Andasinthemulticellularplantssointhemulticellularanimals，alike
primarycontrastisforthwithrepeatedintheinitialclustersofcells。
Producedbytherepeatedfissionsoftheprimitivegerm—cell，eachsuchcluster
presentlyformsitselfintoahollowsphere:the"cleavagecavity"
beingmanifestlyhomologouswiththecavityoftheVilvox—sphere。*InsimpletypesofMetazoa，asthehydroidpolyps，theblastula，
beingthusestablishedinconformitywiththeprimarycontrastofconditions，
therepresentlybeginsasecondarydifferentiationwhich，likethatwehave
seenintheVolvoxbutinamorepronouncedmanner，answerstothesecondary
contrastofconditions;forthissphericalassemblageofcellsbecomesovoid，
andbytheaidofitsciliamovesthroughthewaterbroadendforemost:the
lapsefromhomogeneityofformbeinginsomecasesmademorepronouncedby
theassumptionofasausage—shape。Simultaneouslythecomponentcellsof
thetwoendsbecomeunlikeincharacter。Afarmoremarkeddifferentiation，
orlapseintogreaterheterogeneity，isseenwhenthissingle—layeredspheroid
ofciliatedcellsischangedintoadouble—layeredspheroidbyintroversion
ofoneside:asackwiththemouthsewnupandthebottomthrustinasfar
asitwillgo，servingtoillustratetherelationsofparts。Henceresults
thegastrulawithitsectodermandendoderm;severallyplayingcontrasted
partsinsubsequentdevelopment。Sothatatsuccessivestagesthereisrepeated
thisriseofacontrastofstructuresansweringtoacontrastofconditions
——thatwhichoccursinthesimplecell，thatwhichoccursinthehollowsphereofsuchcells，andthatwhichoccursinthedouble—walledsphere。Illustrationspresentingthelawunderanotheraspect——onefromeach
organickingdom——areinstructive。TheciliatedgermorplanulaofaZoophyte
which，duringitslocomotivestage，isdistinguishableonlyintoouterand
innertissues，nosoonerbecomesfixedthanitsupperendbeginstoassume
adifferentstructurefromitslower。Thedisc—shapedgemmaeoftheMarchantia，
originallyalikeonbothsurfaces，andfallingatrandomwitheitherside
uppermost，immediatelybegintodeveloprootletsontheirundersidesand
stomataontheiruppersides:afactprovingbeyondquestion，thatthisprimarydifferentiationisdeterminedbythisfundamentalcontrastofconditions。Ofcourseinthegermsofhigherorganisms，themetamorphosesimmediately
duetotheinstabilityofthehomogeneous，aresoonmaskedbythosedueto
theassumptionofthehereditarytype。Evenintheearlystagesabovedescribed
therearetobetracedmodificationsthusoriginating。Evenbeforetheprimary
cell—multiplicationbegins，thereissaidtobeanobservabledistinction
betweenthetwopolesoftheegg—cell，foreshadowingthedifferentgerm—layers。
Ofcourseasdevelopmentprogressesassumptionofthetransmittedtypeof
structurequicklyobscurestheseprimarylapsesfromhomogeneity;though
forsometimethefundamentalrelationsofinnerandouterarerecognizable
inthedifferentiations。Butwhathasbeensaidsufficestoestablishthe
allegedgeneraltruth。Itisenoughthatincipientorganisms，settingout
fromrelativelyhomogeneousarrangements，forthwithbegintofallintorelatively
heterogeneousones。Itisenoughthatthemostconspicuousdifferentiations
whichtheydisplay，correspondtothemostmarkeddifferencesofconditions
towhichtheirpartsaresubject。Itisenoughthatthehabitualcontrast
betweenoutsideandinside，whichweknowisproducedininorganicmasses
byunlikenessofexposuretoincidentforces，isparalleledbythefirstcontrastwhichmakesitsappearanceinallorganicmasses。Itremainstopointoutthatintheassemblageoforganismsconstituting
aspecies，theprincipleenunciatedisnolesstraceable。Wehaveabundant
materialsfortheinductionthateachspecieswillnotremainuniform——
iseverbecomingtosomeextentmultiform;andthereisgroundforthededuction
thatthislapsefromhomogeneitytoheterogeneityiscausedbythesubjection
ofitsmemberstounlikecircumstances。Tendingevertospreadfromitsoriginal
habitatintoadjacenthabitats，eachspeciesmusthaveitsperipheralparts
subjecttosetsofforcesunlikethosetowhichitscentralpartsaresubject，
andsomusttendtohaveitsperipheralmembersmadedifferentfromitscentralmembers。§153。Amongmentalphenomenafullestablishmentoftheallegedlaw
