Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

ILLUSTRATIVE OF NATURAL SELECTION. 167
it is true, are acquainted with the influences of climate,
altitude, and other physical conditions, in modifying
the forms and external characteristics of plants; but
I am not aware that any peculiar influence has been
traced to locality, independent of climate. Almost
the only case I can find recorded is mentioned in
that repertory of natural-history facts, "1 The Origin
of Species," viz. that herbaceous groups have a tendency to become arboreal in islands. In the animal
world, I cannot find that any facts have been pointed
out as showing the special influence of locality in
giving a peculiar facies to the several disconnected
species that inhabit it. What I have to adduce on
this matter will therefore, I hope, possess some interest and novelty.
On examining the closely allied species, local forms,
and varieties distributed over the Indian and Malayan
regions, I find that larger or smaller districts, or even
single islands, give a special character to the majority
of their Papilionidoe. For instance: 1. The species
of the Indian region (Sumatra, Java, and Borneo)
are almost invariably smaller than the allied species
inhabiting Celebes and the Moluccas; 2. The species
of New Guinea and Australia are also, though in a
less degree, smaller than the nearest species or varieties of the Moluccas; 3. In the Moluccas themselves the species of Amboyna are the largest; 4.
The species of Celebes equal or even surpass in size
those of Amboyna; 5.: The species and varieties of
Celebes possess a striking character in the form of