342 



Proceedings of the Asiatic Society. 



No. 3, 



and which indeed " most Botanists fail to distinguish" resist all 

 attempts to cross them, while others very different from each other 

 and universally recognised as species easily give origin to fertile 

 hybrids. Man is generally regarded as a single species, but M. Paul 

 Broca brings forward a multitude of facts to shew that between the 

 different races of mankind, the degrees to which crossing is possible 

 vary greatly, and that the Australian and European do not produce 

 a permanent mixed breed. The same appears to be the case in Ceylon 

 where the Portuguese and Dutch have left scarcely any descendants 

 of mixed blood, and where there is good reason, on excellent authority, 

 to infer that were the English now to leave the Island, the same 

 extinction of the mixed race would shortly supervene. Much more 

 might be said on this point, and to show that hybridity is not a simple 

 phenomenon, but exists in all degrees and is affected by slight changes 

 of condition. 



If, then, interbreeding be taken as the criterion of species, resem- 

 blance of apparent character which is in most cases the only point 

 ascertained, is clearly not reliable. The Chinese and Indian pheasants 

 interbreed freely although very different in plumage, &c, and the 

 mere fact of two forms differing to such an extent as to be entitled 

 to receive different names is no argument that their origin is distinct 

 even according to our present knowledge, and on the unproved and 

 apparently improbable assumption that forms of common descent in 

 all cases interbreed freely. 



In the ease adduced by M. Agassiz, we do not know how far the 

 species termed by him distinct are really so on other than grouods of 

 external difference, and the case therefore cannot be argued. It may 

 be that at a former geological period communication existed between 

 the two basins, and that there was a dispersion of species, that since 

 the separation certain of these have so varied in one or both areas 

 as now to be regarded as distinct, while the pickerel has not so varied. 

 Again, two rivers flowing respectively north and south would afford 

 conditions so different that certain forms formerly common might 

 become extinct in one case or the other, whether by change of climate ? 

 by collision with new species of other forms of life, in short by a 

 change in any one of those numerous conditions which affect existence 

 and the destruction of a balance of favourable conditions previously 

 existing. All these are possibilities which, although they can be merely 



etl] 