wouldinvolveananalysistooextensivefortheoccasion。Toshowsatisfactorily
howstatesofconsciousness，relativelyhomogeneous，becomeheterogeneous
throughdifferencesinthechangeswroughtbydifferentexternalforces，
wouldrequireustotraceouttheorganizationofearlyexperiences。Withouthereattemptingthisitmustsufficetosetdowntheconclusionstobedrawn。Thedevelopmentofintelligenceis，underoneofitschiefaspects，a
classifyingoftheunlikethingspreviouslyconfoundedtogether——aformation
ofsub—classesandsub—sub—classes，untiltheonceconfusedaggregateof
objectsknown，isresolvedintoanaggregatewhichunitesgreatheterogeneity
amongitsmultipliedgroups，withcompletehomogeneityamongthemembers
ofeachgroup。Onfollowingthroughascendinggradesofcreatures，thegenesis
ofthatvaststructureofknowledgeacquiredbysight，weseethatinthe
firststage，whereeye—speckssufficeonlyfordiscriminatinglightfrom
darkness，therecanbenoclassificationsofobjectsseen，savethosebased
onthemannerinwhichlightisobstructed，andthedegreeinwhichitis
obstructed。Bysuchundevelopedvisualorgans，theshadowsperceivedwould
bemerelydistinguishedintothoseofthestationaryobjectswhichthecreature
passedduringitsownmovements，andthoseofthemovingobjectswhichcame
nearwhileitwasatrest;sothattheextremelygeneralclassificationof
visiblethingsintostationaryandmoving，wouldbetheearliestformed。
Akindredstepfollows。Whilethesimplesteyescannotdistinguishbetween
anobstructionoflightcausedbyasmallobjectcloseto，andanobstruction
causedbyalargeobjectatsomedistance，eyesalittlemoredevelopedcan
distinguishthem;whencemustresultavaguedifferentiationoftheclass
ofmovingobjectsintothenearerandthemoreremote。Furtherdevelopments
whichmakepossibleabetterestimationofdistancesbyadjustmentofthe
opticaxes，andthosewhich，throughenlargementandsubdivisionoftheretina，
makepossiblethediscriminationofshapes，mustgivegreaterdefiniteness
totheclassesalreadyformed，andsubdividetheseintosmallerclasses，
consistingofobjectslessunlike。Ineveryinfantmaybetracedtheanalogous
transformationofaconfusedaggregateofimpressionsofsurroundingthings，
notrecognizedasdifferingintheirdistances，sizes，andshapes，intoseparate
classesofthingsunlikeoneanotherintheseandvariousotherrespects。
Andinbothcasesthechangefromthisfirstindefinite，incoherent，and
comparativelyhomogeneousconsciousness，toadefinite，coherent，andheterogeneous
one，isduetodifferencesintheactionsofincidentforcesontheorganism。
Thesebriefindicationsmustsuffice。Probablytheywillgiveadequateclue
toanargumentbywhicheachreadermaysatisfyhimselfthatthecourseof
mentalevolutionoffersnoexceptiontothegenerallaw。Infurtheraidof
suchanargument，Iwillhereaddanillustrationwhichiscomprehensibleapartfromtheprocessofmentalevolutionasawhole。Ithasbeenremarked（IamtoldbyColeridge）thatwiththeadvanceof
language，wordswhichwereoriginallyalikeintheirmeaningsacquireunlike
meanings——achangeheexpressedbytheformidableword"de—synonymization。"
Amongindigenouswordsthislossofequivalencecannotbeclearlyshown;
becauseinthemthedivergencesofmeaningbeganbeforethedawnofliterature。
Butamongwordsthathavebeencoined，oradoptedfromotherlanguages，since
thewritingofbookscommenced，itisdemonstrable。Bytheolddivines，miscreant
wasusedinitsetymologicalsenseofunbeliever;butinmodernspeechit
hasentirelylostthissense。Similarlywithevil—doerandmalefactor。Exactly
synonymousasthesearebyderivation，theyarenolongersynonymousbyusage。
Byamalefactorwenowunderstandaconvictedcriminal，whichisfarfrom
beingtheacceptationofevil—doer。TheverbproducebearsinEuclidits
primarymeaning——toprolongordrawout;butthenowlargely—developed
meaningsofproduce，havelittleincommonwiththemeaningsofprolong，
ordrawout。IntheChurchofEnglandliturgyanoddeffectnowresultsfrom
theoccurrenceofpreventinitsoriginalsense——tocomebefore，instead
ofitsmodernspecializedsense——tocomebeforewiththeeffectofarresting。
Butthemostconclusivecasesarethoseinwhichthecontrastedwordsconsist
