darwin and modern science-第38节

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urch。

If　we　consider　all　these　utterances　of　Darwin　in　regard　to　religion　and　to　his　outlook　on　life　（Weltanschauung）；　we　shall　see　at　least　so　much；　that　religious　reflection　could　in　no　way　have　influenced　him　in　regard　to　the　writing　and　publishing　of　his　book　on　〃The　Descent　of　Man〃。　　Darwin　had　early　won　for　himself　freedom　of　thought；　and　to　this　freedom　he　remained　true　to　the　end　of　his　life；　uninfluenced　by　the　customs　and　opinions　of　the　world　around　him。

Darwin　was　thus　inwardly　fortified　and　armed　against　the　host　of　calumnies；　accusations；　and　attacks　called　forth　by　the　publication　of　the　〃Origin　of　Species〃；　and　to　an　even　greater　extent　by　the　appearance　of　the　〃Descent　of　Man〃。　　But　in　his　defence　he　could　rely　on　the　aid　of　a　band　of　distinguished　auxiliaries　of　the　rarest　ability。　　His　faithful　confederate；　Huxley；　was　joined　by　the　botanist　Hooker；　and；　after　longer　resistance；　by　the　famous　geologist　Lyell；　whose　〃conversion〃　afforded　Darwin　peculiar　satisfaction。　　All　three　took　the　field　with　enthusiasm　in　defence　of　the　natural　descent　of　man。　　From　Wallace；　on　the　other　hand；　though　he　shared　with　him　the　idea　of　natural　selection；　Darwin　got　no　support　in　this　matter。　　Wallace　expressed　himself　in　a　strange　manner。　　He　admitted　everything　in　regard　to　the　morphological　descent　of　man；　but　maintained；　in　a　mystic　way；　that　something　else；　something　of　a　spiritual　nature　must　have　been　added　to　what　man　inherited　from　his　animal　ancestors。　　Darwin；　whose　esteem　for　Wallace　was　extraordinarily　high；　could　not　understand　how　he　could　give　utterance　to　such　a　mystical　view　in　regard　to　man；　the　idea　seemed　to　him　so　〃incredibly　strange〃　that　he　thought　some　one　else　must　have　added　these　sentences　to　Wallace's　paper。

Even　now　there　are　thinkers　who；　like　Wallace；　shrink　from　applying　to　man　the　ultimate　consequences　of　the　theory　of　descent。　　The　idea　that　man　is　derived　from　ape…like　forms　is　to　them　unpleasant　and　humiliating。

So　far　I　have　been　depicting　the　development　of　Darwin's　work　on　the　descent　of　man。　　In　what　follows　I　shall　endeavour　to　give　a　condensed　survey　of　the　contents　of　the　book。

It　must　at　once　be　said　that　the　contents　of　Darwin's　work　fall　into　two　parts；　dealing　with　entirely　different　subjects。　　〃The　Descent　of　Man〃　includes　a　very　detailed　investigation　in　regard　to　secondary　sexual　characters　in　the　animal　series；　and　on　this　investigation　Darwin　founded　a　new　theory；　that　of　sexual　selection。　　With　astonishing　patience　he　gathered　together　an　immense　mass　of　material；　and　showed；　in　regard　to　Arthropods　and　Vertebrates；　the　wide　distribution　of　secondary　characters；　which　develop　almost　exclusively　in　the　male；　and　which　enable　him；　on　the　one　hand；　to　get　the　better　of　his　rivals　in　the　struggle　for　the　female　by　the　greater　perfection　of　his　weapons；　and　on　the　other　hand；　to　offer　greater　allurements　to　the　female　through　the　higher　development　of　decorative　characters；　of　song；　or　of　scent…producing　glands。　　The　best　equipped　males　will　thus　crowd　out　the　less　well…equipped　in　the　matter　of　reproduction；　and　thus　the　relevant　characters　will　be　increased　and　perfected　through　sexual　selection。　　It　is；　of　course；　a　necessary　assumption　that　these　secondary　sexual　characters　may　be　transmitted　to　the　female；　although　perhaps　in　rudimentary　form。

