essays on life, art and science-第31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！


Lamarckism；　but　a　nickname　is　not　an　argument。〃

To　this　Professor　Ray　Lankester　rejoined　（Nature；　March　21；　1889）：…

〃It　is　not　unusual　for　children　to　rest　the　head　on　the　left　forearm
or　hand　when　writing；　and　I　doubt　whether　much　value　can　be　attached
to　the　case　described　by　Professor　Hartog。　　The　kind　of　observation
which　his　letter　suggests　is；　however；　likely　to　lead　to　results
either　for　or　against　the　transmission　of　acquired　characters。　　An
old　friend　of　mine　lost　his　right　arm　when　a　schoolboy；　and　has　ever
since　written　with　his　left。　　He　has　a　large　family　and
grandchildren；　but　I　have　not　heard　of　any　of　them　showing　a
disposition　to　left…handedness。〃

From　Nature　（March　21；　1889）　I　take　the　second　instance　communicated
by　Mr。　J。　Jenner…Weir；　who　wrote　as　follows：…

〃Mr。　Marcus　M。　Hartog's　letter　of　March　6th；　inserted　in　last　week's
number　（p。　462）；　is　a　very　valuable　contribution　to　the　growing
evidence　that　acquired　characters　may　be　inherited。　　I　have　long
held　the　view　that　such　is　often　the　case；　and　I　have　myself
observed　several　instances　of　the；　at　least　I　may　say；　apparent
fact。

〃Many　years　ago　there　was　a　very　fine　male　of　the　Capra　megaceros　in
the　gardens　of　the　Zoological　Society。　　To　restrain　this　animal　from
jumping　over　the　fence　of　the　enclosure　in　which　he　was　confined；　a
long；　and　heavy　chain　was　attached　to　the　collar　round　his　neck。　　He
was　constantly　in　the　habit　of　taking　this　chain　up　by　his　horns　and
moving　it　from　one　side　to　another　over　his　back；　in　doing　this　he
threw　his　head　very　much　back；　his　horns　being　placed　in　a　line　with
the　back。　　The　habit　had　become　quite　chronic　with　him；　and　was　very
tiresome　to　look　at。　　I　was　very　much　astonished　to　observe　that　his
offspring　inherited　the　habit；　and　although　it　was　not　necessary　to
attach　a　chain　to　their　necks；　I　have　often　seen　a　young　male
throwing　his　horns　over　his　back　and　shifting　from　side　to　side　an
imaginary　chain。　　The　action　was　exactly　the　same　as　that　of　his
ancestor。　　The　case　of　the　kid　of　this　goat　appears　to　me　to　be
parallel　to　that　of　child　and　parent　given　by　Mr。　Hartog。　　I　think
at　the　time　I　made　this　observation　I　informed　Mr。　Darwin　of　the
fact　by　letter；　and　he　did　not　accuse　me　of　'flat　Lamarckism。'〃

To　this　letter　there　was　no　rejoinder。　　It　may　be　said；　of　course；
that　the　action　of　the　offspring　in　each　of　these　cases　was　due　to
accidental　coincidence　only。　　Anything　can　be　said；　but　the　question
turns　not　on　what　an　advocate　can　say；　but　on　what　a　reasonably
intelligent　and　disinterested　jury　will　believe；　granted　they　might
be　mistaken　in　accepting　the　foregoing　stories；　but　the　world　of
science；　like　that　of　commerce；　is　based　on　the　faith　or　confidence；
which　both　creates　and　sustains　them。　　Indeed　the　universe　itself　is
but　the　creature　of　faith；　for　assuredly　we　know　of　no　other
foundation。　　There　is　nothing　so　generally　and　reasonably　accepted
not　even　our　own　continued　identitybut　questions　may　be　raised
about　it　that　will　shortly　prove　unanswerable。　　We　cannot　so　test
every　sixpence　given　us　in　change　as　to　be　sure　that　we　never　take　a
bad　one；　and　had　better　sometimes　be　cheated　than　reduce　caution　to
an　absurdity。　　Moreover；　we　have　seen　from　the　evidence　given　in　my
preceding　article　that　the　germ…cells　issuing　from　a　parent's　body
can；　and　do；　respond　to　profound　impressions　made　on　the　somatic…
cells。　　This　being　so；　what　impressions　are　more　profound；　what
needs　engage　more　assiduous　attention　than　those　connected　with
self…protection；　the　procuring　of　food；　and　the　continuation　of　the
species？　　If　the　mere　anxiety　connected　with　an　ill…healing　wound
inflicted　on　but　one　generation　is　sometimes　found　to　have　so
impressed　the　germ…cells　that　they　hand　down　its　scars　to　offspring；
how　much　more　shall　not　anxieties　that　have　directed　action　of　all
kinds　from　birth　till　death；　not　in　one　generation　only　but　in　a
longer　series　of　generations　than　the　mind　can　realise　to　itself；
modify；　and　indeed　control；　the　organisation　of　every　species？

