the past condition of organic nature-第1部分

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The　Past　Condition　of　Organic　Nature


by　Thomas　H。　Huxley







IN　the　lecture　which　I　delivered　last　Monday　evening；　I　endeavoured　to
sketch　in　a　very　brief　manner；　but　as　well　as　the　time　at　my　disposal
would　permit；　the　present　condition　of　organic　nature；　meaning　by　that
large　title　simply　an　indication　of　the　great；　broad；　and　general
principles　which　are　to　be　discovered　by　those　who　look　attentively　at
the　phenomena　of　organic　nature　as　at　present　displayed。　　The　general
result　of　our　investigations　might　be　summed　up　thus：　we　found　that　the
multiplicity　of　the　forms　of　animal　life；　great　as　that　may　be；　may　be
reduced　to　a　comparatively　few　primitive　plans　or　types　of　construction；
that　a　further　study　of　the　development　of　those　different　forms
revealed　to　us　that　they　were　again　reducible；　until　we　at　last　brought
the　infinite　diversity　of　animal；　and　even　vegetable　life；　down　to　the
primordial　form　of　a　single　cell。

We　found　that　our　analysis　of　the　organic　world；　whether　animals　or
plants；　showed；　in　the　long　run；　that　they　might　both　be　reduced　into；
and　were；　in　fact；　composed　of；　the　same　constituents。　　And　we　saw　that
the　plant　obtained　the　materials　constituting　its　substance　by　a
peculiar　combination　of　matters　belonging　entirely　to　the　inorganic
world；　that；　then；　the　animal　was　constantly　appropriating　the
nitrogenous　matters　of　the　plant　to　its　own　nourishment；　and　returning
them　back　to　the　inorganic　world；　in　what　we　spoke　of　as　its　waste；　and
that　finally；　when　the　animal　ceased　to　exist；　the　constituents　of　its
body　were　dissolved　and　transmitted　to　that　inorganic　world　whence　they
had　been　at　first　abstracted。　Thus　we　saw　in　both　the　blade　of　grass
and　the　horse　but　the　same　elements　differently　combined　and　arranged。
We　discovered　a　continual　circulation　going　on；the　plant　drawing　in
the　elements　of　inorganic　nature　and　combining　them　into　food　for　the
animal　creation；　the　animal　borrowing　from　the　plant　the　matter　for　its
own　support；　giving　off　during　its　life　products　which　returned
immediately　to　the　inorganic　world；　and　that；　eventually；　the
constituent　materials　of　the　whole　structure　of　both　animals　and　plants
were　thus　returned　to　their　original　source：　there　was　a　constant
passage　from　one　state　of　existence　to　another；　and　a　returning　back
again。

Lastly；　when　we　endeavoured　to　form　some　notion　of　the　nature　of　the
forces　exercised　by　living　beings；　we　discovered　that　theyif　not
capable　of　being　subjected　to　the　same　minute　analysis　as　the
constituents　of　those　beings　themselvesthat　they　were　correlative
withthat　they　were　the　equivalents　of　the　forces　of　inorganic
naturethat　they　were；　in　the　sense　in　which　the　term　is　now　used；
convertible　with　them。　　That　was　our　general　result。

And　now；　leaving　the　Present；　I　must　endeavour　in　the　same　manner　to　put
before　you　the　facts　that　are　to　be　discovered　in　the　Past　history　of
the　living　world；　in　the　past　conditions　of　organic　nature。　　We　have；
to…night；　to　deal　with　the　facts　of　that　historya　history　involving
periods　of　time　before　which　our　mere　human　records　sink　into　utter
insignificancea　history　the　variety　and　physical　magnitude　of　whose
events　cannot　even　be　foreshadowed　by　the　history　of　human　life　and
human　phenomenaa　history　of　the　most　varied　and　complex　character。

