the perpetuation of living beings-第3章

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the　last；　who；　of　course；　married　a　man　who　had　only　five　fingers；　had
four　children；　the　first；　a　boy；　was　born　with　six　toes；　but　the　other
three　were　normal。

Now　observe　what　very　extraordinary　phenomena　are　presented　here。　　You
have　an　accidental　variation　arising　from　what　you　may　call　a
monstrosity；　you　have　that　monstrosity　tendency　or　variation　diluted　in
the　first　instance　by　an　admixture　with　a　female　of　normal　construction；
and　you　would　naturally　expect　that；　in　the　results　of　such　an　union；
the　monstrosity；　if　repeated；　would　be　in　equal　proportion　with　the
normal　type；　that　is　to　say；　that　the　children　would　be　half　and　half；
some　taking　the　peculiarity　of　the　father；　and　the　others　being　of　the
purely　normal　type　of　the　mother；　but　you　see　we　have　a　great
preponderance　of　the　abnormal　type。　Well；　this　comes　to　be　mixed　once
more　with　the　pure；　the　normal　type；　and　the　abnormal　is　again　produced
in　large　proportion；　notwithstanding　the　second　dilution。　　Now　what
would　have　happened　if　these　abnormal　types　had　intermarried　with　each
other；　that　is　to　say；　suppose　the　two　boys　of　Salvator　had　taken　it
into　their　heads　to　marry　their　first　cousins；　the　two　first　girls　of
George；　their　uncle？　　You　will　remember　that　these　are　all　of　the
abnormal　type　of　their　grandfather。　　The　result　would　probably　have
been；　that　their　offspring　would　have　been　in　every　case　a　further
development　of　that　abnormal　type。　　You　see　it　is　only　in　the　fourth；
in　the　person　of　Marie；　that　the　tendency；　when　it　appears　but　slightly
in　the　second　generation；　is　washed　out　in　the　third；　while　the　progeny
of　Andre；　who　escaped　in　the　first　instance；　escape　altogether。

We　have　in　this　case　a　good　example　of　nature's　tendency　to　the
perpetuation　of　a　variation。　Here　it　is　certainly　a　variation　which
carried　with　it　no　use　or　benefit；　and　yet　you　see　the　tendency　to
perpetuation　may　be　so　strong；　that；　notwithstanding　a　great　admixture
of　pure　blood；　the　variety　continues　itself　up　to　the　third　generation；
which　is　largely　marked　with　it。　In　this　case；　as　I　have　said；　there
was　no　means　of　the　second　generation　intermarrying　with　any　but
five…fingered　persons；　and　the　question　naturally　suggests　itself；　What
would　have　been　the　result　of　such　marriage？　　Reaumur　narrates　this
case　only　as　far　as　the　third　generation。　　Certainly　it　would　have　been
an　exceedingly　curious　thing　if　we　could　have　traced　this　matter　any
further；　had　the　cousins　intermarried；　a　six…fingered　variety　of　the
human　race　might　have　been　set　up。

To　show　you　that　this　supposition　is　by　no　means　an　unreasonable　one；
let　me　now　point　out　what　took　place　in　the　case　of　Seth　Wright's
sheep；　where　it　happened　to　be　a　matter　of　moment　to　him　to　obtain　a
breed　or　raise　a　flock　of　sheep　like　that　accidental　variety　that　I
have　describedand　I　will　tell　you　why。　　In　that　part　of　Massachusetts
where　Seth　Wright　was　living；　the　fields　were　separated　by　fences；　and
the　sheep；　which　were　very　active　and　robust；　would　roam　abroad；　and
without　much　difficulty　jump　over　these　fences　into　other　people's
farms。　　As　a　matter　of　course；　this　exuberant　activity　on　the　part　of
the　sheep　constantly　gave　rise　to　all　sorts　of　quarrels；　bickerings；
and　contentions　among　the　farmers　of　the　neighbourhood；　so　it　occurred
to　Seth　Wright；　who　was；　like　his　successors；　more　or　less　'cute；　that
if　he　could　get　a　stock　of　sheep　like　those　with　the　bandy　legs；　they
would　not　be　able　to　jump　over　the　fences　so　readily；　and　he　acted　upon
that　idea。　　He　killed　his　old　ram；　and　as　soon　as　the　young　one　arrived
at　maturity；　he　bred　altogether　from　it。　　The　result　was　even　more
striking　than　in　the　human　experiment　which　I　mentioned　just　now。
Colonel　Humphreys　testifies　that　it　always　happened　that　the　offspring
were　either　pure　Ancons　or　pure　ordinary　sheep；　that　in　no　case　was
there　any　mixing　of　the　Ancons　with　the　others。　　In　consequence　of
this；　in　the　course　of　a　very　few　years；　the　farmer　was　able　to　get　a
very　considerable　flock　of　this　variety；　and　a　large　number　of　them
were　spread　throughout　Massachusetts。　　Most　unfortunately；　howeverI
suppose　it　was　because　they　were　so　commonnobody　took　enough　notice
of　them　to　preserve　their　skeletons；　and　although　Colonel　Humphreys
states　that　he　sent　a　skeleton　to　the　President　of　the　Royal　Society　at
the　same　time　that　he　forwarded　his　paper；　I　am　afraid　that　the　variety
has　entirely　disappeared；　for　a　short　time　after　these　sheep　had　become
prevalent　in　that　district；　the　Merino　sheep　were　introduced；　and　as
their　wool　was　much　more　valuable；　and　as　they　were　a　quiet　race　of
sheep；　and　showed　no　tendency　to　trespass　or　jump　over　fences；　the
Otter　breed　of　sheep；　the　wool　of　which　was　inferior　to　that　of　the
Merino；　was　gradually　allowed　to　die　out。

You　see　that　these　facts　illustrate　perfectly　well　what　may　be　done　if
you　take　care　to　breed　from　stocks　that　are　similar　to　each　other。
After　having　got　a　variation；　if；　by　crossing　a　variation　with　the
original　stock；　you　multiply　that　variation；　and　then　take　care　to　keep
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