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 ¢he 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. 
