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I¡¡should¡¡premise¡¡that¡¡I¡¡use¡¡the¡¡term¡¡Struggle¡¡for¡¡Existence¡¡in¡¡a¡¡large¡¡and¡¡metaphorical¡¡sense£»¡¡including¡¡dependence¡¡of¡¡one¡¡being¡¡on¡¡another£»¡¡and¡¡including¡¡£¨which¡¡is¡¡more¡¡important£©¡¡not¡¡only¡¡the¡¡life¡¡of¡¡the¡¡individual£»¡¡but¡¡success¡¡in¡¡leaving¡¡progeny¡£¡¡Two¡¡canine¡¡animals¡¡in¡¡a¡¡time¡¡of¡¡dearth£»¡¡may¡¡be¡¡truly¡¡said¡¡to¡¡struggle¡¡with¡¡each¡¡other¡¡which¡¡shall¡¡get¡¡food¡¡and¡¡live¡£¡¡But¡¡a¡¡plant¡¡on¡¡the¡¡edge¡¡of¡¡a¡¡desert¡¡is¡¡said¡¡to¡¡struggle¡¡for¡¡life¡¡against¡¡the¡¡drought£»¡¡though¡¡more¡¡properly¡¡it¡¡should¡¡be¡¡said¡¡to¡¡be¡¡dependent¡¡on¡¡the¡¡moisture¡£¡¡A¡¡plant¡¡which¡¡annually¡¡produces¡¡a¡¡thousand¡¡seeds£»¡¡of¡¡which¡¡on¡¡an¡¡average¡¡only¡¡one¡¡comes¡¡to¡¡maturity£»¡¡may¡¡be¡¡more¡¡truly¡¡said¡¡to¡¡struggle¡¡with¡¡the¡¡plants¡¡of¡¡the¡¡same¡¡and¡¡other¡¡kinds¡¡which¡¡already¡¡clothe¡¡the¡¡ground¡£¡¡The¡¡missletoe¡¡is¡¡dependent¡¡on¡¡the¡¡apple¡¡and¡¡a¡¡few¡¡other¡¡trees£»¡¡but¡¡can¡¡only¡¡in¡¡a¡¡far¡­fetched¡¡sense¡¡be¡¡said¡¡to¡¡struggle¡¡with¡¡these¡¡trees£»¡¡for¡¡if¡¡too¡¡many¡¡of¡¡these¡¡parasites¡¡grow¡¡on¡¡the¡¡same¡¡tree£»¡¡it¡¡will¡¡languish¡¡and¡¡die¡£¡¡But¡¡several¡¡seedling¡¡missletoes£»¡¡growing¡¡close¡¡together¡¡on¡¡the¡¡same¡¡branch£»¡¡may¡¡more¡¡truly¡¡be¡¡said¡¡to¡¡struggle¡¡with¡¡each¡¡other¡£¡¡As¡¡the¡¡missletoe¡¡is¡¡disseminated¡¡by¡¡birds£»¡¡its¡¡existence¡¡depends¡¡on¡¡birds£»¡¡and¡¡it¡¡may¡¡metaphorically¡¡be¡¡said¡¡to¡¡struggle¡¡with¡¡other¡¡fruit¡­bearing¡¡plants£»¡¡in¡¡order¡¡to¡¡tempt¡¡birds¡¡to¡¡devour¡¡and¡¡thus¡¡disseminate¡¡its¡¡seeds¡¡rather¡¡than¡¡those¡¡of¡¡other¡¡plants¡£¡¡In¡¡these¡¡several¡¡senses£»¡¡which¡¡pass¡¡into¡¡each¡¡other£»¡¡I¡¡use¡¡for¡¡convenience¡¡sake¡¡the¡¡general¡¡term¡¡of¡¡struggle¡¡for¡¡existence¡£¡¡
