330 



The Journal of Heredity 



use of this caiiacity. "Wc understand 

 today why this should be so, since 

 hehotropism dc]jcnds ujjon the ])resence 

 of photosensitive substances, and it can 

 readi]>' be seen that the question of use 

 or disuse has nothinj^ to do with the 

 production of certain harmless chemical 

 compounds in the body." 



USELESS CAPACITIES 



A more striking? case is that of 

 galvanotropism. Dr. Loeb showed lon^' 

 ago that many animals react in a very 

 definite way to a galvanic current, 

 being made to mo\'e toward one of the 

 electrodes; yet no animal in a state of 

 nature has ever been subjected to a 

 continuous electric current. This capa- 

 city, then, could not possibly have 

 been evolved through use, nor can 

 natural selection have had anything 

 to do wth it. It is equally a puzzle to 

 the vitalist who thinks that every part 

 of an animal is given to it for some 

 purpose. "The only consistent attitude 

 is that of the physicist who assumes that 

 the reactions and structures of animals 

 are consequences of the chemical and 

 physical forces, which no more serve a 

 purpose than those forces resi)onsible 

 for the solar systems. From this view- 

 point it is com]:)rehensible why utterly 

 useless tropisms or structures should 

 occur in animals." 



A famous case for the apparent adap- 

 tation of animals to environment has 

 been the blind cave animals. It is 

 l:nown that in caves blind salamanders, 

 blind fishes and blind insects are com- 

 mon, while such forms are compara- 

 tively rare in the open. This fact has 

 suggested the idea that the darkness of 

 the cave was responsible for the degen- 

 eration of the eyes. But some species 

 of cave-salamanders are blind, while 

 others are nt^t. If disuse is the cause, 

 why are they not all blind alike? 

 Again, a blind fish is found living in 

 the o])en water, f)fT the coast of scjuth- 

 ern California. Why is it blind, in 

 spite of constant ex])osure to the light? 



Recent exjK'riments with fish have 

 shown that blindness can be produced 

 in more than one way: (1) when wide 

 crosses are made, blind embryos are 

 frequently produced; (2) the eyes fail to 



develop if the temperature is kept very 

 low; and finally (3) blind fish can be 

 produced if certain chemicals are added 

 to the water. 



The true explanation of the frequency 

 of blind fish in caves then is fairly 

 obvious. Animals born with defects 

 which would handicap them in open 

 water may survive in a cave, and if 

 they accidentally wander into a cave, 

 they will perpetuate themselves there. 

 The cave is not responsible for produc- 

 ing the blindness, but merely for allow- 

 ing a blind form to live. The idea 

 that the cave adajjts its inmates to 

 life under cave conditions, is, therefore, 

 a misinterpretation. 



"This attitude leaves us in a quan- 

 dary. The whole animated world is 

 seemingly a s\Tnphony of adaptation. 

 We have already mentioned the eye 

 with its refractive media so well curved 

 and placed that a more or less perfect 

 image of outside objects is focussed 

 exactly on the retina; and this in spite 

 of the fact that lens and retina develop 

 independently; we have mentioned and 

 discussed the cases of instincts or auto- 

 matic arrangements which are required 

 to perpetuate life — the attraction of 

 the two sexes and the automatic me- 

 chanisms by which egg and sperm are 

 brought together; the maternal in- 

 stincts by which the young are taken 

 care of; and all those adaptations by 

 which animals get their food and the 

 suitable conditions of {^reservation. Can 

 we understand all these adaptations 

 without a belief in the heredity of 

 acquired characters? As a matter of 

 fact the tenacity with which some 

 authors cling to such a behef is dic- 

 tated by the idea that this is the only 

 alternative to the sujiernaturalistic or 

 vitalistic ideas. The writer is of the 

 opinion that we do not need to depend 

 on the assum])tion of the heredity of 

 acquired characters, but that i)hysio- 

 logical chemistry is adequate for the 

 purpose." 



FOK.MATIOX OF THE EYE 



The fonnation of the eye is a good 

 test case. Uhlenhuth trans])lantcd the 

 eyes of young salamanders into dilTer- 

 ent parts of their liodies where they 



