612 
Willis .— The Origin of Species by Large , rather than by 
endemic forms, this time in the Pacific Islands. Dr. Guppy noticed that 
there seemed to be three principal stages in the development of local 
endemism. In the first stage the island was occupied, so far as a given 
genus was concerned, by one or more widely-ranging species usually of 
very variable nature, such, for example, as Metrosideros polymorpha. In 
the second stage the wide-ranger was accompanied, in some of the islands 
at any rate, by local endemic species more or less closely allied to it, and 
in the third stage there were only local endemics. He therefore imagined, 
just as I had done in the case of India and Ceylon, that the wide- 
ranging species had given rise to the local forms, and that it might—or 
perhaps in any case did—ultimately disappear. The following quota¬ 
tions will suffice to indicate the point of view which Dr. Guppy took 
up in 1906: 
4 One where the extremely variable or polymorphous species plays a 
conspicuous part, as represented in such genera as Alphitoma , Dodonaea , 
Metrosideros , Pisonia , and Wikstroemia , the general principle being that each 
genus is at first represented by a widely ranging, very variable species, 
which ultimately ceases to wander and settles down, and becomes the parent 
of different sets of species in the same groups ’ ( 4 , p. 519). 
4 The role of the polymorphous species belongs alike to the plant and 
to the bird. A species that covers the range of a genus varies at first in 
every region, and ultimately gives birth to new species in some parts of its 
range. Then the wide-ranging species disappears, and the original area is 
divided up into a number of smaller areas, each with its own group of 
species ’ (p. 522). 
Dr. Guppy was so kind as to give me a few notes upon his theory of 
Differentiation, from which I extract the portions shown in quotation marks. 
The theory of Differentiation involves the idea of variation that was always 
held, for example, by Hooker and Huxley, and which they pressed upon 
Darwin,to whom it was always a stumbling-block—that it involved a tendency 
to divergence (cf. Guppy in ‘ Age and Area pp. 104-5). 
‘ The same conception of divergent variation is attributed to Goethe 
by Geddes in his article on Variation in vol. 24 of the 9th edition of the 
“Encyclopaedia Britannica ”, p. 77. The German philosopher held a view 
which included, besides the centripetal force of heredity, that of a progressive 
or centrifugal tendency to adaptation to environment. . . . But there were 
other eminent investigators who seem to have got into the differentiation 
stride as soon as they tackled the subjects of variation and distribution. This 
is indicated in the “ loi primordiale ” of A. de Candolle in his “ Geographie 
Botanique’, ii, p. 1338, where the secondary modifications of the great plant 
groups are attributed to variations in conditions produced in the course of 
geological ages. Huxley, when he handled the gentians, got into the same 
stride, and in his letters to Hooker in Sept. 1886, where he characterizes 
