lectures on evolution-第2章

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Opening　her　fertile　womb；　teemed　at　a　birth

Innumerous　living　creatures；　perfect　forms；

Limbed　and　full…grown。　Out　of　the　ground　uprose；

As　from　his　lair；　the　wild　beast；　where　he　wons

In　forest　wild；　in　thicket；　brake；　or　den；

Among　the　trees　in　pairs　they　rose；　they　walked；

The　cattle　in　the　fields　and　meadows　green；

Those　rare　and　solitary；　these　in　flocks

Pasturing　at　once；　and　in　broad　herds　upsprung。

The　grassy　clods　now　calved；　now　half　appears

The　tawny　lion；　pawing　to　get　free

His　hinder　partsthen　springs；　as　broke　from　bonds；

And　rampant　shakes　his　brinded　mane；　the　ounce；

The　libbard；　and　the　tiger；　as　the　mole

Rising；　the　crumbled　earth　above　them　threw

In　hillocks；　the　swift　stag　from　underground

Bore　up　his　branching　head；　scarce　from　his　mould

Behemoth；　biggest　born　of　earth；　upheaved

His　vastness；　fleeced　the　flocks　and　bleating　rose

As　plants；　ambiguous　between　sea　and　land；

The　river…horse　and　scaly　crocodile。

At　once　came　forth　whatever　creeps　the　ground；

Insect　or　worm。〃



There　is　no　doubt　as　to　the　meaning　of　this　statement；　nor　as　to

what　a　man　of　Milton's　genius　expected　would　have　been　actually

visible　to　an　eye…witness　of　this　mode　of　origination　of

living　things。



The　third　hypothesis；　or　the　hypothesis　of　evolution；　supposes

that；　at　any　comparatively　late　period　of　past　time；　our

imaginary　spectator　would　meet　with　a　state　of　things　very

similar　to　that　which　now　obtains；　but　that　the　likeness　of　the

past　to　the　present　would　gradually　become　less　and　less；　in

proportion　to　the　remoteness　of　his　period　of　observation　from

the　present　day；　that　the　existing　distribution　of　mountains　and

plains；　of　rivers　and　seas；　would　show　itself　to　be　the　product

of　a　slow　process　of　natural　change　operating　upon　more　and　more

widely　different　antecedent　conditions　of　the　mineral　frame…work

of　the　earth；　until；　at　length；　in　place　of　that　frame…work；　he

would　behold　only　a　vast　nebulous　mass；　representing　the

constituents　of　the　sun　and　of　the　planetary　bodies。　Preceding

the　forms　of　life　which　now　exist；　our　observer　would　see

animals　and　plants；　not　identical　with　them；　but　like　them；

increasing　their　differences　with　their　antiquity　and；　at　the

same　time；　becoming　simpler　and　simpler；　until；　finally；　the

world　of　life　would　present　nothing　but　that　undifferentiated

protoplasmic　matter　which；　so　far　as　our　present　knowledge　goes；

is　the　common　foundation　of　all　vital　activity。



The　hypothesis　of　evolution　supposes　that　in　all　this　vast

progression　there　would　be　no　breach　of　continuity；　no　point　at

which　we　could　say　〃This　is　a　natural　process；〃　and　〃This　is　not

a　natural　process；〃　but　that　the　whole　might　be　compared　to　that

wonderful　operation　of　development　which　may　be　seen　going　on

every　day　under　our　eyes；　in　virtue　of　which　there　arises；　out

of　the　semi…fluid　comparatively　homogeneous　substance　which　we

call　an　egg；　the　complicated　organisation　of　one　of　the　higher

animals。　That；　in　a　few　words；　is　what　is　meant　by　the

hypothesis　of　evolution。



I　have　already　suggested　that；　in　dealing　with　these　three

hypotheses；　in　endeavouring　to　form　a　judgment　as　to　which　of

them　is　the　more　worthy　of　belief；　or　whether　none　is　worthy　of

beliefin　which　case　our　condition　of　mind　should　be　that

suspension　of　judgment　which　is　so　difficult　to　all　but　trained

intellectswe　should　be　indifferent　to　all　a　priori

considerations。　The　question　is　a　question　of　historical　fact。

The　universe　has　come　into　existence　somehow　or　other；　and　the

