204 COOK 



modified in adjustments to the different conditions. The 

 "plasticity" might hinder, even, as Professor Metcalf has 

 recently pointed out, for the ability of the species to accom- 

 modate itself promptly would render unnecessary any perma- 

 nent progress in the direction of these particular changes. 1 



Of permanent effects arising from the influence of environ- 

 ment upon adjustment changes, there would remain only the 

 possibility that a species which had once possessed a wide range 

 of accommodation, might lose this by long disuse, and might 

 thus become more narrowly specialized as a result of environ- 

 mental influence. Thus an amphibious species, if confined 

 long enough to a strictly terrestrial habitat, might forget, as it 

 were, how to grow in water. 



That experiments have not yet demonstrated such an effect 

 does not justify a general denial of the possibility. The phe- 

 nomenon would be no less real if it took a hundred or a thousand 

 years to produce it than if it required only five or ten. 2 But in 

 any case the result would be negative rather than positive, 

 involving a diminution of the powers of the species rather than 

 an enlargement of them. There would be a loss of characters 

 instead of an addition, and no occasion to infer that environment 

 had aided evolution. The case would be quite analogous with 

 the influence of environment through natural selection, which is 

 likewise not constructive, but wholly restrictive. 



Much of the existing terminology of evolutionary discussion 

 is calculated to commit us in advance to the doctrine that the 

 adjustment is caused by the environment, whereas the fact is 

 that the organisms are active instead of passive, and are able to 

 put forth their own efforts toward adjustment to the varied 

 external circumstances. It is only in a loose and figurative 

 sense that the environment can be said to cause the adaptive 

 adjustments. The arctic climate "causes" the Esquimaux to 

 clothe themselves in furs, but it does not skin the fur-bearing 



'Metcalf, M. M., 1906. The Influence of Plasticity of Organisms upon Evo- 

 lution, Science, N. S. 23 : 789. 



2 An additional reason for caution in denying the possibility of a loss of the 

 power of accommodation from disuse is found in the phenomenon of " fixing the 

 type" of a variety by selection. The normal diversity tends to disappear when 

 only one carefully selected type of the variety is bred for several generations. 



