79 o THE POPULAR SCIENCE MONTHLY. 



surmise or demonstrate their causes. It is evident that, without the 

 o-enealogical lines which paleontology presents, it is impossible that 

 our hypotheses on this subject can rest on any solid basis. With these 

 lines completed, we will be able, on the other hand, ultimately to 

 reach a demonstration in most if not all the cases which present. 



In the first place, there has long been before the world a theory to 

 account for these changes, and that is the doctrine of use and disuse, 

 propounded by Lamarck. He believed that the use of a part of an 

 animal caused it to grow larger, and that in consequence of disuse a 

 part would grow smaller or become extinct. Another theory is fre- 

 quently spoken of, as though it accounted for the origin of changes, 

 and that is the Natural Selection of Darwin. While naturalists are 

 generally agreed as to the importance of this principle in modifying 

 the results of the creative energy, but few of them regard it as ex- 

 plaining in any way the origin of the changes with which it deals. In 

 the very nature of things, " selection " can not act until alternatives 

 have been presented. And Mr. Darwin and others, who treat of nat- 

 ural selection as though it were a cause of new structures, always pre- 

 mise by admitting that " there is in organic beings a natural tendency 

 to variation." It is in accounting for this variation that the Lamarck- 

 ian hypothesis is useful, and probably expresses a great law of organic 

 nature. In the same way most of those who write of the " influence of 

 the environment" (which Lamarck, by-the-way, fully considered), as 

 though it embraced the causes of evolution, forget that the energy 

 which impresses an animal from this source could have no effect unless 

 the animal possess some impressibility or capacity for response. And 

 they also often forget that an animal capable of free movement is able 

 to modify its environment very materially. 



There is one element of weakness in the Lamarckian theory of use. 

 This is that use implies the presence of something to use, or the exist- 

 ence of a usable part or organ. It is thus incompetent to explain the 

 origin of such a part ab initio, although it may account for the details 

 of its structure, as its segmentation, branching, etc. So I have added 

 to use the energy of effort, and the Lamarckian theory, completed, can 

 be characterized as the theory of the origin of species, by effort, use, 

 and disuse. A prominent cause of change of structure may be here 

 referred to ; and that is, change in consequence of excess or diminu- 

 tion of growth-energy, due to the action of use and effort in disturbing 

 its equilibrium. That is to say, that excessive growth in one place 

 has caused diminished growth in another, and vice versa. This deriva- 

 tive hypothesis explains the origin of many structures wdiich are not 

 useful to the possessor, and of others which appear to be positively 

 injurious. Such characters can not, of course, be accounted for by the 

 direct action of effort and use, which are necessarily directed toward 

 beneficial ends. There are also numerous characters, chiefly of an 

 ornamental nature, as color, etc., which are the direct result of the 