problem　is；　whether　it　came　into　existence　in　one　fashion；　or

whether　it　came　into　existence　in　another；　and；　as　an　essential

preliminary　to　further　discussion；　permit　me　to　say　two　or　three

words　as　to　the　nature　and　the　kinds　of　historical　evidence。



The　evidence　as　to　the　occurrence　of　any　event　in　past　time　may

be　ranged　under　two　heads　which；　for　convenience'　sake；　I　will

speak　of　as　testimonial　evidence　and　as　circumstantial　evidence。

By　testimonial　evidence　I　mean　human　testimony；　and　by

circumstantial　evidence　I　mean　evidence　which　is　not　human

testimony。　Let　me　illustrate　by　a　familiar　example　what　I

understand　by　these　two　kinds　of　evidence；　and　what　is　to　be

said　respecting　their　value。



Suppose　that　a　man　tells　you　that　he　saw　a　person　strike　another

and　kill　him；　that　is　testimonial　evidence　of　the　fact　of

murder。　But　it　is　possible　to　have　circumstantial　evidence　of

the　fact　of　murder；　that　is　to　say；　you　may　find　a　man　dying

with　a　wound　upon　his　head　having　exactly　the　form　and　character

of　the　wound　which　is　made　by　an　axe；　and；　with　due　care　in

taking　surrounding　circumstances　into　account；　you　may　conclude

with　the　utmost　certainty　that　the　man　has　been　murdered；

that　his　death　is　the　consequence　of　a　blow　inflicted　by　another

man　with　that　implement。　We　are　very　much　in　the　habit　of

considering　circumstantial　evidence　as　of　less　value　than

testimonial　evidence；　and　it　may　be　that；　where　the

circumstances　are　not　perfectly　clear　and　intelligible；　it　is　a

dangerous　and　unsafe　kind　of　evidence；　but　it　must　not　be

forgotten　that；　in　many　cases；　circumstantial　is　quite　as

conclusive　as　testimonial　evidence；　and　that；　not　unfrequently；

it　is　a　great　deal　weightier　than　testimonial　evidence。

For　example；　take　the　case　to　which　I　referred　just　now。

The　circumstantial　evidence　may　be　better　and　more　convincing

than　the　testimonial　evidence；　for　it　may　be　impossible；　under

the　conditions　that　I　have　defined；　to　suppose　that　the　man　met

his　death　from　any　cause　but　the　violent　blow　of　an　axe　wielded

by　another　man。　The　circumstantial　evidence　in　favour　of　a

murder　having　been　committed；　in　that　case；　is　as　complete　and

as　convincing　as　evidence　can　be。　It　is　evidence　which　is　open

to　no　doubt　and　to　no　falsification。　But　the　testimony　of　a

witness　is　open　to　multitudinous　doubts。　He　may　have　been

mistaken。　He　may　have　been　actuated　by　malice。　It　has　constantly

happened　that　even　an　accurate　man　has　declared　that　a　thing　has

happened　in　this；　that；　or　the　other　way；　when　a　careful

analysis　of　the　circumstantial　evidence　has　shown　that　it　did

not　happen　in　that　way；　but　in　some　other　way。



We　may　now　consider　the　evidence　in　favour　of　or　against　the

three　hypotheses。　Let　me　first　direct　your　attention　to　what　is

to　be　said　about　the　hypothesis　of　the　eternity　of　the　state　of

things　in　which　we　now　live。　What　will　first　strike　you　is；　that

it　is　a　hypothesis　which；　whether　true　or　false；　is　not　capable

of　verification　by　any　evidence。　For；　in　order　to　obtain　either

circumstantial　or　testimonial　evidence　sufficient　to　prove　the

eternity　of　duration　of　the　present　state　of　nature；　you　must

have　an　eternity　of　witnesses　or　an　infinity　of　circumstances；

and　neither　of　these　is　attainable。　It　is　utterly　impossible

that　such　evidence　should　be　carried　beyond　a　certain　point　of

time；　and　all　that　could　be　said；　at　most；　would　be；　that　so　far

as　the　evidence　could　be　traced；　there　was　nothing　to　contradict

the　hypothesis。　But　when　you　look；　not　to　the　testimonial

evidencewhich；　considering　the　relative　insignificance　of　the

antiquity　of　human　records；　might　not　be　good　for　much　in　this

