essays on life, art and science-第33节

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way；　our　opponents　would　not　be　long　in　letting　us　know　that
absolute　proof　is　unattainable　on　any　subject；　that　reasonable
presumption　is　our　highest　certainty；　and　that　crying　out　for　too
much　evidence　is　as　bad　as　accepting　too　little。　　Truth　is　like　a
photographic　sensitised　plate；　which　is　equally　ruined　by　over　and
by　under　exposure；　and　the　just　exposure　for　which　can　never　be
absolutely　determined。

Surely　if　disuse　can　be　credited　with　the　vast　powers　involved　in
Mr。　Darwin's　statement　that　it　has　probably　〃been　the　main　agent　in
rendering　organs　rudimentary；〃　no　limits　are　assignable　to　the
accumulated　effects　of　habit；　provided　the　effects　of　habit；　or　use
and　disuse；　are　supposed；　as　Mr。　Darwin　supposed　them；　to　be
inheritable　at　all。　　Darwinians　have　at　length　woke　up　to　the
dilemma　in　which　they　are　placed　by　the　manner　in　which　Mr。　Darwin
tried　to　sit　on　the　two　stools　of　use　and　disuse；　and　natural
selection　of　accidental　variations；　at　the　same　time。　　The　knell　of
Charles…Darwinism　is　rung　in　Mr。　Wallace's　present　book；　and　in　the
general　perception　on　the　part　of　biologists　that　we　must　either
assign　to　use　and　disuse　such　a　predominant　share　in　modification　as
to　make　it　the　feature　most　proper　to　be　insisted　on；　or　deny　that
the　modifications；　whether　of　mind　or　body；　acquired　during　a　single
lifetime；　are　ever　transmitted　at　all。　　If　they　can　be　inherited　at
all；　they　can　be　accumulated。　　If　they　can　be　accumulated　at　all；
they　can　be　so；　for　anything　that　appears　to　the　contrary；　to　the
extent　of　the　specific　and　generic　differences　with　which　we　are
surrounded。　　The　only　thing　to　do　is　to　pluck　them　out　root　and
branch：　　they　are　as　a　cancer　which；　if　the　smallest　fibre　be　left
unexcised；　will　grow　again；　and　kill　any　system　on　to　which　it　is
allowed　to　fasten。　　Mr。　Wallace；　therefore；　may　well　be　excused　if
he　casts　longing　eyes　towards　Weismannism。

And　what　was　Mr。　Darwin's　system？　　Who　can　make　head　or　tail　of　the
inextricable　muddle　in　which　he　left　it？　　The　〃Origin　of　Species〃　in
its　latest　shape　is　the　reduction　of　hedging　to　an　absurdity。　　How
did　Mr。　Darwin　himself　leave　it　in　the　last　chapter　of　the　last
edition　of　the　〃Origin　of　Species〃？　　He　wrote：…

〃I　have　now　recapitulated　the　facts　and　considerations　which　have
thoroughly　convinced　me　that　species　have　been　modified　during　a
long　course　of　descent。　　This　has　been　effected　chiefly　through　the
natural　selection　of　numerous；　successive；　slight；　favourable
variations；　aided　in　an　important　manner　by　the　inherited　effects　of
the　use　and　disuse　of　parts；　and　in　an　unimportant　mannerthat　is；
in　relation　to　adaptive　structures　whether　past　or　presentby　the
direct　action　of　external　conditions；　and　by　variations　which　seem
to　us　in　our　ignorance　to　arise　spontaneously。　　It　appears　that　I
formerly　underrated　the　frequency　and　value　of　these　latter　forms　of
variation；　as　leading　to　permanent　modifications　of　structure
independently　of　natural　selection。〃

The　〃numerous；　successive；　slight；　favourable　variations〃　above
referred　to　are　intended　to　be　fortuitous；　accidental；　spontaneous。
It　is　the　essence　of　Mr。　Darwin's　theory　that　this　should　be　so。
Mr。　Darwin's　solemn　statement；　therefore；　of　his　theory；　after　he
had　done　his　best　or　his　worst　with　it；　is；　when　stripped　of
surplusage；　as　follows：…

〃The　modification　of　species　has　been　mainly　effected　by
accumulation　of　spontaneous　variations；　it　has　been　aided　in　an
important　manner　by　accumulation　of　variations　due　to　use　and
disuse；　and　in　an　unimportant　manner　by　spontaneous　variations；　I　do
not　even　now　think　that　spontaneous　variations　have　been　very
important；　but　I　used　once　to　think　them　less　important　than　I　do
now。〃

It　is　a　discouraging　symptom　of　the　age　that　such　a　system　should
have　been　so　long　belauded；　and　it　is　a　sign　of　returning
intelligence　that　even　he　who　has　been　more　especially　the　alter　ego
of　Mr。　Darwin　should　have　felt　constrained　to　close　the　chapter　of
Charles…Darwinism　as　a　living　theory；　and　relegate　it　to　the
important　but　not　very　creditable　place　in　history　which　it　must
henceforth　occupy。　　It　is　astonishing；　however；　that　Mr。　Wallace
should　have　quoted　the　extract　from　the　〃Origin　of　Species〃　just
given；　as　he　has　done　on　p。　412　of　his　〃Darwinism；〃　without
betraying　any　sign　that　he　has　caught　its　driftlessnessfor　drift；
other　than　a　desire　to　hedge；　it　assuredly　has　not　got。　　The　battle
now　turns　on　the　question　whether　modifications　of　either　structure
or　instinct　due　to　use　or　disuse　are　ever　inherited；　or　whether　they
are　not。　　Can　the　effects　of　habit　be　transmitted　to　progeny　at　all？
We　know　that　more　usually　they　are　not　transmitted　to　any
perceptible　extent；　but　we　believe　also　that　occasionally；　and
indeed　not　infrequently；　they　are　inherited　and　even　intensified。
What　are　our　grounds　for　this　opinion？　　It　will　be　my　object　to　put
these　forward　in　the　following　number　of　the　Universal　Review。



