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the¡¡hinny£»¡¡which¡¡is¡¡the¡¡offspring¡¡of¡¡the¡¡female¡­ass¡¡and¡¡stallion¡£¡¡
Much¡¡stress¡¡has¡¡been¡¡laid¡¡by¡¡some¡¡authors¡¡on¡¡the¡¡supposed¡¡fact£»¡¡that¡¡mongrel¡¡animals¡¡alone¡¡are¡¡born¡¡closely¡¡like¡¡one¡¡of¡¡their¡¡parents£»¡¡but¡¡it¡¡can¡¡be¡¡shown¡¡that¡¡this¡¡does¡¡sometimes¡¡occur¡¡with¡¡hybrids£»¡¡yet¡¡I¡¡grant¡¡much¡¡less¡¡frequently¡¡with¡¡hybrids¡¡than¡¡with¡¡mongrels¡£¡¡Looking¡¡to¡¡the¡¡cases¡¡which¡¡I¡¡have¡¡collected¡¡of¡¡cross¡­bred¡¡animals¡¡closely¡¡resembling¡¡one¡¡parent£»¡¡the¡¡resemblances¡¡seem¡¡chiefly¡¡confined¡¡to¡¡characters¡¡almost¡¡monstrous¡¡in¡¡their¡¡nature£»¡¡and¡¡which¡¡have¡¡suddenly¡¡appeared¡¡such¡¡as¡¡albinism£»¡¡melanism£»¡¡deficiency¡¡of¡¡tail¡¡or¡¡horns£»¡¡or¡¡additional¡¡fingers¡¡and¡¡toes£»¡¡and¡¡do¡¡not¡¡relate¡¡to¡¡characters¡¡which¡¡have¡¡been¡¡slowly¡¡acquired¡¡by¡¡selection¡£¡¡Consequently£»¡¡sudden¡¡reversions¡¡to¡¡the¡¡perfect¡¡character¡¡of¡¡either¡¡parent¡¡would¡¡be¡¡more¡¡likely¡¡to¡¡occur¡¡with¡¡mongrels£»¡¡which¡¡are¡¡descended¡¡from¡¡varieties¡¡often¡¡suddenly¡¡produced¡¡and¡¡semi¡­monstrous¡¡in¡¡character£»¡¡than¡¡with¡¡hybrids£»¡¡which¡¡are¡¡descended¡¡from¡¡species¡¡slowly¡¡and¡¡naturally¡¡produced¡£¡¡On¡¡the¡¡whole¡¡I¡¡entirely¡¡agree¡¡with¡¡Dr¡¡Prosper¡¡Lucas£»¡¡who£»¡¡after¡¡arranging¡¡an¡¡enormous¡¡body¡¡of¡¡facts¡¡with¡¡respect¡¡to¡¡animals£»¡¡comes¡¡to¡¡the¡¡conclusion£»¡¡that¡¡the¡¡laws¡¡of¡¡resemblance¡¡of¡¡the¡¡child¡¡to¡¡its¡¡parents¡¡are¡¡the¡¡same£»¡¡whether¡¡the¡¡two¡¡parents¡¡differ¡¡much¡¡or¡¡little¡¡from¡¡each¡¡other£»¡¡namely¡¡in¡¡the¡¡union¡¡of¡¡individuals¡¡of¡¡the¡¡same¡¡variety£»¡¡or¡¡of¡¡different¡¡varieties£»¡¡or¡¡of¡¡distinct¡¡species¡£¡¡
Laying¡¡aside¡¡the¡¡question¡¡of¡¡fertility¡¡and¡¡sterility£»¡¡in¡¡all¡¡other¡¡respects¡¡there¡¡seems¡¡to¡¡be¡¡a¡¡general¡¡and¡¡close¡¡similarity¡¡in¡¡the¡¡offspring¡¡of¡¡crossed¡¡species£»¡¡and¡¡of¡¡crossed¡¡varieties¡£¡¡If¡¡we¡¡look¡¡at¡¡species¡¡as¡¡having¡¡been¡¡specially¡¡created£»¡¡and¡¡at¡¡varieties¡¡as¡¡having¡¡been¡¡produced¡¡by¡¡secondary¡¡laws£»¡¡this¡¡similarity¡¡would¡¡be¡¡an¡¡astonishing¡¡fact¡£¡¡But¡¡it¡¡harmonizes¡¡perfectly¡¡with¡¡the¡¡view¡¡that¡¡there¡¡is¡¡no¡¡essential¡¡distinction¡¡between¡¡species¡¡and¡¡varieties¡£¡¡
