a critical examination of on the origin of species-第3部分

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views　have　one　peculiar　merit；　and　that　is；　that　they　are　perfectly
consistent　with　an　array　of　facts　which　are　utterly　inconsistent　with
and　fatal　to；　any　other　hypothesis　of　progressive　modification　which
has　yet　been　advanced。　　It　is　one　remarkable　peculiarity　of　Mr。
Darwin's　hypothesis　that　it　involves　no　necessary　progression　or
incessant　modification；　and　that　it　is　perfectly　consistent　with　the
persistence　for　any　length　of　time　of　a　given　primitive　stock；
contemporaneously　with　its　modifications。　　To　return　to　the　case　of　the
domestic　breeds　of　pigeons；　for　example；　you　have　the　Dove…cot　pigeon；
which　closely　resembles　the　Rock　pigeon；　from　which　they　all　started；
existing　at　the　same　time　with　the　others。　　And　if　species　are
developed　in　the　same　way　in　nature；　a　primitive　stock　and　its
modifications　may；　occasionally；　all　find　the　conditions　fitted　for
their　existence；　and　though　they　come　into　competition；　to　a　certain
extent；　with　one　another；　the　derivative　species　may　not　necessarily
extirpate　the　primitive　one；　or　'vice　versa'。

Now　palaeontology　shows　us　many　facts　which　are　perfectly　harmonious
with　these　observed　effects　of　the　process　by　which　Mr。　Darwin　supposes
species　to　have　originated；　but　which　appear　to　me　to　be　totally
inconsistent　with　any　other　hypothesis　which　has　been　proposed。　There
are　some　groups　of　animals　and　plants；　in　the　fossil　world；　which　have
been　said　to　belong　to　〃persistent　types；〃　because　they　have　persisted；
with　very　little　change　indeed；　through　a　very　great　range　of　time；
while　everything　about　them　has　changed　largely。　　There　are　families　of
fishes　whose　type　of　construction　has　persisted　all　the　way　from　the
carboniferous　rock　right　up　to　the　cretaceous；　and　others　which　have
lasted　through　almost　the　whole　range　of　the　secondary　rocks；　and　from
the　lias　to　the　older　tertiaries。　　It　is　something　stupendous　thisto
consider　a　genus　lasting　without　essential　modifications　through　all
this　enormous　lapse　of　time　while　almost　everything　else　was　changed
and　modified。

Thus　I　have　no　doubt　that　Mr。　Darwin's　hypothesis　will　be　found
competent　to　explain　the　majority　of　the　phenomena　exhibited　by　species
in　nature；　but　in　an　earlier　lecture　I　spoke　cautiously　with　respect　to
its　power　of　explaining　all　the　physiological　peculiarities　of　species。

There　is；　in　fact；　one　set　of　these　peculiarities　which　the　theory　of
selective　modification；　as　it　stands　at　present；　is　not　wholly
competent　to　explain；　and　that　is　the　group　of　phenomena　which　I
mentioned　to　you　under　the　name　of　Hybridism；　and　which　I　explained　to
consist　in　the　sterility　of　the　offspring　of　certain　species　when
crossed　one　with　another。　　It　matters　not　one　whit　whether　this
sterility　is　universal；　or　whether　it　exists　only　in　a　single　case。
Every　hypothesis　is　bound　to　explain；　or；　at　any　rate；　not　be
inconsistent　with；　the　whole　of　the　facts　which　it　professes　to　account
for；　and　if　there　is　a　single　one　of　these　facts　which　can　be　shown　to
be　inconsistent　with　（I　do　not　merely　mean　inexplicable　by；　but　contrary
to）　the　hypothesis；　the　hypothesis　falls　to　the　ground；it　is　worth
nothing。　　One　fact　with　which　it　is　positively　inconsistent　is　worth　as
much；　and　as　powerful　in　negativing　the　hypothesis；　as　five　hundred。　If
I　am　right　in　thus　defining　the　obligations　of　an　hypothesis；　Mr。
Darwin；　in　order　to　place　his　views　beyond　the　reach　of　all　possible
assault；　ought　to　be　able　to　demonstrate　the　possibility　of　developing
from　a　particular　stock　by　selective　breeding；　two　forms；　which　should
either　be　unable　to　cross　one　with　another；　or　whose　cross…bred
offspring　should　be　infertile　with　one　another。

