144 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



It is now many years ago since the editors of Silliman's Journal 

 requested the late Professor Agassiz to give them his opinion on the 

 following question. In a certain dark subterranean cave, called the 

 Mammoth Cave, there are found some peculiar species of blind fishes . 

 Now the editors of Silliman's Journal wished to know whether Profes- 

 sor Agassiz would hold that these fish had been specially created in 

 these caves, and purposely devoided of eyes which could never be of 

 any use to them; or whether he would allow that these fish had prob- 

 ably descended from other species, but, having got into the dark cave, 

 gradually lost their eyes through disuse. Professor Agassiz, who was 

 a believer in special creation, allowed that this ought to constitute 

 a crucial test as between the two theories of special design and heredi- 

 tary descent. "If physical circumstances," he said, "ever modified 

 organised human beings, it should be easily ascertained here." And . 

 eventually he gave it as his opinion, that these fish "were created/ 

 under the circumstances in which they now live, within the limits oveif 

 which they now range, and with the structural peculiarities which no\T 

 characterise them." 



Since then a great deal of attention has been paid to the fauna of 

 this Mammoth cave, and also to the faunas of other dark caverns, not 

 only in the New, but also in the Old World. In the result, the 

 following general facts have been fully established. 



1. Not only fish, but many representatives of other classes, have 

 been found in dark caves. 



2. WTierever the caves are totally dark, all the animals are blind. 



3. If the animals live near enough to the entrance to receive some 

 degree of light, they may have large and lustrous eyes. 



4. In all cases the species of blind animals are closely alhed to 

 species inhabiting the district where the caves occur; so that the 

 blind species inhabiting the American caves are closely alUed to 

 American species, while those inhabiting European caves are closely 

 allied to European species. 



5. In nearly all cases structural remnants of eyes admit of being 

 detected, in various degrees of obsolescence. In the case of some of 

 the crustaceans of the Mammoth cave the foot-stalks of the eyes are 

 present, although the eyes themselves are entirely absent. 



Now, it is evident that all these general facts are in full agreement 

 with the theory of evolution, while they offer serious diflficulties to 

 the theory of special creation. As Darwin remarks, it is hard to 

 imagine conditions of Hfe more similar than those furnished by deep 



