lectures on evolution-第12部分

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found　among　these　remains。　But　it　is　only　recently　that　the

admirably　conceived　and　most　thoroughly　and　patiently　worked…out

investigations　of　Professor　Marsh　have　given　us　a　just　idea　of

the　vast　fossil　wealth；　and　of　the　scientific　importance；　of

these　deposits。　I　have　had　the　advantage　of　glancing　over　the

collections　in　Yale　Museum；　and　I　can　truly　say　that；　so　far　as

my　knowledge　extends；　there　is　no　collection　from　any　one　region

and　series　of　strata　comparable；　for　extent；　or　for　the　care

with　which　the　remains　have　been　got　together；　or　for　their

scientific　importance；　to　the　series　of　fossils　which　he　has

deposited　there。　This　vast　collection　has　yielded　evidence

bearing　upon　the　question　of　the　pedigree　of　the　horse　of　the

most　striking　character。　It　tends　to　show　that　we　must　look　to

America；　rather　than　to　Europe；　for　the　original　seat　of　the

equine　series；　and　that　the　archaic　forms　and　successive

modifications　of　the　horse's　ancestry　are　far　better　preserved

here　than　in　Europe。



Professor　Marsh's　kindness　has　enabled　me　to　put　before　you　a

diagram；　every　figure　in　which　is　an　actual　representation　of

some　specimen　which　is　to　be　seen　at　Yale　at　this　present　time

（Fig。　9）。





Fig。　9。





The　succession　of　forms　which　he　has　brought　together　carries　us

from　the　top　to　the　bottom　of　the　Tertiaries。　Firstly；　there　is

the　true　horse。　Next　we　have　the　American　Pliocene　form　of　the

horse　（Pliohippus）；　in　the　conformation　of　its　limbs　it

presents　some　very　slight　deviations　from　the　ordinary　horse；

and　the　crowns　of　the　grinding　teeth　are　shorter。　Then　comes　the

Protohippus；　which　represents　the　European

Hipparion；　having　one　large　digit　and　two　small　ones　on

each　foot；　and　the　general　characters　of　the　fore…arm　and　leg　to

which　I　have　referred。　But　it　is　more　valuable　than　the　European

Hipparion　for　the　reason　that　it　is　devoid　of　some　of　the

peculiarities　of　that　formpeculiarities　which　tend　to　show

that　the　European　Hipparion　is　rather　a　member　of　a

collateral　branch；　than　a　form　in　the　direct　line　of　succession。

Next；　in　the　backward　order　in　time；　is　the　Miohippus；

which　corresponds　pretty　nearly　with　the　Anchitherium　of

Europe。　It　presents　three　complete　toesone　large　median　and

two　smaller　lateral　ones；　and　there　is　a　rudiment　of　that　digit；

which　answers　to　the　little　finger　of　the　human　hand。



The　European　record　of　the　pedigree　of　the　horse　stops　here；

in　the　American　Tertiaries；　on　the　contrary；　the　series　of

ancestral　equine　forms　is　continued　into　the　Eocene　formations。

An　older　Miocene　form；　termed　Mesohippus；　has　three　toes

in　front；　with　a　large　splint…like　rudiment　representing　the

little　finger；　and　three　toes　behind。　The　radius　and　ulna；　the

tibia　and　the　fibula；　are　distinct；　and　the　short　crowned　molar

teeth　are　anchitherioid　in　pattern。



But　the　most　important　discovery　of　all　is　the　Orohippus；

which　comes　from　the　Eocene　formation；　and　is　the　oldest　member

of　the　equine　series；　as　yet　known。　Here　we　find　four　complete

toes　on　the　front　limb；　three　toes　on　the　hind　limb；　a　well…

developed　ulna；　a　well…developed　fibula；　and　short…crowned

grinders　of　simple　pattern。



Thus；　thanks　to　these　important　researches；　it　has　become

