autobiography and selected essays-第19节

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I　must　ask　you　to　believe　that　there　is　no　less　conclusive　proof

that　a　still　more　prolonged　succession　of　similar　changes　occurred；

before　the　chalk　was　deposited。　　Nor　have　we　any　reason　to　think

that　the　first　term　in　the　series　of　these　changes　is　known。　　The

oldest　sea…beds　preserved　to　us　are　sands；　and　mud；　and　pebbles；

the　wear　and　tear　of　rocks　which　were　formed　in　still　older　oceans。



But；　great　as　is　the　magnitude　of　these　physical　changes　of　the

world；　they　have　been　accompanied　by　a　no　less　striking　series　of

modifications　in　its　living　inhabitants。



All　the　great　classes　of　animals；　beasts　of　the　field；　fowls　of　the

air；　creeping　things；　and　things　which　dwell　in　the　waters；

flourished　upon　the　globe　long　ages　before　the　chalk　was　deposited。

Very　few；　however；　if　any；　of　these　ancient　forms　of　animal　life

were　identical　with　those　which　now　live。　　Certainly　not　one　of　the

higher　animals　was　of　the　same　species　as　any　of　those　now　in

existence。　　The　beasts　of　the　field；　in　the　days　before　the　chalk；

were　not　our　beasts　of　the　field；　nor　the　fowls　of　the　air　such　as

those　which　the　eye　of　men　has　seen　flying；　unless　his　antiquity

dates　infinitely　further　back　than　we　at　present　surmise。　　If　we

could　be　carried　back　into　those　times；　we　should　be　as　one

suddenly　set　down　in　Australia　before　it　was　colonized。　　We　should

see　mammals；　birds；　reptiles；　fishes；　insects；　snails；　and　the

like；　clearly　recognisable　as　such；　and　yet　not　one　of　them　would

be　just　the　same　as　those　with　which　we　are　familiar；　and　many

would　be　extremely　different。



From　that　time　to　the　present；　the　population　of　the　world　has

undergone　slow　and　gradual；　but　incessant　changes。　　There　has　been

no　grand　catastropheno　destroyer　has　swept　away　the　forms　of　life

of　one　period；　and　replaced　them　by　a　totally　new　creation；　but　one

species　has　vanished　and　another　has　taken　its　place；　creatures　of

one　type　of　structure　have　diminished；　those　of　another　have

increased；　as　time　has　passed　on。　　And　thus；　while　the　differences

between　the　living　creatures　of　the　time　before　the　chalk　and　those

of　the　present　day　appear　startling；　if　placed　side　by　side；　we　are

led　from　one　to　the　other　by　the　most　gradual　progress；　if　we

follow　the　course　of　Nature　through　the　whole　series　of　those

relics　of　her　operations　which　she　has　left　behind。



And　it　is　by　the　population　of　the　chalk　sea　that　the　ancient　and

the　modern　inhabitants　of　the　world　are　most　completely　connected。

The　groups　which　are　dying　out　flourish；　side　by　side；　with　the

groups　which　are　now　the　dominant　forms　of　life。



Thus　the　chalk　contains　remains　of　those　strange　flying　and

swimming　reptiles；　the　pterodactyl；　the　ichthyosaurus；　and　the

plesiosaurus；　which　are　found　in　no　later　deposits；　but　abounded　in

preceding　ages。　　The　chambered　shells　called　ammonites　and

belemnites；　which　are　so　characteristic　of　the　period　preceding　the

cretaceous；　in　like　manner　die　with　it。



But；　amongst　these　fading　remainders　of　a　previous　state　of　things；

are　some　very　modern　forms　of　life；　looking　like　Yankee　pedlars

among　a　tribe　of　Red　Indians。　　Crocodiles　of　modern　type　appear；

bony　fishes；　many　of　them　very　similar　to　existing　species　almost

supplant　the　forms　of　fish　which　predominate　in　more　ancient　seas；

and　many　kinds　of　living　shellfish　first　become　known　to　us　in　the

chalk。　　The　vegetation　acquires　a　modern　aspect。　　A　few　living

animals　are　not　even　distinguishable　as　species；　from　those　which

existed　at　that　remote　epoch。　　The　Globigerina　of　the　present　day；

for　example；　is　not　different　specifically　from　that　of　the　chalk；

and　the　same　may　be　said　of　many　other　Foraminifera。　　I　think　it

probable　that　critical　and　unprejudiced　examination　will　show　that

more　than　one　species　of　much　higher　animals　have　had　a　similar

longevity；　but　the　only　example；　which　I　can　at　present　give

confidently　is　the　snake's…head　lamp…shell　（Terebratulina　caput

serpentis）；　which　lives　in　our　English　seas　and　abounded　（as

Terebratulina　striata　of　authors）　in　the　chalk。



The　longest　line　of　human　ancestry　must　hide　its　diminished　head

before　the　pedigree　of　this　insignificant　shell…fish。　　We

Englishmen　are　proud　to　have　an　ancestor　who　was　present　at　the

Battle　of　Hastings。　　The　ancestors　of　Terebratulina　caput　serpentis

may　have　been　present　at　a　battle　of　Ichthyosauria　in　that　part　of