Summary¡¡of¡¡Chapter¡£¡¡First¡¡crosses¡¡between¡¡forms¡¡sufficiently¡¡distinct¡¡to¡¡be¡¡ranked¡¡as¡¡species£»¡¡and¡¡their¡¡hybrids£»¡¡are¡¡very¡¡generally£»¡¡but¡¡not¡¡universally£»¡¡sterile¡£¡¡The¡¡sterility¡¡is¡¡of¡¡all¡¡degrees£»¡¡and¡¡is¡¡often¡¡so¡¡slight¡¡that¡¡the¡¡two¡¡most¡¡careful¡¡experimentalists¡¡who¡¡have¡¡ever¡¡lived£»¡¡have¡¡come¡¡to¡¡diametrically¡¡opposite¡¡conclusions¡¡in¡¡ranking¡¡forms¡¡by¡¡this¡¡test¡£¡¡The¡¡sterility¡¡is¡¡innately¡¡variable¡¡in¡¡individuals¡¡of¡¡the¡¡same¡¡species£»¡¡and¡¡is¡¡eminently¡¡susceptible¡¡of¡¡favourable¡¡and¡¡unfavourable¡¡conditions¡£¡¡The¡¡degree¡¡of¡¡sterility¡¡does¡¡not¡¡strictly¡¡follow¡¡systematic¡¡affinity£»¡¡but¡¡is¡¡governed¡¡by¡¡several¡¡curious¡¡and¡¡complex¡¡laws¡£¡¡It¡¡is¡¡generally¡¡different£»¡¡and¡¡sometimes¡¡widely¡¡different£»¡¡in¡¡reciprocal¡¡crosses¡¡between¡¡the¡¡same¡¡two¡¡species¡£¡¡It¡¡is¡¡not¡¡always¡¡equal¡¡in¡¡degree¡¡in¡¡a¡¡first¡¡cross¡¡and¡¡in¡¡the¡¡hybrid¡¡produced¡¡from¡¡this¡¡cross¡£¡¡
In¡¡the¡¡same¡¡manner¡¡as¡¡in¡¡grafting¡¡trees£»¡¡the¡¡capacity¡¡of¡¡one¡¡species¡¡or¡¡variety¡¡to¡¡take¡¡on¡¡another£»¡¡is¡¡incidental¡¡on¡¡generally¡¡unknown¡¡differences¡¡in¡¡their¡¡vegetative¡¡systems£»¡¡so¡¡in¡¡crossing£»¡¡the¡¡greater¡¡or¡¡less¡¡facility¡¡of¡¡one¡¡species¡¡to¡¡unite¡¡with¡¡another£»¡¡is¡¡incidental¡¡on¡¡unknown¡¡differences¡¡in¡¡their¡¡reproductive¡¡systems¡£¡¡There¡¡is¡¡no¡¡more¡¡reason¡¡to¡¡think¡¡that¡¡species¡¡have¡¡been¡¡specially¡¡endowed¡¡with¡¡various¡¡degrees¡¡of¡¡sterility¡¡to¡¡prevent¡¡them¡¡crossing¡¡and¡¡blending¡¡in¡¡nature£»¡¡than¡¡to¡¡think¡¡that¡¡trees¡¡have¡¡been¡¡specially¡¡endowed¡¡with¡¡various¡¡and¡¡somewhat¡¡analogous¡¡degrees¡¡of¡¡difficulty¡¡in¡¡being¡¡grafted¡¡together¡¡in¡¡order¡¡to¡¡prevent¡¡them¡¡becoming¡¡inarched¡¡in¡¡our¡¡forests¡£¡¡
The¡¡sterility¡¡of¡¡first¡¡crosses¡¡between¡¡pure¡¡species£»¡¡which¡¡have¡¡their¡¡reproductive¡¡systems¡¡perfect£»¡¡seems¡¡to¡¡depend¡¡on¡¡several¡¡circumstances£»¡¡in¡¡some¡¡cases¡¡largely¡¡on¡¡the¡¡early¡¡death¡¡of¡¡the¡¡embryo¡£¡¡The¡¡sterility¡¡of¡¡hybrids£»¡¡which¡¡have¡¡their¡¡reproductive¡¡systems¡¡imperfect£»¡¡and¡¡which¡¡have¡¡had¡¡this¡¡system¡¡and¡¡their¡¡whole¡¡organisation