THE　DEADLOCK　IN　DARWINISMPART　II　｛29｝



At　the　close　of　my　article　in　last　month's　number　of　the　Universal
Review；　I　said　I　would　in　this　month's　issue　show　why　the　opponents
of　Charles…Darwinism　believe　the　effects　of　habits　acquired　during
the　lifetime　of　a　parent　to　produce　an　effect　on　their　subsequent
offspring；　in　spite　of　the　fact　that　we　can　rarely　find　the　effect
in　any　one　generation；　or　even　in　several；　sufficiently　marked　to
arrest　our　attention。

I　will　now　show　that　offspring　can　be；　and　not　very　infrequently　is；
affected　by　occurrences　that　have　produced　a　deep　impression　on　the
parent　organismthe　effect　produced　on　the　offspring　being　such　as
leaves　no　doubt　that　it　is　to　be　connected　with　the　impression
produced　on　the　parent。　　Having　thus　established　the　general
proposition；　I　will　proceed　to　the　more　particular　onethat　habits；
involving　use　and　disuse　of　special　organs；　with　the　modifications
of　structure　thereby　engendered；　produce　also　an　effect　upon
offspring；　which；　though　seldom　perceptible　as　regards　structure　in
a　single；　or　even　in　several　generations；　is　nevertheless　capable　of
being　accumulated　in　successive　generations　till　it　amounts　to
specific　and　generic　difference。　　I　have　found　the　first　point　as
much　as　I　can　treat　within　the　limits　of　this　present　article；　and
will　avail　myself　of　the　hospitality　of　the　Universal　Review　next
month　to　deal　with　the　second。

The　proposition　which　I　have　to　defend　is　one　which　no　one　till
recently　would　have　questioned；　and　even　now；　those　who　look　most
askance　at　it　do　not　venture　to　dispute　it　unreservedly；　they　every
now　and　then　admit　it　as　conceivable；　and　even　in　some　cases
probable；　nevertheless　they　seek　to　minimise　it；　and　to　make　out
that　there　is　little　or　no　connection　between　the　great　mass　of　the
cells　of　which　the　body　is　composed；　and　those　cells　that　are　alone
capable　of　reproducing　the　entire　organism。　　The　tendency　is　to
assign　to　these　last　a　life　of　their　own；　apart　from；　and
unconnected　with　that　of　the　other　cells　of　the　body；　and　to　cheapen
all　evidence　that　tends　to　prove　any　response　on　their　part　to　the
past　history　of　the　individual；　and　hence　ultimately　of　the　race。

Professor　Weismann　is　the　foremost　exponent　of　those　who　take　this
line。　　He　has　naturally　been　welcomed　by　English　Charles…Darwinians；
for　if　his　view　can　be　sustained；　then　it　can　be　contended　that　use
and　disuse　produce　no　transmissible　effect；　and　the　ground　is　cut
from　under　Lamarck's　feet；　if；　on　the　other　hand；　his　view　is
unfounded；　the　Lamarckian　reaction；　already　strong；　will　gain　still
further　strength。　　The　issue；　therefore；　is　important；　and　is　being
fiercely　contested　by　those　who　have　invested　their　all　of
reputation　for　discernment　in　Charles…Darwinian　securities。

Professor　Weismann's　theory　is；　that　at　every　new　birth　a　part　of
the　substance　which　proceeds　from　parents　and　which　goes　to　form　the
new　embryo　is　not　used　up　in　forming　the　new　animal；　but　remains
apart　to　generate　the　germ…cellsor　perhaps　I　should　say　〃germ…
plasm〃which　the　new　animal　itself　will　in　due　course　issue。

Contrasting　the　generally　received　view　with　his　own；　Professor
Weismann　says　that　according　to　the　first　of　these　〃the　organism
produces　germ…cells　afresh　again　and　again；　and　that　it　produces
them　entirely　from　its　own　substance。〃　　While　by　the　second　〃the
germ…cells　are　no　longer　looked　upon　as　the　product　of　the　parent's
body；　at　least　as　far　as　their　essential　partthe　specific　germ…
plasmis　concerned；　they　are　rather　considered　as　something　which
is　to　be　placed　in　contrast　with　the　tout　ensemble　of　the　cells
which　make　up　the　parent's　body；　and　the　germ…cells　of　succeeding
generations　stand　in　a　similar　relation　to　one　another　as　a　series
of　generations　of　unicellular　organisms　arising　by　a　continued
process　of　cell…division。〃　｛30｝

On　another　page　he　writes：…

〃I　believe　that　heredity　depends　upon　the　fact　that　a　small　portion
of　the　effective　substance　of　the　germ；　the　germ…plasm；　remains
unchanged　during　the　development　of　the　ovum　into　an　organism；　and
that　this　part　of　the　germ…plasm　serves　as　a　foundation　from　which
the　germ…cells　of　the　new　organi