6o2 THE POPULAR SCIENCE MONTHLY. 



to the existing conditions. Tliis adaptation finds expression in tbe 

 survival of the fittest in the struggle for life ; that is to say, those in- 

 dividuals continue to live and reproduce their kind whose structure 

 enables them to undergo changed conditions without succumbing, 

 while otliers, because they cannot adapt themselves, perish, leaving 

 no posterity, no trace of their having ever existed, save, perhaps, in 

 the geological strata of their epoch. The special advantage which 

 has once insured the survival of an organism, while its congeners 

 which possessed no such advantage perished, is fixed by heredity; it 

 o^rows under the influence of that same law of survival which insures 

 ihe u]^per-hand in the struggle for life to the organisms possessing the 

 advantage in the highest degree; in virtue of the law of the coordina- 

 tion and subordination of parts and functions, it brings about in the 

 whole organism very extensive modifications which insure its fixity; 

 and the sum total of the new characters becomes sufficiently stable to 

 convey to the mind which observes it the impression of the persistence 

 of forms and the existence of types, whereas in fact there exist only 

 changes amid which there remain, in virtue of the law of heredity, 

 traits of resemblance to a common ancestor or stock. 



Such are, in brief, the principal laws of biological phenomena, and 

 the chief theories which have been devised for the purpose of assigning 

 to them causes. When, in order to establish or to impugn laws and 

 theories so far-reaching as these, we can have recourse to direct 

 expei-iment and observation, the mind is satisfied and its certitude 

 reposes on an immovable basis. But when a theory has to do with 

 origins in the remote past, or even in the present, but inaccessible to 

 experiment, our certitude rests on no solid foundation. In the ab- 

 sence of experiment, we have to be content with opinions formed ac- 

 cording to the rules of induction and of analogy, and possessing more 

 or less probability. Among views of this sort, those appear to have 

 greatest weight which, in their contexture and in the method of their 

 formation, are most in harmony with those beliefs of which we are 

 most certain ; which rest on the same general principles ; which, so 

 to speak, are incorporated with our beliefs, so that, were they to suc- 

 cumb to criticism, their fall would compromise the entire system. In 

 other words, they must occupy tlieir own place in a general philosophy, 

 there appearing as so many links in a chain attached, on the one 

 liand, to laws and theories which account for them, and, on the other, 

 to laws and theories which without them cannot be exjilained. 



Could we look for this result from the only general system of 

 philosophy which has existed down to the present day ? Having been 

 wa-itten at a time when the science of life had for its generalizations 

 only conclusions from Bichat's researches, the hypotheses of Gall, and 

 the results of classification, that portion of the positive philosoj^hy 

 which treats of biology is too far behind the actual state of science to 