A¡¡struggle¡¡for¡¡existence¡¡inevitably¡¡follows¡¡from¡¡the¡¡high¡¡rate¡¡at¡¡which¡¡all¡¡organic¡¡beings¡¡tend¡¡to¡¡increase¡£¡¡Every¡¡being£»¡¡which¡¡during¡¡its¡¡natural¡¡lifetime¡¡produces¡¡several¡¡eggs¡¡or¡¡seeds£»¡¡must¡¡suffer¡¡destruction¡¡during¡¡some¡¡period¡¡of¡¡its¡¡life£»¡¡and¡¡during¡¡some¡¡season¡¡or¡¡occasional¡¡year£»¡¡otherwise£»¡¡on¡¡the¡¡principle¡¡of¡¡geometrical¡¡increase£»¡¡its¡¡numbers¡¡would¡¡quickly¡¡become¡¡so¡¡inordinately¡¡great¡¡that¡¡no¡¡country¡¡could¡¡support¡¡the¡¡product¡£¡¡Hence£»¡¡as¡¡more¡¡individuals¡¡are¡¡produced¡¡than¡¡can¡¡possibly¡¡survive£»¡¡there¡¡must¡¡in¡¡every¡¡case¡¡be¡¡a¡¡struggle¡¡for¡¡existence£»¡¡either¡¡one¡¡individual¡¡with¡¡another¡¡of¡¡the¡¡same¡¡species£»¡¡or¡¡with¡¡the¡¡individuals¡¡of¡¡distinct¡¡species£»¡¡or¡¡with¡¡the¡¡physical¡¡conditions¡¡of¡¡life¡£¡¡It¡¡is¡¡the¡¡doctrine¡¡of¡¡Malthus¡¡applied¡¡with¡¡manifold¡¡force¡¡to¡¡the¡¡whole¡¡animal¡¡and¡¡vegetable¡¡kingdoms£»¡¡for¡¡in¡¡this¡¡case¡¡there¡¡can¡¡be¡¡no¡¡artificial¡¡increase¡¡of¡¡food£»¡¡and¡¡no¡¡prudential¡¡restraint¡¡from¡¡marriage¡£¡¡Although¡¡some¡¡species¡¡may¡¡be¡¡now¡¡increasing£»¡¡more¡¡or¡¡less¡¡rapidly£»¡¡in¡¡numbers£»¡¡all¡¡cannot¡¡do¡¡so£»¡¡for¡¡the¡¡world¡¡would¡¡not¡¡hold¡¡them¡£¡¡
There¡¡is¡¡no¡¡exception¡¡to¡¡the¡¡rule¡¡that¡¡every¡¡organic¡¡being¡¡naturally¡¡increases¡¡at¡¡so¡¡high¡¡a¡¡rate£»¡¡that¡¡if¡¡not¡¡destroyed£»¡¡the¡¡earth¡¡would¡¡soon¡¡be¡¡covered¡¡by¡¡the¡¡progeny¡¡of¡¡a¡¡single¡¡pair¡£¡¡Even¡¡slow¡­breeding¡¡man¡¡has¡¡doubled¡¡in¡¡twenty¡­five¡¡years£»¡¡and¡¡at¡¡this¡¡rate£»¡¡in¡¡a¡¡few¡¡thousand¡¡years£»¡¡there¡¡would¡¡literally¡¡not¡¡be¡¡standing¡¡room¡¡for¡¡his¡¡progeny¡£¡¡Linnaeus¡¡has¡¡calculated¡¡that¡¡if¡¡an¡¡annual¡¡plant¡¡produced¡¡only¡¡two¡¡seeds¡¡and¡¡there¡¡is¡¡no¡¡plant¡¡so¡¡unproductive¡¡as¡¡this¡¡and¡¡their¡¡seedlings¡¡next¡¡year¡¡produced¡¡two£»¡¡and¡¡so¡¡on£»¡¡then¡¡in¡¡twenty¡