116 THE ORIGIN OF SPECIES 



and from the incessant advice given in agricultural works, even in 

 the ancient Encyclopaedias of China, to be very cautious in trans- 

 porting animals from one district to another. And as it is not 

 likely that man should have succeeded in selecting so many breeds 

 and sub-breeds with constitutions specially fitted for their own 

 districts, the result must, I think, be due to habit. On the other 

 hand, natural selection would inevitably tend to preserve those 

 individuals which were born with constitutions best adapted to 

 any country which they inhabited. In treatises on many kinds of 

 cultivated plants, certain varieties are said to withstand certain 

 climates better than others; this is strikingly shown in works on 

 fruit-trees published in the United States, in which certain varieties 

 are habitually recommended for the Northern and others for the 

 Southern States; and as most of these varieties are of recent ori- 

 gin, they cannot owe their constitutional differences to habit. The 

 case of the Jerusalem artichoke, which is never propagated in 

 England by seed, and of which, consequently, new varieties have 

 not been produced, has even been advanced, as proving that ac- 

 climatization cannot be effected, for it is now as tender as ever it 

 was! The case, also, of the kidney-bean has been often cited for 

 a similar purpose, and with much greater weight; but until some 

 one will sow, during a score of generations, his kidney-beans so 

 early that a very large proportion are destroyed by frost, and then 

 collect seed from the few survivors, with care to prevent accidental 

 crosses, and then again get seed from these seedlings, with the 

 same precautions, the experiment cannot be said to have been 

 tried. Nor let it be supposed that differences in the constitution of 

 seedling kidney-beans never appear, for an account has been pub- 

 lished how much more hardy some seedlings are than others; and 

 of this fact T have myself observed striking instances. 



On the whole, we may conclude that habit, or use and disuse, 

 have, in some cases, played a considerable part in the modification 

 of the constitution and structure; r^ut that the effects have often 

 been largely combined with, and sometimes overmastered by, the 

 natural selection of innate variations. 



CORRELATED VARIATION 



/ I mean by this expression that the whole organization is so tied 

 ( together, during its growth and development, that when slight 

 / variations in any one part occur and are accumulated through 

 * _natural selection, other parts become modified. This is a very im- 

 portant subject, most imperfectly understood, and no doubt wholly 

 different classes of facts may be here easily confounded together. 



