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That¡¡natural¡¡selection¡¡will¡¡always¡¡act¡¡with¡¡extreme¡¡slowness£»¡¡I¡¡fully¡¡admit¡£¡¡Its¡¡action¡¡depends¡¡on¡¡there¡¡being¡¡places¡¡in¡¡the¡¡polity¡¡of¡¡nature£»¡¡which¡¡can¡¡be¡¡better¡¡occupied¡¡by¡¡some¡¡of¡¡the¡¡inhabitants¡¡of¡¡the¡¡country¡¡undergoing¡¡modification¡¡of¡¡some¡¡kind¡£¡¡The¡¡existence¡¡of¡¡such¡¡places¡¡will¡¡often¡¡depend¡¡on¡¡physical¡¡changes£»¡¡which¡¡are¡¡generally¡¡very¡¡slow£»¡¡and¡¡on¡¡the¡¡immigration¡¡of¡¡better¡¡adapted¡¡forms¡¡having¡¡been¡¡checked¡£¡¡But¡¡the¡¡action¡¡of¡¡natural¡¡selection¡¡will¡¡probably¡¡still¡¡oftener¡¡depend¡¡on¡¡some¡¡of¡¡the¡¡inhabitants¡¡becoming¡¡slowly¡¡modified£»¡¡the¡¡mutual¡¡relations¡¡of¡¡many¡¡of¡¡the¡¡other¡¡inhabitants¡¡being¡¡thus¡¡disturbed¡£¡¡Nothing¡¡can¡¡be¡¡effected£»¡¡unless¡¡favourable¡¡variations¡¡occur£»¡¡and¡¡variation¡¡itself¡¡is¡¡apparently¡¡always¡¡a¡¡very¡¡slow¡¡process¡£¡¡The¡¡process¡¡will¡¡often¡¡be¡¡greatly¡¡retarded¡¡by¡¡free¡¡intercrossing¡£¡¡Many¡¡will¡¡exclaim¡¡that¡¡these¡¡several¡¡causes¡¡are¡¡amply¡¡sufficient¡¡wholly¡¡to¡¡stop¡¡the¡¡action¡¡of¡¡natural¡¡selection¡£¡¡I¡¡do¡¡not¡¡believe¡¡so¡£¡¡On¡¡the¡¡other¡¡hand£»¡¡I¡¡do¡¡believe¡¡that¡¡natural¡¡selection¡¡will¡¡always¡¡act¡¡very¡¡slowly£»¡¡often¡¡only¡¡at¡¡long¡¡intervals¡¡of¡¡time£»¡¡and¡¡generally¡¡on¡¡only¡¡a¡¡very¡¡few¡¡of¡¡the¡¡inhabitants¡¡of¡¡the¡¡same¡¡region¡¡at¡¡the¡¡same¡¡time¡£¡¡I¡¡further¡¡believe£»¡¡that¡¡this¡¡very¡¡slow£»¡¡intermittent¡¡action¡¡of¡¡natural¡¡selection¡¡accords¡¡perfectly¡¡well¡¡with¡¡what¡¡geology¡¡tells¡¡us¡¡of¡¡the¡¡rate¡¡and¡¡manner¡¡at¡¡which¡¡the¡¡inhabitants¡¡of¡¡this¡¡world¡¡have¡¡changed¡£¡¡
Slow¡¡though¡¡the¡¡process¡¡of¡¡selection¡¡may¡¡be£»¡¡if¡¡feeble¡¡man¡¡can¡¡do¡¡much¡¡by¡¡his¡¡powers¡¡of¡¡artificial¡¡selection£»¡¡I¡¡can¡¡see¡¡no¡¡limit¡¡to¡¡the¡¡amount¡¡of¡¡change£»¡¡to¡¡the¡¡beauty¡¡and¡¡infinite¡¡complexity¡¡of¡¡the¡¡coadaptations¡¡between¡¡all¡¡organic¡¡beings£»¡¡one¡¡with¡¡another¡¡and¡¡with¡¡their¡¡physical¡¡conditions¡¡of¡¡life£»¡¡which¡¡may¡¡be¡¡effected¡¡in¡¡the¡¡long¡¡course¡¡of¡¡time¡¡by¡¡nature's¡¡power¡¡of¡¡selection¡£¡¡
Extinction
