darwin and modern science-第39部分

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cal　condition；　are　by　far　the　most　serviceable　for　classification。〃　　（Loc。　cit。）　　It　has　also　to　be　remembered　that　NUMEROUS　separate　points　of　agreement　are　of　much　greater　importance　than　the　amount　of　similarity　or　dissimilarity　in　a　few　points。

The　hypotheses　as　to　descent　current　at　the　present　day　may　be　divided　into　two　main　groups。　　The　first　group　seeks　for　the　roots　of　the　human　race　not　among　any　of　the　families　of　the　apesthe　anatomically　nearest　formsnor　among　their　very　similar　but　less　specialised　ancestral　forms；　the　fossil　representatives　of　which　we　can　know　only　in　part；　but；　setting　the　monkeys　on　one　side；　it　seeks　for　them　lower　down　among　the　fossil　Eocene　Pseudo…　lemuridae　or　Lemuridae　（Cope）；　or　even　among　the　primitive　pentadactylous　Eocene　forms；　which　may　either　have　led　directly　to　the　evolution　of　man　（Adloff）；　or　have　given　rise　to　an　ancestral　form　common　to　apes　and　men　（Klaatsch　（Klaatsch　in　his　last　publications　speaks　in　the　main　only　of　an　ancestral　form　common　to　men　and　anthropoid　apes。）；　Giuffrida…Ruggeri）。　　The　common　ancestral　form；　from　which　man　and　apes　are　thus　supposed　to　have　arisen　independently；　may　explain　the　numerous　resemblances　which　actually　exist　between　them。　　That　is　to　say；　all　the　characters　upon　which　the　great　structural　resemblance　between　apes　and　man　depends　must　have　been　present　in　their　common　ancestor。　　Let　us　take　an　example　of　such　a　common　character。　　The　bony　external　ear…passage　is　in　general　as　highly　developed　in　the　lower　Eastern　monkeys　and　the　anthropoid　apes　as　in　man。　　This　character　must；　therefore；　have　already　been　present　in　the　common　primitive　form。　　In　that　case　it　is　not　easy　to　understand　why　the　Western　monkeys　have　not　also　inherited　the　character；　instead　of　possessing　only　a　tympanic　ring。　　But　it　becomes　more　intelligible　if　we　assume　that　forms　with　a　primitive　tympanic　ring　were　the　original　type；　and　that　from　these　were　evolved；　on　the　one　hand；　the　existing　New　World　monkeys　with　persistent　tympanic　ring；　and　on　the　other　an　ancestral　form　common　to　the　lower　Old　World　monkeys；　the　anthropoid　apes　and　man。　　For　man　shares　with　these　the　character　in　question；　and　it　is　also　one　of　the　〃unimportant〃　characters　required　by　Darwin。　　Thus　we　have　two　divergent　lines　arising　from　the　ancestral　form；　the　Western　monkeys　（Platyrrhine）　on　the　one　hand；　and　an　ancestral　form　common　to　the　lower　Eastern　monkeys；　the　anthropoid　apes；　and　man；　on　the　other。　　But　considerations　similar　to　those　which　showed　it　to　be　impossible　that　man　should　have　developed　from　an　ancestor　common　to　him　and　the　monkeys；　yet　outside　of　and　parallel　with　these；　may　be　urged　also　against　the　likelihood　of　a　parallel　evolution　of　the　lower　Eastern　monkeys；　the　anthropoid　apes；　and　man。　　The　anthropoid　apes　have　in　common　with　man　many　characters　which　are　not　present　in　the　lower　Old　World　monkeys。　　These　characters　must　therefore　have　been　present　in　the　ancestral　form　common　to　the　three　groups。　　But　here；　again；　it　is　difficult　to　understand　why　the　lower　Eastern　monkeys　should　not　also　have　inherited　these　characters。　　As　this　is　not　the　case；　there　remains　no　alternative　but　to　assume　divergent　evolution　from　an　indifferent　form。　　The　lower　Eastern　monkeys　are　carrying　on　the　evolution　in　one　directionI　might　almost　say　towards　a　blind　alleywhile　anthropoids　and　men　have　struck　out　a　progressive　path；　at　first　in　common；　which　explains　the　many　points　of　resemblance　between　them；　without　regarding　man　as　derived　directly　from　the　anthropoids。　　Their　many　striking　points　of　agreement　indicate　a　common　descent；　and　cannot　be　explained　as　phenomena　of　convergence。

