the darwinian hypothesis-第1章

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The　Darwinian　Hypothesis


by　Thomas　H。　Huxley










DARWIN　ON　THE　ORIGIN　OF　SPECIES。

THERE　is　a　growing　immensity　in　the　speculations　of　science　to　which　no
human　thing　or　thought　at　this　day　is　comparable。　　Apart　from　the
results　which　science　brings　us　home　and　securely　harvests；　there　is　an
expansive　force　and　latitude　in　its　tentative　efforts；　which　lifts　us
out　of　ourselves　and　transfigures　our　mortality。　　We　may　have　a
preference　for　moral　themes；　like　the　Homeric　sage；　who　had　seen　and
known　much：

　　　　〃Cities　of　men
　　　　And　manners；　climates；　councils；　governments〃；

yet　we　must　end　by　confession　that

　　　　〃The　windy　ways　of　men
　　　　Are　but　dust　which　rises　up
　　　　And　is　lightly　laid　again；〃

in　comparison　with　the　work　of　nature；　to　which　science　testifies；　but
which　has　no　boundaries　in　time　or　space　to　which　science　can
approximate。

There　is　something　altogether　out　of　the　reach　of　science；　and　yet　the
compass　of　science　is　practically　illimitable。　　Hence　it　is　that　from
time　to　time　we　are　startled　and　perplexed　by　theories　which　have　no
parallel　in　the　contracted　moral　world；　for　the　generalizations　of
science　sweep　on　in　ever…widening　circles；　and　more　aspiring　flights；
through　a　limitless　creation。　　While　astronomy；　with　its　telescope；
ranges　beyond　the　known　stars；　and　physiology；　with　its　microscope；　is
subdividing　infinite　minutiae；　we　may　expect　that　our　historic
centuries　may　be　treated　as　inadequate　counters　in　the　history　of　the
planet　on　which　we　are　placed。　　We　must　expect　new　conceptions　of　the
nature　and　relations　of　its　denizens；　as　science　acquires　the　materials
for　fresh　generalizations；　nor　have　we　occasion　for　alarms　if　a　highly
advanced　knowledge；　like　that　of　the　eminent　Naturalist　before　us；
confronts　us　with　an　hypothesis　as　vast　as　it　is　novel。　　This
hypothesis　may　or　may　not　be　sustainable　hereafter；　it　may　give　way　to
something　else；　and　higher　science　may　reverse　what　science　has　here
built　up　with　so　much　skill　and　patience；　but　its　sufficiency　must　be
tried　by　the　tests　of　science　alone；　if　we　are　to　maintain　our　position
as　the　heirs　of　Bacon　and　the　acquitters　of　Galileo。　　We　must　weigh
this　hypothesis　strictly　in　the　controversy　which　is　coming；　by　the　only
tests　which　are　appropriate；　and　by　no　others　whatsoever。

The　hypothesis　to　which　we　point；　and　of　which　the　present　work　of　Mr。
Darwin　is　but　the　preliminary　outline；　may　be　stated　in　his　own
language　as　follows：〃Species　originated　by　means　of　natural
selection；　or　through　the　preservation　of　the　favoured　races　in　the
struggle　for　life。〃　　To　render　this　thesis　intelligible；　it　is
necessary　to　interpret　its　terms。　　In　the　first　place；　what　is　a
species？　　The　question　is　a　simple　one；　but　the　right　answer　to　it　is
hard　to　find；　even　if　we　appeal　to　those　who　should　know　most　about
it。　　It　is　all　those　animals　or　plants　which　have　descended　from　a
single　pair　of　parents；　it　is　the　smallest　distinctly　definable　group
of　living　organisms；　it　is　an　eternal　and　immutable　entity；　it　is　a　mere
abstraction　of　the　human　intellect　having　no　existence　in　nature。　　Such
are　a　few　of　the　significations　attached　to　this　simple　word　which　may
be　culled　from　authoritative　sources；　and　if；　leaving　terms　and
theoretical　subtleties　aside；　we　turn　to　facts　and　endeavour　to　gather　a
meaning　for　ourselves；　by　studying　the　things　to　which；　in　practice；
the　name　of　species　is　applied；　it　profits　us　little。　For　practice
varies　as　much　as　theory。　　Let　the　botanist　or　the　zoologist　examine　and
describe　the　productions　of　a　country；　and　one　will　pretty　certainly
disagree　with　the　other　as　to　the　number；　limits；　and　definitions　of
the　species　into　which　he　groups　the　very　same　things。　　In　these
islands；　we　are　in　the　habit　of　regarding　mankind　as　of　one　species；　but
a　fortnight's　steam　will　land　us　in　a　country　where　divines　and
savants；　for　once　in　agreement；　vie　with　one　another　in　loudness　of
assertion；　if　not　in　cogency　of　proof；　that　men　are　of　different
species；　and；　more　particularly；　that　the　species　negro　is　so　distinct
from　our　own　that　the　Ten　Commandments　have　actually　no　reference　to
him。　　Even　in　the　calm　region　of　entomology；　where；　if　anywhere　in　this
sinful　world；　passion　and　prejudice　should　fail　to　stir　the　mind；　one
learned　coleopterist　will　fill　ten　attractive　volumes　with　descriptions
of　species　of　beetles；　nine…tenths　of　which　are　immediately　declared　by
his　brother　beetle…mongers　to　be　no　species　at　all。

