the darwinian hypothesis-第4章

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If　he　wish　to　perpetuate　the　difference；　to　form　a　breed　with　the
peculiarity　in　question　strongly　marked；　he　selects　such　male　and
female　individuals　as　exhibit　the　desired　character；　and　breeds　from
them。　　Their　offspring　are　then　carefully　examined；　and　those　which
exhibit　the　peculiarity　the　most　distinctly　are　selected　for　breeding；
and　this　operation　is　repeated　until　the　desired　amount　of　divergence
from　the　primitive　stock　is　reached。　　It　is　then　found　that　by
continuing　the　process　of　selectionalways　breeding；　that　is；　from
well…marked　forms；　and　allowing　no　impure　crosses　to　interfere；a　race
may　be　formed；　the　tendency　of　which　to　reproduce　itself　is　exceedingly
strong；　nor　is　the　limit　to　the　amount　of　divergence　which　may　be　thus
produced　known；　but　one　thing　is　certain；　that；　if　certain　breeds　of
dogs；　or　of　pigeons；　or　of　horses；　were　known　only　in　a　fossil　state；
no　naturalist　would　hesitate　in　regarding　them　as　distinct　species。

But；　in　all　these　cases　we　have　'human　interference'。　　Without　the
breeder　there　would　be　no　selection；　and　without　the　selection　no
race。　　Before　admitting　the　possibility　of　natural　species　having
originated　in　any　similar　way；　it　must　be　proved　that　there　is　in　nature
some　power　which　takes　the　place　of　man；　and　performs　a　selection　'sua
sponte'。　　It　is　the　claim　of　Mr。　　Darwin　that　he　professes　to　have
discovered　the　existence　and　the　'modus　operandi'　of　this　natural
selection；　as　he　terms　it；　and；　if　he　be　right；　the　process　is　perfectly
simple　and　comprehensible；　and　irresistibly　deducible　from　very
familiar　but　well　nigh　forgotten　facts。

Who；　for　instance；　has　duly　reflected　upon　all　the　consequences　of　the
marvellous　struggle　for　existence　which　is　daily　and　hourly　going　on
among　living　beings？　　Not　only　does　every　animal　live　at　the　expense　of
some　other　animal　or　plant；　but　the　very　plants　are　at　war。　　The　ground
is　full　of　seeds　that　cannot　rise　into　seedlings；　the　seedlings　rob　one
another　of　air；　light　and　water；　the　strongest　robber　winning　the　day；
and　extinguishing　his　competitors。　　Year　after　year；　the　wild　animals
with　which　man　never　interferes　are；　on　the　average；　neither　more　nor
less　numerous　than　they　were；　and　yet　we　know　that　the　annual　produce　of
every　pair　is　from　one　to　perhaps　a　million　young；so　that　it　is
mathematically　certain　that；　on　the　average；　as　many　are　killed　by
natural　causes　as　are　born　every　year；　and　those　only　escape　which
happen　to　be　a　little　better　fitted　to　resist　destruction　than　those
which　die。　　The　individuals　of　a　species　are　like　the　crew　of　a
foundered　ship；　and　none　but　good　swimmers　have　a　chance　of　reaching
the　land。

Such　being　unquestionably　the　necessary　conditions　under　which　living
creatures　exist；　Mr。　　Darwin　discovers　in　them　the　instrument　of
natural　selection。　　Suppose　that　in　the　midst　of　this　incessant
competition　some　individuals　of　a　species　（A）　present　accidental
variations　which　happen　to　fit　them　a　little　better　than　their　fellows
for　the　struggle　in　which　they　are　engaged；　then　the　chances　are　in
favour；　not　only　of　these　individuals　being　better　nourished　than　the
others；　but　of　their　predominating　over　their　fellows　in　other　ways；　and
of　having　a　better　chance　of　leaving　offspring；　which　will　of　course
tend　to　reproduce　the　peculiarities　of　their　parents。　　Their　offspring
will；　by　a　parity　of　reasoning；　tend　to　predominate　over　their
contemporaries；　and　there　being　（suppose）　no　room　for　more　than　one
species　such　as　A；　the　weaker　variety　will　eventually　be　destroyed　by
the　new　destructive　influence　which　is　thrown　into　the　scale；　and　the
stronger　will　take　its　place。　　Surrounding　conditions　remaining
unchanged；　the　new　variety　（which　we　may　call　B）supposed；　for
argument's　sake；　to　be　the　best　adapted　for　these　conditions　which　can
be　got　out　of　the　original　stockwill　remain　unchanged；　all　accidental
deviations　from　the　type　becoming　at　once　extinguished；　as　less　fit　for
their　post　than　B　itself。　　The　tendency　of　B　to　persist　will　grow　with
its　persistence　through　successive　generations；　and　it　will　acquire　all
the　characters　of　a　new　species。