the　sea　which；　when　the　chalk　was　forming；　flowed　over　the　site　of

Hastings。　　While　all　around　has　changed；　this　Terebratulina　has

peacefully　propagated　its　species　from　generation　to　generation；

and　stands　to　this　day；　as　a　living　testimony　to　the　continuity　of

the　present　with　the　past　history　of　the　globe。





Up　to　this　moment　I　have　stated；　so　far　as　I　know；　nothing　but

well…authenticated　facts；　and　the　immediate　conclusions　which　they

force　upon　the　mind。



But　the　mind　is　so　constituted　that　it　does　not　willingly　rest　in

facts　and　immediate　causes；　but　seeks　always　after　a　knowledge　of

the　remoter　links　in　the　chain　of　causation。



Taking　the　many　changes　of　any　given　spot　of　the　earth's　surface；

from　sea　to　land　and　from　land　to　sea；　as　an　established　fact；　we

cannot　refrain　from　asking　ourselves　how　these　changes　have

occurred。　　And　when　we　have　explained　themas　they　must　be

explainedby　the　alternate　slow　movements　of　elevation　and

depression　which　have　affected　the　crust　of　the　earth；　we　go　still

further　back；　and　ask；　Why　these　movements？



I　am　not　certain　that　any　one　can　give　you　a　satisfactory　answer　to

that　question。　　Assuredly　I　cannot。　　All　that　can　be　said；　for

certain；　is；　that　such　movements　are　part　of　the　ordinary　course　of

nature；　inasmuch　as　they　are　going　on　at　the　present　time。　　Direct

proof　may　be　given；　that　some　parts　of　the　land　of　the　northern

hemisphere　are　at　this　moment　insensibly　rising　and　others

insensibly　sinking；　and　there　is　indirect；　but　perfectly

satisfactory；　proof；　that　an　enormous　area　now　covered　by　the

Pacific　has　been　deepened　thousands　of　feet；　since　the　present

inhabitants　of　that　sea　came　into　existence。



Thus　there　is　not　a　shadow　of　a　reason　for　believing　that　the

physical　changes　of　the　globe；　in　past　times　have　been　effected　by

other　than　natural　causes。



Is　there　any　more　reason　for　believing　that　the　concomitant

modifications　in　the　forms　of　the　living　inhabitants　of　the　globe

have　been　brought　about　in　other　ways？



Before　attempting　to　answer　this　question；　let　us　try　to　form　a

distinct　mental　picture　of　what　has　happened；　in　some　special　case。



The　crocodiles　are　animals　which；　as　a　group；　have　a　very　vast

antiquity。　　They　abounded　ages　before　the　chalk　was　deposited；　they

throng　the　rivers　in　warm　climates；　at　the　present　day。　　There　is　a

difference　in　the　form　of　the　joints　of　the　back…bone；　and　in　some

minor　particulars；　between　the　crocodiles　of　the　present　epoch　and

those　which　lived　before　the　chalk；　but　in　the　cretaceous　epoch；　as

I　have　already　mentioned；　the　crocodiles　had　assumed　the　modern

type　of　structure。　　Notwithstanding　this；　the　crocodiles　of　the

chalk　are　not　identically　the　same　as　those　which　lived　in　the

times　called　〃older　tertiary；〃　which　succeeded　the　cretaceous

epoch；　and　the　crocodiles　of　the　older　tertiaries　are　not　identical

with　those　of　the　newer　tertiaries；　nor　are　these　identical　with

existing　forms。　　I　leave　open　the　question　whether　particular

species　may　have　lived　on　from　epoch　to　epoch。　　But　each　epoch　has

had　its　peculiar　crocodiles；　though　all；　since　the　chalk；　have

belonged　to　the　modern　type；　and　differ　simply　in　their

proportions；　and　in　such　structural　particulars　as　are　discernible

only　to　trained　eyes。



How　is　the　existence　of　this　long　succession　of　different　species

of　crocodiles　to　be　accounted　for？



Only　two　suppositions　seem　to　be　open　to　usEither　each　species　of

crocodile　has　been　specially　created；　or　it　has　arisen　out　of　some

pre…existing　form　by　the　operation　of　natural　causes。



Choose　your　hypothesis；　I　have　chosen　mine。　　I　can　find　no　warranty

for　believing　in　the　distinct　creation　of　a　score　of　successive

species　of　crocodiles　in　the　course　of　countless　ages　of　time。

Science　gives　no　countenance　to　such　a　wild　fancy；　nor　can　even　the

perverse　ingenuity　of　a　commentator　pretend　to　discover　this　sense；

in　the　simple　words　in　which　the　writer　of　Genesis　records　the

proceedings　of　the　fifth　and　sixth　days　of　the　Creation。



On　the　other　hand；　I　see　no　good　reason　for　doubting　the　necessary

alternative；　that　all　these　varied　species　have　been　evolved　from

pre…existing　crocodilian　forms；　by　the　operation　of　causes　as

completely　a　part　of　the　common　order　of　nature；　as　those　which

have　effected　the　changes　of　the　inorganic　world。



Few　will　venture　to　affirm　that　the　reasoning　which　applies　to

crocodiles　loses　its　force　among　other　animals；　or　among　plants。

If　one　series　of　spe