INTRODUCTION. XXX111 



entertain doubts respecting the far more important and 

 significant Darwinian hypothesis. We may doubt that 

 the hypothesis of Natural Selection is as well-founded 

 as the Newtonian theory of Gravitation ; or, admitting 

 Natural Selection as an undoubted vera causa, we may 

 strongly doubt that it was the sole agency employed by 

 Nature in the derivation and fashioning of her innumer- 

 able types and varieties of life. We may doubt the 

 universal applicability of the hypothesis, even though 

 we must acknowledge that our biologists have produced 

 much evidence in its favour. And those who prefer to 

 doubt may still doubt the descent of man from an extinct 

 variety of the ape species, though it is really easier to 

 believe, and is more likely to be true, than the infinitely 

 wider Theory of Development, from which, if established, 

 it would of course follow as an evident corollary. In the 

 present case, the corollary, if the least satisfactory, is 

 the most significant part of the theory ; and already, 

 independent of the theory, in our undoubted ancestor, 

 the Cave-man, we have more than half-way bridged the 

 gulf between us and our still more questionable " country 

 cousin," the gorilla. 



But, as said, we may still doubt a little longer our 

 alleged animal origin, as we may doubt Haeckel's hypo- 

 thesis of the Spontaneous Generation of life, which, 

 though it can hardly as yet be pronounced an article of 

 scientific faith, is probably destined at no "distant date to 

 become one. And we may entertain degrees of doubts 

 about all these hypotheses, even though we concede that 

 each one of them is on the right lines of truth, and is 

 gradually feeling its way nearer and nearer to it. For 

 that some doubt is inseparable from every hypothesis is 

 implied in the very notion of a hypothesis ; and all who 

 know the logical and psychological conditions which 