The　truth　is　that　the　number　of　distinguishable　living　creatures　almost
surpasses　imagination。　At　least　a　hundred　thousand　such　kinds　of
insects　alone　have　been　described　and　may　be　identified　in　collections；
and　the　number　of　separable　kinds　of　living　things　is　under　estimated
at　half　a　million。　　Seeing　that　most　of　these　obvious　kinds　have　their
accidental　varieties；　and　that　they　often　shade　into　others　by
imperceptible　degrees；　it　may　well　be　imagined　that　the　task　of
distinguishing　between　what　is　permanent　and　what　fleeting；　what　is　a
species　and　what　a　mere　variety；　is　sufficiently　formidable。

But　is　it　not　possible　to　apply　a　test　whereby　a　true　species　may　be
known　from　a　mere　variety？　　Is　there　no　criterion　of　species？　　Great
authorities　affirm　that　there　isthat　the　unions　of　members　of　the
same　species　are　always　fertile；　while　those　of　distinct　species　are
either　sterile；　or　their　offspring；　called　hybrids；　are　so。　　It　is
affirmed　not　only　that　this　is　an　experimental　fact；　but　that　it　is　a
provision　for　the　preservation　of　the　purity　of　species。　　Such　a
criterion　as　this　would　be　invaluable；　but；　unfortunately；　not　only　is
it　not　obvious　how　to　apply　it　in　the　great　majority　of　cases　in　which
its　aid　is　needed；　but　its　general　validity　is　stoutly　denied。　　The
Hon。　and　Rev。　Mr。　Herbert；　a　most　trustworthy　authority；　not　only
asserts　as　the　result　of　his　own　observations　and　experiments　that　many
hybrids　are　quite　as　fertile　as　the　parent　species；　but　he　goes　so　far
as　to　assert　that　the　particular　plant　'Crinum　capense'　is　much　more
fertile　when　crossed　by　a　distinct　species　than　when　fertilised　by　its
proper　pollen！　On　the　other　hand；　the　famous　Gaertner；　though　he　took
the　greatest　pains　to　cross　the　primrose　and　the　cowslip；　succeeded
only　once　or　twice　in　several　years；　and　yet　it　is　a　well…established
fact　that　the　primrose　and　the　cowslip　are　only　varieties　of　the　same
kind　of　plant。　　Again；　such　cases　as　the　following　are　well
established。　　The　female　of　species　A；　if　crossed　with　the　male　of
species　B；　is　fertile；　but；　if　the　female　of　B　is　crossed　with　the　male
of　A；　she　remains　barren。　　Facts　of　this　kind　destroy　the　value　of　the
supposed　criterion。

If；　weary　of　the　endless　difficulties　involved　in　the　determination　of
species；　the　investigator；　contenting　himself　with　the　rough　practical
distinction　of　separable　kinds；　endeavours　to　study　them　as　they　occur
in　natureto　ascertain　their　relations　to　the　conditions　which
surround　them；　their　mutual　harmonies　and　discordances　of　structure；
the　bond　of　union　of　their　parts　and　their　past　history；　he　finds
himself；　according　to　the　received　notions；　in　a　mighty　maze；　and　with；