evident　that；　so　far　as　our　present　knowledge　extends；　the

history　of　the　horse…type　is　exactly　and　precisely　that　which

could　have　been　predicted　from　a　knowledge　of　the　principles　of

evolution。　And　the　knowledge　we　now　possess　justifies　us

completely　in　the　anticipation；　that　when　the　still　lower　Eocene

deposits；　and　those　which　belong　to　the　Cretaceous　epoch；　have

yielded　up　their　remains　of　ancestral　equine　animals；　we　shall

find；　first；　a　form　with　four　complete　toes　and　a　rudiment　of

the　innermost　or　first　digit　in　front；　with；　probably；　a

rudiment　of　the　fifth　digit　in　the　hind　foot；　while；　in　still

older　forms；　the　series　of　the　digits　will　be　more　and　more

complete；　until　we　come　to　the　five…toed　animals；　in　which；　if

the　doctrine　of　evolution　is　well　founded；　the　whole　series　must

have　taken　its　origin。



That　is　what　I　mean　by　demonstrative　evidence　of　evolution。

An　inductive　hypothesis　is　said　to　be　demonstrated　when　the

facts　are　shown　to　be　in　entire　accordance　with　it。　If　that　is

not　scientific　proof；　there　are　no　merely　inductive　conclusions

which　can　be　said　to　be　proved。　And　the　doctrine　of　evolution；

at　the　present　time；　rests　upon　exactly　as　secure　a　foundation

as　the　Copernican　theory　of　the　motions　of　the　heavenly　bodies

did　at　the　time　of　its　promulgation。　Its　logical　basis　is

precisely　of　the　same　characterthe　coincidence　of　the　observed

facts　with　theoretical　requirements。



The　only　way　of　escape；　if　it　be　a　way　of　escape；　from　the

conclusions　which　I　have　just　indicated；　is　the　supposition　that

all　these　different　equine　forms　have　been　created　separately　at

separate　epochs　of　time；　and；　I　repeat；　that　of　such　an

hypothesis　as　this　there　neither　is；　nor　can　be；　any　scientific

evidence；　and；　assuredly；　so　far　as　I　know；　there　is　none　which

is　supported；　or　pretends　to　be　supported；　by　evidence　or

authority　of　any　other　kind。　I　can　but　think　that　the　time　will

come　when　such　suggestions　as　these；　such　obvious　attempts　to

escape　the　force　of　demonstration；　will　be　put　upon　the　same

footing　as　the　supposition　made　by　some　writers；　who　are　I

believe　not　completely　extinct　at　present；　that　fossils　are　mere

simulacra；　are　no　indications　of　the　former　existence　of　the

animals　to　which　they　seem　to　belong；　but　that　they　are　either

sports　of　nature；　or　special　creations；　intendedas　I　heard

suggested　the　other　dayto　test　our　faith。



In　fact；　the　whole　evidence　is　in　favour　of　evolution；　and　there

is　none　against　it。　And　I　say　this；　although　perfectly　well

aware　of　the　seeming　difficulties　which　have　been　built　up　upon

what　appears　to　the　uninformed　to　be　a　solid　foundation。　I　meet

constantly　with　the　argument　that　the　doctrine　of　evolution

cannot　be　well　founded；　because　it　requires　the　lapse　of　a　very

vast　period　of　time；　while　the　duration　of　life　upon　the　earth

thus　implied　is　inconsistent　with　the　conclusions　arrived　at　by

the　astronomer　and　the　physicist。　I　may　venture　to　say　that　I　am

familiar　with　those　conclusions；　inasmuch　as　some　years　ago；

when　President　of　the　Geological　Society　of　London；　I　took　the

liberty　of　criticising　them；　and　of　showing　in　what　respects；　as

it　appeared　to　me；　they　lacked　complete　and　thorough

demonstration。　But；　putting　that　point　aside；　suppose　that；　as