¡¡disturbed¡¡by¡¡being¡¡compounded¡¡of¡¡two¡¡distinct¡¡species£»¡¡seems¡¡closely¡¡allied¡¡to¡¡that¡¡sterility¡¡which¡¡so¡¡frequently¡¡affects¡¡pure¡¡species£»¡¡when¡¡their¡¡natural¡¡conditions¡¡of¡¡life¡¡have¡¡been¡¡disturbed¡£¡¡This¡¡view¡¡is¡¡supported¡¡by¡¡a¡¡parallelism¡¡of¡¡another¡¡kind£»¡¡namely£»¡¡that¡¡the¡¡crossing¡¡of¡¡forms¡¡only¡¡slightly¡¡different¡¡is¡¡favourable¡¡to¡¡the¡¡vigour¡¡and¡¡fertility¡¡of¡¡their¡¡offspring£»¡¡and¡¡that¡¡slight¡¡changes¡¡in¡¡the¡¡conditions¡¡of¡¡life¡¡are¡¡apparently¡¡favourable¡¡to¡¡the¡¡vigour¡¡and¡¡fertility¡¡of¡¡all¡¡organic¡¡beings¡£¡¡It¡¡is¡¡not¡¡surprising¡¡that¡¡the¡¡degree¡¡of¡¡difficulty¡¡in¡¡uniting¡¡two¡¡species£»¡¡and¡¡the¡¡degree¡¡of¡¡sterility¡¡of¡¡their¡¡hybrid¡­offspring¡¡should¡¡generally¡¡correspond£»¡¡though¡¡due¡¡to¡¡distinct¡¡causes£»¡¡for¡¡both¡¡depend¡¡on¡¡the¡¡amount¡¡of¡¡difference¡¡of¡¡some¡¡kind¡¡between¡¡the¡¡species¡¡which¡¡are¡¡crossed¡£¡¡Nor¡¡is¡¡it¡¡surprising¡¡that¡¡the¡¡facility¡¡of¡¡effecting¡¡a¡¡first¡¡cross£»¡¡the¡¡fertility¡¡of¡¡the¡¡hybrids¡¡produced£»¡¡and¡¡the¡¡capacity¡¡of¡¡being¡¡grafted¡¡together¡¡though¡¡this¡¡latter¡¡capacity¡¡evidently¡¡depends¡¡on¡¡widely¡¡different¡¡circumstances¡¡should¡¡all¡¡run£»¡¡to¡¡a¡¡certain¡¡extent£»¡¡parallel¡¡with¡¡the¡¡systematic¡¡affinity¡¡of¡¡the¡¡forms¡¡which¡¡are¡¡subjected¡¡to¡¡experiment£»¡¡for¡¡systematic¡¡affinity¡¡attempts¡¡to¡¡express¡¡all¡¡kinds¡¡of¡¡resemblance¡¡between¡¡all¡¡species¡£¡¡
First¡¡crosses¡¡between¡¡forms¡¡known¡¡to¡¡be¡¡varieties£»¡¡or¡¡sufficiently¡¡alike¡¡to¡¡be¡¡considered¡¡as¡¡varieties£»¡¡and¡¡their¡¡mongrel¡¡offspring£»¡¡are¡¡very¡¡generally£»¡¡but¡¡not¡¡quite¡¡universally£»¡¡fertile¡£¡¡Nor¡¡is¡¡this¡¡nearly¡¡general¡¡and¡¡perfect¡¡fertility¡¡surprising£»¡¡when¡¡we¡¡remember¡¡how¡¡liable¡¡we¡¡are¡¡to¡¡argue¡¡in¡¡a¡¡circle¡¡with¡¡respect¡¡to¡¡varieties¡¡in¡¡a¡¡state¡¡of¡¡nature£»¡¡and¡¡when¡¡we¡¡remember¡¡that¡¡the¡¡greater¡¡number¡¡of¡¡varieties¡¡have¡¡been¡¡produced¡¡under¡¡domestication¡¡by¡¡the¡¡selection¡¡of¡¡mere¡¡external¡¡differences£»¡¡and¡¡not¡¡of¡¡differences¡¡in¡¡the¡¡reproductive¡¡system¡£¡¡In¡¡all¡¡other¡¡respects£»¡¡excluding¡¡fertility£»¡¡there¡¡is¡¡a¡¡close¡¡general¡¡resemblance¡¡between¡¡hybrids¡¡and¡¡mongrels¡£¡¡Finally£»¡¡then£»¡¡the¡¡facts¡¡briefly¡¡given¡¡in¡¡this¡¡chapter¡¡do¡¡not¡¡seem¡¡to¡¡me¡¡opposed¡¡to£»¡¡but¡¡even¡¡rather¡¡to¡¡support¡¡the¡¡view£»¡¡that¡¡there¡¡is¡¡no¡¡fundamental¡¡distinction¡¡between¡¡species¡¡and¡¡varieties¡£¡¡¡¡
