them；that　every　plant　has　its　indirect　helpers　in　the　birds　that
  scatter　abroad　its　seed；　and　the　animals　that　manure　it　with　their
  dung；I　say；　when　these　things　are　considered；　it　seems　impossible
  that　any　variation　which　may　arise　in　a　species　in　nature　should　not
  tend　in　some　way　or　other　either　to　be　a　little　better　or　worse　than
  the　previous　stock；　if　it　is　a　little　better　it　will　have　an　advantage
  over　and　tend　to　extirpate　the　latter　in　this　crush　and　struggle；　and　if
  it　is　a　little　worse　it　will　itself　be　extirpated。
  I　know　nothing　that　more　appropriately　expresses　this；　than　the　phrase；
  〃the　struggle　for　existence〃；　because　it　brings　before　your　minds；　in　a
  vivid　sort　of　way；　some　of　the　simplest　possible　circumstances
  connected　with　it。　　When　a　struggle　is　intense　there　must　be　some　who
  are　sure　to　be　trodden　down；　crushed；　and　overpowered　by　others；　and
  there　will　be　some　who　just　manage　to　get　through　only　by　the　help　of
  the　slightest　accident。　　I　recollect　reading　an　account　of　the　famous
  retreat　of　the　French　troops；　under　Napoleon；　from　Moscow。　　Worn　out；
  tired；　and　dejected；　they　at　length　came　to　a　great　river　over　which
  there　was　but　one　bridge　for　the　passage　of　the　vast　army。　Disorganised
  and　demoralised　as　that　army　was；　the　struggle　must　certainly　have　been
  a　terrible　oneevery　one　heeding　only　himself；　and　crushing　through
  the　ranks　and　treading　down　his　fellows。　　The　writer　of　the　narrative；
  who　was　himself　one　of　those　who　were　fortunate　enough　to　succeed　in
  getting　over；　and　not　among　the　thousands　who　were　left　behind　or
  forced　into　the　river；　ascribed　his　escape　to　the　fact　that　he　saw
  striding　onward　through　the　mass　a　great　strong　fellow；one　of　the
  French　Cuirassiers；　who　had　on　a　large　blue　cloakand　he　had　enough
  presence　of　mind　to　catch　and　retain　a　hold　of　this　strong　man's
  cloak。　　He　says；　〃I　caught　hold　of　his　cloak；　and　although　he　swore　at
  me　and　cut　at　and　struck　me　by　turns；　and　at　last；　when　he　found　he
  could　not　shake　me　off；　fell　to　entreating　me　to　leave　go　or　I　should
  prevent　him　from　escaping；　besides　not　assisting　myself；　I　still　kept
  tight　hold　of　him；　and　would　not　quit　my　grasp　until　he　had　at　last
  dragged　me　through。〃　　Here　you　see　was　a　case　of　selective　savingif
  we　may　so　term　itdepending　for　its　success　on　the　strength　of　the
  cloth　of　the　Cuirassier's　cloak。　　It　is　the　same　in　nature；　every
  species　has　its　bridge　of　Beresina；　it　has　to　fight　its　way　through　and
  struggle　with　other　species；　and　when　well　nigh　overpowered；　it　may　be
  that　the　smallest　chance；　something　in　its　colour；　perhapsthe
  minutest　circumstancewill　turn　the　scale　one　way　or　the　other。
  Suppose　that　by　a　variation　of　the　black　race　it　had　produced　the　white
  man　at　any　timeyou　know　that　the　Negroes　are　said　to　believe　this　to
  have　been　the　case；　and　to　imagine　that　Cain　was　the　first　white　man；
  and　that　we　are　his　descendantssuppose　that　this　had　ever　happened；
  and　that　the　first　residence　of　this　human　being　was　on　the　West　Coast
  of　Africa。　　There　is　no　great　structural　difference　between　the　white
  man　and　the　Negro；　and　yet　there　is　something　so　singularly　different
  in　the　constitution　of　the　two；　that　the　malarias　of　that　country；　which
  do　not　hurt　the　black　at　all；　cut　off　and　destroy　the　white。　　Then　you
  see　there　would　have　been　a　selective　operation　performed；　if　the　white
  man　had　risen　in　that　way；　he　would　have　been　selected　out　and　removed
  by　means　of　the　malaria。　　Now　there　really　is　a　very　curious　case　of
  selection　of　this　sort　among　pigs；　and　it　is　a　case　of　selection　of
  colour　too。　　In　the　woods　of　Florida　there　are　a　great　many　pigs；　and
  it　is　a　very　curious　thing　that　they　are　all　black；　every　one　of　them。
  Professor　Wyman　was　there　some　years　ago；　and　on　noticing　no　pigs　but
  these　black　ones；　he　asked　some　of　the　people　how　it　was　that　they　had
  no　white　pigs；　and　the　reply　was　that　in　the　woods　of　Florida　there　was
  a　root　which　they　called　the　Paint　Root；　and　that　if　the　white　pigs
  were　to　eat　any　of　it；　it　had　the　effect　of　making　their　hoofs　crack；
  and　they　died；　but　if　the　black　pigs　eat　any　of　it；　it　did　not　hurt
  them　at　all。　　Here　was　a　very　simple　case　of　natural　selection。　　A
  skilful　breeder　could　not　more　carefully　develope　the　black　breed　of
  pigs；　and　weed　out　all　the　white　pigs；　than　the　Paint　Root　does。
  To　show　you　how　remarkably　indirect　may　be　such　natural　selective
  agencies　as　I　have　referred　to；　I　will　conclude　by　noticing　a　case
  mentioned　by　Mr。　Darwin；　and　which　is　certainly　one　of　the　most　curious
  of　its　kind。　　It　is　that　of　the　Humble　Bee。　　It　has　been　noticed　that
  there　are　a　great　many　more　humble　bees　in　the　neighbourhood　of　towns；
  than　out　in　the　open　country；　and　the　explanation　of　the　matter　is
  this：　the　humble　bees　build　nests；　in　which　they　store　their　honey　and
  deposit　the　larvae　and　eggs。　　The　field　mice　are　amazingly　fond　of　the
  honey　and　larvae；　therefore；　wherever　there　are　plenty　of　field　mice；　as
  in　the　country；　the　humble　bees　are　kept　down；　but　in　the　neighbourhood
  of　towns；　the　number　of　cats　which　prowl　about　the　fields　eat　up　the
  field　mice；　and　of　course　the　more　mice　they　eat　up　the　less　there　are
  to　prey　upon　the　larvae　of　the　beesthe　cats　are　therefore　the　INDIRECT
  HELPERS　of　the　bees！*　　Coming　back　a　step　farther　we　may　say　that　the
  old　maids　are　also　indirect　friends　of　the　humble　bees；　and　indirect
  enemies　of　the　field　mice；　as　they　keep　the　cats　which　eat　up　the
  latter！　　This　is　an　illustration　somewhat　beneath　the　dignity　of　the
  subject；　perhaps；　but　it　occurs　to　me　in　passing；　and　with　it　I　will
  conclude　this　lecture。
  ＇footnote＇　*The　humble　bees；　on　the　other　hand；　are　direct　helpers　of
  some　plants；　such　as　the　heartsease　and　red　clover；　which　are
  fertilized　by　the　visits　of　the　bees；　and　they　are　indirect　helpers　of
  the　numerous　insects　which　are　more　or　less　completely　supported　by　the
  heartsease　and　red　clover。
  End