darwin and modern science-第33章

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　far　the　influence　of　natural　selection　can　be　demonstrated　in　regard　to　civilised　nations。　　In　the　final　section；　which　deals　with　the　proofs　that　all　civilised　nations　were　once　barbarians；　Darwin　again　uses　the　results　gained　by　other　investigators；　such　as　Lubbock　and　Tylor。　　There　are　two　sets　of　facts　which　prove　the　proposition　in　question。　　In　the　first　place；　we　find　traces　of　a　former　lower　state　in　the　customs　and　beliefs　of　all　civilised　nations；　and　in　the　second　place；　there　are　proofs　to　show　that　savage　races　are　independently　able　to　raise　themselves　a　few　steps　in　the　scale　of　civilisation；　and　that　they　have　thus　raised　themselves。

In　the　sixth　chapter　of　the　work；　Morphology　comes　into　the　foreground　once　more。　　Darwin　first　goes　back；　however；　to　the　argument　based　on　the　great　difference　between　the　mental　powers　of　the　highest　animals　and　those　of　man。　　That　this　is　only　quantitative；　not　qualitative；　he　has　already　shown。　　Very　instructive　in　this　connection　is　the　reference　to　the　enormous　difference　in　mental　powers　in　another　class。　　No　one　would　draw　from　the　fact　that　the　cochineal　insect　（Coccus）　and　the　ant　exhibit　enormous　differences　in　their　mental　powers；　the　conclusion　that　the　ant　should　therefore　be　regarded　as　something　quite　distinct；　and　withdrawn　from　the　class　of　insects　altogether。

Darwin　next　attempts　to　establish　the　SPECIFIC　genealogical　tree　of　man；　and　carefully　weighs　the　differences　and　resemblances　between　the　different　families　of　the　Primates。　　The　erect　position　of　man　is　an　adaptive　character；　just　as　are　the　various　characters　referable　to　aquatic　life　in　the　seals；　which；　notwithstanding　these；　are　ranked　as　a　mere　family　of　the　Carnivores。　　The　following　utterance　is　very　characteristic　of　Darwin　（〃Descent　of　Man〃；　page　231。）：　　〃If　man　had　not　been　his　own　classifier；　he　would　never　have　thought　of　founding　a　separate　order　for　his　own　reception。〃　　In　numerous　characters　not　mentioned　in　systematic　works；　in　the　features　of　the　face；　in　the　form　of　the　nose；　in　the　structure　of　the　external　ear；　man　resembles　the　apes。　　The　arrangement　of　the　hair　in　man　has　also　much　in　common　with　the　apes；　as　also　the　occurrence　of　hair　on　the　forehead　of　the　human　embryo；　the　beard；　the　convergence　of　the　hair　of　the　upper　and　under　arm　towards　the　elbow；　which　occurs　not　only　in　the　anthropoid　apes；　but　also　in　some　American　monkeys。　　Darwin　here　adopts　Wallace's　explanation　of　the　origin　of　the　ascending　direction　of　the　hair　in　the　forearm　of　the　orang；that　it　has　arisen　through　the　habit　of　holding　the　hands　over　the　head　in　rain。　　But　this　explanation　cannot　be　maintained　when　we　consider　that　this　disposition　of　the　hair　is　widely　distributed　among　the　most　different　mammals；　being　found　in　the　dog；　in　the　sloth；　and　in　many　of　the　lower　monkeys。

