essays on life, art and science-第36节

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has　shown　reason　for　rejecting　Mr。　Darwin's　conclusion。　　I　do　not；
however；　dwell　upon　these　facts　now　as　evidence　of　a　transmitted
change　of　bodily　form；　or　of　instinct　due　to　use　and　disuse　or
habit；　what　they　prove　is　that　the　germ…cells　within　the　parent's
body　do　not　stand　apart　from　the　other　cells　of　the　body　so
completely　as　Professor　Weismann　would　have　us　believe；　but　that；　as
Professor　Hering；　of　Prague；　has　aptly　said；　they　echo　with　more　or
less　frequency　and　force　to　the　profounder　impressions　made　upon
other　cells。

I　may　say　that　Professor　Weismann　does　not　more　cavalierly　wave
aside　the　mass　of　evidence　collected　by　Mr。　Darwin　and　a　host　of
other　writers；　to　the　effect　that　mutilations　are　sometimes
inherited；　than　does　Mr。　Wallace；　who　says　that；　〃as　regards
mutilations；　it　is　generally　admitted　that　they　are　not　inherited；
and　there　is　ample　evidence　on　this　point。〃　　It　is　indeed　generally
admitted　that　mutilations；　when　not　followed　by　disease；　are　very
rarely；　if　ever；　inherited；　and　Mr。　Wallace's　appeal　to　the　〃ample
evidence〃　which　he　alleges　to　exist　on　this　head；　is　much　as　though
he　should　say　that　there　is　ample　evidence　to　show　that　the　days　are
longer　in　summer　than　in　winter。　　〃Nevertheless；〃　he　continues；　〃a
few　cases　of　apparent　inheritance　of　mutilations　have　been　recorded；
and　these；　if　trustworthy；　are　difficulties　in　the　way　of　the
theory。〃　。　。　。　〃The　often…quoted　case　of　a　disease　induced　by
mutilation　being　inherited　（Brown…Sequard's　epileptic　guinea…pigs）
has　been　discussed　by　Professor　Weismann　and　shown　to　be　not
conclusive。　　The　mutilation　itselfa　section　of　certain　nerveswas
never　inherited；　but　the　resulting　epilepsy；　or　a　general　state　of
weakness；　deformity；　or　sores；　was　sometimes　inherited。　　It　is；
however；　possible　that　the　mere　injury　introduced　and　encouraged　the
growth　of　certain　microbes；　which；　spreading　through　the　organism；
sometimes　reached　the　germ…cells；　and　thus　transmitted　a　diseased
condition　to　the　offspring。〃　｛35｝

I　suppose　a　microbe　which　made　guinea…pigs　eat　their　toes　off　was
communicated　to　the　germ…cells　of　an　unfortunate　guinea…pig　which
had　been　already　microbed　by　it；　and　made　the　offspring　bite　its
toes　off　too。　　The　microbe　has　a　good　deal　to　answer　for。

On　the　case　of　the　deterioration　of　horses　in　the　Falkland　Islands
after　a　few　generations；　Professor　Weismann　says：…

〃In　such　a　case　we　have　only　to　assume　that　the　climate　which　is
unfavourable；　and　the　nutriment　which　is　insufficient　for　horses；
affect　not　only　the　animal　as　a　whole　but　also　its　germ…cells。　　This
would　result　in　the　diminution　in　size　of　the　germ…cells；　the
effects　upon　the　offspring　being　still　further　intensified　by　the
insufficient　nourishment　supplied　during　growth。　　But　such　results
would　not　depend　upon　the　transmission　by　the　germ…cells　of　certain
peculiarities　due　to　the　unfavourable　climate；　which　only　appear　in
the　full…grown　horse。〃

But　Professor　Weismann　does　not　like　such　cases；　and　admits　that　he
cannot　explain　the　facts　in　connection　with　the　climatic　varieties
of　certain　butterflies；　except　〃by　supposing　the　passive　acquisition
of　characters　produced　by　the　direct　influence　of　climate。〃

Nevertheless　in　his　next　paragraph　but　one　he　calls　such　cases
〃doubtful；〃　and　proposes　that　for　the　moment　they　should　be　left
aside。　　He　accordingly　leaves　them；　but　I　have　not　yet　found　what
other　moment　he　considered　auspicious　for　returning　to　them。　　He
tells　us　that　〃new　experiments　will　be　necessary；　and　that　he　has
himself　already　begun　to　undertake　them。〃　　Perhaps　he　will　give　us
the　results　of　these　experiments　in　some　future　bookfor　that　they
will　prove　satisfactory　to　him　can　hardly；　I　think；　be　doubted。　　He
writes：…

〃Leaving　on　one　side；　for　the　moment；　these　doubtful　and
insufficiently　investigated　cases；　we　may　still　maintain　that　the
assumption　that　changes　induced　by　external　conditions　in　the
organism　as　a　whole　are　communicated　to　the　germ…cells　after　the
manner　indicated　in　Darwin's　hypothesis　of　pangenesis；　is　wholly
unnecessary　for　the　explanation　of　these　phenomena。　　Still　we　cannot
exclude　the　possibility　of　such　a　transmission　occasionally
occurring；　for　even　if　the　greater　part　of　the　effects　must　be
attributable　to　natural　selection；　there　might　be　a　smaller　part　in
certain　cases　which　depends　on　this　exceptional　factor。〃