Chapter¡¡9¡¡¡­¡¡On¡¡the¡¡Imperfection¡¡of¡¡the¡¡Geological¡¡Record

IN¡¡the¡¡sixth¡¡chapter¡¡I¡¡enumerated¡¡the¡¡chief¡¡objections¡¡which¡¡might¡¡be¡¡justly¡¡urged¡¡against¡¡the¡¡views¡¡maintained¡¡in¡¡this¡¡volume¡£¡¡Most¡¡of¡¡them¡¡have¡¡now¡¡been¡¡discussed¡£¡¡One£»¡¡namely¡¡the¡¡distinctness¡¡of¡¡specific¡¡forms£»¡¡and¡¡their¡¡not¡¡being¡¡blended¡¡together¡¡by¡¡innumerable¡¡transitional¡¡links£»¡¡is¡¡a¡¡very¡¡obvious¡¡difficulty¡£¡¡I¡¡assigned¡¡reasons¡¡why¡¡such¡¡links¡¡do¡¡not¡¡commonly¡¡occur¡¡at¡¡the¡¡present¡¡day£»¡¡under¡¡the¡¡circumstances¡¡apparently¡¡most¡¡favourable¡¡for¡¡their¡¡presence£»¡¡namely¡¡on¡¡an¡¡extensive¡¡and¡¡continuous¡¡area¡¡with¡¡graduated¡¡physical¡¡conditions¡£¡¡I¡¡endeavoured¡¡to¡¡show£»¡¡that¡¡the¡¡life¡¡of¡¡each¡¡species¡¡depends¡¡in¡¡a¡¡more¡¡important¡¡manner¡¡on¡¡the¡¡presence¡¡of¡¡other¡¡already¡¡defined¡¡organic¡¡forms£»¡¡than¡¡on¡¡climate£»¡¡and£»¡¡therefore£»¡¡that¡¡the¡¡really¡¡governing¡¡conditions¡¡of¡¡life¡¡do¡¡not¡¡graduate¡¡away¡¡quite¡¡insensibly¡¡like¡¡heat¡¡or¡¡moisture¡£¡¡I¡¡endeavoured£»¡¡also£»¡¡to¡¡show¡¡that¡¡intermediate¡¡varieties£»¡¡from¡¡existing¡¡in¡¡lesser¡¡numbers¡¡than¡¡the¡¡forms¡¡which¡¡they¡¡connect£»¡¡will¡¡generally¡¡be¡¡beaten¡¡out¡¡and¡¡exterminated¡¡during¡¡the¡¡course¡¡of¡¡further¡¡modification¡¡and¡¡improvement¡£¡¡The¡¡main¡¡cause£»¡¡however£»¡¡of¡¡innumerable¡¡intermediate¡¡links¡¡not¡¡now¡¡occurring¡¡everywhere¡¡throughout¡¡nature¡¡depends¡¡on¡¡the¡¡very¡¡process¡¡of¡¡natural¡¡selection£»¡¡through¡¡which¡¡new¡¡varieties¡¡continually¡¡take¡¡the¡¡places¡¡of¡¡and¡¡exterminate¡¡their¡¡parent¡­forms¡£¡¡But¡¡just¡¡in¡¡proportion¡¡as¡¡this¡¡process¡¡of¡¡extermination¡¡has¡¡acted¡¡on¡¡an¡¡enormous¡¡scale£»¡¡so¡¡must¡¡the¡¡number¡¡of¡¡intermediate¡¡varieties£»¡¡which¡¡have¡¡formerly¡¡existed¡¡on¡¡the¡¡earth£»¡¡be¡¡truly¡¡enormous¡£¡¡Why¡¡then¡¡is¡¡not¡¡every¡¡geological¡¡formation¡¡and¡¡every¡¡stratum¡¡full¡¡of¡¡such¡¡intermediate¡¡links£¿¡¡Geology¡¡assuredly¡¡does¡¡not¡¡reveal¡¡any¡¡such¡¡finely¡¡graduated¡¡organic¡¡chain£»¡¡and¡¡this£»¡¡perhaps£»¡¡is¡¡the¡¡most¡¡obvious¡¡and¡¡gravest¡¡objection¡¡which¡¡can¡¡be¡¡urged¡¡against¡¡my¡¡theory¡£¡¡The¡¡explanation¡¡lies£»¡¡as¡¡I¡¡believe£»¡¡in¡¡the¡¡extreme¡¡imperfection¡¡of¡¡the¡¡geological¡¡record¡£¡¡
