essays on life, art and science-第36章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！


use　and　disuse；　and　a　residuary　impression　is　left　that　Mr。　Wallace
is　endorsing　Professor　Weismann's　view；　but　I　have　found　it
impossible　to　collect　anything　that　enables　me　to　define　his
position　confidently　in　this　respect。

This　is　natural　enough；　for　Mr。　Wallace　has　entitled　his　book
〃Darwinism；〃　and　a　work　denying　that　use　and　disuse　produced　any
effect　could　not　conceivably　be　called　Darwinism。　　Mr。　Herbert
Spencer　has　recently　collected　many　passages　from　〃The　Origin　of
Species〃　and　from　〃Animals　and　Plants　under　Domestication；〃　｛26｝
which　show　how　largely；　after　all；　use　and　disuse　entered　into　Mr。
Darwin's　system；　and　we　know　that　in　his　later　years　he　attached
still　more　importance　to　them。　　It　was　out　of　the　question；
therefore；　that　Mr。　Wallace　should　categorically　deny　that　their
effects　were　inheritable。　　On　the　other　hand；　the　temptation　to
adopt　Professor　Weismann's　view　must　have　been　overwhelming　to　one
who　had　been　already　inclined　to　minimise　the　effects　of　use　and
disuse。　　On　the　whole；　one　does　not　see　what　Mr。　Wallace　could　do；
other　than　what　he　has　doneunless；　of　course；　he　changed　his
title；　or　had　been　no　longer　Mr。　Wallace。

Besides；　thanks　to　the　works　of　Mr。　Spencer；　Professor　Mivart；
Professor　Semper；　and　very　many　others；　there　has　for　some　time　been
a　growing　perception　that　the　Darwinism　of　Charles　Darwin　was
doomed。　　Use　and　disuse　must　either　do　even　more　than　is　officially
recognised　in　Mr。　Darwin's　later　concessions；　or　they　must　do　a
great　deal　less。　　If　they　can　do　as　much　as　Mr。　Darwin　himself　said
they　did；　why　should　they　not　do　more？　　Why　stop　where　Mr。　Darwin
did？　　And　again；　where　in　the　name　of　all　that　is　reasonable　did　he
really　stop？　　He　drew　no　line；　and　on　what　principle　can　we　say　that
so　much　is　possible　as　effect　of　use　and　disuse；　but　so　much　more
impossible？　　If；　as　Mr。　Darwin　contended；　disuse　can　so　far　reduce
an　organ　as　to　render　it　rudimentary；　and　in　many　cases　get　rid　of
it　altogether；　why　cannot　use　create　as　much　as　disuse　can　destroy；
provided　it　has　anything；　no　matter　how　low　in　structure；　to　begin
with？　　Let　us　know　where　we　stand。　　If　it　is　admitted　that　use　and
disuse　can　do　a　good　deal；　what　does　a　good　deal　mean？　　And　what　is
the　proportion　between　the　shares　attributable　to　use　and　disuse　and
to　natural　selection　respectively？　　If　we　cannot　be　told　with
absolute　precision；　let　us　at　any　rate　have　something　more　definite
than　the　statement　that　natural　selection　is　〃the　most　important
means　of　modification。〃

Mr。　Darwin　gave　us　no　help　in　this　respect；　and　worse　than　this；　he
contradicted　himself　so　flatly　as　to　show　that　he　had　very　little
definite　idea　upon　the　subject　at　all。　　Thus　in　respect　to　the
winglessness　of　the　Madeira　beetles　he　wrote：…

〃In　some　cases　we　might　easily　put　down　to　disuse　modifications　of
structure；　which　are　wholly　or　mainly　due　to　natural　selection。　　Mr。
Wollaston　has　discovered　the　remarkable　fact　that　200　beetles；　out
of　the　550　species　（but　more　are　now　known）　inhabiting　Madeira；　are
so　far　deficient　in　wings　that　they　cannot　fly；　and　that　of　the　29
endemic　genera　no　less　than　23　have　all　their　species　in　this
condition！　　Several　facts；namely；　that　beetles　in　many　parts　of
the　world　are　frequently　blown　out　to　sea　and　perish；　that　the
beetles　in　Madeira；　as　observed　by　Mr。　Wollaston；　lie　much　concealed
until　the　wind　lulls　and　the　sun　shines；　that　the　proportion　of
wingless　beetles　is　larger　on　the　exposed　Desertas　than　in　Madeira
itself；　and　especially　the　extraordinary　fact；　so　strongly　insisted
on　by　Mr。　Wollaston；　that　certain　large　groups　of　beetles；　elsewhere
excessively　numerous；　which　absolutely　require　the　use　of　their
wings　are　here　almost　entirely　absent；these　several　considerations
make　me　believe　that　the　wingless　condition　of　so　many　Madeira
beetles　is　mainly　due　to　the　action　of　natural　selection；　COMBINED
PROBABLY　WITH　DISUSE　＇italics　mine＇。　　For　during　many　successive
generations　each　individual　beetle　which　flew　least；　either　from　its
wings　having　been　ever　so　little　less　perfectly　developed　or　from
indolent　habit；　will　have　had　the　best　chance　of　surviving；　from　not
being　blown　out　to　sea；　and；　on　the　other　hand；　those　beetles　which
most　readily　took　to　flight　would　oftenest　have　been　blown　to　sea；
and　thus　destroyed。〃　｛27｝

