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Show 166 LAWS OF VARIATION. CHAP. V. to ask Colonel Poole whether such face-stripes ever occur in the eminently striped Katty;var breed of h?rses, an d was, as We have Seen , answered m the affirmative. What now are we to say to these several facts? We see several very distinct species of the horse-ge~us becoming, by simple variation, stripe~ on the legs hke a zebra, or striped on the shoulders hke an ass. In ~he horse we see this tendency strong whenever a dun tint appears-a tint which approac~es to that of the general colouring of the other s~eCies of the g~nus. The appearance of the stripes IS not accompanied by any change of form or by any other new character. We see this tendency to become striped most strongly displayed in hybrids from between several of the most distinct species. Now observe the case of the s~veral ?reeds. of pigeons : they are descended from a pigeon (Including two or three sub-species or geographical races) of a bluish colour, with certain bars and other marks; and when any breed assumes by simple variation a bluish tint, these bars and other marks invariably reappear; but without any other change of form or character. w ·hen the oldest and truest breeds of various colours are cro~sed, we see a strong tendency for the blue tint and bars and marks to reappear in the mongrels. I have stated that the most probable hypothesis to account for the reappearance of very ancient characters, isthat there is a tendency in the young of each successive generation to produce the long-lost character, and that this tendency, from unknown causes, sometimes prevails. And we have just seen that in several species of the horse-genus the stripes are either plainer or appear more commonly in the young than in the old. Call the breeds of pigeons, some of which have bred tru.e for centuries, species; and how exactly parallel IS the case with that of the species of the horse-genus ! CHAP. V. SUMMARY. 167 For myself, I venture confidently to look back thousands o.n thousands of generations, and I see an animal striped hke a zebra, but perhaps otherwise very differently constructed, the common parent of our domestic horse whether or not it be descended from one or more wild stocks, of the ass, the hemionus, quagga, and zebra. He who believes that each equine species was independently created, will, I presume, assert that each species has been created with a tendency to vary, both ~nder nature and under domestication, in this partwular manner, so as often to become striped like other species of the genus; and that each has been ?reat~d. with a strong tendency, when crossed with species Inha?Iting distant quarters of the world, to produce hybrids resembling in their stripes, not their own pa.ren~s, ~ut ot~er species of the genus. To admit this v1ew Is, as It seems to me, to reject a real for an unreal, or at least for an unknown, cause. It makes the works of God a mere mockery and deception ; I would a~ost as soon ~elieve with the old and ignorant cosmogomsts, that fossil shells had never lived but had ~e~n created in stone so as to ·mock the shells now hving on the sea-shore. Summary.-Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we p~etend to assign any reason why this or that part differs, more or less, from the same part in the parents. Bu~ whenever we have the means of instituting a compar~ son, the same laws appear to have acted in pro. dumng the lesser differences between varieties of the same species, and the greater differences between species of. the same genus. The external conditions of life, as clim~te a~d food, &c., seem to have induced some slight modifications. Habit in producing constitutional dif- |