We　must　deal　with　the　history；　then；　in　the　first　place；　as　we　should
deal　with　all　other　histories。　　The　historical　student　knows　that　his
first　business　should　be　to　inquire　into　the　validity　of　his　evidence；
and　the　nature　of　the　record　in　which　the　evidence　is　contained；　that
he　may　be　able　to　form　a　proper　estimate　of　the　correctness　of　the
conclusions　which　have　been　drawn　from　that　evidence。　　So；　here；　we
must　pass；　in　the　first　place；　to　the　consideration　of　a　matter　which
may　seem　foreign　to　the　question　under　discussion。　　We　must　dwell　upon
the　nature　of　the　records；　and　the　credibility　of　the　evidence　they
contain；　we　must　look　to　the　completeness　or　incompleteness　of　those
records　themselves；　before　we　turn　to　that　which　they　contain　and
reveal。　　The　question　of　the　credibility　of　the　history；　happily　for　us；
will　not　require　much　consideration；　for；　in　this　history；　unlike　those
of　human　origin；　there　can　be　no　cavilling；　no　differences　as　to　the
reality　and　truth　of　the　facts　of　which　it　is　made　up；　the　facts　state
themselves；　and　are　laid　out　clearly　before　us。

But；　although　one　of　the　greatest　difficulties　of　the　historical　student
is　cleared　out　of　our　path；　there　are　other　difficultiesdifficulties
in　rightly　interpreting　the　facts　as　they　are　presented　to　uswhich
may　be　compared　with　the　greatest　difficulties　of　any　other　kinds　of
historical　study。

What　is　this　record　of　the　past　history　of　the　globe；　and　what　are　the
questions　which　are　involved　in　an　inquiry　into　its　completeness　or
incompleteness？　　That　record　is　composed　of　mud；　and　the　question　which
we　have　to　investigate　this　evening　resolves　itself　into　a　question　of
the　formation　of　mud。　　You　may　think；　perhaps；　that　this　is　a　vast
stepof　almost　from　the　sublime　to　the　ridiculousfrom　the
contemplation　of　the　history　of　the　past　ages　of　the　world's　existence
to　the　consideration　of　the　history　of　the　formation　of　mud！　　But；　in
nature；　there　is　nothing　mean　and　unworthy　of　attention；　there　is
nothing　ridiculous　or　contemptible　in　any　of　her　works；　and　this
inquiry；　you　will　soon　see；　I　hope；　takes　us　to　the　very　root　and
foundations　of　our　subject。

How；　then；　is　mud　formed？　　Always；　with　some　trifling　exception；　which　I
need　not　consider　nowalways；　as　the　result　of　the　action　of　water；
wearing　down　and　disintegrating　the　surface　of　the　earth　and　rocks　with
which　it　comes　in　contactpounding　and　grinding　it　down；　and　carrying
the　particles　away　to　places　where　they　cease　to　be　disturbed　by　this
mechanical　action；　and　where　they　can　subside　and　rest。　　For　the　ocean；
urged　by　winds；　washes；　as　we　know；　a　long　extent　of　coast；　and　every
wave；　loaded　as　it　is　with　particles　of　sand　and　gravel　as　it　breaks
upon　the　shore；　does　something　towards　the　disintegrating　process。　　And
thus；　slowly　but　surely；　the　hardest　rocks　are　gradually　ground　down　to
a　powdery　substance；　and　the　mud　thus　formed；　coarser　or　finer；　as　the
case　may　be；　is　carried　by　the　rush　of　the　tides；　or　currents；　till　it
reaches　the　comparatively　deeper　parts　of　the　ocean；　in　which　it　can
sink　to　the　bottom；　that　is；　to　parts　where　there　is　a　depth　of　about
fourteen　or　fifteen　fathoms；　a　depth　at　which　the　water　is；　usually；
nearly　motionless；　and　in　which；　of　course；　the　finer　particles　of　this
detritus；　or　mud　as　we　call　it；　sinks　to　the　bottom。

