essays on life, art and science-第29部分

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tells　us；　on　the　first　page　of　his　preface；　that　he　has　no　intention
of　dealing　even　in　outline　with　the　vast　subject　of　evolution　in
general；　and　has　only　tried　to　give　such　an　account　of　the　theory　of
natural　selection　as　may　facilitate　a　clear　conception　of　Darwin's
work。　　How　far　he　has　succeeded　is　a　point　on　which　opinion　will
probably　be　divided。　　Those　who　find　Mr。　Darwin's　works　clear　will
also　find　no　difficulty　in　understanding　Mr。　Wallace；　those；　on　the
other　hand；　who　find　Mr。　Darwin　puzzling　are　little　likely　to　be
less　puzzled　by　Mr。　Wallace。　　He　continues：…

〃The　objections　now　made　to　Darwin's　theory　apply　solely　to　the
particular　means　by　which　the　change　of　species　has　been　brought
about；　not　to　the　fact　of　that　change。〃

But　〃Darwin's　theory〃as　Mr。　Wallace　has　elsewhere　proved　that　he
understandshas　no　reference　〃to　the　fact　of　that　change〃that　is
to　say；　to　the　fact　that　species　have　been　modified　in　course　of
descent　from　other　species。　　This　is　no　more　Mr。　Darwin's　theory
than　it　is　the　reader's　or　my　own。　　Darwin's　theory　is　concerned
only　with　〃the　particular　means　by　which　the　change　of　species　has
been　brought　about〃；　his　contention　being　that　this　is　mainly　due　to
the　natural　survival　of　those　individuals　that　have　happened　by　some
accident　to　be　born　most　favourably　adapted　to　their　surroundings；
or；　in　other　words；　through　accumulation　in　the　common　course　of
nature　of　the　more　lucky　variations　that　chance　occasionally
purveys。　　Mr。　Wallace's　words；　then；　in　reality　amount　to　this；　that
the　objections　now　made　to　Darwin's　theory　apply　solely　to　Darwin's
theory；　which　is　all　very　well　as　far　as　it　goes；　but　might　have
been　more　easily　apprehended　if　he　had　simply　said；　〃There　are
several　objections　now　made　to　Mr。　Darwin's　theory。〃

It　must　be　remembered　that　the　passage　quoted　above　occurs　on　the
first　page　of　a　preface　dated　March　1889；　when　the　writer　had
completed　his　task；　and　was　most　fully　conversant　with　his　subject。
Nevertheless；　it　seems　indisputable　either　that　he　is　still
confusing　evolution　with　Mr。　Darwin's　theory；　or　that　he　does　not
know　when　his　sentences　have　point　and　when　they　have　none。

I　should　perhaps　explain　to　some　readers　that　Mr。　Darwin　did　not
modify　the　main　theory　put　forward；　first　by　Buffon；　to　whom　it
indisputably　belongs；　and　adopted　from　him　by　Erasmus　Darwin；
Lamarck；　and　many　other　writers　in　the　latter　half　of　the　last
century　and　the　earlier　years　of　the　present。　　The　early
evolutionists　maintained　that　all　existing　forms　of　animal　and
vegetable　life；　including　man；　were　derived　in　course　of　descent
with　modification　from　forms　resembling　the　lowest　now　known。

Mr。　Darwin　went　as　far　as　this；　and　farther　no　one　can　go。　　The
point　at　issue　between　him　and　his　predecessors　involves　neither　the
main　fact　of　evolution；　nor　yet　the　geometrical　ratio　of　increase；
and　the　struggle　for　existence　consequent　thereon。　　Messrs。　Darwin
and　Wallace　have　each　thrown　invaluable　light　upon　these　last　two
points；　but　Buffon；　as　early　as　1756；　had　made　them　the　keystone　of
his　system。　　〃The　movement　of　nature；〃　he　then　wrote；　〃turns　on　two
immovable　pivots：　　one；　the　illimitable　fecundity　which　she　has
given　to　all　species：　　the　other；　the　innumerable　difficulties　which
reduce　the　results　of　that　fecundity。〃　　Erasmus　Darwin　and　Lamarck
followed　in　the　same　sense。　　They　thus　admit　the　survival　of　the
fittest　as　fully　as　Mr。　Darwin　himself；　though　they　do　not　make　use
of　this　particular　expression。　　The　dispute　turns　not　upon　natural
selection；　which　is　common　to　all　writers　on　evolution；　but　upon　the
nature　and　causes　of　the　variations　that　are　supposed　to　be　selected
from　and　thus　accumulated。　　Are　these　mainly　attributable　to　the
inherited　effects　of　use　and　disuse；　supplemented　by　occasional
sports　and　happy　accidents？　　Or　are　they　mainly　due　to　sports　and
happy　accidents；　supplemented　by　occasional　inherited　effects　of　use
and　disuse？

The　Lamarckian　system　has　all　along　been　maintained　by　Mr。　Herbert
Spencer；　who；　in　his　〃Principles　of　Biology；〃　published　in　1865；
showed　how　impossible　it　was　that　accidental　variations　should
accumulate　at　all。　　I　am　not　sure　how　far　Mr。　Spencer　would　consent
to　being　called　a　Lamarckian　pure　and　simple；　nor　yet　how　far　it　is
strictly　accurate　to　call　him　one；　nevertheless；　I　can　see　no
important　difference　in　the　main　positions　taken　by　him　and　by
Lamarck。