This¡¡subject¡¡will¡¡be¡¡more¡¡fully¡¡discussed¡¡in¡¡our¡¡chapter¡¡on¡¡Geology£»¡¡but¡¡it¡¡must¡¡be¡¡here¡¡alluded¡¡to¡¡from¡¡being¡¡intimately¡¡connected¡¡with¡¡natural¡¡selection¡£¡¡Natural¡¡selection¡¡acts¡¡solely¡¡through¡¡the¡¡preservation¡¡of¡¡variations¡¡in¡¡some¡¡way¡¡advantageous£»¡¡which¡¡consequently¡¡endure¡£¡¡But¡¡as¡¡from¡¡the¡¡high¡¡geometrical¡¡powers¡¡of¡¡increase¡¡of¡¡all¡¡organic¡¡beings£»¡¡each¡¡area¡¡is¡¡already¡¡fully¡¡stocked¡¡with¡¡inhabitants£»¡¡it¡¡follows¡¡that¡¡as¡¡each¡¡selected¡¡and¡¡favoured¡¡form¡¡increases¡¡in¡¡number£»¡¡so¡¡will¡¡the¡¡less¡¡favoured¡¡forms¡¡decrease¡¡and¡¡become¡¡rare¡£¡¡Rarity£»¡¡as¡¡geology¡¡tells¡¡us£»¡¡is¡¡the¡¡precursor¡¡to¡¡extinction¡£¡¡We¡¡can£»¡¡also£»¡¡see¡¡that¡¡any¡¡form¡¡represented¡¡by¡¡few¡¡individuals¡¡will£»¡¡during¡¡fluctuations¡¡in¡¡the¡¡seasons¡¡or¡¡in¡¡the¡¡number¡¡of¡¡its¡¡enemies£»¡¡run¡¡a¡¡good¡¡chance¡¡of¡¡utter¡¡extinction¡£¡¡But¡¡we¡¡may¡¡go¡¡further¡¡than¡¡this£»¡¡for¡¡as¡¡new¡¡forms¡¡are¡¡continually¡¡and¡¡slowly¡¡being¡¡produced£»¡¡unless¡¡we¡¡believe¡¡that¡¡the¡¡number¡¡of¡¡specific¡¡forms¡¡goes¡¡on¡¡perpetually¡¡and¡¡almost¡¡indefinitely¡¡increasing£»¡¡numbers¡¡inevitably¡¡must¡¡become¡¡extinct¡£¡¡That¡¡the¡¡number¡¡of¡¡specific¡¡forms¡¡has¡¡not¡¡indefinitely¡¡increased£»¡¡geology¡¡shows¡¡us¡¡plainly£»¡¡and¡¡indeed¡¡we¡¡can¡¡see¡¡reason¡¡why¡¡they¡¡should¡¡not¡¡have¡¡thus¡¡increased£»¡¡for¡¡the¡¡number¡¡of¡¡places¡¡in¡¡the¡¡polity¡¡of¡¡nature¡¡is¡¡not¡¡indefinitely¡¡great£»¡¡not¡¡that¡¡we¡¡have¡¡any¡¡means¡¡of¡¡knowing¡¡that¡¡any¡¡one¡¡region¡¡has¡¡as¡¡yet¡¡got¡¡its¡¡maximum¡¡of¡¡species¡£¡¡probably¡¡no¡¡region¡¡is¡¡as¡¡yet¡¡fully¡¡stocked£»¡¡for¡¡at¡¡the¡¡Cape¡¡of¡¡Good¡¡Hope£»¡¡where¡¡more¡¡species¡¡of¡¡plants¡¡are¡¡crowded¡¡together¡¡than¡¡in¡¡any¡¡other¡¡quarter¡¡of¡¡the¡¡world£»¡¡some¡¡foreign¡¡plants¡¡have¡¡become¡¡naturalised£»¡¡without¡¡causing£»¡¡as¡¡far¡¡as¡¡we¡¡know£»¡¡the¡¡extinction¡¡of¡¡any¡¡natives¡£¡¡
Furthermore£»¡¡the¡¡species¡¡which¡¡are¡¡most¡¡numerous¡¡in¡¡individuals¡¡will¡¡have¡¡the¡¡best¡¡chance¡¡of¡¡producing¡¡within¡¡any¡¡given¡¡period¡¡favourable¡¡variations¡£¡¡We¡¡have¡¡evidence¡¡of¡¡this£»¡¡in¡¡the¡¡facts¡¡given¡¡in¡¡the¡¡second¡¡chapter£»¡¡showing¡¡that¡¡it¡¡is¡¡the¡¡common¡¡species¡¡which¡¡afford¡¡the¡¡greatest¡¡number¡¡of¡¡recorded¡¡varieties£»¡¡or¡¡incipient¡¡species¡£¡¡Hence£»¡¡rare¡¡species¡¡will¡¡be¡¡less¡¡quickly¡¡modified¡¡or¡¡improved¡¡within¡¡any¡¡given¡¡period£»¡¡and¡¡they¡¡will¡¡consequently¡¡be¡¡beaten¡¡in¡¡the¡¡race¡¡for¡¡life¡¡by¡¡the¡¡modified¡¡descendants¡¡of¡¡the¡¡commoner¡¡species¡£¡¡
