14 Willis.— The Evolution of Species in Ceylon, 
did it survive the dry one which followed, unless it was really suited to 
a comparatively large range. In one year the plant may have to compete 
only with two or three others, in the next with five or six, and with new 
arrivals of animals or diseases, &c. If a species such as one of the R or 
RR forms be suited to local conditions, it must be to averages, and how 
did a species evolve to suit an average, and when did it decide that the 
average was fulfilled ? Accepting mutation, as one must accept it, it is 
evident that the parent must have been able to stand the conditions in 
some variety, and why should it give rise to a local form, which one cannot 
conceive as any better suited to them (on an average) ? 
Not only do the endemics as a whole show these increasing areas 
of distribution on a regular numerical plan, but the single families and the 
single genera show the same thing, as has 
already been explained in the preceding argu- 
ment, and as may be illustrated by the case 
of Doona , a rough outline of whose distribution 
is given in the accompanying cut. D ♦ zeylanica 
has an area of distribution overlapping all the 
other species, which show smaller and smaller 
areas within it. If one set out to explain 
the distribution of endemic or other species in 
Ceylon by Natural Selection, one has to explain 
why every family and genus has approximately 
the same proportion of areas VR, R, RR, RC, 
C, and VC, when one can only pretend to talk 
of local conditions in the case of VR. 
The idea that endemic species were evolved 
to suit local conditions is based largely upon 
Wallace. 1 So long as we imagined islands — 
taken as a whole — as their habitats, it was 
possible to say that the local flora, the local 
fauna, local soil, local conditions generally, varied for each island, as for 
instance in the Galapagos. And this idea was encouraged by the fact 
that the studies of endemism have mostly been made in zoology, and 
an animal confined to one island will often be able to roam over the whole 
island. It received its first real and severe shock from the investigations 
of Gulick 2 on the local endemic forms of the Mollusca in Hawaii. 
But when one comes to try to apply this idea to the endemic plants 
of Ceylon, which are often very local zvithin the island (25,000 sq. miles), 
one rapidly gets into great difficulties. The climates of two mountain tops 
in the island only differ in averages, and how do plants evolve to suit an 
Fig. 2. Distribution diagram for 
the genus Doona. 
1 Island Life, and other papers and books. 
? Evolution, Racial and Habitudinal. Washington, 1905. 