ofthesamepartsdifferentlycombined，asingounderandundergo。Wego
underatree，andweundergoapain。Butthough，ifanalyticallyconsidered，
themeaningswouldbethesamewerethewordstransposed，habithassofar
modifiedtheirmeaningsthatwecouldnotwithoutabsurdityspeakofundergoing
atreeandgoingunderapain。Manysuchinstancesshowthatbetweentwo
wordswhichareoriginallyoflikeforce，anequilibriumcannotbemaintained。
Unlesstheyaredailyusedinexactlyequaldegrees，inexactlysimilarrelations
（whichisinfinitelyimprobable），therenecessarilyariesahabitofassociating
oneratherthantheotherwithparticularacts，orobjects。Suchahabit
oncecommenced，becomesconfirmed;andgraduallytheirhomogeneityofmeaningdisappears。Shouldanydifficultybefeltinunderstandinghowthesementalchanges
exemplifyalawofphysicaltransformationsthatarewroughtbyphysical
forces，itwilldisappearoncontemplatingactsofmindasnervousfunctions。
Itwillbeseenthateachlossofequilibriumaboveinstanced，isaloss
offunctionalequalitybetweensometwoelementsofthenervoussystem。And
itwillbeseenthat，asinothercases，thislossoffunctionalequalityisduetodifferencesintheincidenceofforces。§154。Massesofmen，incommonwithallothermasses，showalike
proclivitysimilarlycaused。Smallcombinationsandlargesocietiesequally
manifestit;andintheone，asintheother，bothgovernmentalandindustrial
differentiationsareinitiatedbyit。Letusglanceatthefactsundertheseheads。Abusiness—partnership，balancedastheauthoritiesofitsmembersmay
theoreticallybe，presentlybecomesaunioninwhichtheauthorityofone
partneristacitlyrecognizedasgreaterthanthatoftheotherorothers。
Thoughtheshareholdershavegivenequalpowerstothedirectorsoftheir
company，inequalitiesofpowersoonariseamongthem;andoftenthesupremacy
ofsomeonedirectorgrowssomarked，thathisdecisionsdeterminethecourse
whichtheboardtakes。Norinassociationsforpolitical，charitable，literary，
orotherpurposes，dowefailtofindalikeprocessofdivisionintodominant
andsubordinateparties;eachhavingitsleader，itsmembersoflessinfluence，
anditsmassofuninfluentialmembers。Theseminorinstancesinwhichunorganized
groupsofmen，standinginhomogeneousrelations，maybewatchedgradually
passingintoorganizedgroupsofmenstandinginheterogeneousrelations，
giveuskeytosocialinequalities。Barbarousandcivilizedcommunitiesare
alikecharacterizedbyseparationintoclasses，aswellasbyseparation
ofeachclassintomoreimportantandlessimportantunits;andthisstructure
isthegradually—consolidatedresultofaprocesslikethatdailyexemplified
intradingandothercombinations。Solongasmenareconstitutedtoact
ononeanother，eitherbyphysicalforceorbyforceofcharacterthestruggles
forsupremacymustfinallybedecidedinfavourofsomeclassorsomeone;
andthedifferenceoncecommencedmusttendtobecomeevermoremarked。Its
unstableequilibriumbeingdestroyed，theuniformmustgravitatewithincreasing
rapidityintothemultiform。Andsosupremacyandsubordinationmustestablish
themselves，asweseetheydo，throughoutthewholestructureofasociety，
fromthegreatclass—divisionspervadingitsentirebody，downtovillage
cliques，andevendowntoeveryposseofschoolboys。Probablyitwillbe
objectedthatsuchchangesresult，notfromthehomogeneityoftheoriginal
aggregations，butfromtheirnon—homogeneity——fromcertainslightdifferences
existingamongtheirunitsattheoutset。Thisisdoubtlesstheproximate
cause。Instrictness，suchchangesmustberegardedastransformationsof
therelativelyhomogeneousintotherelativelyheterogeneous。Butanaggregation
ofmenabsolutelyalikeintheirendowments，wouldeventuallyundergoasimilar
transformation。Forintheabsenceofuniformityinthelivesseverallyled
bythem——intheiroccupations，physicalconditions，domesticrelations，
andtrainsofthoughtandfeeling——theremustarisedifferencesamongthem;
andthesemusteventuallyinitiatesocialdifferentiations。Eveninequalities
ofhealthcausedbyaccidentswill，byentailinginequalitiesofphysical
andmentalpower，disturbtheexactbalanceofmutualinfluencesamongtheunits;andthebalanceoncedisturbed，willinevitablybelost。Turningtotheindustrialorganization，andnotingthatitsdivisioninto