I　see　Professor　S。　H。　Vines；　in　the　article　on　Weismann's　theory
referred　to　in　my　preceding　article；　says　Mr。　Darwin　〃held　that　it
was　not　the　sudden　variations　due　to　altered　external　conditions
which　become　permanent；　but　those　slowly　produced　by　what　he　termed
'the　accumulative　action　of　changed　conditions　of　life。'〃　　Nothing
can　be　more　soundly　Lamarckian；　and　nothing　should　more　conclusively
show　that；　whatever　else　Mr。　Darwin　was；　he　was　not　a　Charles…
Darwinian；　but　what　evidence　other　than　inferential　can　from　the
nature　of　the　case　be　adduced　in　support　of　this；　as　I　believe；
perfectly　correct　judgment？　　None　know　better　than　they　who　clamour
for　direct　evidence　that　their　master　was　right　in　taking　the
position　assigned　to　him　by　Professor　Vines；　that　they　cannot
reasonably　look　for　it。　　With　us；　as　with　themselves；　modification
proceeds　very　gradually；　and　it　violates　our　principles　as　much　as
their　own　to　expect　visible　permanent　progress；　in　any　single
generation；　or　indeed　in　any　number　of　generations　of　wild　species
which　we　have　yet　had　time　to　observe。　　Occasionally　we　can　find
such　cases；　as　in　that　of　Branchipus　stagnalis；　quoted　by　Mr。
Wallace；　or　in　that　of　the　New　Zealand　Kea　whose　skin；　I　was　assured
by　the　late　Sir　Julius　von　Haast；　has　already　been　modified　as　a
consequence　of　its　change　of　food。　　Here　we　can　show　that　in　even　a
few　generations　structure　is　modified　under　changed　conditions　of
existence；　but　as　we　believe　these　cases　to　occur　comparatively
rarely；　so　it　is　still　more　rarely　that　they　occur　when　and　where　we
can　watch　them。　　Nature　is　eminently　conservative；　and　fixity　of
type；　even　under　considerable　change　of　conditions；　is　surely　more
important　for　the　well…being　of　any　species　than　an　over…ready　power
of　adaptation　to；　it　may　be；　passing　changes。　　There　could　be　no
steady　progress　if　each　generation　were　not　mainly　bound　by　the
traditions　of　those　that　have　gone　before　it。　　It　is　evolution　and
not　incessant　revolution　that　both　parties　are　upholding；　and　this
being　so；　rapid　visible　modification　must　be　the　exception；　not　the
rule。　　I　have　quoted　direct　evidence　adduced　by　competent　observers；
which　is；　I　believe；　sufficient　to　establish　the　fact　that　offspring
can　be　and　is　sometimes　modified　by　the　acquired　habits　of　a
progenitor。　　I　will　now　proceed　to　the　still　more；　as　it　appears　to
me；　cogent　proof　afforded　by　general　considerations。

What；　let　me　ask；　are　the　principal　phenomena　of　heredity？　　There
must　be　physical　continuity　between　parent；　or　parents；　and
offspring；　so　that　the　offspring　is；　as　Erasmus　Darwin　well　said；　a
kind　of　elongation　of　the　life　of　the　parent。

Erasmus　Darwin　put　the　matter　so　well　that　I　may　as　well　give　his
words　in　full；　he　wrote：…

〃Owing　to　the　imperfection　of　language　the　offspring　is　termed　a　new
animal；　but　is　in　truth　a　branch　or　elongation　of　the　parent；　since
a　part　of　the　embryon　animal　is；　or　was；　a　part　of　the　parent；　and
therefore；　in　strict　language；　cannot　be　said　to　be　entirely　new　at
the　time　of　its　production；　and　therefore　it　may　retain　some　of　the
habits　of　the　parent　system。

