Eachorganasitisdeveloped，serves，byitsactionsandreactionsonthe
rest，toinitiatenewcomplexities。Thefirstpulsationsofthefoetalheart
mustsimultaneouslyaidtheunfoldingofeverypart。Thegrowthofeachtissue，
bytakingfromthebloodspecialproportionsofelements，mustmodifythe
constitutionoftheblood;andsomustmodifythenutritionofalltheother
tissues。Thedistributiveactions，implyingastheydoacertainwaste，necessitate
anadditiontothebloodofeffetematters，whichmustinfluencetherest
ofthesystem，andperhaps，assomethink，initiatetheformationofexcretory
organs。Thenervousconnexionsestablishedamongthevisceramustfurther
multiplytheirmutualinfluences。Andsoisitwitheverymodificationof
structure——everyadditionalpartandeveryalterationintheratiosof
parts。Proofofamoredirectkindisfurnishedbythefact，thatthesame
germmaybeevolvedintodifferentformsaccordingtocircumstances。Thus，
duringitsearlieststages，everygermissexless——originateseithermale
orfemaleasthebalanceofforcesactingonitdetermines。Again，there
isthefamiliartruththatthelarvaofaworking—beewilldevelopintoa
queen—beeif，beforeacertainperiod，itisfedafteramannerlikethat
inwhichthelarvaeofqueen—beesarefed。Thenthereisthestillmorestriking
evidencefurnishedbyantsandtermites。Riley，Grassi，Haviland，andHart，
haveshownthatdifferencesofnutritionnotonlyoriginatethedifferences
betweenmalesandfemalesbutalsothedifferenttraitsofsolders，workers，
andnurses。*Varying
degreeofnutrition，afterinitiatingtheunlikenessofsex，thendetermines
theunlikenessesofexternalorganspossessedbythevariousclassesofsexless
individuals。Nextcomestheevidence，stillmoredirectlyrelevant，supplied
bytheeffectsofcastration。Iftheremovalofcertainorganspreventsthe
developmentofcertainotherorgansinremotepartsofthesystem——inman
thevocalstructures，thebeard，sometraitsofgeneralform，someinstincts
andothermentalcharacters——thenitisclearthatwheretheseorganshave
notbeenremoved，thepresenceofthemdeterminestheoccurrenceofthese
variouschangesofdevelopment，anddoubtlessmanyminoroneswhichareunobtrusive。
Herethefactthatonecauseproducesmanyeffectsinthecourseoforganic
evolutionisindisputable。Doubtlessweare，andmustevercontinue，unable
toconceivethosemysteriouspropertieswhichmakethegermwhensubject
tofitinfluencesundergothespecialchangesinitiating，andmainlyconstituting，
thetransformationsofanunfoldingorganism;thoughwemayconsistently
supposethattheyrepresentaninfiniteseriesofinheritedmodifications
consequentontheinstabilityofthehomogeneous，themultiplicationofeffects，
andonefurtherfactorstilltobesetforth。Allherecontendedisthat，
givenagermpossessingthesemysteriousproperties，theevolutionofan
organismfromitdepends，inpart，onthatmultiplicationofeffectswhich
wehaveseentobeonecauseofevolutioningeneral，sofaraswehaveyettracedit。When，leavingthedevelopmentofsingleplantsandanimals，wepassto
thatoftheEarth\'sFloraandFauna，thecourseoftheargumentagainbecomes
clearandsimple。Though，asbeforeadmitted，thefragmentaryfactsPalaeontology
hasaccumulated，donotclearlywarrantusinsayingthat，inthelapseof
geologictime，therehavebeenevolvedmoreheterogeneousorganisms，and
moreheterogeneousassemblagesoforganisms;yetweshallnowseethatthere
musteverhavebeenatendencytowardstheseresults。Weshallfindthat
theproductionofmanyeffectsbyonecause，which，asalreadyshown，has
beenallalongincreasingthephysicalheterogeneityoftheEarth，hasfurther
necessitatedanincreasingheterogeneityofitsinhabitingorganisms，individuallyandcollectively。Anillustrationwillmakethisclear。Supposethatbyupheavals，occurring，astheyareknowntodo，atlong
intervals，theEastIndianArchipelagowereraisedintoacontinent，and
achainofmountainsformedalongtheaxisofelevation。Bythefirstof
theseupheavals，theplantsandanimalsofBorneo，Sumatra，NewGuinea，and
therest，wouldbesubjectedtoslightly—modifiedsetsofconditions。The
climateofeachwouldbealteredintemperature，inhumidity，andinits
periodicalvariations，whilethelocaldifferenceswouldbemultiplied。The
modificationswouldeffect，perhapsinappreciably，theentireFloraandFauna
