

seenthatinsofarasthemembersofaspeciesaresubjecttodifferent

setsofincidentforces，theyaredifferentiated，ordividedintovarieties。

Hereitremainstoaddthatsuchofthemasaresubjecttolikesetsofincident

forces，aresegregated。Forbytheprocessof"naturalselection，"

thereisacontinualpurificationofeachspeciesfromthoseindividuals

whichdepartfromthecommontypeinwaysthatunfitthemfortheconditions

oftheirexistence。Consequently，thereisacontinualleavingbehindof

thoseindividualswhichareinallrespectsfitfortheconditionsoftheir

existence，andarethereforenearlyalike。Thecircumstancestowhichany

speciesisexposed，beinganinvolvedcombinationofincidentforces;and

themembersofthespecieshavingamongthemsomethatdiffermorethanis

usualfromtheaveragestructurerequiredformeetingtheseforces;itresults

thattheseforcesareconstantlyseparatingsuchdivergentindividualsfrom

therest，andsopreservingtheuniformityoftherest——keepingupits

integrityasaspeciesorvariety。Justasthechangingautumnleavesare

pickedoutbythewindfromamongthegreenonesaroundthem，orjustas，

touseProf。Huxley\'ssimile，thesmallerfragmentspassthroughasieve

whilethelargerarekeptback;so，theuniformincidenceofexternalforces

affectsthemembersofagroupoforganismssimilarlyinproportionasthey

aresimilar，anddifferentlyinproportionastheyaredifferent;andthus

iseversegregatingthelikebypartingtheunlikefromthem。Whetherthese

separatedmembersarekilledoff，asmostlyhappens，orwhether，asotherwise

happens，theysurviveandmultiplyintoadistinctvariety，inconsequence

oftheirfitnesstocertainpartially—unlikeconditions，mattersnottothe

argument。Theonecaseconformstothelawthattheunlikeunitsofanaggregate

aresortedintotheirkindsandparted，whenuniformlysubjecttothesame

incidentforces，andtheothertotheconverselawthatthelikeunitsof

anaggregatearepartedandseparatelygroupedwhensubjecttodifferent

incidentforces。AndonconsultingMr。Darwin\'sremarksondivergenceof

character，itwillbeseenthatthesegregationsthuscausedtendevertobecomemoredefinite。§167。Mentalevolutionunderoneofitsleadingaspects，wefound

toconsistintheformationinthemindofgroupsoflikeobjectsandlike

relations——adifferentiationofthevariousthingsoriginallyconfounded

togetherinoneassemblage，andanintegrationofeachseparateorderof

thingsintoaseparategroup（§153）。Hereitremainstopointoutthat

whileunlikenessintheincidentforcesisthecauseofsuchdifferentiations，

likenessintheincidentforcesisthecauseofsuchintegrations。Forwhat

istheprocessthroughwhichclassificationsareestablished？Howdoplants

becomegroupedinthemindofthebotanistintoorders，genera，andspecies？

Eachplantheexaminesyieldshimacertaincompleximpression。Nowandthen

hepicksupaplantlikeonebeforeseen;andtherecognitionofitisthe

productioninhimofalikeconnectedgroupofsensations，byalikeconnected

groupofattributes。Thatistosaythereisproducedthroughoutthenerve—centres

concerned，acombinedsetofchanges，similartoacombinedsetofchanges

beforeproduced。Consideredanalytically，eachsuchcombinedsetofchanges

isacombinedsetofmolecularmodificationswroughtintheaffectedpart

oftheorganism。Oneveryrepetitionoftheimpression，alikecombinedset

ofmolecularmodificationsissuperposedonthepreviousones，andmakes

themgreater:thusgeneratinganinternalplexusof。modifications，withits

answeringidea，correspondingtothesesimilarexternalobjects。Meanwhile，

anotherkindofplantproducesinthebrainofthebotanistanothersetof

molecularmodifications——asetwhichdoesnotagreewiththeonewehave

beenconsidering，butdisagreeswithit;andbyrepetitionofsuchthere

isgeneratedadifferentideaansweringtoadifferentspecies。What，now，

isthenatureofthisprocessexpressedingeneralterms？Ontheonehand

therearethelikeandunlikethingsfromwhichseverityemanatethegroups

offorcesbywhichweperceivethem。Ontheotherhand，therearetheorgans

ofsenseandpercipientcentres，throughwhich，inthecourseofobservation，

thesegroupsofforcespass。Inpassingthroughthemthelikegroupsofforces

aresegregated，orseparatedfromtheunlikegroupsofforces;andeachsuch

separateseriesofgroupsofforces，answeringtoanexternalgenusorspecies，

producesanideaofthegenusorspecies。Webeforesawthataswellasa

separationofmixedmattersbythesameforce，thereisaseparationofmixed

forcesbythesamematter;andherewemayfurtherseethattheunlikeforces

soseparated，workunlikestructuralchangesintheaggregatethatseparates

them——structuralchangeseachofwhichthusrepresentstheintegratedseriesofmotionsthathasproducedit。Byaparallelprocess，therelationsofco—existenceandsequenceamong

