n6 /. LIONEL TAYLER [august 



inevitably result an organism which tends to vary more and more 

 definitely. 



To determine how far evolution has been dependent on one or 

 more of these three factors, it is necessary to estimate — 



I. The direct accommodative power of environment over proto- 



plasm, if it exists. 



II. The power existing in protoplasm of responding to conditions 



which favour its activity, and the relation, if any, that 

 somatic response bears to germinal in multicellular organism. 



III. Whether the responsive power (II.) or the direct influence of 



environment (I.) are altered in relation to present by past 

 accommodations, or variations, or both, and if so, the relative 

 importance of the character, intensity, and persistency of 

 these past conditions in producing more or less permanent 

 or transitory modifications or variations in organisms. 



It follows from the preceding argument that it is necessary to 

 understand the theoretical capability of each of these three sets of 

 factors to account for the process of evolution, and to endeavour to 

 form some estimate of the probable primitive material from which 

 the present forms of life have proceeded. 



In this article I propose to examine this question from three 

 aspects, first, the theoretical capability of natural selection, secondly, 

 some of the chief difficulties advanced against this principle, and 

 lastly, a few of the more general properties of protoplasm and the 

 inferences which these main characteristics appear to justify. 



The Limitations of the Principle of Natural Selection. 



Ever since the publication of the " Origin of the Species " in 1859, 

 there have been steadily rising into greater prominence, two lines of 

 thought which seem to lead to fundamentally opposite conceptions of 

 the principles which underlie the process of organic evolution. One 

 tendency manifests itself in an increasingly marked disposition to 

 minimise the claims of — use and climatic — inheritance, and to explain 

 the course of evolution by the single principle of selection and certain 

 fundamental properties of protoplasm. The other school of thought 

 tends as emphatically to disregard this selection principle, and to rely 

 on the responsive power of protoplasm and the influence of environ- 

 ment as the main causes of evolutionary development. Some of the 

 members of this school also add to these assumed properties of proto- 

 plasm, other innate tendencies by which protoplasm is supposed to be 

 capable of developing along definite lines which are independent of 

 environment. In the one case, the supporters of selection maintained 

 that, as no case of supposed use-inheritance had ever been brought 

 forward which could not be as easily, or even more easily, accounted 



