darwin and modern science-第43部分

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yres　has　awakened　the　fossil　primates　of　the　Pampas　formation　to　new　life；　he　even　believes　that　in　Tetraprothomo；　represented　by　a　femur；　he　has　discovered　a　direct　ancestor　of　man。　　Lehmann…Nitsche　is　working　at　the　other　side　of　the　gulf　between　apes　and　men；　and　he　describes　a　remarkable　first　cervical　vertebra　（atlas）　from　Monte　Hermoso　as　belonging　to　a　form　which　may　bear　the　same　relation　to　Homo　sapiens　in　South　America　as　Homo　primigenius　does　in　the　Old　World。　　After　a　minute　investigation　he　establishes　a　human　species　Homo　neogaeus；　while　Ameghino　ascribes　this　atlas　vertebra　to　his　Tetraprothomo。

Thus　throughout　the　whole　scientific　world　there　is　arising　a　new　life；　an　eager　endeavour　to　get　nearer　to　Huxley's　problema　maximum；　to　penetrate　more　deeply　into　the　origin　of　the　human　race。　　There　are　to…day　very　few　experts　in　anatomy　and　zoology　who　deny　the　animal　descent　of　man　in　general。　　Religious　considerations；　old　prejudices；　the　reluctance　to　accept　man；　who　so　far　surpasses　mentally　all　other　creatures；　as　descended　from　〃soulless〃　animals；　prevent　a　few　investigators　from　giving　full　adherence　to　the　doctrine。　　But　there　are　very　few　of　these　who　still　postulate　a　special　act　of　creation　for　man。　　Although　the　majority　of　experts　in　anatomy　and　zoology　accept　unconditionally　the　descent　of　man　from　lower　forms；　there　is　much　diversity　of　opinion　among　them　in　regard　to　the　special　line　of　descent。

In　trying　to　establish　any　special　hypothesis　of　descent；　whether　by　the　graphic　method　of　drawing　up　genealogical　trees　or　otherwise；　let　us　always　bear　in　mind　Darwin's　words　（〃Descent　of　Man〃；　page　229。）　and　use　them　as　a　critical　guiding　line：　　〃As　we　have　no　record　of　the　lines　of　descent；　the　pedigree　can　be　discovered　only　by　observing　the　degrees　of　resemblance　between　the　beings　which　are　to　be　classed。〃　　Darwin　carries　this　further　by　stating　〃that　resemblances　in　several　unimportant　structures；　in　useless　and　rudimentary　organs；　or　not　now　functionally　active；　or　in　an　embryological　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；