150 THE ORIGIN OF SPECIES 



cither in form or in structure. There is always a certain 

 amount of deviation, not only from the precise characters 

 of a single parent, but when, as in most animals and many 

 plants, the sexes are lodged in distinct individuals, from 

 an exact mean between the two parents. And indeed, on 

 general principles, this slight deviation seems as intelligible 

 as the general similarity, if we reflect how complex the 

 co-operating " bundles of forces " are, and how improbable 

 it is that, in any case, their true resultant shall coincide 

 with any mean between the more obvious characters of 

 the two parents. Whatever be its cause, however, the 

 co-existence of this tendency to minor variation with the 

 tendency to general similarity, is of vast importance in its 

 bearing on the question of the origin of species. 



As a general rule, the extent to which an offspring differs 

 from its parent is slight enough ; but, occasionally, the 

 amount of difference is much more strongly marked, and 

 then the divergent offspring receives the name of a Variety. 

 Multitudes, of what there is every reason to believe are 

 such varieties, are known, but the origin of very few has 

 been accurately recorded, and of these we will select two 

 as more especially illustrative of the main features of 

 variation. The first of them is that of the " Ancon," or 

 " Otter " sheep, of which a careful account is given by 

 Colonel David Humphreys, F.R.S., in a letter to Sir Joseph 

 Banks, published in the Philosophical Transactions for 

 1813. It appears that one Seth Wright, the proprietor of a 

 farm on the banks of the Charles River, in Massachusetts, 

 possessed a flock of fifteen ewes and a ram of the ordinary 

 kind. In the year 1791, one of the ewes presented her 

 owner with a male lamb, differing, for no assignable reason, 

 from its parents by a proportionally long body and short 

 bandy legs, whence it was unable to emulate its relatives in 

 those sportive leaps over the neighbours' fences, in which 

 they were in the habit of indulging, much to the good 

 farmer's vexation. 



The second case is that detailed by a no less unexception- 

 able authority than Reaumur, in his Art de faire clore les 

 Poulets. A Maltese couple, named Kellcia, whose hands 

 and feet were constructed upon the ordinary human model, 

 had born to them a son, Gratio, who possessed six perfectly 

 movable fingers on each hand, and six toes, not quite so 

 well formed, on each foot. No cause could be assigned for 

 the appearance of this unusual variety of the human species. 