¡years¡¡there¡¡would¡¡be¡¡a¡¡million¡¡plants¡£¡¡The¡¡elephant¡¡is¡¡reckoned¡¡to¡¡be¡¡the¡¡slowest¡¡breeder¡¡of¡¡all¡¡known¡¡animals£»¡¡and¡¡I¡¡have¡¡taken¡¡some¡¡pains¡¡to¡¡estimate¡¡its¡¡probable¡¡minimum¡¡rate¡¡of¡¡natural¡¡increase£º¡¡it¡¡will¡¡be¡¡under¡¡the¡¡mark¡¡to¡¡assume¡¡that¡¡it¡¡breeds¡¡when¡¡thirty¡¡years¡¡old£»¡¡and¡¡goes¡¡on¡¡breeding¡¡till¡¡ninety¡¡years¡¡old£»¡¡bringing¡¡forth¡¡three¡¡pairs¡¡of¡¡young¡¡in¡¡this¡¡interval£»¡¡if¡¡this¡¡be¡¡so£»¡¡at¡¡the¡¡end¡¡of¡¡the¡¡fifth¡¡century¡¡there¡¡would¡¡be¡¡alive¡¡fifteen¡¡million¡¡elephants£»¡¡descended¡¡from¡¡the¡¡first¡¡pair¡£¡¡
But¡¡we¡¡have¡¡better¡¡evidence¡¡on¡¡this¡¡subject¡¡than¡¡mere¡¡theoretical¡¡calculations£»¡¡namely£»¡¡the¡¡numerous¡¡recorded¡¡cases¡¡of¡¡the¡¡astonishingly¡¡rapid¡¡increase¡¡of¡¡various¡¡animals¡¡in¡¡a¡¡state¡¡of¡¡nature£»¡¡when¡¡circumstances¡¡have¡¡been¡¡favourable¡¡to¡¡them¡¡during¡¡two¡¡or¡¡three¡¡following¡¡seasons¡£¡¡Still¡¡more¡¡striking¡¡is¡¡the¡¡evidence¡¡from¡¡our¡¡domestic¡¡animals¡¡of¡¡many¡¡kinds¡¡which¡¡have¡¡run¡¡wild¡¡in¡¡several¡¡parts¡¡of¡¡the¡¡world£º¡¡if¡¡the¡¡statements¡¡of¡¡the¡¡rate¡¡of¡¡increase¡¡of¡¡slow¡­breeding¡¡cattle¡¡and¡¡horses¡¡in¡¡South¡¡America£»¡¡and¡¡latterly¡¡in¡¡Australia£»¡¡had¡¡not¡¡been¡¡well¡¡authenticated£»¡¡they¡¡would¡¡have¡¡been¡¡quite¡¡incredible¡£¡¡So¡¡it¡¡is¡¡with¡¡plants£º¡¡cases¡¡could¡¡be¡¡given¡¡of¡¡introduced¡¡plants¡¡which¡¡have¡¡become¡¡common¡¡throughout¡¡whole¡¡islands¡¡in¡¡a¡¡period¡¡of¡¡less¡¡than¡¡ten¡¡years£»¡¡Several¡¡of¡¡the¡¡plants¡¡now¡¡most¡¡numerous¡¡over¡¡the¡¡wide¡¡plains¡¡of¡¡La¡¡Plata£»¡¡clothing¡¡square¡¡leagues¡¡of¡¡surface¡¡almost¡¡to¡¡the¡¡exclusion¡¡of¡¡all¡¡other¡¡plants£»¡¡have¡¡been¡¡introduced¡¡from¡¡Europe£»¡¡and¡¡there¡¡are¡¡plants¡¡which¡¡now¡¡range¡¡in¡¡India£»¡¡as¡¡I¡¡hear¡¡from¡¡Dr¡¡Falconer£»¡¡from¡¡Cape¡¡Comorin¡¡to¡¡the¡¡Himalaya£»¡