The　question　at　issue　between　the　Lamarckians；　supported　by　Mr。
Spencer　and　a　growing　band　of　those　who　have　risen　in　rebellion
against　the　Charles…Darwinian　system　on　the　one　hand；　and　Messrs。
Darwin　and　Wallace　with　the　greater　number　of　our　more　prominent
biologists　on　the　other；　involves　the　very　existence　of　evolution　as
a　workable　theory。　　For　it　is　plain　that　what　Nature　can　be　supposed
able　to　do　by　way　of　choice　must　depend　on　the　supply　of　the
variations　from　which　she　is　supposed　to　choose。　　She　cannot　take
what　is　not　offered　to　her；　and　so　again　she　cannot　be　supposed　able
to　accumulate　unless　what　is　gained　in　one　direction　in　one
generation；　or　series　of　generations；　is　little　likely　to　be　lost　in
those　that　presently　succeed。　　Now　variations　ascribed　mainly　to　use
and　disuse　can　be　supposed　capable　of　being　accumulated；　for　use　and
disuse　are　fairly　constant　for　long　periods　among　the　individuals　of
the　same　species；　and　often　over　large　areas；　moreover；　conditions
of　existence　involving　changes　of　habit；　and　thus　of　organisation；
come　for　the　most　part　gradually；　so　that　time　is　given　during　which
the　organism　can　endeavour　to　adapt　itself　in　the　requisite
respects；　instead　of　being　shocked　out　of　existence　by　too　sudden
change。　　Variations；　on　the　other　hand；　that　are　ascribed　to　mere
chance　cannot　be　supposed　as　likely　to　be　accumulated；　for　chance　is
notoriously　inconstant；　and　would　not　purvey　the　variations　in
sufficiently　unbroken　succession；　or　in　a　sufficient　number　of
individuals；　modified　similarly　in　all　the　necessary　correlations　at
the　same　time　and　place　to　admit　of　their　being　accumulated。　　It　is
vital　therefore　to　the　theory　of　evolution；　as　was　early　pointed　out
by　the　late　Professor　Fleeming　Jenkin　and　by　Mr。　Herbert　Spencer；
that　variations　should　be　supposed　to　have　a　definite　and　persistent
principle　underlying　them；　which　shall　tend　to　engender　similar　and
simultaneous　modification；　however　small；　in　the　vast　majority　of
individuals　composing　any　species。　　The　existence　of　such　a
principle　and　its　permanence　is　the　only　thing　that　can　be　supposed
capable　of　acting　as　rudder　and　compass　to　the　accumulation　of
variations；　and　of　making　it　hold　steadily　on　one　course　for　each
species；　till　eventually　many　havens；　far　remote　from　one　another；
are　safely　reached。

It　is　obvious　that　the　having　fatally　impaired　the　theory　of　his
predecessors　could　not　warrant　Mr。　Darwin　in　claiming；　as　he　most
fatuously　did；　the　theory　of　evolution。　　That　he　is　still　generally
believed　to　have　been　the　originator　of　this　theory　is　due　to　the
fact　that　he　claimed　it；　and　that　a　powerful　literary　backing　at
once　came　forward　to　support　him。　　It　seems　at　first　sight
improbable　that　those　who　too　zealously　urged　his　claims　were
unaware　that　so　much　had　been　written　on　the　subject；　but　when　we
find　even　Mr。　Wallace　himself　as　profoundly　ignorant　on　this　subject
as　he　still　either　is；　or　affects　to　be；　there　is　no　limit
assignable　to　the　ignorance　or　affected　ignorance　of　the　kind　of
biologists　who　would　write　reviews　in　leading　journals　thirty　years
ago。　　Mr。　Wallace　writes：…

〃A　few　great　naturalists；　struck　by　the　very　slight　difference
between　many　of　these　species；　and　the　numerous　links　that　exist
between　the　most　different　forms　of　animals　and　plants；　and　also
observing　that　a　great　many　species　do　vary　considerably　in　their
forms；　colours　and　habits；　conceived　the　idea　that　they　might　be　all
produced　one　from　the　other。　　The　most　eminent　of　these　writers　was
a　great　French　naturalist；　Lamarck；　who　published　an　elaborate　work；
the　Philosophie　Zoologique；　in　which　he　endeavoured　to　prove　that
all　animals　whatever　are　descended　from　other　species　of　animals。
He　attributed　the　change　of　species　chiefly　to　the　effect　of　changes
in　the　conditions　of　lifesuch　as　climate；　food；　&c。；　and
especially　to　the　desires　and　efforts　of　the　animals　themselves　to
improve　their　condition；　leading　to　a　modification　of　form　or　size
in　certain　parts；　owing　to　the　well…known　physiological　law　that　all
organs　are　strengthened　by　constant　use；　while　they　are　weakened　or
even　completely　lost　by　disuse　。　。　。

〃The　only　other　important　work　dealing　with　the　question　was　the
celebrated　'Vestiges　of　Creation；'　published　anonymously；　but　now
acknowledged　to　have　been　written　by　the　late　Robert　Chambers。〃

None　are　so　blind　as　those　who　will　not　see；　and　it　would　be　waste
of　time　to　argue　with　the　invincible　ignorance　of　one　who　thinks
Lamarck　and　Buffon　conceived　that　all　species　were　produced　from　one
another；　more　especially　as　I　have　already　dealt　at　some　length　with
the　early　evolutionists　in　my　work；　〃Evolution；　Old　and　New；〃　first
published　ten　years　ago；