the　astronomers；　or　some　of　them；　and　some　physical

philosophers；　tell　us；　it　is　impossible　that　life　could　have

endured　upon　the　earth　for　as　long　a　period　as　is　required　by

the　doctrine　of　evolutionsupposing　that　to　be　provedI　desire

to　be　informed；　what　is　the　foundation　for　the　statement　that

evolution　does　require　so　great　a　time？　The　biologist　knows

nothing　whatever　of　the　amount　of　time　which　may　be　required　for

the　process　of　evolution。　It　is　a　matter　of　fact　that　the　equine

forms　which　I　have　described　to　you　occur；　in　the　order　stated；

in　the　Tertiary　formations。　But　I　have　not　the　slightest　means

of　guessing　whether　it　took　a　million　of　years；　or　ten　millions；

or　a　hundred　millions；　or　a　thousand　millions　of　years；　to　give

rise　to　that　series　of　changes。　A　biologist　has　no　means　of

arriving　at　any　conclusion　as　to　the　amount　of　time　which　may　be

needed　for　a　certain　quantity　of　organic　change。　He　takes　his

time　from　the　geologist。　The　geologist；　considering　the　rate　at

which　deposits　are　formed　and　the　rate　at　which　denudation　goes

on　upon　the　surface　of　the　earth；　arrives　at　more　or　less

justifiable　conclusions　as　to　the　time　which　is　required　for　the

deposit　of　a　certain　thickness　of　rocks；　and　if　he　tells　me　that

the　Tertiary　formations　required　500；000；000　years　for　their

deposit；　I　suppose　he　has　good　ground　for　what　he　says；　and　I

take　that　as　a　measure　of　the　duration　of　the　evolution　of　the

horse　from　the　Orohippus　up　to　its　present　condition。

And；　if　he　is　right；　undoubtedly　evolution　is　a　very　slow

process；　and　requires　a　great　deal　of　time。　But　suppose；　now；

that　an　astronomer　or　a　physicistfor　instance；　my　friend　Sir

William　Thomsontells　me　that　my　geological　authority　is　quite

wrong；　and　that　he　has　weighty　evidence　to　show　that　life　could

not　possibly　have　existed　upon　the　surface　of　the　earth

500；000；000　years　ago；　because　the　earth　would　have　then　been

too　hot　to　allow　of　life；　my　reply　is：　〃That　is　not　my　affair；

settle　that　with　the　geologist；　and　when　you　have　come　to　an

agreement　among　yourselves　I　will　adopt　your　conclusion。〃

We　take　our　time　from　the　geologists　and　physicists；　and　it　is

monstrous　that；　having　taken　our　time　from　the　physical

philosopher's　clock；　the　physical　philosopher　should　turn　round

upon　us；　and　say　we　are　too　fast　or　too　slow。　What　we　desire　to

know　is；　is　it　a　fact　that　evolution　took　place？　As　to　the

amount　of　time　which　evolution　may　have　occupied；　we　are　in　the

hands　of　the　physicist　and　the　astronomer；　whose　business　it　is

to　deal　with　those　questions。



I　have　now；　ladies　and　gentlemen；　arrived　at　the　conclusion　of

the　task　which　I　set　before　myself　when　I　undertook　to　deliver

these　lectures。　My　purpose　has　been；　not　to　enable　those　among

you　who　have　paid　no　attention　to　these　subjects　before；　to

leave　this　room　in　a　condition　to　decide　upon　the　validity　or

the　invalidity　of　the　hypothesis　of　evolution；　but　I　have

desired　to　put　before　you　the　principles　upon　which　all

hypotheses　respecting　the　history　of　Nature　must　be　judged；

and　furthermore；　to　make　apparent　the　nature　of　the　evidence　and

the　amount　of　cogency　which　is　to　be　expected　and　may　be

obtained　from　it。　To　this　end；　I　have　not　hesitated　to　regard

you　as　genuine　students　and　persons　desirou