After　further　careful　analysis　of　the　anatomical　characters　Darwin　reaches　the　conclusion　that　the　New　World　monkeys　（Platyrrhine）　may　be　excluded　from　the　genealogical　tree　altogether；　but　that　man　is　an　offshoot　from　the　Old　World　monkeys　（Catarrhine）　whose　progenitors　existed　as　far　back　as　the　Miocene　period。　　Among　these　Old　World　monkeys　the　forms　to　which　man　shows　the　greatest　resemblance　are　the　anthropoid　apes；　which；　like　him；　possess　neither　tail　nor　ischial　callosities。　　The　platyrrhine　and　catarrhine　monkeys　have　their　primitive　ancestor　among　extinct　forms　of　the　Lemuridae。　　Darwin　also　touches　on　the　question　of　the　original　home　of　the　human　race　and　supposes　that　it　may　have　been　in　Africa；　because　it　is　there　that　man's　nearest　relatives；　the　gorilla　and　the　chimpanzee；　are　found。　　But　he　regards　speculation　on　this　point　as　useless。　　It　is　remarkable　that；　in　this　connection；　Darwin　regards　the　loss　of　the　hair…covering　in　man　as　having　some　relation　to　a　warm　climate；　while　elsewhere　he　is　inclined　to　make　sexual　selection　responsible　for　it。　　Darwin　recognises　the　great　gap　between　man　and　his　nearest　relatives；　but　similar　gaps　exist　at　other　parts　of　the　mammalian　genealogical　tree：　　the　allied　forms　have　become　extinct。　　After　the　extermination　of　the　lower　races　of　mankind；　on　the　one　hand；　and　of　the　anthropoid　apes　on　the　other；　which　will　undoubtedly　take　place；　the　gulf　will　be　greater　than　ever；　since　the　baboons　will　then　bound　it　on　the　one　side；　and　the　white　races　on　the　other。　　Little　weight　need　be　attached　to　the　lack　of　fossil　remains　to　fill　up　this　gap；　since　the　discovery　of　these　depends　upon　chance。　　The　last　part　of　the　chapter　is　devoted　to　a　discussion　of　the　earlier　stages　in　the　genealogy　of　man。　　Here　Darwin　accepts　in　the　main　the　genealogical　tree；　which　had　meantime　been　published　by　Haeckel；　who　traces　the　pedigree　back　through　Monotremes；　Reptiles；　Amphibians；　and　Fishes；　to　Amphioxus。

Then　follows　an　attempt　to　reconstruct；　from　the　atavistic　characters；　a　picture　of　our　primitive　ancestor　who　was　undoubtedly　an　arboreal　animal。　　The　occurrence　of　rudiments　of　parts　in　one　sex　which　only　come　to　full　development　in　the　other　is　next　discussed。　　This　state　of　things　Darwin　regards　as　derived　from　an　original　hermaphroditism。　　In　regard　to　the　mammary　glands　of　the　male　he　does　not　accept　the　theory　that　they　are　vestigial；　but　considers　them　rather　as　not　fully　developed。

The　last　chapter　of　Part　I　deals　with　the　question　whether　the　different　races　of　man　are　to　be　regarded　as　different　species；　or　as　sub…species　of　a　race　of　monophyletic　origin。　　The　striking　differences　between　the　races　are　first　emphasised；　and　the　question　of　the　fertility　or　infertility　of　hybrids　is　discussed。　　That　fertility　is　the　more　usual　is　shown　by　the　excessive　fertility　of　the　hybrid　population　of　Brazil。　　This；　and　the　great　variability　of　the　distinguishing　characters　of　the　different　races；　as　well　as　the　fact　that　all　grades　of　transition　stages　are　found　between　these；　while　considerable　general　agreement　exists；　tell　in　favour　of　the　unity　of　the　races　and　lead　to　the　conclusion　that　they　all　had　a　common　primitive　ancestor。

Darwin　therefore　classifies　all　the　different　races　as　sub…species　of　ONE　AND　THE　SAME　SPECIES。　　Then　follows　an　interesting　inquiry　into　the　reasons　for　the　extinction　of　human　races。　　He　recognises　as　the　ultimate　reason　the　injurious　effects　of　a　change　of　the　conditions　of　life；　which　may　bring　about　an　increase　in　infantile　mortality；　and　a　diminished　fertility。　It　is　precisely　the　reproductive　system；　among　animals　also；　which　is　most　susceptible　to　changes　in　the　environment。

The　final　section　of　this　chapter　deals　with　the　formation　of　the　races　of　mankind。　　Darwin　discusses　the　question　how　far　the　direct　effect　of　different　conditions　of　life；　or　the　inherited　effects　of　increased　use　or　disuse　may　have　brought　about　the　characteristic　differences　between　the　different　races。　　Even　in　regard　to　the　origin　of　the　colour　of　the　skin　he　rejects　the　transmitted　effects　of　an　original　difference　of　climate　as　an　explanation。　　In　so　doing　he　is　following　his　tendency　to　exclude　Lamarckian　explanations　as　far　as　possible。　　But　here　he　makes　gratuitous　difficulties　from　which；　since　natural　selection　fails；　there　is　no　escape　except　by　bringing　in　the　principle　of　sexual　selection；　to　which；　he　regarded　it　as　possible；　skin…colouring；　arrangement　of　hair；　and　form　of　features　might　be　traced。　　But　with　his　characteristic　conscientiousness　he　guards　himself　thus：　　〃I　do　not　intend　to　assert　that　sexual　selection　will　account　for　all　the　differences　between　the　races。〃　　（〃Descent　of　Man〃；　page　308。）