From¡¡these¡¡several¡¡considerations¡¡I¡¡think¡¡it¡¡inevitably¡¡follows£»¡¡that¡¡as¡¡new¡¡species¡¡in¡¡the¡¡course¡¡of¡¡time¡¡are¡¡formed¡¡through¡¡natural¡¡selection£»¡¡others¡¡will¡¡become¡¡rarer¡¡and¡¡rarer£»¡¡and¡¡finally¡¡extinct¡£¡¡The¡¡forms¡¡which¡¡stand¡¡in¡¡closest¡¡competition¡¡with¡¡those¡¡undergoing¡¡modification¡¡and¡¡improvement£»¡¡will¡¡naturally¡¡suffer¡¡most¡£¡¡And¡¡we¡¡have¡¡seen¡¡in¡¡the¡¡chapter¡¡on¡¡the¡¡Struggle¡¡for¡¡Existence¡¡that¡¡it¡¡is¡¡the¡¡most¡¡closely¡­allied¡¡forms£»¡¡varieties¡¡of¡¡the¡¡same¡¡species£»¡¡and¡¡species¡¡of¡¡the¡¡same¡¡genus¡¡or¡¡of¡¡related¡¡genera£»¡¡which£»¡¡from¡¡having¡¡nearly¡¡the¡¡same¡¡structure£»¡¡constitution£»¡¡and¡¡habits£»¡¡generally¡¡come¡¡into¡¡the¡¡severest¡¡competition¡¡with¡¡each¡¡other¡£¡¡Consequently£»¡¡each¡¡new¡¡variety¡¡or¡¡species£»¡¡during¡¡the¡¡progress¡¡of¡¡its¡¡formation£»¡¡will¡¡generally¡¡press¡¡hardest¡¡on¡¡its¡¡nearest¡¡kindred£»¡¡and¡¡tend¡¡to¡¡exterminate¡¡them¡£¡¡We¡¡see¡¡the¡¡same¡¡process¡¡of¡¡extermination¡¡amongst¡¡our¡¡domesticated¡¡productions£»¡¡through¡¡the¡¡selection¡¡of¡¡improved¡¡forms¡¡by¡¡man¡£¡¡Many¡¡curious¡¡instances¡¡could¡¡be¡¡given¡¡showing¡¡how¡¡quickly¡¡new¡¡breeds¡¡of¡¡cattle£»¡¡sheep£»¡¡and¡¡other¡¡animals£»¡¡and¡¡varieties¡¡of¡¡flowers£»¡¡take¡¡the¡¡place¡¡of¡¡older¡¡and¡¡inferior¡¡kinds¡£¡¡In¡¡Yorkshire£»¡¡it¡¡is¡¡historically¡¡known¡¡that¡¡the¡¡ancient¡¡black¡¡cattle¡¡were¡¡displaced¡¡by¡¡the¡¡long¡­horns£»¡¡and¡¡that¡¡these¡¡'were¡¡swept¡¡away¡¡by¡¡the¡¡short¡­horns'¡¡£¨I¡¡quote¡¡the¡¡words¡¡of¡¡an¡¡agricultural¡¡writer£©¡¡'as¡¡if¡¡by¡¡some¡¡murderous¡¡pestilence¡£'¡¡
Divergence¡¡of¡¡Character
The¡¡principle£»¡¡which¡¡I¡¡have¡¡designated¡¡by¡¡this¡¡term£»¡¡is¡¡of¡¡high¡¡importance¡¡on¡¡my¡¡theory£»¡¡and¡¡explains£»¡¡as¡¡I¡¡believe£»¡¡several¡¡important¡¡facts¡£¡¡In¡¡the¡¡first¡¡place£»¡¡varieties£»¡¡even¡¡strongly¡­marked¡¡ones£»¡¡though¡¡having¡¡somewhat¡¡of¡¡the¡¡character¡¡of¡¡species¡¡as¡¡is¡¡shown¡¡by¡¡the¡¡hopeless¡¡doubts¡¡in¡¡many¡¡cases¡¡how¡¡to¡¡rank¡¡them¡¡yet¡¡certainly¡¡differ¡¡from¡¡each¡¡other¡¡far¡¡less¡¡than¡¡do¡¡good¡¡and¡¡distinct¡¡species¡£¡¡Nevertheless£»¡¡according¡¡to¡¡my¡¡view£»¡¡varieties¡¡are