For；　you　see；　if　you　have　not　done　that　you　have　not　strictly　fulfilled
all　the　conditions　of　the　problem；　you　have　not　shown　that　you　can
produce；　by　the　cause　assumed；　all　the　phenomena　which　you　have　in
nature。　　Here　are　the　phenomena　of　Hybridism　staring　you　in　the　face；
and　you　cannot　say；　'I　can；　by　selective　modification；　produce　these
same　results。'　　Now；　it　is　admitted　on　all　hands　that；　at　present；　so
far　as　experiments　have　gone；　it　has　not　been　found　possible　to　produce
this　complete　physiological　divergence　by　selective　breeding。　　I　stated
this　very　clearly　before；　and　I　now　refer　to　the　point；　because；　if　it
could　be　proved；　not　only　that　this　'has'　not　been　done；　but　that　it
'cannot'　be　done；　if　it　could　be　demonstrated　that　it　is　impossible　to
breed　selectively；　from　any　stock；　a　form　which　shall　not　breed　with
another；　produced　from　the　same　stock；　and　if　we　were　shown　that　this
must　be　the　necessary　and　inevitable　results　of　all　experiments；　I　hold
that　Mr。　Darwin's　hypothesis　would　be　utterly　shattered。

But　has　this　been　done？　or　what　is　really　the　state　of　the　case？　　It　is
simply　that；　so　far　as　we　have　gone　yet　with　our　breeding；　we　have　not
produced　from　a　common　stock　two　breeds　which　are　not　more　or　less
fertile　with　one　another。

I　do　not　know　that　there　is　a　single　fact　which　would　justify　any　one　in
saying　that　any　degree　of　sterility　has　been　observed　between　breeds
absolutely　known　to　have　been　produced　by　selective　breeding　from　a
common　stock。　　On　the　other　hand；　I　do　not　know　that　there　is　a　single
fact　which　can　justify　any　one　in　asserting　that　such　sterility　cannot
be　produced　by　proper　experimentation。　　For　my　own　part；　I　see　every
reason　to　believe　that　it　may；　and　will　be　so　produced。　　For；　as　Mr。
Darwin　has　very　properly　urged；　when　we　consider　the　phenomena　of
sterility；　we　find　they　are　most　capricious；　we　do　not　know　what　it　is
that　the　sterility　depends　on。　　There　are　some　animals　which　will　not
breed　in　captivity；　whether　it　arises　from　the　simple　fact　of　their
being　shut　up　and　deprived　of　their　liberty；　or　not；　we　do　not　know；
but　they　certainly　will　not　breed。　　What　an　astounding　thing　this　is；　to
find　one　of　the　most　important　of　all　functions　annihilated　by　mere
imprisonment！

So；　again；　there　are　cases　known　of　animals　which　have　been　thought　by
naturalists　to　be　undoubted　species；　which　have　yielded　perfectly
fertile　hybrids；　while　there　are　other　species　which　present　what
everybody　believes　to　be　varieties*　which　are　more　or　less　infertile
with　one　another。　　There　are　other　cases　which　are　truly　extraordinary；
there　is　one；　for　example；　which　has　been　carefully　examined；of　two
kinds　of　sea…weed；　of　which　the　male　element　of　the　one；　which　we　may
call　A；　fertilizes　the　female　element　of　the　other；　B；　while　the　male
element　of　B　will　not　fertilize　the　female　element　of　A；　so　that；　while
the　former　experiment　seems　to　show　us　that　they　are　'varieties'；　the
latter　leads　to　the　conviction　that　they　are　'species'。

