DARWINISM NOT AN HYPOTHESIS. 29 



please ; they are rather compelled and obliged to accept 

 it, according to the general principle observed in all natural 

 sciences, that we must accept and retain for the explanation 

 of phenomena any theory which, though it has only a 

 feeble basis, is compatible with the actual facts — until it is 

 replaced by a better one. If we do not adopt it, we re- 

 nounce a scientific explanation of phenomena, and this is, 

 in fact, the position which many biologists still maintain. 

 They look upon the whole domain of animate nature as a 

 perfect mystery, and upon the origin of animals and plants, 

 the phenomena of their development and affinities, as quite 

 inexplicable and miraculous; in fact, they will not allow that 

 there can be a true understanding of them. 



Those opponents of Darwin who do not exactly \\dsh to 

 renounce a scientific explanation are in the habit of saying, 

 " Darwin's theory of the common origin of the different 

 species is only one hypothesis; we oppose to it another, 

 the hypothesis that the individual animal and vegetable 

 species have not developed one from another by descent, 

 but that they have come into existence independently of 

 one another, by a still undiscovered law of nature." But as 

 long as it is not shown how this coming into existence is 

 to be conceived of, and what that " law of nature " is — as 

 long as not even probable grounds of explanation can be 

 brought forward to account for the independent coming 

 into existence of animal and vegetable species, so long this 

 counter-hypothesis is in fact no hypothesis, but an empty 

 unmeaning phrase. Darwin's theory ought, moreover, not 

 to be called an hypothesis. For a scientific hypothesis 

 is a supposition, postulating the existence of unknown 



properties or motional phenomena of natural bodies, wliich 

 3 



