NATURAL SELECTION NOT ALWAYS THE CAUSE. 219 



which are genera of terrestrial habits, are (with but few exceptions) 

 dextral in form ; while the other genera, which are plant feeders and 

 constantly hanging to branches or leaves, present many species that are 

 constantly sinistral, and many others that are both dextral and sinis- 

 tral. Why should Achatinella adusta in Pauoa and Makiki be constantly 

 sinistral when the most nearly allied A. producia found in the same 

 valleys is both dextral and sinistral ? Why should A . bacca and A . 

 abbreviate, in Palolo and Waialae be constantly dextral when other 

 species of Achatinella in the same valleys are for the most part sinistral ? 

 Is there any adaptation to the environment possessed by a dextral 

 form which would be lost if the form was reversed ? If not, natural 

 selection could not have anything to do with that part of its char- 

 acter. Bulimella rosea is sinistral, while B. bulimoides is dextral. If 

 in this respect they should exchange forms, would any disadvantage 

 be experienced by either species? It is impossible to conceive of any 

 disadvantage that would follow, and, therefore, I can not believe that 

 this difference in the two species was in the first place due to natural, 

 sexual, or any other form of selection. 



There are many other specific distinctions presented in this family 

 which seem to be of no advantage, though they are not so far removed 

 from all suggestion of the possibility of use as the character we have 

 just been considering. The brilliant colors and varied patterns pre- 

 sented by many of the arboreal species would be of advantage to them- 

 selves if they served as warning of nauseous qualities to creatures that 

 are liable to prey upon them ; but no such conditions exist. The birds 

 of the forest region are for the most part fruit and nectar feeding; 

 and the ants and mice which in recent years have made sad havoc 

 with the mountain snails unfortunately do not spare the highly colored 

 species. 



There can be no doubt that when representatives of different genera 

 occupy the same trees they remain segregated through the influence 

 of sexual instincts, which must be associated with some means of rec- 

 ognizing those of their own group ; but it is not at all probable that 

 the colors and patterns of any species are recognized by their mates, 

 or have been developed under the influence of sexual selection. 

 There is, therefore, strong reason to doubt whether selection of any 

 kind has been concerned in the production of the beautiful colors and 

 patterns of these species, unless possibly correspondences in color 

 within the limits of a genus are, in some cases, due to the inheritance 

 of tendencies produced by selection when conditions were very differ- 

 ent from what we now find. But the divergences in color and pattern 

 in the species of one genus can not be thus explained. 



