Thisisaverynoteworthycircumstance，anddoubtlesswillonedayhelptofurnishanexplanationofthegreatgulfwhichintervenesbetweenthelowestmanandthehighestapeinintellectualpower；*butithaslittlesystematicvalue，forthesimplereasonthat，asmaybeconcludedfromwhathasbeenalreadysaidrespectingcranialcapacity，thedifferenceinweightofbrainbetweenthehighestandthelowestmenisfargreater，bothrelativelyandabsolutely，thanthatbetweenthelowestmanandthehighestape。Thelatter，ashasbeenseen，isrepresentedby，saytwelveouncesofcerebralsubstanceabsolutely，orby32：20relatively；butasthelargestrecordedhumanbrainweighedbetween65and66ounces，theformerdifferenceisrepresentedbymorethan33ouncesabsolutely，orby65：32relatively。Regardedsystematically，thecerebraldifferencesofmanandapesarenotofmorethangenericvalue；hisFamilydistinctionrestingchieflyonhisdentition，hispelvis，andhislowerlimbs。
[Footnote]*Isay’help’tofurnish：forIbynomeansbelievethatitwasanyoriginaldifferenceofcerebralquality，orquantitywhichcausedthatdivergencebetweenthehumanandthepithecoidstirpes，whichhasendedinthepresentenormousgulfbetweenthem。Itisnodoubtperfectlytrue，inacertainsense，thatalldifferenceoffunctionisaresultofdifferenceofstructure；or，inotherwords，ofdifferenceinthecombinationoftheprimarymolecularforcesoflivingsubstance；and，startingfromthisundeniableaxiom，objectorsoccasionally，andwithmuchseemingplausibility，arguethatthevastintellectualchasmbetweentheApeandManimpliesacorrespondingstructuralchasmintheorgansoftheintellectualfunctions；sothat，itissaid，thenon-discoveryofsuchvastdifferencesproves，notthattheyareabsent，butthatScienceisincompetenttodetectthem。Averylittleconsideration，however，will，Ithink，showthefallacyofthisreasoning。Itsvalidityhangsupontheassumption，thatintellectualpowerdependsaltogetheronthebrain——whereasthebrainisonlyoneconditionoutofmanyonwhichintellectualmanifestationsdepend；theothersbeing，chiefly，theorgansofthesensesandthemotorapparatuses，especiallythosewhichareconcernedinprehensionandintheproductionofarticulatespeech。
Amanborndumb，notwithstandinghisgreatcerebralmassandhisinheritanceofstrongintellectualinstincts，wouldbecapableoffewhigherintellectualmanifestationsthananOrangoraChimpanzee，ifhewereconfinedtothesocietyofdumbassociates。Andyettheremightnotbetheslightestdiscernibledifferencebetweenhisbrainandthatofahighlyintelligentandcultivatedperson。Thedumbnessmightbetheresultofadefectivestructureofthemouth，orofthetongue，orameredefectiveinnervationoftheseparts；oritmightresultfromcongenitaldeafness，causedbysomeminutedefectoftheinternalear，whichonlyacarefulanatomistcoulddiscover。
Theargument，thatbecausethereisanimmensedifferencebetweenaMan’sintelligenceandanApe’s，therefore，theremustbeanequallyimmensedifferencebetweentheirbrains，appearstometobeaboutaswellbasedasthereasoningbywhichoneshouldendeavourtoprovethat，becausethereisa\"greatgulf\"betweenawatchthatkeepsaccuratetimeandanotherthatwillnotgoatall，thereisthereforeagreatstructuralhiatusbetweenthetwowatches。Ahairinthebalance-wheel，alittlerustonapinion，abendinatoothoftheescapement，asomethingsoslightthatonlythepractisedeyeofthewatchmakercandiscoverit，maybethesourceofallthedifference。
Andbelieving，asIdo，withCuvier，thatthepossessionofarticulatespeechisthegranddistinctivecharacterofman（whetheritbeabsolutelypeculiartohimornot），Ifinditveryeasytocomprehend，thatsomeequallyinconspicuousstructuraldifferencemayhavebeentheprimarycauseoftheimmeasurableandpracticallyinfinitedivergenceoftheHumanfromtheSimianStirps。