276 DEFINITE ACTION OF THE Chap. XXIII. 



individuals exposed to nearly the same conditions, and one alone is 

 affected, we may conclude that the constitution of the individual is 

 of far higher importance than the conditions to which it has been 

 exposed. It seems, indeed, to be a general rule that conspicuous 

 variations occur rarely, and in one individual alone out of millions, 

 though all may have been exposed, as far as we can judge, to nearly 

 the same conditions. As the most strongly marked variations 

 graduate insensibly into the most trifling, we are led by the same 

 train of thought to attribute each slight variation much more to 

 innate differences of constitution, however caused, than to the 

 definite action of the surrounding conditions. 



We are led to the same conclusion by considering the cases, 

 formerly alluded to, of fowls and pigeons, which have varied and 

 will no doubt go on var^'ing in directly opposite ways, though kept 

 during many generations under nearly the same conditions. Some, 

 for instance, are born with their beaks, wings, tails, legs, &c., a 

 little longer, and others with these same parts a little shorter. By 

 the long-continued selection of such slight individual differences 

 which occur in birds kej^t in the same aviary, widely different races 

 could certainly be formed ; and long-continued selection, important 

 as is the result, does nothing but preserve the variations which arise, 

 as it appears to us, spontaneously. 



In these cases we see that domesticated animals vary in an 

 indefinite number of particulars, though treated as imiformly as 

 is possible. On the other hand, there are instances of animals and 

 plants, which, though they have been exposed to very different 

 conditions, both under nature and domestication, have varied in 

 nearly the same manner. Mr. Layard informs me that he has 

 observed amongst the Caffres of South Africa a dog singularly like 

 an arctic Esquimaux dog. Pigeons in India present nearly the 

 same wide diversities of colour as in Europe; and I have seen 

 chequered and simply barred pigeons, and pigeons with blue and 

 white loins, from Sierra Leone, Madeira, England, and India. New 

 varieties of flowers are continually raised in different parts of Great 

 Britain, but many of these are found by the judges at our exhibitions 

 to be almost identical with old varieties. A vast number of new 

 fruit-trees and culinary vegetables have been produced in North 

 America : these differ from European varieties in the same general 

 manner as the several varieties raised in Europe differ from one 

 another ; and no one has ever pretended that the climate of America 

 has given to the many American varieties any general character by 

 which they can be recognised. Nevertheless, from the facts pre- 

 viously advanced on the authority of Mr. Meehan with respect to 

 American and European forest-trees it would be rash to affirm that 

 varieties raised in the two countries would not in the course of 

 ages assume a distinctive character. Dr. M. Masters has recorded a 

 striking fact *** bearing on this subject: he raised numerous plants 



" 'Gardener's Chronicle,' 1857, p. 629. 