I　may　be　permitted　a　remark　as　to　Darwin's　attitude　towards　Lamarck。　　While；　at　an　earlier　stage；　when　he　was　engaged　in　the　preliminary　labours　for　his　immortal　work；　〃The　Origin　of　Species〃；　Darwin　expresses　himself　very　forcibly　against　the　views　of　Lamarck；　speaking　of　Lamarckian　〃nonsense；〃　（〃Life　and　Letters〃；　Vol。　II。　page　23。）；　and　of　Lamarck's　〃absurd；　though　clever　work〃　（Loc。　cit。　page　39。）　and　expressly　declaring；　〃I　attribute　very　little　to　the　direct　action　of　climate；　etc。〃　　（Loc。　cit。　（1856）；　page　82。）　yet　in　later　life　he　became　more　and　more　convinced　of　the　influence　of　external　conditions。　　In　1876；　that　is；　two　years　after　the　appearance　of　the　second　edition　of　〃The　Descent　of　Man〃；　he　writes　with　his　usual　candid　honesty：　　〃In　my　opinion　the　greatest　error　which　I　have　committed；　has　been　not　allowing　sufficient　weight　to　the　direct　action　of　the　environment；　i。e。　food；　climate；　etc。　independently　of　natural　selection。〃　　（Ibid。　Vol。　III。　page　159。）　　It　is　certain　from　this　change　of　opinion　that；　if　he　had　been　able　to　make　up　his　mind　to　issue　a　third　edition　of　〃The　Descent　of　Man〃；　he　would　have　ascribed　a　much　greater　influence　to　the　effect　of　external　conditions　in　explaining　the　different　characters　of　the　races　of　man　than　he　did　in　the　second　edition。　He　would　also　undoubtedly　have　attributed　less　influence　to　sexual　selection　as　a　factor　in　the　origin　of　the　different　bodily　characteristics；　if　indeed　he　would　not　have　excluded　it　altogether。

In　Part　III　of　the　〃Descent〃　two　additional　chapters　are　devoted　to　the　discussion　of　sexual　selection　in　relation　to　man。　　These　may　be　very　briefly　referred　to。　　Darwin　here　seeks　to　show　that　sexual　selection　has　been　operative　on　man　and　his　primitive　progenitor。　　Space　fails　me　to　follow　out　his　interesting　arguments。　　I　can　only　mention　that　he　is　inclined　to　trace　back　hairlessness；　the　development　of　the　beard　in　man；　and　the　characteristic　colour　of　the　different　human　races　to　sexual　selection。　　Since　bareness　of　the　skin　could　be　no　advantage；　but　rather　a　disadvantage；　this　character　cannot　have　been　brought　about　by　natural　selection。　　Darwin　also　rejected　a　direct　influence　of　climate　as　a　cause　of　the　origin　of　the　skin…colour。　　I　have　already　expressed　the　opinion；　based　on　the　development　of　his　views　as　shown　in　his　letters；　that　in　a　third　edition　Darwin　would　probably　have　laid　more　stress　on　the　influence　of　external　environment。　　He　himself　feels　that　there　are　gaps　in　his　proofs　here；　and　says　in　self…criticism：　　〃The　views　here　advanced；　on　the　part　which　sexual　selection　has　played　in　the　history　of　man；　want　scientific　precision。〃　　（〃Descent　of　Man〃；　page　924。）　　I　need　here　only　point　out　that　it　is　impossible　to　explain　the　graduated　stages　of　skin…　colour　by　sexual　selection；　since　it　would　have　produced　races　sharply　defined　by　their　colour　and　not　united　to　other　races　by　transition　stages；　and　this；　it　is　well　known；　is　not　the　case。　　Moreover；　the　fact　established　by　me　（〃Die　Hautfarbe　des　Menschen〃；　〃Mitteilungen　der　Anthropologischen　Gesellschaft　in　Wien〃；　Vol。　XXXIV。　pages　331…352。）；　that　in　all　races　the　ventral　side　of　the　trunk　is　paler　than　the　dorsal　side；　and　the　inner　surface　of　the　extremities　paler　than　the　outer　side；　cannot　be　explained　by　sexual　selection　in　the　Darwinian　sense。

With　this　I　conclude　my　brief　survey　of　the　rich　contents　of　Darwin's　book。　I　may　be　permitted　to　conclude　by　quoting　the　magnificent　final　words　of　〃The　Descent　of　Man〃：　　〃We　must；　however；　acknowledge；　as　it　seems　to　me；　that　man；　with　all　his　noble　qualities；　with　sympathy　which　feels　for　the　most　debased；　with　benevolence　which　extends　not　only　to　other　men　but　to　the　h