234 AMPLIFICATION AND REDUCTION 



Reduction is the term used to connote the converse of amplification, 

 and it also may be either individual or phyletic, where the develop- 

 ment of the mature organism, either in whole or in part, in external 

 form or in internal structure, falls short of that of the ancestry, the 

 condition would be described as reduced : such a state may be held 

 to result from a check in the development before maturity, as shown 

 in the ancestry, had been attained. If such a condition become a 

 character of an evolutionary sequence, then it would rank as a phyletic 

 reduction. 



Progressive amplification and progressive reduction are phenomena 

 which may be illustrated in any phyletic sequence, and the question 

 whether or not, and how far either has been operative in the history 

 of descent in any specific case is virtually the equivalent of enquiry 

 into its evolutionary history. The character of the progression may have 

 varied at different times : in any stock a period of evolutionary advance 

 may have been succeeded by a period of retrogression or the converse. 

 Further, it is to be noted that amplification or reduction may affect the 

 organism as a whole, or only special parts of it. Moreover, different 

 parts of the same organism may show evidence of having behaved in 

 exactly converse ways in the course of descent. Examples of this are 

 seen in every case of correlation, the amplification of one part habitually 

 entailing the reduction of another. 



To produce any organism as it is seen to-day, the two factors of 

 amplification and reduction have been constantly possible throughout 

 descent. The organism itself may be held to represent the sum of all 

 such progressions and retrogressions, phyletic and individual. It is obvious 

 that while reduction may have been active in the later phases, the balance 

 taken over the whole evolutionary history must have been on the side 

 of amplification, otherwise the organism would be non-existent. This 

 may seem a mere platitude ; but it is essential to state it, in view of the 

 overestimate of the factor of reduction, as shown in most morphological 

 discussions. This has resulted from the greater readiness with which 

 evidence of reduction comes to hand, together with the method of our 

 comparisons, which habitually start from pronounced " types." 



The common criterion is that of mere size, but this carries with it 

 differences of complexity, either of external form, or of internal structure, 

 or usually of both. As a rule it is impossible to tell from a single 

 specimen, or even from a number of representatives of a constant species 

 whether the organism has been reduced or amplified in the course of 

 its antecedent phyletic history : it does not bear any certain index of 

 these points in its individual characters, unless in cases where reduction 

 has led to change of the original function of a part. It is primarily upon 

 the comparison of organisms related to any given species that an opinion 

 may be based how far amplification or reduction respectively have been 

 operative in its evolution. 



