the perpetuation of living beings-第4节

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that　variation　distinct　from　the　original　stock；　and　make　them　breed
together；then　you　may　almost　certainly　produce　a　race　whose　tendency
to　continue　the　variation　is　exceedingly　strong。

This　is　what　is　called　〃selection〃；　and　it　is　by　exactly　the　same
process　as　that　by　which　Seth　Wright　bred　his　Ancon　sheep；　that　our
breeds　of　cattle；　dogs；　and　fowls；　are　obtained。　　There　are　some
possibilities　of　exception；　but　still；　speaking　broadly；　I　may　say　that
this　is　the　way　in　which　all　our　varied　races　of　domestic　animals　have
arisen；　and　you　must　understand　that　it　is　not　one　peculiarity　or　one
characteristic　alone　in　which　animals　may　vary。　　There　is　not　a　single
peculiarity　or　characteristic　of　any　kind；　bodily　or　mental；　in　which
offspring　may　not　vary　to　a　certain　extent　from　the　parent　and　other
animals。

Among　ourselves　this　is　well　known。　　The　simplest　physical　peculiarity
is　mostly　reproduced。　I　know　a　case　of　a　man　whose　wife　has　the　lobe　of
one　of　her　ears　a　little　flattened。　　An　ordinary　observer　might
scarcely　notice　it；　and　yet　every　one　of　her　children　has　an
approximation　to　the　same　peculiarity　to　some　extent。　　If　you　look　at
the　other　extreme；　too；　the　gravest　diseases；　such　as　gout；　scrofula；
and　consumption；　may　be　handed　down　with　just　the　same　certainty　and
persistence　as　we　noticed　in　the　perpetuation　of　the　bandy　legs　of　the
Ancon　sheep。

However；　these　facts　are　best　illustrated　in　animals；　and　the　extent　of
the　variation；　as　is　well　known；　is　very　remarkable　in　dogs。　　For
example；　there　are　some　dogs　very　much　smaller　than　others；　indeed；　the
variation　is　so　enormous　that　probably　the　smallest　dog　would　be　about
the　size　of　the　head　of　the　largest；　there　are　very　great　variations　in
the　structural　forms　not　only　of　the　skeleton　but　also　in　the　shape　of
the　skull；　and　in　the　proportions　of　the　face　and　the　disposition　of
the　teeth。

The　Pointer；　the　Retriever；　Bulldog；　and　the　Terrier；　differ　very
greatly；　and　yet　there　is　every　reason　to　believe　that　every　one　of
these　races　has　arisen　from　the　same　source；that　all　the　most
important　races　have　arisen　by　this　selective　breeding　from　accidental
variation。

A　still　more　striking　case　of　what　may　be　done　by　selective　breeding；
and　it　is　a　better　case；　because　there　is　no　chance　of　that　partial
infusion　of　error　to　which　I　alluded；　has　been　studied　very　carefully
by　Mr。　Darwin；the　case　of　the　domestic　pigeons。　　I　dare　say　there　may
be　some　among　you　who　may　be　pigeon　'fanciers'；　and　I　wish　you　to
understand　that　in　approaching　the　subject；　I　would　speak　with　all
humility　and　hesitation；　as　I　regret　to　say　that　I　am　not　a　pigeon
fancier。　　I　know　it　is　a　great　art　and　mystery；　and　a　thing　upon　which　a
man　must　not　speak　lightly；　but　I　shall　endeavour；　as　far　as　my
understanding　goes；　to　give　you　a　summary　of　the　published　and
unpublished　information　which　I　have　gained　from　Mr。　Darwin。

Among　the　enormous　variety；I　believe　there　are　somewhere　about　a
hundred　and　fifty　kinds　of　pigeons；there　are　four　kinds　which　may　be
selected　as　representing　the　extremest　divergences　of　one　kind　from
another。　　Their　names　are　the　Carrier；　the　Pouter；　the　Fantail；　and　the
Tumbler。　　In　the　large　diagrams　they　are　each　represented　in　their
relative　sizes　to　each　other。　　This　first　one　is　the　Carrier；　you　will
notice　this　large　excrescence　on　its　beak；　it　has　a　comparatively　small
head；　there　is　a　bare　space　round　the　eyes；　it　has　a　long　neck；　a　very
long　beak；　very　strong　legs；　large　feet；　long　wings；　and　so　on。　　The
second　one　is　the　Pouter；　a　very　large　bird；　with　very　long　legs　and
beak。　　It　is　called　the　Pouter　because　it　is　in　the　habit　of　causing
its　gullet　to　swell　up　by　inflating　it　with　air。　　I　should　tell　you　that
all　pigeons　have　a　tendency　to　do　this　at　times；　but　in　the　Pouter　it
is　carried　to　an　enormous　extent。　　The　birds　appear　to　be　quite　proud
of　their　power　of　swelling　and　puffing　themselves　out　in　this　way；　and
I　think　it　is　about　as　droll　a　sight　as　you　can　well　see　to　look　at　a
cage　full　of　these　pigeons　puffing　and　blowing　themselves　out　in　this
ridiculous　manner。

The　third　kind　I　mentionedthe　Fantailis　a　small　bird；　with
exceedingly　small　legs　and　a　very　small　beak。　　It　is　most　curiously
distinguished　by　the　size　and　extent　of　its　tail；　which；　instead　of
containing　twelve　feathers；　may　have　many　more；say　thirty；　or　even
moreI　believe　there　are　some　with　as　many　as　forty…two。　　This　bird
has　a　curious　habit　of　spreading　out　the　feathers　of　its　tail　in　such　a
way　that　they　reach　forward；　and　touch　its　head；　and　if　this　can　be
accomplished；　I　believe　it　is　looked　upon　as　a　point　of　great　beauty。