I　repeatedly　tried　to　understand　Mr。　Darwin's　theory　of　pangenesis；
and　so　often　failed　that　I　long　since　gave　the　matter　up　in　despair。
I　did　so　with　the　less　unwillingness　because　I　saw　that　no　one　else
appeared　to　understand　the　theory；　and　that　even　Mr。　Darwin's
warmest　adherents　regarded　it　with　disfavour。　　If　Mr。　Darwin　means
that　every　cell　of　the　body　throws　off　minute　particles　that　find
their　way　to　the　germ…cells；　and　hence　into　the　new　embryo；　this　is
indeed　difficult　of　comprehension　and　belief。　　If　he　means　that　the
rhythms　or　vibrations　that　go　on　ceaselessly　in　every　cell　of　the
body　communicate　themselves　with　greater　or　less　accuracy　or
perturbation；　as　the　case　may　be；　to　the　cells　that　go　to　form
offspring；　and　that　since　the　characteristics　of　matter　are
determined　by　vibrations；　in　communicating　vibrations　they　in　effect
communicate　matter；　according　to　the　view　put　forward　in　the　last
chapter　of　my　book　〃Luck　or　Cunning；〃　｛36｝　then　we　can　better
understand　it。　　I　have　nothing；　however；　to　do　with　Mr。　Darwin's
theory　of　pangenesis　beyond　avoiding　the　pretence　that　I　understand
either　the　theory　itself　or　what　Professor　Weismann　says　about　it；
all　I　am　concerned　with　is　Professor　Weismann's　admission；　made
immediately　afterwards；　that　the　somatic　cells　may；　and　perhaps
sometimes　do；　impart　characteristics　to　the　germ…cells。

〃A　complete　and　satisfactory　refutation　of　such　an　opinion；〃　he
continues；　〃cannot　be　brought　forward　at　present〃；　so　I　suppose　we
must　wait　a　little　longer；　but　in　the　meantime　we　may　again　remark
that；　if　we　admit　even　occasional　communication　of　changes　in　the
somatic　cells　to　the　germ…cells；　we　have　let　in　the　thin　end　of　the
wedge；　as　Mr。　Darwin　did　when　he　said　that　use　and　disuse　did　a　good
deal　towards　modification。　　Buffon；　in　his　first　volume　on　the　lower
animals；　｛37｝　dwells　on　the　impossibility　of　stopping　the　breach
once　made　by　admission　of　variation　at　all。　　〃If　the　point；〃　he
writes；　〃were　once　gained；　that　among　animals　and　vegetables　there
had　been；　I　do　not　say　several　species；　but　even　a　single　one；　which
had　been　produced　in　the　course　of　direct　descent　from　another
species；　if；　for　example；　it　could　be　once　shown　that　the　ass　was
but　a　degeneration　from　the　horsethen　there　is　no　farther　limit　to
be　set　to　the　power　of　Nature；　and　we　should　not　be　wrong　in
supposing　that　with　sufficient　time　she　could　have　evolved　all　other
organised　forms　from　one　primordial　type。〃　　So　with　use　and　disuse
and　transmission　of　acquired　characteristics　generallyonce　show
that　a　single　structure　or　instinct　is　due　to　habit　in　preceding
generations；　and　we　can　impose　no　limit　on　the　results　achievable　by
accumulation　in　this　respect；　nor　shall　we　be　wrong　in　conceiving　it
as　possible　that　all　specialisation；　whether　of　structure　or
instinct；　may　be　due　ultimately　to　habit。

How　far　this　can　be　shown　to　be　probable　is；　of　course；　another
matter；　but　I　am　not　immediately　concerned　with　this；　all　I　am
concerned　with　now　is　to　show　that　the　germ…cells　not　unfrequently
become　permanently　affected　by　events　that　have　made　a　profound
impression　upon　the　somatic　cells；　in　so　far　that　they　transmit　an
obvious　reminiscence　of　the　impression　to　the　embryos　which　they　go
subsequently　towards　forming。　　This　is　all　that　is　necessary　for　my
case；　and　I　do　not　find　that　Professor　Weismann；　after　all；　disputes
it。

But　here；　again；　comes　the　difficulty　of　saying　what　Professor
Weismann　does；　and　what　he　does　not；　dispute。　　One　moment　he　gives
all　that　is　wanted　for　the　Lamarckian　contention；　the　next　he　denies
common…sense　the　bare　necessaries　of　life。　　For　a　more　exhaustive
and　detailed　criticism　of　Professor　Weismann's　position；　I　would
refer　the　reader　to　an　admirably　clear　article　by　Mr。　Sidney　H。
Vines；　which　appeared　in　Nature；　October　24；　1889。　　I　can　only　say
that　while　reading　Professor　Weismann's　book；　I　feel　as　I　do　when　I
read　those　of　Mr。　Darwin；　and　of　a　good　many　other　writers　on
biology　whom　I　need　not　name。　　I　become　like　a　fly　in　a　window…pane。
I　see　the　sunshine　and　freedom　beyond；　and　buzz　up　and　down　their
pages；　ever　hopeful　to　get　through　them　to　the　fresh　air　without；
but　ever　kept　back　by　a　mysterious　something；　which　I　feel　but
cannot　either　grasp　or　see。　　It　was　not　thus　when　I　read　Buffon；
Erasmus　Darwin；　and　Lamarck；　it　is　not　thus　when　I　read　such
articles　as　Mr。　Vines's　just　referred　to。　　Love　of　self…display；　and
the　want　of　singleness　of　mind　that　it　inevitably　engendersthese；
I　suppose；　are　the　sins　that　glaze　the　casements　of　most　men's
minds；　and　from　these；　no　matter　how　hard　he　tries　to　free　himself；
nor　how　much　he　despises　them；　who　is　altogether　exempt？

Finally；　then；　when　we　consider　the　immense　mass　of　evidence
referred　to　bri