G ALTON AND STATISTICAL STUDY OF INHERITANCE 165 



improvement in any one of these respects without a sacrifice in 

 other directions. If the fleetness is increased, the engines must 

 be larger, and more space must be given up to coal, and this 

 diminishes the remaining accommodation. 



" Evolution may produce an altogether new type of vessel that 

 shall be more efficient than the old one, but when a particular 

 type has become adapted to its functions, through long experience, 

 it is not possible to produce a mere variety of its type that shall 

 have increased efficiency in some one particular without detriment 

 to the rest. So it is with animals." 



Neo-Lamarckians are fond of asserting that natural selection 

 cannot bring about an adaptation which involves the coordinated 

 modification of many correlated parts; and they may be inter- 

 ested in the clear demonstration which I have quoted from 

 Galton of the way natural selection brings about coordination. 



His assertion that after a coordinated type has been estab- 

 lished it cannot be changed by the mere selection of individual 

 differences, seems to be well founded, so far as the modification 

 by artificial selection of a type which has been established by 

 natural selection is in question. As it is with vessels, so it is 

 with animals in the hands of a breeder who, having in mind 

 some one point of excellence, picks out the individual animals in 

 which the desired peculiarity is most marked, and, propagating 

 from them, destroys all the others. 



A breeder of domesticated animals or of cultivated plants, 

 who devotes his attention to one or two characteristics, must soon 

 reach a point where no further improvement is practicable unless 

 the species is at the same time greatly modified in many other 

 respects. This fact does not prove that specific stability is due 

 to anything else than selection, but only that no great change 

 is possible without the coordinated modification of all the corre- 

 lated features, and this is just what we should expect, on Gal ton's 

 own showing, as the effect of long ages of selection. Here, as in 

 so many other cases, artificial selection proves to be an imperfect 

 analogy ; for while the breeder may utterly destroy all the animals 

 except the few which he positively selects, extermination in the 

 struggle for existence is often so slow as to be imperceptible. 

 Before a failing genetic line is utterly cut off, it may continue 



