Chap. V. SUMMARY. 167 



For myself, I venture confidently to look back thousands 

 on thousands of generations, and I see an animal striped 

 like 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 inde- 

 pendently created, will, I presume, assert that each 

 species has been created with a tendency to vary, both 

 under nature and under domestication, in this par- 

 ticular manner, so as often to become striped like 

 other species of the genus ; and that each has been 

 created with a strong tendency, when crossed with species 

 inhabiting distant quarters of the world, to produce 

 hybrids resembling in their stripes, not their own 

 parents, but other species of the genus. To admit 

 this view 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 almost as soon believe with the old and ignorant 

 cosmogonists, that fossil shells had never lived, but had 

 been created in stone so as to mock the shells now 

 living on the sea-shore. 



Summary. — Our ignorance of the laws of variation is 

 profound. Not in one case out of a hundred can we 

 pretend to assign any reason why this or that part 

 differs, more or less, from the same part in the parents. 

 But whenever we have the means of instituting a com- 

 parison, the same laws appear to have acted in pro- 

 ducing 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 

 climate and food, &c, seem to have induced some slight 

 modifications. Habit in producing constitutional dif- 