As　we　have　said；　this　theory　of　sexual　selection　takes　up　a　great　deal　of　space　in　Darwin's　book；　and　it　need　only　be　considered　here　in　so　far　as　Darwin　applied　it　to　the　descent　of　man。　　To　this　latter　problem　the　whole　of　Part　I　is　devoted；　while　Part　III　contains　a　discussion　of　sexual　selection　in　relation　to　man；　and　a　general　summary。　　Part　II　treats　of　sexual　selection　in　general；　and　may　be　disregarded　in　our　present　study。　Moreover；　many　interesting　details　must　necessarily　be　passed　over　in　what　follows；　for　want　of　space。

The　first　part　of　the　〃Descent　of　Man〃　begins　with　an　enumeration　of　the　proofs　of　the　animal　descent　of　man　taken　from　the　structure　of　the　human　body。　　Darwin　chiefly　emphasises　the　fact　that　the　human　body　consists　of　the　same　organs　and　of　the　same　tissues　as　those　of　the　other　mammals；　he　shows　also　that　man　is　subject　to　the　same　diseases　and　tormented　by　the　same　parasites　as　the　apes。　　He　further　dwells　on　the　general　agreement　exhibited　by　young；　embryonic　forms；　and　he　illustrates　this　by　two　figures　placed　one　above　the　other；　one　representing　a　human　embryo；　after　Eaker；　the　other　a　dog　embryo；　after　Bischoff。　　（〃Descent　of　Man〃　（Popular　Edition；　1901）；　fig。　1；　page　14。）

Darwin　finds　further　proofs　of　the　animal　origin　of　man　in　the　reduced　structures；　in　themselves　extremely　variable；　which　are　either　absolutely　useless　to　their　possessors；　or　of　so　little　use　that　they　could　never　have　developed　under　existing　conditions。　　Of　such　vestiges　he　enumerates：　　the　defective　development　of　the　panniculus　carnosus　（muscle　of　the　skin）　so　widely　distributed　among　mammals；　the　ear…muscles；　the　occasional　persistence　of　the　animal　ear…point　in　man；　the　rudimentary　nictitating　membrane　（plica　semilunaris）　in　the　human　eye；　the　slight　development　of　the　organ　of　smell；　the　general　hairiness　of　the　human　body；　the　frequently　defective　development　or　entire　absence　of　the　third　molar　（the　wisdom　tooth）；　the　vermiform　appendix；　the　occasional　reappearance　of　a　bony　canal　（foramen　supracondyloideum）　at　the　lower　end　of　the　humerus；　the　rudimentary　tail　of　man　（the　so…called　taillessness）；　and　so　on。　　Of　these　rudimentary　structures　the　occasional　occurrence　of　the　animal　ear…point　in　man　is　most　fully　discussed。　　Darwin's　attention　was　called　to　this　interesting　structure　by　the　sculptor　Woolner。　　He　figures　such　a　case　observed　in　man；　and　also　the　head　of　an　alleged　orang…foetus；　the　photograph　of　which　he　received　from　Nitsche。