at　most；　the　dimmest　adumbration　of　a　plan。　　If　he　starts　with　any　one
clear　conviction；　it　is　that　every　part　of　a　living　creature　is
cunningly　adapted　to　some　special　use　in　its　life。　　Has　not　his　Paley
told　him　that　that　seemingly　useless　organ；　the　spleen；　is　beautifully
adjusted　as　so　much　packing　between　the　other　organs？　　And　yet；　at　the
outset　of　his　studies；　he　finds　that　no　adaptive　reason　whatsoever　can
be　given　for　one…half　of　the　peculiarities　of　vegetable　structure；　he
also　discovers　rudimentary　teeth；　which　are　never　used；　in　the　gums　of
the　young　calf　and　in　those　of　the　foetal　whale；　insects　which　never
bite　have　rudimental　jaws；　and　others　which　never　fly　have　rudimental
wings；　naturally　blind　creatures　have　rudimental　eyes；　and　the　halt
have　rudimentary　limbs。　　So；　again；　no　animal　or　plant　puts　on　its
perfect　form　at　once；　but　all　have　to　start　from　the　same　point；
however　various　the　course　which　each　has　to　pursue。　　Not　only　men　and
horses；　and　cats　and　dogs；　lobsters　and　beetles；　periwinkles　and
mussels；　but　even　the　very　sponges　and　animalcules　commence　their
existence　under　forms　which　are　essentially　undistinguishable；　and　this
is　true　of　all　the　infinite　variety　of　plants。　　Nay；　more；　all　living
beings　march　side　by　side　along　the　high　road　of　development；　and
separate　the　later　the　more　like　they　are；　like　people　leaving　church；
who　all　go　down　the　aisle；　but　having　reached　the　door　some　turn　into
the　parsonage；　others　go　down　the　village；　and　others　part　only　in　the
next　parish。　　A　man　in　his　development　runs　for　a　little　while　parallel
with；　though　never　passing　through；　the　form　of　the　meanest　worm；　then
travels　for　a　space　beside　the　fish；　then　journeys　along　with　the　bird
and　the　reptile　for　his　fellow　travellers；　and　only　at　last；　after　a
brief　companionship　with　the　highest　of　the　four…footed　and　four…handed
world；　rises　into　the　dignity　of　pure　manhood。　　No　competent　thinker　of
the　present　day　dreams　of　explaining　these　indubitable　facts　by　the
notion　of　the　existence　of　unknown　and　undiscoverable　adaptations　to
purpose。　　And　we　would　remind　those　who；　ignorant　of　the　facts；　must　be
moved　by　authority；　that　no　one　has　asserted　the　incompetence　of　the
doctrine　of　final　causes；　in　its　application　to　physiology　and　anatomy；
more　strongly　than　our　own　eminent　anatomist；　Professor　Owen；　who；
speaking　of　such　cases；　says　（'On　the　Nature　of　Limbs'；　pp。　39；　40）：　〃I
think　it　will　be　obvious　that　the　principle　of　final　adaptations　fails
to　satisfy　all　the　conditions　of　the　problem。〃

But；　if　the　doctrine　of　final　causes　will　not　help　us　to　comprehend　the
anomalies　of　living　structure；　the　principle　of　adaptation　must　surely
lead　us　to　understand　why　certain　living　beings　are　found　in　certain
regions　of　the　world　and　not　in　others。　　The　palm；　as　we　know；　will　not
grow　in　our　climate；　nor　the　oak　in　Greenland。　　The　white　bear　cannot
live　where　the　tiger　thrives；　nor　'vice　versa'；　and　the　more　the
natural　habits　of　animal　and　vegetable　species　are　examined；　the　more
do　they　seem；　on　the　whole；　limited　to　particular　provinces。　　But　when
we　look　into　the　facts　established　by　the　study　of　the　geographical
distribution　of　animals　and　plants　it　seems　utterly　hopeless　to　attempt
to　understand　the　strange　and　apparently　capricious　relations　which
they　exhibit。　　One　would　be　inclined　to　suppose　'a　priori'　that　every
country　must　be　naturally　peopled　by　those　animals　that　are　fittest　to
live　and　thrive　in　it。　　And　yet　how；　on　this　hypothesis；　are　we　to
account　for　the　absence　of　cattle　in　the　Pampas　of　South　America；　when
those　parts　of　the　New　World　were　discovered？　　It　is　not　that　they　were
unfit　for　cattle；　for　millions　of　cattle　now　run　wild　there；　and　the
like　holds　good　of　Australia　and　New　Zealand。　　It　is　a　curious
circumstance；　in　fact；　that　the　animals　and　plants　of　the　Northern
Hemisphere　are　not　only　as　well　adapted　to　live　in　the　Southern
Hemisphere　as　its　own　autochthones；　but　are　in