¡which¡¡have¡¡been¡¡imported¡¡from¡¡America¡¡since¡¡its¡¡discovery¡£¡¡In¡¡such¡¡cases£»¡¡and¡¡endless¡¡instances¡¡could¡¡be¡¡given£»¡¡no¡¡one¡¡supposes¡¡that¡¡the¡¡fertility¡¡of¡¡these¡¡animals¡¡or¡¡plants¡¡has¡¡been¡¡suddenly¡¡and¡¡temporarily¡¡increased¡¡in¡¡any¡¡sensible¡¡degree¡£¡¡The¡¡obvious¡¡explanation¡¡is¡¡that¡¡the¡¡conditions¡¡of¡¡life¡¡have¡¡been¡¡very¡¡favourable£»¡¡and¡¡that¡¡there¡¡has¡¡consequently¡¡been¡¡less¡¡destruction¡¡of¡¡the¡¡old¡¡and¡¡young£»¡¡and¡¡that¡¡nearly¡¡all¡¡the¡¡young¡¡have¡¡been¡¡enabled¡¡to¡¡breed¡£¡¡In¡¡such¡¡cases¡¡the¡¡geometrical¡¡ratio¡¡of¡¡increase£»¡¡the¡¡result¡¡of¡¡which¡¡never¡¡fails¡¡to¡¡be¡¡surprising£»¡¡simply¡¡explains¡¡the¡¡extraordinarily¡¡rapid¡¡increase¡¡and¡¡wide¡¡diffusion¡¡of¡¡naturalised¡¡productions¡¡in¡¡their¡¡new¡¡homes¡£¡¡
In¡¡a¡¡state¡¡of¡¡nature¡¡almost¡¡every¡¡plant¡¡produces¡¡seed£»¡¡and¡¡amongst¡¡animals¡¡there¡¡are¡¡very¡¡few¡¡which¡¡do¡¡not¡¡annually¡¡pair¡£¡¡Hence¡¡we¡¡may¡¡confidently¡¡assert£»¡¡that¡¡all¡¡plants¡¡and¡¡animals¡¡are¡¡tending¡¡to¡¡increase¡¡at¡¡a¡¡geometrical¡¡ratio£»¡¡that¡¡all¡¡would¡¡most¡¡rapidly¡¡stock¡¡every¡¡station¡¡in¡¡which¡¡they¡¡could¡¡any¡¡how¡¡exist£»¡¡and¡¡that¡¡the¡¡geometrical¡¡tendency¡¡to¡¡increase¡¡must¡¡be¡¡checked¡¡by¡¡destruction¡¡at¡¡some¡¡period¡¡of¡¡life¡£¡¡Our¡¡familiarity¡¡with¡¡the¡¡larger¡¡domestic¡¡animals¡¡tends£»¡¡I¡¡think£»¡¡to¡¡mislead¡¡us£º¡¡we¡¡see¡¡no¡¡great¡¡destruction¡¡falling¡¡on¡¡them£»¡¡and¡¡we¡¡forget¡¡that¡¡thousands¡¡are¡¡annually¡¡slaughtered¡¡for¡¡food£»¡¡and¡¡that¡¡in¡¡a¡¡state¡¡of¡¡nature¡¡an¡¡equal¡¡number¡¡would¡¡have¡¡somehow¡¡to¡¡be¡¡disposed¡¡of¡£¡¡
