1905.] NATURAL SCIENCES OF PHILADELPHIA. 209 



Specific determination is made chiefly upon color. Some few cases 

 of color in serpents are protective or warning, but very many species 

 in most large genera are marked by differences in pattern or tint so 

 inconspicuous, that in view of the want of keen eyesight in snakes, it 

 does not seem credible that they can serve the ends usually regarded 

 as useful. The range of color variation in many species is extraordi- 

 narily great, and some brilliantly colored species are mainly subter- 

 ranean, both of which facts are inconsistent with the theory of recog- 

 nition markings. Recognition in snakes is probably much more served 

 by the olfactory than by the optic sense. Sexual selection cannot be 

 a cause, for few species are known to present differences characteristic 

 of sex. 



Pigments in reptiles probably result from waste products of meta- 

 bolism, which doubtless is influenced by external conditions and food. 

 It is not, however, the existence of color, but its precise distribution in 

 species which is here in question, and the minuteness of the differences 

 in many cases between species of a genus, or between species belonging 

 to distinct genera but occupying the same range, renders it doubtful 

 if the utility principle can be held to explain them adequately. At the 

 same time the subject is very obscure. 



The opinion held by the extreme Neo-Darwinians is a deduction from 

 the denial of the inheritance of acquired characters urged by the Weiss- 

 man school. It is true that the experimental evidence for such inheri- 

 tance is far from establishing it, but, on the other hand, none but that 

 of negative kind can ever be brought against it, and as a philosophical 

 proposition it has a right to consideration. The further assumption 

 that Natural Selection necessarily requires the disappearance of "indif- 

 ferent" characters which are outside of the law of utility, is unwar- 

 ranted. As far as is now known, inheritance and variation are ulti- 

 mate facts of organic life. Congenital variation occurs within rela- 

 tively narrow limits about a mean, and if it be held that the characters 

 we have been considering have come to be of this kind, so long as they 

 are not injurious but merely "indifferent," no reason can be assigned, 

 aside from the necessity of completing a logical system, why they 

 may not be continued in succeeding generations. 



Natural Selection is too often spoken of as if it were a positive force 

 in evolution. It is not so. The struggle for existence is no more than 

 the trial which conditions success, and Natural Selection does no more 

 than determine the failures by means of their detrimental structures. 

 It cannot directly affect those merely neutral. 



The fact that characters such as the presence of brilliant colors in 

 subterranean species, and the fusions among head plates which there 

 is especially good reason to regard as "indifferent," have become fixed 

 to the point of specific or generic value, directly contradicts Mr. Wal- 

 lace's law of exclusive utility. Their continuance, furthermore, would 

 seem to require explanation under a doctrine of absolute non-inheri- 

 tance of acquired characters. 



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