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-bf 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 producta and Achatinella 

 adusta; and within the groves of this valley upon which we look on 

 our left were created Achatinella stewartii and Achatinella johnsonii; 

 while behind us a mile to the northeast, in the jungle that clings to 