The¡¡only¡¡difference¡¡between¡¡organisms¡¡which¡¡annually¡¡produce¡¡eggs¡¡or¡¡seeds¡¡by¡¡the¡¡thousand£»¡¡and¡¡those¡¡which¡¡produce¡¡extremely¡¡few£»¡¡is£»¡¡that¡¡the¡¡slow¡­breeders¡¡would¡¡require¡¡a¡¡few¡¡more¡¡years¡¡to¡¡people£»¡¡under¡¡favourable¡¡conditions£»¡¡a¡¡whole¡¡district£»¡¡let¡¡it¡¡be¡¡ever¡¡so¡¡large¡£¡¡The¡¡condor¡¡lays¡¡a¡¡couple¡¡of¡¡eggs¡¡and¡¡the¡¡ostrich¡¡a¡¡score£»¡¡and¡¡yet¡¡in¡¡the¡¡same¡¡country¡¡the¡¡condor¡¡may¡¡be¡¡the¡¡more¡¡numerous¡¡of¡¡the¡¡two£º¡¡the¡¡Fulmar¡¡petrel¡¡lays¡¡but¡¡one¡¡egg£»¡¡yet¡¡it¡¡is¡¡believed¡¡to¡¡be¡¡the¡¡most¡¡numerous¡¡bird¡¡in¡¡the¡¡world¡£¡¡One¡¡fly¡¡deposits¡¡hundreds¡¡of¡¡eggs£»¡¡and¡¡another£»¡¡like¡¡the¡¡hippobosca£»¡¡a¡¡single¡¡one£»¡¡but¡¡this¡¡difference¡¡does¡¡not¡¡determine¡¡how¡¡many¡¡individuals¡¡of¡¡the¡¡two¡¡species¡¡can¡¡be¡¡supported¡¡in¡¡a¡¡district¡£¡¡A¡¡large¡¡number¡¡of¡¡eggs¡¡is¡¡of¡¡some¡¡importance¡¡to¡¡those¡¡species£»¡¡which¡¡depend¡¡on¡¡a¡¡rapidly¡¡fluctuating¡¡amount¡¡of¡¡food£»¡¡for¡¡it¡¡allows¡¡them¡¡rapidly¡¡to¡¡increase¡¡in¡¡number¡£¡¡But¡¡the¡¡real¡¡importance¡¡of¡¡a¡¡large¡¡number¡¡of¡¡eggs¡¡or¡¡seeds¡¡is¡¡to¡¡make¡¡up¡¡for¡¡much¡¡destruction¡¡at¡¡some¡¡period¡¡of¡¡life£»¡¡and¡¡this¡¡period¡¡in¡¡the¡¡great¡¡majority¡¡of¡¡cases¡¡is¡¡an¡¡early¡¡one¡£¡¡If¡¡an¡¡animal¡¡can¡¡in¡¡any¡¡way¡¡protect¡¡its¡¡own¡¡eggs¡¡or¡¡young£»¡¡a¡¡small¡¡number¡¡may¡¡be¡¡produced£»¡¡and¡¡yet¡¡the¡¡average¡¡stock¡¡be¡¡fully¡¡kept¡¡up£»¡¡but¡¡if¡¡many¡¡eggs¡¡or¡¡young¡¡are¡¡destroyed£»¡¡many¡¡must¡¡be¡¡produced£»¡¡or¡¡the¡¡species¡¡will¡¡become¡¡extinct¡£¡¡It¡¡would¡¡suffice¡¡to¡¡keep¡¡up¡¡the¡¡full¡¡number¡¡of¡¡a¡¡tree£»¡¡which¡¡lived¡¡on¡¡an¡¡average¡¡for¡¡a¡¡thousand¡¡years£»¡¡if¡¡a¡¡single¡¡seed¡¡were¡¡produced¡¡once¡¡in¡¡a¡¡thousand¡¡years£»¡¡supposing¡¡that¡¡this¡¡seed¡¡were¡¡never¡¡destroyed£»¡¡and¡¡could¡¡be¡¡ensured¡¡to¡¡germinate¡¡in¡¡a¡¡fitting¡¡place¡£¡¡So¡¡that¡¡in¡¡all¡¡cases£»¡¡the¡¡average¡¡number¡¡of¡¡any¡¡animal¡¡or¡¡plant¡¡depends¡¡only¡¡indirectly¡¡on¡¡the¡¡number¡¡of¡¡its¡¡eggs¡¡or¡¡seeds¡£¡¡
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