ORIGIN OF CAVE LIFE. 95 



ORIGIN OF CAVE LIFE. 



There are three fundamental questions which deserve attention in 

 considering the origin of the present cave fauna: (1) How did the 

 animals get into the caves? (2) What was their condition when they 

 entered the cave? and (3) How have they reached their present con- 

 dition? 



HOW DID THE ANIMALS GET INTO THE CAVES ? 



Most writers upon the origin of cave life make no mention of how 

 animals have reached caves, but confine their discussion to the modifica- 

 tions and the causes of the modifications which animals undergo after 

 having become cave inhabitants. 



There is practical agreement that cave animals have descended from 

 non-cavernicolous forms. There is a difference of opinion as to the precise 

 manner of their original entrance into caves and much discussion as to 

 the causes of their modifications. 



Lankester (1893, 389) explains the colonizing of caves and the origin 

 of blind cave forms as follows: 



This instance [that of the blind cave animals] can be fully explained by natural 

 selection acting on congenital fortuitous variations; many animals are thus bom with 

 distorted or defective eyes whose parents have not had their eyes submitted to any 

 peculiar conditions. Supposing a number of some species of arthropod or fish to be 

 swept into a cavern or to be carried from less to greater depths in the sea; those 

 individuals with perfect eyes would follow the glimmer of light and eventually escape 

 to the outer air or the shallower depths, leaving behind those with imperfect eyes to 

 breed in the dark place. A natural selection would thus be effected. In every suc- 

 ceeding generation (bred in the dark place) this would be the case, and even those 

 with weak but still seeing eyes would in the course of time escape, until only a pure 

 race of eyeless or blind animals would be left in the cavern or deep sea. 



No one who has been within a limestone cavern and has thus gained 

 a conception of what a sudden transmission from epigean to subter- 

 ranean conditions must mean to an animal accustomed to secure food 

 by means of its eyes can seriously consider such an origin of cave 

 inhabitants. Further, as Eigenmann (1900, 57) suggests, cave animals, 

 with or without eyes (and their near relatives outside too, for that 

 matter), do not "follow the glimmer of light," but shun it. 



Animals accidentally driven into caves are often found. The list 

 from Mayfield's Cave includes 17 strays belonging to 6 different orders. 

 Eigenmann (1900, 55, 57) cites another case, that of sunfishes carried 

 into caves. But there is no evidence whatever that any epigean species 

 has thus become established in a subterranean abode. 