I　believe　I　have　shown　in　the　above　sketch　that　a　theory　which　derives　man　directly　from　lower　forms　without　regarding　apes　as　transition…types　leads　ad　absurdum。　　The　close　structural　relationship　between　man　and　monkeys　can　only　be　understood　if　both　are　brought　into　the　same　line　of　evolution。　　To　trace　man's　line　of　descent　directly　back　to　the　old　Eocene　mammals；　alongside　of；　but　with　no　relation　to　these　very　similar　forms；　is　to　abandon　the　method　of　exact　comparison；　which；　as　Darwin　rightly　recognised；　alone　justifies　us　in　drawing　up　genealogical　trees　on　the　basis　of　resemblances　and　differences。　　The　farther　down　we　go　the　more　does　the　ground　slip　from　beneath　our　feet。　　Even　the　Lemuridae　show　very　numerous　divergent　conditions；　much　more　so　the　Eocene　mammals　（Creodonta；　Condylarthra）；　the　chief　resemblance　of　which　to　man　consists　in　the　possession　of　pentadactylous　hands　and　feet！　　Thus　the　farther　course　of　the　line　of　descent　disappears　in　the　darkness　of　the　ancestry　of　the　mammals。　　With　just　as　much　reason　we　might　pass　by　the　Vertebrates　altogether；　and　go　back　to　the　lower　Invertebrates；　but　in　that　case　it　would　be　much　easier　to　say　that　man　has　arisen　independently；　and　has　evolved；　without　relation　to　any　animals；　from　the　lowest　primitive　form　to　his　present　isolated　and　dominant　position。　　But　this　would　be　to　deny　all　value　to　classification；　which　must　after　all　be　the　ultimate　basis　of　a　genealogical　tree。　　We　can；　as　Darwin　rightly　observed；　only　infer　the　line　of　descent　from　the　degree　of　resemblance　between　single　forms。　　If　we　regard　man　as　directly　derived　from　primitive　forms　very　far　back；　we　have　no　way　of　explaining　the　many　points　of　agreement　between　him　and　the　monkeys　in　general；　and　the　anthropoid　apes　in　particular。　　These　must　remain　an　inexplicable　marvel。

I　have　thus；　I　trust；　shown　that　the　first　class　of　special　theories　of　descent；　which　assumes　that　man　has　developed；　parallel　with　the　monkeys；　but　without　relation　to　them；　from　very　low　primitive　forms　cannot　be　upheld；　because　it　fails　to　take　into　account　the　close　structural　affinity　of　man　and　monkeys。　　I　cannot　but　regard　this　hypothesis　as　lamentably　retrograde；　for　it　makes　impossible　any　application　of　the　facts　that　have　been　discovered　in　the　course　of　the　anatomical　and　embryological　study　of　man　and　monkeys；　and　indeed　prejudges　investigations　of　that　class　as　pointless。　　The　whole　method　is　perverted；　an　unjustifiable　theory　of　descent　is　first　formulated　with　the　aid　of　the　imagination；　and　then　we　are　asked　to　declare　that　all　structural　relations　between　man　and　monkeys；　and　between　the　different　groups　of　the　latter；　are　valueless；the　fact　being　that　they　are　the　only　true　basis　on　which　a　genealogical　tree　can　be　constructed。