impressions，becomesortedintokindsandgrouped。Whentwophenomenathat

havebeenexperiencedinagivenorder，arerepeatedinthesameorder，those

nerve—centreswhichbeforewereaffectedbythetransitionareagainaffected;

andsuchmolecularmodificationastheyreceivedfromthefirstmotionpropagated

throughthemisincreasedbythissecondmotion。Eachsuchmotionworksa

structuralalterationwhich，inconformitywiththelawsetforthinChapter

IX，involvesadiminishedresistancetoallsuchmotionsthatafterwards

occur。Thesegregationofthesesuccessivemotions（ormorestrictly，the

permanentlyeffectiveportionsofexpandedtheminovercomingresistance）

thusbecomesthecauseof，andthemeasureof，thementalconnexionsbetween

theimpressionswhichthephenomenaproduced。Meanwhile，phenomenadifferent

fromthese，beingphenomenathataffectdifferentnervouselements，will

havetheirconnexionsseverallyrepresentedbymotionsalongotherroutes;

andalongeachoftheseotherroutes，thenervousdischargeswillseverally

takeplacewithareadinessproportionatetothefrequencywithwhichexperience

repeatstheconnexionsofphenomena。Theclassificationofrelationsmust

hencegoonparipassuwiththeclassificationoftherelatedthings。In

commonwiththemixedsensationsreceivedfromtheexternalworld，themixed

relationsitpresentscannotbeimpressedontheorganism。withoutmoreor

lesssegregationofthemresulting。Andthroughthiscontinuoussortingand

groupingofchangesormotions，whichconstitutesnervousfunction，there

isgraduallywroughtthatsortingandgroupingofmatter，whichconstitutesnervousstructure。§168。Insocialevolution，thecollectingtogetherofthelikeand

theseparationoftheunlikebyincidentforces，isprimarilydisplayedin

thesamemanneraswesawittobeamonggroupsofinferiorcreatures。The

humanracestendtodifferentiateandintegrate，asdoracesofotherlivingforms。Oftheforceswhicheffectandmaintainthesegregationsofmankind，may

firstbenamedthoseexternalonesclassedasphysicalconditions。Theclimate

andfoodwhicharefavourabletoanindigenouspeople，aremoreorlessdetrimental

toanalienpeopleofdifferentbodilyconstitution。Intropicalregions

thenorthernracescannotpermanentlyexist:ifnotkilledoffinthefirst

generation，theyaresointhesecond，and，asinIndia，canmaintaintheir

footingonlybytheartificialprocessofcontinuousimmigrationandemigration。

Thatistosay，theexternalforcesactingequallyontheinhabitantsof

agivenlocality，tendtoexpelallwhoarenotofacertaintype，andthus

tokeepuptheintegrationofthosewhoareofthattype。Evenamongthe

Indianpeoplesthemselvesthelikehappens:someofthehill—tribesbeing

segregatedbysurvivingthemalariousinfluenceswhichkilloffHinduswho

entertheirhabitat。Theotherfoxesconspiringtoproducethesenational

segregations，arethosementalonesshownintheaffinitiesofmenforothers

likethemselves。Unitsofonesocietywhoareobligedtoresideinanother，

generallyformcoloniesinthemidstofthatother——smallsocietiesof

theirown。Raceswhichhavebeenartificiallysevered，showtendenciesto

re—unite。Nowthoughthesesegregationscausedbythemutuallikingsofkindred

men，donotseemduetothegeneralprincipleenunciated，theyreallyare

thusinterpretable。Whentreatingofthedirectionofmotion（§80），

itwasshownthattheactionsperformedbymenforthesatisfactionoftheir

wants，arealwaysmotionsalonglinesofleastresistance。Thefeelingscharacterizing

amemberofagivenrace，arefeelingswhichgetcompletesatisfactiononly

amongothermembersofthatraceasatisfactionpartlyderivedfromsympathy

withthosehavinglikefeelings，butmainlyderivedfromtheadaptedsocial

conditionswhichgrowupwheresuchfeelingsprevail。When，therefore，a

citizenofanynationis，aswesee，attractedtowardsothersofhisnation，

therationaleisthatcertainagencieswhichwecalldesires，movehimin

thedirectionofleastresistance。Humanmotions，likeallothermotions，

beingdeterminedbythedistributionofforces，itfollowsthatsuchsegregations

ofracesasarenotproducedbyincidentexternalforces，areproducedbyforceswhichtheunitsoftheracesexerciseononeanother。Duringthedevelopmentofeachsocietyweseeanalogoussegregationscaused

