Tendency of Species to form Varieties. 



6357 



On the Tendency of Species to form Varieties. 

 By Thomas Boyd, Esq. 



I have read the papers on the variation of species in the ' Zoologist' 

 (Zool. 6292—6308) with much interest; and yet they have left an 

 unsatisfactory feeling in my mind : on asking myself, "What does all 

 this prove?" the only answer I could make was, "A possibility." 

 They seem, in common with very much of the argument and discus- 

 sion on allied subjects in the present day, like a return to the old 

 philosophy, " the anticipation of Nature," as Bacon calls it, and the 

 only result attained, or likely to be attained by it, is that we lose our- 

 selves in doubt, like the ancient philosophers, 



" And find no end, in wandering mazes lost." 



The argument, it seems to me, starts upon the smallest possible 

 basis of facts, the known variation in species, and then goes on, 

 without any additional fact, to the possibility or probability of an 

 indefinite extension of this variation. Is this w r ise ! Is it in accord- 

 ance with the spirit of modern Science ? 



But the last of the three papers referred to goes much further than 

 the others; it is much more definite in its aim, it claims something 

 of the character of a proof, and it carries the argument into ground 

 scarcely touched before. After ably sketching out the effects of 

 external circumstances on the numbers and variation of animals, the 

 author lays down two points,— -first, "that the animal population of a 

 country is generally stationary, being kept down by a periodical 

 deficiency of food and other checks," and secondly, " that the com- 

 parative abundance or scarcity of the individuals of the several 

 species is entirely due to their organization and resulting habits, 

 which, rendering it more difficult to procure a regular supply of food 

 and to provide for their personal safety in some cases than in others, 

 can only be balanced by a difference in the population, which have to 

 exist in a given area." This, it seems to me, is far more general and 

 comprehensive than is warranted by the facts of the case ; all that is 

 proved is that the want of food and the inability of self-preservation 

 do exercise an influence over the number of species, and that it is 

 probable that these are two main causes of numerical variation ; but 

 to go beyond this is to ground conclusions upon our ignorance, for 

 there may be many causes, of which we know nothing, which exercise 

 powerful influence over these phenomena. 



In the next paragraph allusion is made to the probability that some 