But　here　is　the　last　great　variety；the　Tumbler；　and　of　that　great
variety；　one　of　the　principal　kinds；　and　one　most　prized；　is　the
specimen　represented　herethe　short…faced　Tumbler。　　Its　beak　is
reduced　to　a　mere　nothing。　　Just　compare　the　beak　of　this　one　and　that
of　the　first　one；　the　CarrierI　believe　the　orthodox　comparison　of　the
head　and　beak　of　a　thoroughly　well…bred　Tumbler　is　to　stick　an　oat　into
a　cherry；　and　that　will　give　you　the　proper　relative　proportions　of　the
head　and　beak。　　The　feet　and　legs　are　exceedingly　small；　and　the　bird
appears　to　be　quite　a　dwarf　when　placed　side　by　side　with　this　great
Carrier。

These　are　differences　enough　in　regard　to　their　external　appearance；　but
these　differences　are　by　no　means　the　whole　or　even　the　most　important
of　the　differences　which　obtain　between　these　birds。　　There　is　hardly　a
single　point　of　their　structure　which　has　not　become　more　or　less
altered；　and　to　give　you　an　idea　of　how　extensive　these　alterations　are；
I　have　here　some　very　good　skeletons；　for　which　I　am　indebted　to　my
friend；　Mr。　Tegetmeier；　a　great　authority　in　these　matters；　by　means　of
which；　if　you　examine　them　by…and…by；　you　will　be　able　to　see　the
enormous　difference　in　their　bony　structures。

I　had　the　privilege；　some　time　ago；　of　access　to　some　important　MSS。　of
Mr。　Darwin；　who；　I　may　tell　you；　has　taken　very　great　pains　and　spent
much　valuable　time　and　attention　on　the　investigation　of　these
variations；　and　getting　together　all　the　facts　that　bear　upon　them。　　I
obtained　from　these　MSS。　the　following　summary　of　the　differences
between　the　domestic　breeds　of　pigeons；　that　is　to　say；　a　notification
of　the　various　points　in　which　their　organization　differs。　　In　the
first　place；　the　back　of　the　skull　may　differ　a　good　deal；　and　the
development　of　the　bones　of　the　face　may　vary　a　great　deal；　the　back
varies　a　good　deal；　the　shape　of　the　lower　jaw　varies；　the　tongue
varies　very　greatly；　not　only　in　correlation　to　the　length　and　size　of
the　beak；　but　it　seems　also　to　have　a　kind　of　independent　variation　of
its　own。　　Then　the　amount　of　naked　skin　round　the　eyes；　and　at　the　base
of　the　beak；　may　vary　enormously；　so　may　the　length　of　the　eyelids；　the
shape　of　the　nostrils；　and　the　length　of　the　neck。　　I　have　already
noticed　the　habit　of　blowing　out　the　gullet；　so　remarkable　in　the
Pouter；　and　comparatively　so　in　the　others。　　There　are　great
differences；　too；　in　the　size　of　the　female　and　the　male；　the　shape　of
the　body；　the　number　and　width　of　the　processes　of　the　ribs；　the
development　of　the　ribs；　and　the　size；　shape；　and　development　of　the
breastbone。　　We　may　notice；　too；and　I　mention　the　fact　because　it　has
been　disputed　by　what　is　assumed　to　be　high　authority；the　variation
in　the　number　of　the　sacral　vertebrae。　　The　number　of　these　varies　from
eleven　to　fourteen；　and　that　without　any　diminution　in　the　number　of
the　vertebrae　of　the　back　or　of　the　tail。　　Then　the　number　and　position
of　the　tail…feathers　may　vary　enormously；　and　so　may　the　number　of　the
primary　and　secondary　feathers　of　the　wings。　　Again；　　the　length　of　the
feet　and　of　the　beak；although　they　have　no　relation　to　each　other；
yet　appear　to　go　together；that　is；　you　have　a　long　beak　wherever　you
have　long　feet。　　There　are　differences　also　in　the　periods　of　the
acquirement　of　the　perfect　plumage；the　size　and　shape　of　the
eggs；the　nature　of　flight；　and　the　powers　of　flight；so…called
〃homing〃　birds　having　enormous　flying　powers；*　while；　on　the　other
hand；　the　little　Tumbler　is　so　called　because　of　its　extraordinary
faculty　of　turning　head　over　heels　in　the　air；　instead　of　pursuing　a
direct　course。　　And；　lastly；　the　dispositions　and　voices　of　the　birds
may　vary。　　Thus　the　case　of　the　pigeons　shows　you　that　there　is　hardly
a　single　particular；whether　of　instinct；　or　habit；　or　bony　structure；
or　of　plumage；of　either　the　internal　economy　or　the　external　shape；
in　which　some　variation　or　change　may　not　take　place；　which；　by
selective　breeding；　may　become　perpetuated；　and　form　the　foundation　of；
and　give　rise　to；　a　new　race。

　　　　＇footnote：　The　〃Carrier；〃　I　learn　from　Mr。　Tegetmeier；　does
　　　　not　'carry'；　a　high…bred　bird　of　this　breed　being　but　a
　　　　poor　flier。　　The　birds　which　fly　long　distances；　and　come
　　　　home；〃homing〃　birds；and　are　consequently　used　as
　　　　carriers；　are　not　〃carriers〃　in　the　fancy　sense。＇

If　you　carry　in　your　mind's　eye　these　four　varieties　of　pigeons；　you
will　bear　with　you　as　good　a　notion　as　you　can　have；　perhaps；　of　the
enormous