210 COOK 



of evolution as isolated groups or are merely adjustments to 

 different conditions, any more than it could be ascertained with- 

 out local study whether an individual bird-skin represented a 

 regular resident, a migrant, or a still more accidental visitor. 



In this merely taxonomic or nomenclatorial sense the envi- 

 ronment can be said to cause species, but such a statement has 

 no warrant in the field of evolution. If we have undertaken to 

 diagnose species by characters which represent merely environ- 

 mental adjustments our only course for the future is to recognize 

 and rectify our mistakes, and not attempt to utilize them as the 

 basis of doctrines of environmental causes of evolution. 



For physiological and evolutionary purposes the species is not 

 to be thought of in the mere systematic sense, as represented by 

 the original specimen or even by the form in which the plant 

 appears in what are supposed to be its normal conditions. The 

 ■physiological and evolutionary species covers all the forms tinder 

 zvhich the organism can maintain itself and complete its life- 

 history, to say nothing of the definitely abnormal results shown 

 when conditions are too adverse. 



Adjustment characters, as such, are not inherited, according 

 to the usual definition of inheritance, that is, they are not 

 necessarily repeated in each generation, but are readily recover- 

 able when needed, even after long periods of time. The plant 

 or animal if kept for many generations under the same envi- 

 ronment may continue to show the same adjustment, but this 

 may be completely changed by transfer to other conditions of 

 growth. Thus at 4000 feet coffee has a more strict and upright 

 habit of growth, darker, firmer foliage and larger seeds than 

 at 2000 feet, but if seedlings from the two altitudes be exchanged 

 they always grow into trees showing the characters appropriate 

 to their new situations. 



It appears, therefore, that both kinds of fitness, the general 

 features which adapt the species as a whole to its place in nature, 

 and the special powers of adjustment which assure to the indi- 

 vidual a certain latitude of environmental opportunities, are 

 normal characters of species, quite as much as those which 

 have no such acute relations to the environment. Unless we 

 can resume and carry to completion the Darwinian task of 