So　much　for　this　most　modern　method　of　classification；　which　has　probably　found　adherents　because　it　would　deliver　us　from　the　relationship　to　apes　which　many　people　so　much　dislike。　　In　contrast　to　it　we　have　the　second　class　of　special　hypotheses　of　descent；　which　keeps　strictly　to　the　nearest　structural　relationships。　　This　is　the　only　basis　that　justifies　the　drawing　up　of　a　special　hypothesis　of　descent。　　If　this　fundamental　proposition　be　recognised；　it　will　be　admitted　that　the　doctrine　of　special　descent　upheld　by　Haeckel；　and　set　forth　in　Darwin's　〃Descent　of　Man〃；　is　still　valid　to…day。　　In　the　genealogical　tree；　man's　place　is　quite　close　to　the　anthropoid　apes；　these　again　have　as　their　nearest　relatives　the　lower　Old　World　monkeys；　and　their　progenitors　must　be　sought　among　the　less　differentiated　Platyrrhine　monkeys；　whose　most　important　characters　have　been　handed　on　to　the　present　day　New　World　monkeys。　　How　the　different　genera　are　to　be　arranged　within　the　general　scheme　indicated　depends　in　the　main　on　the　classificatory　value　attributed　to　individual　characters。　　This　is　particularly　true　in　regard　to　Pithecanthropus；　which　I　consider　as　the　root　of　a　branch　which　has　sprung　from　the　anthropoid　ape　root　and　has　led　up　to　man；　the　latter　I　have　designated　the　family　of　the　Hominidae。

For　the　rest；　there　are；　as　we　have　said；　various　possible　ways　of　constructing　the　narrower　genealogy　within　the　limits　of　this　branch　including　men　and　apes；　and　these　methods　will　probably　continue　to　change　with　the　accumulation　of　new　facts。　　Haeckel　himself　has　modified　his　genealogical　tree　of　the　Primates　in　certain　details　since　the　publication　of　his　〃Generelle　Morphologie〃　in　1866；　but　its　general　basis　remains　the　same。　　（Haeckel's　latest　genealogical　tree　is　to　be　found　in　his　most　recent　work；　〃Unsere　Ahnenreihe〃。　　Jena；　1908。）　　All　the　special　genealogical　trees　drawn　up　on　the　lines　laid　down　by　Haeckel　and　Darwin　and　that　of　Dubois　may　be　specially　mentionedare　based；　in　general；　on　the　close　relationship　of　monkeys　and　men；　although　they　may　vary　in　detail。　　Various　hypotheses　have　been　formulated　on　these　lines；　with　special　reference　to　the　evolution　of　man。　　〃Pithecanthropus〃　is　regarded　by　some　authorities　as　the　direct　ancestor　of　man；　by　others　as　a　side…　track　failure　in　the　attempt　at　the　evolution　of　man。　　The　problem　of　the　monophyletic　or　polyphyletic　origin　of　the　human　race　has　also　been　much　discussed。　　Sergi　（Sergi　G。　〃Europa〃；　1908。）　inclines　towards　the　assumption　of　a　polyphyletic　origin　of　the　three　main　races　of　man；　the　African　primitive　form　of　which　has　given　rise　also　to　the　gorilla　and　chimpanzee；　the　Asiatic　to　the　Orang；　the　Gibbon；　and　Pithecanthropus。　　Kollmann　regards　existing　human　races　as　derived　from　small　primitive　races　（pigmies）；　and　considers　that　Homo　primigenius　must　have　arisen　in　a　secondary　and　degenerative　manner。

But　this　is　not　the　place；　nor　have　I　the　space　to　criticise　the　various　special　theories　of　descent。　　One；　however；　must　receive　particular　notice。　According　to　Ameghino；　the　South　American　monkeys　（Pitheculites）　from　the　oldest　Tertiary　of　the　Pampas　are　the　forms　from　which　have　arisen　the　existing　American　monkeys　on　the　one　hand；　and　on　the　other；　the　extinct　South　American　Homunculidae；　which　are　also　small　forms。　　From　these　last；　anthropoid　apes　and　man　have；　he　believes；　been　evolved。　　Among　the　progenitors　of　man；　Ameghino　reckons　the　form　discovered　by　him　（Tetraprothomo）；　from　which　a　South　American　primitive　man；　Homo　pampaeus；　might　be　directly　evolved；　while　on　the　other　hand　all　the　lower　Old　World　monkeys　may　have　arisen　from　older　fossil　South　American　forms　（Clenialitidae）；　the　distribution　of　which　may　be　explained　by　the　bridge　formerly　existing　between　South　A