We　should　like　to　know；　first；　somewhere　about　how　much　disuse　was
able　to　do　after　all；　and　moreover　why；　if　it　can　do　anything　at
all；　it　should　not　be　able　to　do　all。　　Mr。　Darwin　says：　　〃Any　change
in　structure　and　function　which　can　be　effected　by　small　stages　is
within　the　power　of　natural　selection。〃　　〃And　why　not；〃　we　ask；
〃within　the　power　of　use　and　disuse？〃　　Moreover；　on　a　later　page　we
find　Mr。　Darwin　saying：…

〃IT　APPEARS　PROBABLE　THAT　DISUSE　HAS　BEEN　THE　MAIN　AGENT　IN
RENDERING　ORGANS　RUDIMENTARY　＇italics　mine＇。　　It　would　at　first　lead
by　slow　steps　to　the　more　and　more　complete　reduction　of　a　part；
until　at　last　it　has　become　rudimentaryas　in　the　case　of　the　eyes
of　animals　inhabiting　dark　caverns；　and　of　the　wings　of　birds
inhabiting　oceanic　islands；　which　have　seldom　been　forced　by　beasts
of　prey　to　take　flight；　and　have　ultimately　lost　the　power　of
flying。　　Again；　an　organ；　useful　under　certain　conditions；　might
become　injurious　under　others；　AS　WITH　THE　WINGS　OF　BEETLES　LIVING
ON　SMALL　AND　EXPOSED　ISLANDS；　and　in　this　case　natural　selection
will　have　aided　in　reducing　the　organ；　until　it　was　rendered
harmless　and　rudimentary　＇italics　mine＇。〃　｛28｝

So　that　just　as　an　undefined　amount　of　use　and　disuse　was　introduced
on　the　earlier　page　to　supplement　the　effects　of　natural　selection
in　respect　of　the　wings　of　beetles　on　small　and　exposed　islands；　we
have　here　an　undefined　amount　of　natural　selection　introduced　to
supplement　the　effects　of　use　and　disuse　in　respect　of　the　identical
phenomena。　　In　the　one　passage　we　find　that　natural　selection　has
been　the　main　agent　in　reducing　the　wings；　though　use　and　disuse
have　had　an　appreciable　share　in　the　result；　in　the　other；　it　is　use
and　disuse　that　have　been　the　main　agents；　though　an　appreciable
share　in　the　result　must　be　ascribed　to　natural　selection。

Besides；　who　has　seen　the　uncles　and　aunts　going　away　with　the
uniformity　that　is　necessary　for　Mr。　Darwin's　contention？　　We　know
that　birds　and　insects　do　often　get　blown　out　to　sea　and　perish；　but
in　order　to　establish　Mr。　Darwin's　position　we　want　the　evidence　of
those　who　watched　the　reduction　of　the　wings　during　the　many
generations　in　the　course　of　which　it　was　being　effected；　and　who
can　testify　that　all；　or　the　overwhelming　majority；　of　the　beetles
born　with　fairly　well…developed　wings　got　blown　out　to　sea；　while
those　alone　survived　whose　wings　were　congenitally　degenerate。　　Who
saw　them　go；　or　can　point　to　analogous　cases　so　conclusive　as　to
compel　assent　from　any　equitable　thinker？

Darwinians　of　the　stamp　of　Mr。　Thiselton　Dyer；　Professor　Ray
Lankester；　or　Mr。　Romanes；　insist　on　their　pound　of　flesh　in　the
matter　of　irrefragable　demonstration。　　They　complain　of　us　for　not
bringing　forward　some　one　who　has　been　able　to　detect　the　movement
of　the　hour…hand　of　a　watch　during　a　second　of　time；　and　when　we
fail　to　do　so；　declare　triumphantly　that　we　have　no　evidence　that
there　is　any　connection　between　the　beating　of　a　second　and　the
movement　of　the　hour…hand。　　When　we　say　that　rain　comes　from　the
condensation　of　moisture　in　the　atmosphere；　they　demand　of　us　a
rain…drop　from　moisture　not　yet　condensed。　　If　they　stickle　for
proof　and　cavil　on　the　ninth　part　of　a　hair；　as　they　do　when　we
bring　forward　what　we　deem　excellent　instances　of　the　transmission
of　an　acquired　characteristic；　why　may　not　we；　too；　demand　at　any
rate　some　evidence　that　the　unmodified　beetles　actually　did　always；
or　nearly　always；　get　blown　out　to　sea；　during　the　reduction　above
referred　to；　and　that　it　is　to　this　fact；　and　not　to　the　masterly
inactivity　of　their　fathers　and　mothers；　that　the　Madeira　beetles
owe　their　winglessness？　　If　we　began　stickling　for　proof　in　this
way；　our　opponents　would　not　be　long　in　letting　us　know　that
absolute　proof　is　unattainable　on　any　s