-SECT, i.] INTRODUCTION. 3 



In the next place, not only do Specific forms exist in Nature, 

 but they exist in such a way as to tit the place in Nature in 

 which they are placed ; that is to say, the Specific form which an 

 organism has, is adapted to the position which it fills. This again 

 is a relative truth, for the adaptation is not absolute. 



These two facts constitute the problem : 



I. The forms of living things are various and, on the whole, 

 are Discontinuous or Specific. 



II. The Specific forms, on the whole, jit the places they 

 have to live in. 



How have these Discontinuous forms been brought into exist- 

 ence, and how is it they are thus adapted ? This is the question 

 the naturalist is to answer. To answer it completely he must find 

 (1) The modes and (2) TJie causes by which these things have 

 come to pass. 



Before considering the ways in which naturalists have tried to 

 answer these questions, it is necessary to look at some other 

 phenomena characteristic of Life. We have said that at a given 

 moment, or point of time, the specific forms of living things com- 

 pose a discontinuous series. The element of time thus intro- 

 duced is of consequence, arid leads to important considerations. 

 For the condition of the organized world is not a fixed condition, 

 but changes from moment to moment, and that which can be pre- 

 dicated of its condition at one moment may not at any other point 

 of time be true. This process of change is brought about partly by 

 progressive changes in the bodies of the individuals themselves, 

 but chiefly by the constant succession of individuals, the parents 

 dying, their offspring succeeding them. It is then a matter of 

 observation that the offspring born of parents belonging to any 

 one Specific Group do as a rule conform to that Specific Group 

 themselves, and that the form of the body, the mechanisms and 

 the instincts of the offspring, are on the whole similar to those 

 which their parents had. But like most general assertions about 

 living things this is true not absolutely but relatively only. For 

 though on the whole the offspring is like the parent or parents, its 

 form is perhaps never identical with theirs, but generally differs 

 from it perceptibly and sometimes materially. To this pheno- 

 menon, namely, the occurrence of differences between the structure, 

 the instincts, or other elements which compose the mechanism of 

 the offspring, and those which were proper to the parent, the name 

 Variation has been given. 



We have seen above that the two leading facts respecting the 

 forms of living things are first that they shew specific differen- 

 tiation, and secondly that they are adapted. To these we may 

 now add a third, that in the succession from parent to offspring 

 there is, or may be, Variation. It is upon the fact of the exist- 

 ence of this phenomenon of Variation that all inductive -theories 

 of Evolution have been based. 



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