Darwin's　interpretation　of　Woolner's　case　as　having　arisen　through　a　folding　over　of　the　free　edge　of　a　pointed　ear　has　been　fully　borne　out　by　my　investigations　on　the　external　ear。　（G。　Schwalbe；　〃Das　Darwin'sche　Spitzohr　beim　menschlichen　Embryo〃；　〃Anatom。　Anzeiger〃；　1889；　pages　176…　189；　and　other　papers。）　　In　particular；　it　was　established　by　these　investigations　that　the　human　foetus；　about　the　middle　of　its　embryonic　life；　possesses　a　pointed　ear　somewhat　similar　to　that　of　the　monkey　genus　Macacus。　　One　of　Darwin's　statements　in　regard　to　the　head　of　the　orang…　foetus　must　be　corrected。　　A　LARGE　ear　with　a　point　is　shown　in　the　photograph　（〃Descent　of　Man〃；　fig。3；　page　24。）；　but　it　can　easily　be　demonstratedand　Deniker　has　already　pointed　this　outthat　the　figure　is　not　that　of　an　orang…foetus　at　all；　for　that　form　has　much　smaller　ears　with　no　point；　nor　can　it　be　a　gibbon…foetus；　as　Deniker　supposes；　for　the　gibbon　ear　is　also　without　a　point。　　I　myself　regard　it　as　that　of　a　Macacus…embryo。　　But　this　mistake；　which　is　due　to　Nitsche；　in　no　way　affects　the　fact　recognised　by　Darwin；　that　ear…forms　showing　the　point　characteristic　of　the　animal　ear　occur　in　man　with　extraordinary　frequency。

Finally；　there　is　a　discussion　of　those　rudimentary　structures　which　occur　only　in　ONE　sex；　such　as　the　rudimentary　mammary　glands　in　the　male；　the　vesicula　prostatica；　which　corresponds　to　the　uterus　of　the　female；　and　others。　　All　these　facts　tell　in　favour　of　the　common　descent　of　man　and　all　other　vertebrates。　　The　conclusion　of　this　section　is　characteristic：　　〃IT　IS　ONLY　OUR　NATURAL　PREJUDICE；　AND　THAT　ARROGANCE　WHICH　MADE　OUR　FOREFATHERS　DECLARE　THAT　THEY　WERE　DESCENDED　FROM　DEMI…GODS；　WHICH　LEADS　US　TO　DEMUR　TO　THIS　CONCLUSION。　　BUT　THE　TIME　WILL　BEFORE　LONG　COME；　WHEN　IT　WILL　BE　THOUGHT　WONDERFUL　THAT　NATURALISTS；　WHO　WERE　WELL　ACQUAINTED　WITH　THE　COMPARATIVE　STRUCTURE　AND　DEVELOPMENT　OF　MAN；　AND　OTHER　MAMMALS；　SHOULD　HAVE　BELIEVED　THAT　EACH　WAS　THE　WORK　OF　A　SEPARATE　ACT　OF　CREATION。〃　　（Ibid。　page　36。）

In　the　second　chapter　there　is　a　more　detailed　discussion；　again　based　upon　an　extraordinary　wealth　of　facts；　of　the　problem　as　to　the　manner　in　which；　and　the　causes　through　which；　man　evolved　from　a　lower　form。　　Precisely　the　same　causes　are　here　suggested　for　the　origin　of　man；　as　for　the　origin　of　species　in　general。　　Variability；　which　is　a　necessary　assumption　in　regard　to　all　transformations；　occurs　in　man　to　a　high　degree。　　Moreover；　the　rapid　multiplication　of　the　human　race　creates　conditions　which　necessitate　an　energetic　struggle　for　existence；　and　thus　afford　scope　for　the　intervention　of　natural　selection。　　Of　the　exercise　of　ARTIFICIAL　selection　in　the　human　race；　there　is　nothing　to　be　said；　unless　we　cite　such　cases　as　the　grenadiers　of　Frederick　William　I；　or　the　population　of　ancient　Sparta。　　In　the　passages　already　referred　to　and　in　those　which　follow；　the　transmission　of　acquired　characters；　upon　which　Darwin　does　not　dwell；　is　taken　for　granted。　　In　man；　direct　effects　of　changed　conditions　can　be　demonstrated　（for　instance　in　regard　to　bodily　size）；　and　there　are　also　proofs　of　the　influence　exerted　on　his　physical　constitution　by　increased　use　or　disuse。　　Reference　is　here　made　to　the　fact；　established　by　Forbes；　that　the　Quechua…Indians　of　the　high　plateaus　of　Peru　show　a　striking　development　of　lungs　and　thorax；　as　a　result　of　livi