regulativeandoperativeisprimarilydetermined，likethepreceeding，by
differencesofpower（womenandslavesbeingthefirstworkingclasses）;
admitting，too，thatevenamongsavagessomesmallspecializationsarise
fromindividualaptitudes;wegoontoobservethatthelargeindustrial
divisionsintowhichsocietiesgravitate，areduetounlikenessesofexternal
circumstances。Suchdivisionsareabsentuntilsuchunlikenessesareestablished。
Nomadictribesdonotpermanentlyexposeanygroupsoftheirmemberstospecial
localconditions;nordoesastationarytribe，whenoccupyingonlyasmall
area，maintainfromgenerationtogenerationmarkedcontrastsinthelocal
conditionsofitsmembers;andinsuchtribestherearenodecidedeconomic
differentiations。Butacommunitywhich，byconquest，orotherwise，hasoverspread
alargetract，andhasbecomesofarsettledthatitsmembersliveanddie
intheirrespectivedistricts，keepsitsseveralsectionsindifferentcircumstances;
andthentheynolongerremainalikeintheiroccupations。Thosewholive
dispersedcontinuetohuntorcultivatetheearth;thosewhospreadtothe
sea—shorefallintomaritimeoccupations;whiletheinhabitantsofsomespot
chosen，perhapsforitscentrality，asoneofperiodicassemblage，become
traders，andatownspringsup。Intheadaptationsofthesesocialunits
totheirrespectivefunctions，weseeaprogressfromuniformitytomultiformity
causedbyunlikeincidenceofforces。Laterintheprocessofsocialevolution
theselocaladaptationsaregreatlymultiplied。Differencesinsoilandclimate，
causetheruralinhabitantsindifferentpartsofthekingdomtohavetheir
occupationspartiallyspecialized，andtobecomeknownaschieflyproducing
cattle，orsheep，orwheat，oroats，orhops，orfruit。Peoplelivingwhere
coal—fieldsarediscoveredaretransformedintocolliers;Cornishmentake
tominingbecauseCornwallismetalliferous;andiron—manufactureisthe
dominantindustrywhereiron—stoneisplentiful。Liverpoolhastakentoimporting
cotton，becauseofitsproximitytothedistrictwherecotton—goodsaremade;
andforanalogousreasonsHullhasbecomethechiefportatwhichforeign
woolsarebroughtin。Thusingeneralandindetail，industrialheterogeneities
ofthesocialorganismprimarydependonlocalinfluences。Thosedivisions
oflabourwhich，underanotheraspect，wereinterpretedasduetothesetting
upofmotioninthedirectionsofleastresistance（§80），arehereinterpreted
asduetodifferencesintheincidentforces;andthetwointerpretations
arequiteconsistentwitheachother。Forthatwhichineachdeterminesthe
directionofleastresistance，isthedistributionoftheforcestobeovercome;
andhenceunlikenessesofdistributioninseparatelocalities，entailsunlikenessesinthelinesofhumanactionsinthoselocalities——entailsindustrialdifferentiations。§155。Ithasstilltobeshownthatthisgeneraltruthisdemonstrable
apriori——thattheinstabilityofthehomogeneousisacorollaryfromthe
persistenceofforce。Alreadythishasbeentacitlyimplied，buthereitwillbepropertoexpandthetacitimplicationintodefiniteproof。Onstrikingamassofmatterwithsuchforceaseithertoindentitor
makeitflytopieces，weseeboththattheblowaffectsdifferentlyits
differentparts，andthatthedifferencesareconsequentontheunlikerelations
ofitspartstotheforceimpressed。Thepartstruckisdrivenintowards
thecentreofthemass。Itthuscompresses，andtendstodisplace，themore
centrallysituatedportions。These，however，cannotbecompressedorthrust
outoftheirplaceswithoutpressingonsurroundingportions。Andwhenthe
blowisviolentenoughtofracturethemass，wesee，intheradialdispersion
ofthefragments，thattheoriginalmomentumhasbeendividedintonumerous
minormomenta，unlikeintheirdirections。Weseethatthepartsaredifferently
affectedbythedisruptiveforce，becausetheyaredifferentlyrelatedto
itintheirdirectionsandattachments——thattheeffectsbeingthejoint
productsoftheforceandtheconditionscannotbealikeinpartswhichare
differentlyconditioned。Abodyonwhichradiantheatisfalling，exemplifies
thistruthstillmoreclearly。Takethesimplestcase——thatofasphere。
