EVOLUTION, RACIAL AND HABITUDINAL, 
CONTROLLED BY SEGREGATION. 
By Rev. JoHN THomAS GULICK. 
CHAPTER I. 
INTRODUCTION. 
I. Facts CALLING FoR EXPLANATION. 
When a number of closely related varieties and species, occupying 
adjoining districts of very limited extent, come under observation, 
the problems connected with the origin of species are liable to be 
forced upon us. It was therefore natural that when, in 1851 and 
1852, I was engaged in collecting the extremely local species of snails 
found on the island of Oahu, my mind was often occupied with these 
questions. I observed that each large section of the world had its 
own peculiar forms of life, and it seemed reasonable to assume that 
the center of creation for each form had, in most cases, been within 
the district where it is now found. The most wonderful limitation in 
the areas of distribution for each species, and accordingly the most 
remarkable localization of the center of creation for each, was, how- 
ever, found in the case of the many species of snails living on the trees 
of the mountain forests of Hawaii. Each valley seemed to be inhab- 
ited by peculiar forms. Valleys only a mile apart were occupied by 
distinct varieties, and often by different species. Groves of candle- 
nut tree (Aleurites triloba), occupying valleys 5 and 6 miles apart, 
were found to be the homes of completely separate sets of species of 
snails. I had found not simply a large section of the world within 
which peculiar species had originated, but ascending a certain moun- 
tain ridge a few miles from Honolulu, and looking down, I could say, 
‘“That valley to the right, a couple of miles in length and half a mile 
in width, is the birthplace of the Achatinella productaand Achatinella 
adusta; and within the groves of this valley upon which we look on 
our left were created Achatinella stewart and Achatinella johnsonit; 
while behind us a mile to the northeast, in the jungle that clings to 
I 