casebut　to　the　circumstantial　evidence；　then　you　find　that

this　hypothesis　is　absolutely　incompatible　with　such　evidence　as

we　have；　which　is　of　so　plain　and　so　simple　a　character　that　it

is　impossible　in　any　way　to　escape　from　the　conclusions　which　it

forces　upon　us。



You　are；　doubtless；　all　aware　that　the　outer　substance　of　the

earth；　which　alone　is　accessible　to　direct　observation；　is　not

of　a　homogeneous　character；　but　that　it　is　made　up　of　a　number

of　layers　or　strata；　the　titles　of　the　principal　groups　of　which

are　placed　upon　the　accompanying　diagram。　Each　of　these　groups

represents　a　number　of　beds　of　sand；　of　stone；　of　clay；　of

slate；　and　of　various　other　materials。



On　careful　examination；　it　is　found　that　the　materials　of　which

each　of　these　layers　of　more　or　less　hard　rock　are　composed　are；

for　the　most　part；　of　the　same　nature　as　those　which　are　at

present　being　formed　under　known　conditions　on　the　surface　of

the　earth。　For　example；　the　chalk；　which　constitutes　a　great

part　of　the　Cretaceous　formation　in　some　parts　of　the　world；　is

practically　identical　in　its　physical　and　chemical　characters

with　a　substance　which　is　now　being　formed　at　the　bottom　of　the

Atlantic　Ocean；　and　covers　an　enormous　area；　other　beds　of　rock

are　comparable　with　the　sands　which　are　being　formed　upon　sea…

shores；　packed　together；　and　so　on。　Thus；　omitting　rocks　of

igneous　origin；　it　is　demonstrable　that　all　these　beds　of　stone；

of　which　a　total　of　not　less　than　seventy　thousand　feet　is

known；　have　been　formed　by　natural　agencies；　either　out　of　the

waste　and　washing　of　the　dry　land；　or　else　by　the　accumulation

of　the　exuviae　of　plants　and　animals。　Many　of　these　strata　are

full　of　such　exuviaethe　so…called　〃fossils。〃　Remains　of

thousands　of　species　of　animals　and　plants；　as　perfectly

recognisable　as　those　of　existing　forms　of　life　which　you　meet

with　in　museums；　or　as　the　shells　which　you　pick　up　upon　the

sea…beach；　have　been　imbedded　in　the　ancient　sands；　or　muds；　or

limestones；　just　as　they　are　being　imbedded　now；　in　sandy；　or

clayey；　or　calcareous　subaqueous　deposits。　They　furnish　us　with

a　record；　the　general　nature　of　which　cannot　be　misinterpreted；

of　the　kinds　of　things　that　have　lived　upon　the　surface　of　the

earth　during　the　time　that　is　registered　by　this　great　thickness

of　stratified　rocks。　But　even　a　superficial　study　of　these

fossils　shows　us　that　the　animals　and　plants　which　live　at　the

present　time　have　had　only　a　temporary　duration；　for　the　remains

of　such　modern　forms　of　life　are　met　with；　for　the　most　part；

only　in　the　uppermost　or　latest　tertiaries；　and　their　number

rapidly　diminishes　in　the　lower　deposits　of　that　epoch。　In　the

older　tertiaries；　the　places　of　existing　animals　and　plants　are

taken　by　other　forms；　as　numerous　and　diversified　as　those　which

live　now　in　the　same　localities；　but　more　or　less　different　from

them；　in　the　mesozoic　rocks；　these　are　replaced　by　others　yet

more　divergent　from　modern　types；　and；　in　the　paleozoic

formations；　the　contrast　is　still　more　marked。　Thus　the

circumstantial　evidence　absolutely　negatives　the　conception　of

the　eternity　of　the　present　condition　of　things。　We　can　say；

with　certainty；　that　the　present　condition　of　things　has　existed

for　a　comparatively　short　period；　and　that；　so　far　as　animal　and

vegetable　nature　are　concerned；　it　has　been　preceded　by　a

different　condition。　We　can　pursue　this　evidence　until　we　reach

the　lowest　of　the　stratified　rocks；　in　which　we　lose　the

indications　of　life　altogether。　The　hypothesis　of　the　eternity

of　the　present　state　of　nature　may　therefore　be　put　out

of　court。





F