Or；　again；　if　you　take　a　river；　rushing　down　from　its　mountain　sources；
brawling　over　the　stones　and　rocks　that　intersect　its　path；　loosening；
removing；　and　carrying　with　it　in　its　downward　course　the　pebbles　and
lighter　matters　from　its　banks；　it　crushes　and　pounds　down　the　rocks
and　earths　in　precisely　the　same　way　as　the　wearing　action　of　the　sea
waves。　　The　matters　forming　the　deposit　are　torn　from　the　mountain…side
and　whirled　impetuously　into　the　valley；　more　slowly　over　the　plain；
thence　into　the　estuary；　and　from　the　estuary　they　are　swept　into　the
sea。　　The　coarser　and　heavier　fragments　are　obviously　deposited　first；
that　is；　as　soon　as　the　current　begins　to　lose　its　force　by　becoming
amalgamated　with　the　stiller　depths　of　the　ocean；　but　the　finer　and
lighter　particles　are　carried　further　on；　and　eventually　deposited　in　a
deeper　and　stiller　portion　of　the　ocean。

It　clearly　follows　from　this　that　mud　gives　us　a　chronology；　for　it　is
evident　that　supposing　this；　which　I　now　sketch；　to　be　the　sea　bottom；
and　supposing　this　to　be　a　coast…line；　from　the　washing　action　of　the
sea　upon　the　rock；　wearing　and　grinding　it　down　into　a　sediment　of　mud；
the　mud　will　be　carried　down；　and　at　length；　deposited　in　the　deeper
parts　of　this　sea　bottom；　where　it　will　form　a　layer；　and　then；　while
that　first　layer　is　hardening；　other　mud　which　is　coming　from　the　same
source　will；　of　course；　be　carried　to　the　same　place；　and；　as　it　is
quite　impossible　for　it　to　get　beneath　the　layer　already　there；　it
deposits　itself　above　it；　and　forms　another　layer；　and　in　that　way　you
gradually　have　layers　of　mud　constantly　forming　and　hardening　one　above
the　other；　and　conveying　a　record　of　time。

It　is　a　necessary　result　of　the　operation　of　the　law　of　gravitation　that
the　uppermost　layer　shall　be　the　youngest　and　the　lowest　the　oldest；
and　that　the　different　beds　shall　be　older　at　any　particular　point　or
spot　in　exactly　the　ratio　of　their　depth　from　the　surface。　　So　that　if
they　were　upheaved　afterwards；　and　you　had　a　series　of　these　different
layers　of　mud；　converted　into　sandstone；　or　limestone；　as　the　case
might　be；　you　might　be　sure　that　the　bottom　layer　was　deposited　first；
and　that　the　upper　layers　were　formed　afterwards。　　Here；　you　see；　is　the
first　step　in　the　historythese　layers　of　mud　give　us　an　idea　of　time。

The　whole　surface　of　the　earth；I　speak　broadly；　and　leave　out　minor
qualifications；is　made　up　of　such　layers　of　mud；　so　hard；　the
majority　of　them；　that　we　call　them　rock　whether　limestone　or
sandstone；　or　other　varieties　of　rock。　　And；　seeing　that　every　part　of
the　crust　of　the　earth　is　made　up　in　this　way；　you　might　think　that　the
determination　of　the　chronology；　the　fixing　of　the　time　which　it　has
taken　to　form　this　crust　is　a　comparatively　simple　matter。　　Take　a
broad　average；　ascertain　how　fast　the　mud　is　deposited　upon　the　bottom
of　the　sea；　or　in　the　estuary　of　rivers；　take　it　to　be　an　inch；　or　two；
or　three　inches　a　year；　or　whatever　you　may　roughly　estimate　it　at；
then　take　the　total　thickness　of　the　whole　series　of　stratified　rocks；
which　geologists　estimate　at　twelve　or　thirteen　miles；　or　about　seventy
thousand　feet；　make　a　sum　in　short　division；　divide　the　total　thickness
by　that　of　the　quantity　deposited　in　one　year；　and　the　result　will；　of
course；　give　you　the　number　of　years　which　the　crust　has　taken　to　form。

Truly；　that　looks　a　very　simple　process！　　It　would　be　so　except　for
certain　difficulties；　the　very　first　of　which