inanalogousways。Afewofthemresultfromminornaturalaffinities;but

thosemostimportantoneswhichconstitutepoliticalandindustrialorganization，

resultfromtheunionofmeninwhomsimilaritieshavebeenproducedbytraining。

Menbroughtuptobodilylabouraremenwhohavehadwroughtinthemacertain

likeness——alikenesswhich，inrespectoftheirpowersofaction，obscures

andsubordinatestheirnaturaldifferences。Thosetrainedtobrain—workhave

acquiredacertainothercommunityofcharacterwhichmakesthem，associal

units，morelikeoneanotherthanlikethosetrainedtomanualoccupations。

Andthereariseclass—segregationsansweringtothesesuper—inducedlikenesses。

Moredefinitesegregationstakeplaceamongthemoredefinitelyassimilated

membersofanyclasswhoarebroughtuptothesamecalling。Evenwherethe

necessitiesoftheirworkforbidconcentrationinonelocality，asamong

artizanshappenswithmasonsandbricklayers，andamongtradershappenswith

theretaildistributers，andamongprofessionalshappenswiththemedical

men，therearenotwantingOperativeBuilders\'Unions，andGrocers\'Societies，

andMedicalAssociations，implyingaprocessofsiftingoutandgrouping。

Andwhere，asamongthemanufacturingclasses，thefunctionsdischargeddo

notrequirethedispersionofcitizenswhoareartificiallyassimilated，

thereisanaggregationoftheminspeciallocalities，andaconsequentincrease

inthedefinitenessofindustrialdivisions。If，now，weseekthecauses

ofthesesegregations，consideredasresultsofforceandmotion，weare

broughttothesamegeneralprincipleasbefore。Thislikenessproducedin

themembersofanyclassorsub—classbytraining，isanaptitudeacquired

bythemforsatisfyingtheirwantsinlikeways。Thatis，theoccupation

hasbecometoeachalineofleastresistance。Henceunderthatpressure

whichdeterminesallmentoactivitythesesimilarly——modifiedsocialunits

aresimilarlyaffected，andtendtotakesimilarcourses。If，then，there

beanylocalitywhich，eitherbyitsphysicalpeculiaritiesorbypeculiarities

wroughtonitduringsocialevolution，isrenderedaplacewhereacertain

kindofindustrialactionmeetswithlessresistancethanelsewhere，itfollows

fromthelawofdirectionofmotionthatthosesocialunitswhohavebeen

mouldedtothiskindofindustrialaction，willbesegregatedbymovingtowards

thisplace。If，forinstance，theproximityofcoalandironminestoanavigable

river，givestoGlasgowanadvantageinthebuildingofiron—ships—ifthe

totallabourrequiredtoproduceagivenvessel，andgetitsequivalentin

foodandclothing，islesstherethanelsewhere;thereiscausedaconcentration

ofiron—shipbuildersatGlasgow，eitherbydetentionofthepopulationborn

toiron—shipbuilding，orbyimmigrationofthoseelsewhereengagedinit，

orbyboth。Theprincipleequallyholdswheretheoccupationismercantile

insteadofmanufacturing。Stock—brokersclusterwheretheamountofeffort

tobeseverallygonethroughbythemindischargingtheirfunctions，and

obtainingtheirprofits，islessthanelsewhere。Alocalexchangehaving

oncebeenestablished，becomesaplacewheretheresistancetobeovercome

byeachissmallerthaninanyotherplace;and，beinglikeunitsunderstress

ofcommondesires，pursuitofthecourseofleastresistancebyeachinvolvestheiraggregationaroundthisplace。Ofcourse，withunitssocomplexasthosewhichconstituteasociety，

andwithforcessoinvolvedasthosewhichmovethem，theresultingselections

andseparationsmustbefarmoreentangled，orfarlessdefinite，thanthose

wehavehithertoconsidered。Formen\'slikenessesbeingofvariouskinds，

leadtovariousordersofsegregation。Therearelikenessesofdisposition，

likenessesoftaste，likenessesproducedbyeducation，likenessesthatresult

fromclass—habits，likenessesofpoliticalfeeling;anditneedsbuttoglance

roundatthecaste—divisions，theassociationsforphilanthropic，scientific，

andartisticpurposes，thereligiouspartiesandsocialcliques，toseethat

somespeciesoflikenessamongthecomponentmembersofeachbodydetermines

theirunion。Nowthedifferentsegregativeprocesses，bytraversingoneanother

andoftenbytheirindirectantagonism，moreorlessobscureoneanother\'s

effects，andpreventanyonedifferentiatedclassfromcompletelyintegrating。