essays on life, art and science-第30部分

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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　organism　are　produced。　　There　is；
therefore；　continuity　of　the　germ…plasm　from　one　generation　to
another。　　One　might　represent　the　germ…plasm　by　the　metaphor　of　a
long　creeping　root…stock　from　which　plants　arise　at　intervals；　these
latter　representing　the　individuals　of　successive　generations。〃　｛31｝

Mr。　Wallace；　who　does　not　appear　to　have　read　Professor　Weismann's
essays　themselves；　but　whose　remarks　are；　no　doubt；　ultimately
derived　from　the　sequel　to　the　passage　just　quoted　from　page　266　of
Professor　Weismann's　book；　contends　that　the　impossibility　of　the
transmission　of　acquired　characters　follows　as　a　logical　result　from
Professor　Weismann's　theory；　inasmuch　as　the　molecular　structure　of
the　germ…plasm　that　will　go　to　form　any　succeeding　generation　is
already　predetermined　within　the　still　unformed　embryo　of　its
predecessor；　〃and　Weismann；〃　continues　Mr。　Wallace；　〃holds　that
there　are　no　facts　which　really　prove　that　acquired　characters　can
be　inherited；　although　their　inheritance　has；　by　most　writers；　been
considered　so　probable　as　hardly　to　stand　in　need　of　direct　proof。〃
｛32｝

Professor　Weismann；　in　passages　too　numerous　to　quote；　shows　that　he
recognises　this　necessity；　and　acknowledges　that　the　non…
transmission　of　acquired　characters　〃forms　the　foundation　of　the
views〃　set　forth　in　his　book；　p。　291。

Professor　Ray　Lankester　does　not　commit　himself　absolutely　to　this
view；　but　lends　it　support　by　saying　（Nature；　December　12；　1889）：
〃It　is　hardly　necessary　to　say　that　it　has　never　yet　been　shown
experimentally　that　ANYTHING　acquired　by　one　generation　is
transmitted　to　the　next　（putting　aside　diseases）。〃

Mr。　Romanes；　writing　in　Nature；　March　18；　1890；　and　opposing　certain
details　of　Professor　Weismann's　theory；　so　far　supports　it　as　to　say
that　〃there　is　the　gravest　possible　doubt　lying　against　the
supposition　that　any　really　inherited　decrease　is　due　to　the
inherited　effects　of　disuse。〃　　The　〃gravest　possible　doubt〃　should
mean　that　Mr。　Romanes　regards　it　as　a　moral　certainty　that　disuse
has　no　transmitted　effect　in　reducing　an　organ；　and　it　should　follow
that　he　holds　use　to　have　no　transmitted　effect　in　its　development。
The　sequel；　however；　makes　me　uncertain　how　far　Mr。　Romanes　intends
this；　and　I　would　refer　the　reader　to　the　article　which　Mr。　Romanes
has　just　published　on　Weismann　in　the　Contemporary　Review　for　this
current　month。

The　burden　of　Mr。　Thiselton　Dyer's　controversy　with　the　Duke　of
Argyll　（see　Nature；　January　16；　1890；　et　seq。）　was　that　there　was　no
evidence　in　support　of　the　transmission　of　any　acquired
modification。　　The　orthodoxy　of　science；　therefore；　must　be　held　as
giving　at　any　rate　a　provisional　support　to　Professor　Weismann；　but
all　of　them；　including　even　Professor　Weismann　himself；　shrink　from
committing　themselves　to　the　opinion　that　the　germ…cells　of　any
organisms　remain　in　all　cases　unaffected　by　the　events　that　occur　to
the　other　cells　of　the　same　organism；　and　until　they　do　this　they
have　knocked　the　bottom　out　of　their　case。

From　among　the　passages　in