essays on life, art and science-第26章

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companions；　and　on　the　first　scarcity　of　food　were　thus　enabled　to
outlive　them。〃　｛23｝

〃Which　occurred〃　is　evidently　〃which　happened　to　occur〃　by　some
chance　or　accident　unconnected　with　use　and　disuse。　　The　word
〃accident〃　is　never　used；　but　Mr。　Wallace　must　be　credited　with　this
instance　of　a　desire　to　give　his　readers　a　chance　of　perceiving　that
according　to　his　distinctive　feature　evolution　is　an　affair　of　luck；
rather　than　of　cunning。　　Whether　his　readers　actually　did　understand
this　as　clearly　as　Mr。　Wallace　doubtless　desired　that　they　should；
and　whether　greater　development　at　this　point　would　not　have　helped
them　to　fuller　apprehension；　we　need　not　now　inquire。　　What　was
gained　in　distinctness　might　have　been　lost　in　distinctiveness；　and
after　all　he　did　technically　put　us　upon　our　guard。

Nevertheless　he　too　at　a　pinch　takes　refuge　in　Lamarckism。　　In
relation　to　the　manner　in　which　the　eyes　of　soles；　turbots；　and
other　flat…fish　travel　round　the　head　so　as　to　become　in　the　end
unsymmetrically　placed；　he　says：…

〃The　eyes　of　these　fish　are　curiously　distorted　in　order　that　both
eyes　may　be　upon　the　upper　side；　where　alone　they　would　be　of　any
use。　。　。　。　Now　if　we　suppose　this　process；　which　in　the　young　is
completed　in　a　few　days　or　weeks；　to　have　been　spread　over　thousands
of　generations　during　the　development　of　these　fish；　those　usually
surviving　WHOSE　EYES　RETAINED　MORE　AND　MORE　OF　THE　POSITION　INTO
WHICH　THE　YOUNG　FISH　TRIED　TO　TWIST　THEM　＇italics　mine＇；　the　change
becomes　intelligible。〃　｛24｝　　When　it　was　said　by　Professor　Ray
Lankesterwho　knows　as　well　as　most　people　what　Lamarck　taught
that　this　was　〃flat　Lamarckism；〃　Mr。　Wallace　rejoined　that　it　was
the　survival　of　the　modified　individuals　that　did　it　all；　not　the
efforts　of　the　young　fish　to　twist　their　eyes；　and　the　transmission
to　descendants　of　the　effects　of　those　efforts。　　But　this；　as　I　said
in　my　book；　〃Evolution；　Old　and　New；〃　｛25｝　is　like　saying　that
horses　are　swift　runners；　not　by　reason　of　the　causes；　whatever　they
were；　that　occasioned　the　direct　line　of　their　progenitors　to　vary
towards　ever　greater　and　greater　swiftness；　but　because　their　more
slow…going　uncles　and　aunts　go　away。　　Plain　people　will　prefer　to
say　that　the　main　cause　of　any　accumulation　of　favourable
modifications　consists　rather　in　that　which　brings　about　the　initial
variations；　and　in　the　fact　that　these　can　be　inherited　at　all；　than
in　the　fact　that　the　unmodified　individuals　were　not　successful。
People　do　not　become　rich　because　the　poor　in　large　numbers　go　away；
but　because　they　have　been　lucky；　or　provident；　or　more　commonly
both。　　If　they　would　keep　their　wealth　when　they　have　made　it　they
must　exclude　luck　thenceforth　to　the　utmost　of　their　power；　and
their　children　must　follow　their　example；　or　they　will　soon　lose
their　money。　　The　fact　that　the　weaker　go　to　the　wall　does　not　bring
about　the　greater　strength　of　the　stronger；　it　is　the　consequence　of
this　last　and　not　the　causeunless；　indeed；　it　be　contended　that　a
knowledge　that　the　weak　go　to　the　wall　stimulates　the　strong　to
exertions　which　they　would　not　otherwise　so　make；　and　that　these
exertions　produce　inheritable　modifications。　　Even　in　this　case；
however；　it　would　be　the　exertions；　or　use　and　disuse；　that　would　be
the　main　agents　in　the　modification。　　But　it　is　not　often　that　Mr。
Wallace　thus　backslides。　　His　present　position　is　that　acquired　（as
distinguished　from　congenital）　modifications　are　not　inherited　at
all。　　He　does　not　indeed　put　his　faith　prominently　forward　and　pin
himself　to　it　as　plainly　as　could　be　wished；　but　under　the　heading；
〃The　Non…Heredity　of　Acquired　Characters；〃　he　writes　as　follows　on
p。　440　of　his　recent　work　in　reference　to　Professor　Weismann's
Theory　of　Heredity：…

〃Certain　observations　on　the　embryology　of　the　lower　animals　are
held　to　afford　direct　proof　of　this　theory　of　heredity；　but　they　are
too　technical　to　be　made　clear　to　ordinary　readers。　　A　logical
result　of　the　theory　is　the　impossibility　of　the　transmission　of
acquired　characters；　since　the　molecular　structure　of　the　germ…plasm
is　already　determined　within　the　embryo；　and　Weismann　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。

〃We　have　already　seen　in　the　earlier　part　of　this　chapter　that　many
instances　of　change；　imputed　to　the　inheritance　of　acquired
variations；　are　really　cases　of　selection。〃

And　the　rest　of　the　remarks　tend　to　convey　the　impression　that　Mr。
Wallace　adopts　Professor　Weismann's　view；　but；　curiously　enough；
though　I　have　gone　through　Mr。　Wallace's　book　with　a　special　view　to
this　particular　point；　I　have　not　been　able　to　find　him　definitely
committing　himself　either　to　the　assertion　that　acquired
modifications　never　are　inherited；　or　that　they　sometimes　are　so。
It　is　abundantly　laid　down　that　Mr。　Darwin　laid　too　much　stress　on
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　selecti