But；　on　the　other　hand；　if　the　conditions　of　life　change　in　any　degree；
however　slight；　B　may　no　longer　be　that　form　which　is　best　adapted　to
withstand　their　destructive；　and　profit　by　their　sustaining；　influence；
in　which　case　if　it　should　give　rise　to　a　more　competent　variety　（C）；
this　will　take　its　place　and　become　a　new　species；　and　thus；　by
'natural　selection'；　the　species　B　and　C　will　be　successively　derived
from　A。

That　this　most　ingenious　hypothesis　enables　us　to　give　a　reason　for　many
apparent　anomalies　in　the　distribution　of　living　beings　in　time　and
space；　and　that　it　is　not　contradicted　by　the　main　phenomena　of　life
and　organization　appear　to　us　to　be　unquestionable；　and　so　far　it　must
be　admitted　to　have　an　immense　advantage　over　any　of　its　predecessors。
But　it　is　quite　another　matter　to　affirm　absolutely　either　the　truth　or
falsehood　of　Mr。　Darwin's　views　at　the　present　stage　of　the　inquiry。
Goethe　has　an　excellent　aphorism　defining　that　state　of　mind　which　he
calls　'Thatige　Skepsis'aactive　doubt。　　It　is　doubt　which　so　loves
truth　that　it　neither　dares　rest　in　doubting；　nor　extinguish　itself　by
unjustified　belief；　and　we　commend　this　state　of　mind　to　students　of
species；　with　respect　to　Mr。　Darwin's　or　any　other　hypothesis；　as　to
their　origin。　The　combined　investigations　of　another　20　years　may；
perhaps；　enable　naturalists　to　say　whether　the　modifying　causes　and　the
selective　power；　which　Mr。　Darwin　has　satisfactorily　shown　to　exist　in
nature；　are　competent　to　produce　all　the　effects　he　ascribes　to　them；
or　whether；　on　the　other　hand；　he　has　been　led　to　over…estimate　the
value　of　his　principle　of　natural　selection；　as　greatly　as　Lamarck
overestimated　his　vera　causa　of　modification　by　exercise。

But　there　is；　at　all　events；　one　advantage　possessed　by　the　more　recent
writer　over　his　predecessor。　　Mr。　Darwin　abhors　mere　speculation　as
nature　abhors　a　vacuum。　　He　is　as　greedy　of　cases　and　precedents　as　any
constitutional　lawyer；　and　all　the　principles　he　lays　down　are　capable
of　being　brought　to　the　test　of　observation　and　experiment。　　The　path
he　bids　us　follow　professes　to　be；　not　a　mere　airy　track；　fabricated　of
ideal　cobwebs；　but　a　solid　and　broad　bridge　of　facts。　　If　it　be　so；　it
will　carry　us　safely　over　many　a　chasm　in　our　knowledge；　and　lead　us　to
a　region　free　from　the　snares　of　those　fascinating　but　barren　Virgins；
the　Final　Causes；　against　whom　a　high　authority　has　so　justly　warned　us。
〃My　sons；　dig　in　the　vineyard；〃　were　the　last　words　of　the　old　man　in
the　fable；　and；　though　the　sons　found　no　treasure；　they　made　their
fortunes　by　the　grapes。







End