128 
Rev. J. T. Gulick on the 
any action of the same principle. I have never maintained 
that any species can long escape the action of natural selec- 
tion ; but I have that natural selection cannot produce trans- 
formation of a race unless it secures the propagation of other 
than average forms of that race ; that it cannot be a cause of 
divergence unless to this condition is added the independent 
generation (i. e. isolation) of groups that are subjected to some 
diversity in its action ; and that, in isolated groups, some of 
the divergent characters may be due to other causes of trans- 
formation. In the passage I have quoted from p. 142 he 
expresses great confidence in the proof that all specific charac- 
ters are developed and fixed by natural selection; but in the 
discussion that follows concerning the influence of natural 
selection he claims as belonging to this principle sets of influ- 
ences which are usually included under sexual selection and 
which he cannot regard as due to the reactions between the 
species and its environment (see i Darwinism,’ pp. 282-285), 
and even then it is found too narrow to cover all the facts of 
specific divergence ; for when he comes to consider the origin 
and development of accessory plumes he has to abandon the 
theory to which he has clung through the greater part of the 
book. Speaking of the enormously lengthened plumes of the 
“ bird of paradise and of the peacock,” he says, on page 293, 
u The fact that they have been developed to so great an extent 
in a few species is an indication of such perfect adaptation to 
the conditions of existence, such complete success in the battle 
of life, that there is, in the adult male at all events, a surplus 
of strength, vitality , and growth-power , which is able to expand 
itself in this way without injury . That such is the case is 
shown by the great abundance of most of the species which 
possess these wonderful superfluities of plumage. . . . Why , 
in allied species, the development of accessory plumes has taken 
different forms, we are unable to say , except that it may be due 
to that individual variability which has served as the starting- 
point for so much of what seems to us to be strange in form 
or fantastic in colour, both in the animal and vegetable world.” 
(The italics are mine.) According to the theory he has else- 
where maintained, these superfluities of form and colour which 
are not controlled by natural selection should present u a series 
of inconstant varieties mingled together, not a distinct segre- 
gation of forms” (p. 148) ; but in this passage he teaches 
that they have assumed different forms in allied species. On 
p. 141 he maintains that characters which are neither bene- 
ficial nor injurious are from their very nature unstable and 
cannot become specific, while here he offers a suggestion as 
to how they have become specific. There is, then, a problem 