¡¡species¡¡in¡¡the¡¡process¡¡of¡¡formation£»¡¡or¡¡are£»¡¡as¡¡I¡¡have¡¡called¡¡them£»¡¡incipient¡¡species¡£¡¡How£»¡¡then£»¡¡does¡¡the¡¡lesser¡¡difference¡¡between¡¡varieties¡¡become¡¡augmented¡¡into¡¡the¡¡greater¡¡difference¡¡between¡¡species£¿¡¡That¡¡this¡¡does¡¡habitually¡¡happen£»¡¡we¡¡must¡¡infer¡¡from¡¡most¡¡of¡¡the¡¡innumerable¡¡species¡¡throughout¡¡nature¡¡presenting¡¡well¡­marked¡¡differences£»¡¡whereas¡¡varieties£»¡¡the¡¡supposed¡¡prototypes¡¡and¡¡parents¡¡of¡¡future¡¡well¡­marked¡¡species£»¡¡present¡¡slight¡¡and¡¡ill¡­defined¡¡differences¡£¡¡Mere¡¡chance£»¡¡as¡¡we¡¡may¡¡call¡¡it£»¡¡might¡¡cause¡¡one¡¡variety¡¡to¡¡differ¡¡in¡¡some¡¡character¡¡from¡¡its¡¡parents£»¡¡and¡¡the¡¡offspring¡¡of¡¡this¡¡variety¡¡again¡¡to¡¡differ¡¡from¡¡its¡¡parent¡¡in¡¡the¡¡very¡¡same¡¡character¡¡and¡¡in¡¡a¡¡greater¡¡degree£»¡¡but¡¡this¡¡alone¡¡would¡¡never¡¡account¡¡for¡¡so¡¡habitual¡¡and¡¡large¡¡an¡¡amount¡¡of¡¡difference¡¡as¡¡that¡¡between¡¡varieties¡¡of¡¡the¡¡same¡¡species¡¡and¡¡species¡¡of¡¡the¡¡same¡¡genus¡£¡¡
As¡¡has¡¡always¡¡been¡¡my¡¡practice£»¡¡let¡¡us¡¡seek¡¡light¡¡on¡¡this¡¡head¡¡from¡¡our¡¡domestic¡¡productions¡£¡¡We¡¡shall¡¡here¡¡find¡¡something¡¡analogous¡£¡¡A¡¡fancier¡¡is¡¡struck¡¡by¡¡a¡¡pigeon¡¡having¡¡a¡¡slightly¡¡shorter¡¡beak£»¡¡another¡¡fancier¡¡is¡¡struck¡¡by¡¡a¡¡pigeon¡¡having¡¡a¡¡rather¡¡longer¡¡beak£»¡¡and¡¡on¡¡the¡¡acknowledged¡¡principle¡¡that¡¡'fanciers¡¡do¡¡not¡¡and¡¡will¡¡not¡¡admire¡¡a¡¡medium¡¡standard£»¡¡but¡¡like¡¡extremes£»'¡¡they¡¡both¡¡go¡¡on¡¡£¨as¡¡has¡¡actually¡¡occurred¡¡with¡¡tumbler¡­pigeons£©¡¡choosing¡¡and¡¡breeding¡¡from¡¡birds¡¡with¡¡longer¡¡and¡¡longer¡¡beaks£»¡¡or¡¡with¡¡shorter¡¡and¡¡shorter¡¡beaks¡£¡¡Again£»¡¡we¡¡may¡¡suppose¡¡that¡¡at¡¡an¡¡early¡¡period¡¡one¡¡man¡¡preferred¡¡swifter¡¡horses£»¡¡another¡¡stronger¡¡and¡¡more¡¡bulky¡¡horses¡£¡¡The¡¡early¡¡differences¡¡would¡¡be¡¡very¡¡slight£»¡¡in¡¡the¡¡course¡¡of¡¡time£»¡¡from¡¡the¡¡continued¡¡selection¡¡of¡¡swifter¡¡horses¡¡by¡¡some¡¡breeders£»¡¡and¡¡of¡¡stronger¡¡ones¡¡by¡¡others£»¡¡the¡¡differences¡¡would¡¡become¡¡greater£»¡¡and¡¡would¡¡be¡¡noted¡¡as¡¡forming¡¡two¡¡sub¡­breeds£»¡¡finally£»¡¡after¡¡the¡¡lapse¡¡of¡¡centuries£»¡¡the¡¡sub¡­breeds¡¡would¡¡become¡¡converted¡¡into¡¡two¡¡well¡­established¡¡and¡¡dis

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