oftheregion。Thechangeoflevelwouldentailadditionalmodifications，
varyingindifferentspecies，andalsoindifferentmembersofthesamespecies，
accordingtotheirdistancefromtheaxisofelevation。Plantsgrowingonly
onthesea—shoreinspeciallocalities，mightbecomeextinct。Others，living
onlyinswampsofacertainhumidity，would，iftheysurvivedatall，probably
undergovisiblechangesofappearance。Whilemoremarkedalterationswould
occurinsomeoftheplantsthatspreadoverthelandsnewlyraisedoutof
thewater。Theanimalsandinsectslivingonthesemodifiedplants，would
themselvesbeinsomedegreemodifiedbychangesoffood，aswellasbychanges
ofclimate;andthemodificationswouldbemoremarkedwhere，fromthedwindling
ordisappearanceofonekindofplant，analliedkindwaseaten。Inthelapse
ofthemanygenerationsarisingbeforethenextupheaval，thesensibleor
insensiblealterationsthusproducedineachspecies，wouldbecomeorganized
——inalltheraceswhichsurvivedtherewouldbemoreorlessadaptation
tothenewconditions。Thenextupheavalwouldsuperinducefurtherorganic
changes，implyingwiderdivergencesfromtheprimaryforms;andsorepeatedly。
Now，however，observethatthisrevolutionwouldnotbeasubstitutionof
athousandmodifiedspeciesforthethousandoriginalspecies;butinplace
ofthethousandoriginalspeciestherewouldariseseveralthousandspecies，
orvarieties，orchangedforms。Eachspeciesbeingdistributedoveranarea
ofsomeextent，andtendingcontinuallytocolonizethenewareaexposed，
itsdifferentmemberswouldbesubjecttodifferentsetsofchanges。Plants
andanimalsmigratingtowardstheequatorwouldnotbeaffectedinthesame
waywithothersmigratingfromit。Thosewhichspreadtowardsthenewshores，
wouldundergochangesunlikethechangesundergonebythosewhichspread
intothemountains。Thus，eachoriginalraceoforganismswouldbecomethe
rootfromwhichdivergedseveralraces，differingmoreorlessfromitand
fromoneanother;andwhilesomeofthesemightsubsequentlydisappear，probably
morethanonewouldsurviveintothenextgeologicperiod。Notonlywould
certainmodificationsbethuscausedbychangesofphysicalconditionsand
food，butalso，insomecases，othermodificationscausedbychangesofhabit。
Thefaunaofeachisland，peopling，stepbystep，thenewly—raisedtracts，
wouldeventuallycomeincontactwiththefaunasofotherislands;andsome
membersoftheseotherfaunaswouldbeunlikeanycreaturesbeforeseen。
Herbivoresmeetingwithnewbeastsofpreywould，insomecases，beledinto
modesofdefenceorescapedifferingfromthosepreviouslyused;andsimultaneously
thebeastsofpreywouldmodifytheirmodesofpursuitandattack。Weknow
thatwhencircumstancesdemandit，suchchangesofhabitdotakeplacein
animals;andweknowthatifthenewhabitsbecomethedominantones，they
musteventuallyinsomedegreealtertheorganization。Note，now，afurther
consequence。Theremustarisenotsimplyatendencytowardsthedifferentiation
ofeachraceoforganismsintoseveralraces;butalsoatendencytothe
occasionalproductionofasomewhathigherorganism。Takeninthemass，these
divergentvarieties，whichhavebeencausedbyfreshphysicalconditions
andhabitsoflife，willexhibitalterationsquiteindefiniteinkindand
degree，andalterationsthatdonotnecessarilyconstituteanadvance。Probably
inmostcasesthemodifiedtypewillbenotappreciablymoreheterogeneous
thantheoriginalone。Butitmustnowandthenoccurthatsomedivision
ofaspecies，fallingintocircumstanceswhichgiveitrathermorecomplex
experiences，anddemandactionssomewhatmoreinvolved，willhavecertain
ofitsorgansfurtherdifferentiatedinproportionatelysmalldegrees——
willbecomeslightlymoreheterogeneous。Hence，therewillfromtimetotime
ariseanincreasedheterogeneitybothoftheEarth\'sfloraandfauna，and
ofindividualracesincludedinthem。Omittingdetailedexplanations，and
allowingforqualificationswhichcannotherebespecified，itissufficiently
clearthatgeologicalmutationshaveallalongtendedtocomplicatetheforms
oflife，whetherregardedseparatelyorcollectivelyThatmultiplication
ofeffectswhichhasbeenapart—causeofthetransformationoftheEarth\'s
crustfromthesimpleintothecomplex，hassimultaneouslyledtoaparallel
transformationoftheLifeuponitssurface。（*）