In¡¡the¡¡first¡¡place¡¡it¡¡should¡¡always¡¡be¡¡borne¡¡in¡¡mind¡¡what¡¡sort¡¡of¡¡intermediate¡¡forms¡¡must£»¡¡on¡¡my¡¡theory£»¡¡have¡¡formerly¡¡existed¡£¡¡I¡¡have¡¡found¡¡it¡¡difficult£»¡¡when¡¡looking¡¡at¡¡any¡¡two¡¡species£»¡¡to¡¡avoid¡¡picturing¡¡to¡¡myself£»¡¡forms¡¡directly¡¡intermediate¡¡between¡¡them¡£¡¡But¡¡this¡¡is¡¡a¡¡wholly¡¡false¡¡view£»¡¡we¡¡should¡¡always¡¡look¡¡for¡¡forms¡¡intermediate¡¡between¡¡each¡¡species¡¡and¡¡a¡¡common¡¡but¡¡unknown¡¡progenitor£»¡¡and¡¡the¡¡progenitor¡¡will¡¡generally¡¡have¡¡differed¡¡in¡¡some¡¡respects¡¡from¡¡all¡¡its¡¡modified¡¡descendants¡£¡¡To¡¡give¡¡a¡¡simple¡¡illustration£º¡¡the¡¡fantail¡¡and¡¡pouter¡¡pigeons¡¡have¡¡both¡¡descended¡¡from¡¡the¡¡rock¡­pigeon£»¡¡if¡¡we¡¡possessed¡¡all¡¡the¡¡intermediate¡¡varieties¡¡which¡¡have¡¡ever¡¡existed£»¡¡we¡¡should¡¡have¡¡an¡¡extremely¡¡close¡¡series¡¡between¡¡both¡¡and¡¡the¡¡rock¡­pigeon£»¡¡but¡¡we¡¡should¡¡have¡¡no¡¡varieties¡¡directly¡¡intermediate¡¡between¡¡the¡¡fantail¡¡and¡¡pouter£»¡¡none£»¡¡for¡¡instance£»¡¡combining¡¡a¡¡tail¡¡somewhat¡¡expanded¡¡with¡¡a¡¡crop¡¡somewhat¡¡enlarged£»¡¡the¡¡characteristic¡¡features¡¡of¡¡these¡¡two¡¡breeds¡£¡¡These¡¡two¡¡breeds£»¡¡moreover£»¡¡have¡¡become¡¡so¡¡much¡¡modified£»¡¡that¡¡if¡¡we¡¡had¡¡no¡¡historical¡¡or¡¡indirect¡¡evidence¡¡regarding¡¡their¡¡origin£»¡¡it¡¡would¡¡not¡¡have¡¡been¡¡possible¡¡to¡¡have¡¡determined¡¡from¡¡a¡¡mere¡¡comparison¡¡of¡¡their¡¡structure¡¡with¡¡that¡¡of¡¡the¡¡rock¡­pigeon£»¡¡whether¡¡they¡¡had¡¡descended¡¡from¡¡this¡¡species¡¡or¡¡from¡¡some¡¡other¡¡allied¡¡species£»¡¡such¡¡as¡¡C¡£¡¡oenas¡£¡¡
So¡¡with¡¡natural¡¡species£»¡¡if¡¡we¡¡look¡¡to¡¡forms¡¡very¡¡distinct£»¡¡for¡¡instance¡¡to¡¡the¡¡horse¡¡and¡¡tapir£»¡¡we¡¡have¡¡no¡¡reason¡¡to¡¡suppose¡¡that¡¡links¡¡ever¡¡existed¡¡directly¡¡intermediate¡¡between¡¡them£»¡¡but¡¡between¡¡each¡¡and¡¡an¡¡unknown¡¡common¡¡parent¡£¡¡The¡¡common¡¡parent¡¡will¡¡have¡¡had¡¡i

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