　　　　*＇footnote＇　And　as　I　conceive　with　very　good　reason；　but　if
　　　　any　objector　urges　that　we　cannot　prove　that　they　have　been
　　　　produced　by　artificial　or　natural　selection；　the　objection
　　　　must　be　admittedultrasceptical　as　it　is。　　But　in　science；
　　　　scepticism　is　a　duty。

When　we　see　how　capricious　and　uncertain　this　sterility　is；　how　unknown
the　conditions　on　which　it　depends；　I　say　that　we　have　no　right　to
affirm　that　those　conditions　will　not　be　better　understood　by　and　by；
and　we　have　no　ground　for　supposing　that　we　may　not　be　able　to
experiment　so　as　to　obtain　that　crucial　result　which　I　mentioned　just
now。　　So　that　though　Mr。　　Darwin's　hypothesis　does　not　completely
extricate　us　from　this　difficulty　at　present；　we　have　not　the　least
right　to　say　it　will　not　do　so。

There　is　a　wide　gulf　between　the　thing　you　cannot　explain　and　the　thing
that　upsets　you　altogether。　　There　is　hardly　any　hypothesis　in　this
world　which　has　not　some　fact　in　connection　with　it　which　has　not　been
explained；　but　that　is　a　very　different　affair　to　a　fact　that　entirely
opposes　your　hypothesis；　in　this　case　all　you　can　say　is；　that　your
hypothesis　is　in　the　same　position　as　a　good　many　others。

Now；　as　to　the　third　test；　that　there　are　no　other　causes　competent　to
explain　the　phenomena；　I　explained　to　you　that　one　should　be　able　to
say　of　an　hypothesis；　that　no　other　known　causes　than　those　supposed　by
it　are　competent　to　give　rise　to　the　phenomena。　　Here；　I　think；　Mr。
Darwin's　view　is　pretty　strong。　　I　really　believe　that　the　alternative
is　either　Darwinism　or　nothing；　for　I　do　not　know　of　any　rational
conception　or　theory　of　the　organic　universe　which　has　any　scientific
position　at　all　beside　Mr。　Darwin's。　　I　do　not　know　of　any　proposition
that　has　been　put　before　us　with　the　intention　of　explaining　the
phenomena　of　organic　nature；　which　has　in　its　favour　a　thousandth　part
of　the　evidence　which　may　be　adduced　in　favour　of　Mr。　Darwin's　views。
Whatever　may　be　the　objections　to　his　views；　certainly　all　others　are
absolutely　out　of　court。

Take　the　Lamarckian　hypothesis；　for　example。　　Lamarck　was　a　great
naturalist；　and　to　a　certain　extent　went　the　right　way　to　work；　he
argued　from　what　was　undoubtedly　a　true　cause　of　some　of　the　phenomena
of　organic　nature。　　He　said　it　is　a　matter　of　experience　that　an　animal
may　be　modified　more　or　less　in　consequence　of　its　desires　and
consequent　actions。　Thus；　if　a　man　exercise　himself　as　a　blacksmith；
his　arms　will　become　strong　and　muscular；　such　organic　modification　is
a　result　of　this　particular　action　and　exercise。　　Lamarck　thought　that
by　a　very　simple　supposition　based　on　this　truth　he　could　explain　the
origin　of　the　various　animal　species：　he　said；　for　example；　that　the
short…legged　birds　which　live　on　fish　had　been　converted　into　the
long…legged　waders　by　desiring　to　get　the　fish　without　wetting　their
bodies；　and　so　stretching　their　legs　more　and　more　through　successive
generations。　　If　Lamarck　could　have　shown　experimentally；　that　even
races　of　animals　could　be　produced　in　this　way；　there　might　have　been
some　ground　for　his　speculations。　　But　he　could　show　nothing　of　the
kind；　and　his　hypothesis　has　pretty　well　dropped　into　oblivion；　as　it
deserved　to　do。　　I　said　in　an　earlier　lecture　that　there　are　hypotheses
and　hypotheses；　and　when　people　tell　you　that　Mr。　　Darwin's
strongly…based　hypothesis　is　nothing　but　a　mere　modification　of
Lamarck's；　you　will　know　what　to　think　of　their　capacity　f