Whilethepartnearesttotheradiatingcentrereceivestheraysatright
angles，theraysstriketheotherpartsoftheexposedsideatallangles
from90°downto0°。Themolecularvibrationspropagatedthrough
themassfromthesurfacewhichreceivestheheat，proceedinwardsatangles
differingforeachpoint。Further，theinteriorpartsreachedbythevibrations
proceedingfromallpointsoftheheatedside，mustbedissimilarlyaffected
inproportionastheirpositionsaredissimilar。Sothatwhethertheybe
ontherecipientarea，inthemiddle，orattheremoteside，theconstituentmoleculesarethrownintostatesofvibrationmoreorlessunlikeoneanother。Butnow，whatistheultimatemeaningoftheconclusionthataforceproduces
differentchangesthroughoutauniformmass，becausethepartsofthemass
standindifferentrelationstotheforce？Fullytounderstandthis，wemust
contemplateeachpartassimultaneouslysubjecttootherforces——those
ofgravitation，ofcohesion，molecularmotion，etc。Theeffectwroughtby
anadditionalforce，mustbearesultantofitandtheforcesalreadyin
action。Iftheforcesalreadyinactionontwopartsofanyaggregate，are
differentintheirresultantdirections，theeffectsproducedonthesetwo
partsbyequaladditionalforcesmustbedifferentintheirdirections。Why
musttheybedifferent？Becausesuchunlikenessasexistsbetweenthetwo
setsoffactors，ismadebythepresenceintheoneofsomespecially—directed
forcethatisnotpresentintheother;andthatthisforcewillproduce
aneffect，renderingthetotalresultintheonecaseunlikethatinthe
other，isanecessarycorollaryfromthepersistenceofforce。Stillmore
manifestdoesitbecomethatthedissimilarly—placedpartsofanyaggregate
mustbedissimilarlymodifiedbyanincidentforce，whenwerememberthat
thequantitiesoftheincidentforcetowhichtheyareseverallysubject，
arenotequal，asabovesupposed，butarenearlyalwaysunequal。Lookagain
attheaboveexamples。Theamountsofanyexternalradiantforcewhichthe
differentpartsofanaggregatereceive，arewidelycontrasted:wehavethe
contrastbetweenthequantityfallingonthesidenexttheradiatingcentre，
andthequantity，orrathernoquantity，fallingontheoppositeside;we
havecontrastsinthequantitiesreceivedbydifferently—placedareason
theexposedside;andwehaveendlesscontrastsbetweenthequantitiesreceived
bythevariouspartsoftheinterior。Similarlywhenmechanicalforceis
expendedonanyaggregate，eitherbycollision，continuedpressure，ortension，
theamountsofstraindistributedthroughoutthemassaremanifestlyunlike
forunlikepositions。Anditisobviousthatordinarychemicalactionaffects
surfacemorethancentre，andoftenonepartofthesurfacemorethananother。
Buttosaythedifferentpartsofanaggregatereceivedifferentquantities
ofanyforcecapableofchangingthem，istosaythatiftheywerebefore
homogeneoustheymustberenderedtoaproportionateextentheterogeneous;
since，forcebeingpersistent，thedifferentquantitiesofitfallingon
thedifferentparts，mustworkinthemdifferentquantitiesofeffect—different
changes。Yetonemorekindreddeductionisrequiredtocompletetheargument。
Evenapartfromtheactionofanyexternalforce，theequilibriumofahomogeneous
aggregatemustbedestroyedbytheunequalactionsofitspartsononeanother。
Thatmutualinfluencewhichproducesaggregation（nottomentionothermutual
influences）mustworkdifferenteffectsonthedifferentparts;sincethey
areseverallyexposedtoitinunlikeamountsanddirections。Thiswillbe
clearlyseenonrememberingthattheportionsofwhichthewholeismade
up，maybeseverallyregardedasminorwholes;thatoneachoftheseminor
wholes，theactionoftheentireaggregatethenbecomesanexternalincident
force;thatsuchexternalincidentforcemust，asaboveshown，workunlike
changesinthepartsofanysuchminorwhole;andthatiftheminorwholes
areseverallythusrenderedheterogeneous，theentireaggregateisrenderedheterogeneous。Theinstabilityofthehomogeneousisthusdeduciblefromthatprimordial
truthwhichunderliesourintelligence。Onestablehomogeneityonly，ishypothetically
possible。Ifcentresofforce，absolutelyuniformintheirpowers，werediffused
withabsoluteuniformitythroughunlimitedspace，theywouldremaininequilibrium。