〃At　the　earliest　period　of　its　existence　the　embryon　would　seem　to
consist　of　a　living　filament　with　certain　capabilities　of
irritation；　sensation；　volition；　and　association；　and　also　with　some
acquired　habits　or　propensities　peculiar　to　the　parent；　the　former
of　these　are　in　common　with　other　animals；　the　latter　seem　to
distinguish　or　produce　the　kind　of　animal；　whether　man　or　quadruped；
with　the　similarity　of　feature　or　form　to　the　parent。〃　｛39｝

Those　who　accept　evolution　insist　on　unbroken　physical　continuity
between　the　earliest　known　life　and　ourselves；　so　that　we　both　are
and　are　not　personally　identical　with　the　unicellular　organism　from
which　we　have　descended　in　the　course　of　many　millions　of　years；
exactly　in　the　same　way　as　an　octogenarian　both　is　and　is　not
personally　identical　with　the　microscopic　impregnate　ovum　from　which
he　grew　up。　　Everything　both　is　and　is　not。　　There　is　no　such　thing
as　strict　identity　between　any　two　things　in　any　two　consecutive
seconds。　　In　strictness　they　are　identical　and　yet　not　identical；　so
that　in　strictness　they　violate　a　fundamental　rule　of　strictness
namely；　that　a　thing　shall　never　be　itself　and　not　itself　at　one　and
the　same　time；　we　must　choose　between　logic　and　dealing　in　a
practical　spirit　with　time　and　space；　it　is　not　surprising；
therefore；　that　logic；　in　spite　of　the　show　of　respect　outwardly
paid　to　her；　is　told　to　stand　aside　when　people　come　to　practice。
In　practice　identity　is　generally　held　to　exist　where　continuity　is
only　broken　slowly　and　piecemeal；　nevertheless；　that　occasional
periods　of　even　rapid　change　are　not　held　to　bar　identity；　appears
from　the　fact　that　no　one　denies　this　to　hold　between　the
microscopically　small　impregnate　ovum　and　the　born　child　that
springs　from　it；　nor　yet；　therefore；　between　the　impregnate　ovum　and
the　octogenarian　into　which　the　child　grows；　for　both　ovum　and
octogenarian　are　held　personally　identical　with　the　newborn　baby；
and　things　that　are　identical　with　the　same　are　identical　with　one
another。

The　first；　then；　and　most　important　element　of　heredity　is　that
there　should　be　unbroken　continuity；　and　hence　sameness　of
personality；　between　parents　and　offspring；　in　neither　more　nor　less
than　the　same　sense　as　that　in　which　any　other　two　personalities　are
said　to　be　the　same。　　The　repetition；　therefore；　of　its
developmental　stages　by　any　offspring　must　be　regarded　as　something
which　the　embryo　repeating　them　has　already　done　once；　in　the　person
of　one　or　other　parent；　and　if　once；　then；　as　many　times　as　there
have　been　generations　between　any　given　embryo　now　repeating　it；　and
the　point　in　life　from　which　we　startedsay；　for　example；　the
amoeba。　　In　the　case　of　asexually　and　sexually　produced　organisms
alike；　the　offspring　must　be　held　to　continue　the　personality　of　the
parent　or　parents；　and　hence　on　the　occasion　of　every　fresh
development；　to　be　repeating　something　which　in　the　person　of　its
parent　or　parents　it　has　done　once；　and　if　once；　then　any　number　of
times；　already。

It　is　obvious；　therefore；　that　the　germ…plasm　（or　whatever　the　fancy
word　for　it　may　be）　of　any　one　generation　is　as　physically　identical
with　the　germ…plasm　of　its　predecessor　as　any　two　things　can　be。
The　difference　between　Professor　Weismann　and；　we　will　say；
Heringians　consists　in　the　fact　that　the　first　maintains　the　new
germ…plasm　when　on　the　point　of　repeating　its　developmental
processes　to　take　practically　no　cognisance　of　anything　that　has
happened　to　it　since　the　last　occasion　on　which　it　developed　itself；
while　the　latter　maintain　that　offspring　takes　much　the　same　kind　of
account　of　what　has　happened　to　it　in　the　persons　of　its　parents
since　the　last　occasion　on　which　it　developed　itself；　as　people　in
ordinary　life　take　of　things　that　happen　to　them。　　In　daily　life
people　let　fairly　normal　circumstances　come　and　go　without　much　heed
as　matters　of　course。　　If　they　have　been　lucky　they　make　a　note　of
it　and　try　to　repeat　their　success。　　If