ON THE PROGRESS OF SCIENCE. DC 



nitrogenous substances, either fats or hydrates of carbon, and that 

 the burning of albumen is not in any way concerned in the pro- 

 duction of muscular power." 



The theory of Darwin, that species are not rigidly limited, and 

 have not been created at various times comjilete and unchange- 

 able, but have been gradually and indefinitely varied, from exter- 

 nal circumstances, from natural efforts to accommodate them- 

 selves to surrounding changes, and from the necessity of yielding 

 to force in the struggle for existence, has continually gained 

 ground, and now numbers among its advocates many of the first 

 naturalists of Europe and this country. The opponents of this 

 theory have their strong jooints in accommodating definitions of a 

 species, the phenomena of hybridity, and the non-occurrence of 

 these changes before our eyes. If species were created as we 

 now see them, the more we subdivide them by extended obser- 

 vation the more we increase the number of the supposed crea- 

 tions ; and yet we have no well authenticated instance of a new 

 creation, and in no other opei'ations of nature such a want of con- 

 tinuity, such a perpetually recurring creative miracle. The ten- 

 dency seems to be to the belief that there are no such natural 

 divisions as species, genei'a, families, etc., but that they are merely 

 convenient terms for subdivisions, having a permanence which 

 may outlive many generations of man, and yet which are not ab- 

 solutely fixed. Such is the length of geological periods now 

 admitted, that the phenomena of hybridity may be legitimately 

 explained on the theory of the continuity of succession ; the infe- 

 cundit}'' may just as well be due to physical differences arising 

 from long-continued variation, as to an original organic constitu- 

 tion ; indeed, the acknowledged degrees of h3'bridity are best 

 explained on Darwin's theory. Darwin insists upon time for the 

 changes by natural selection ; and no one will pretend, at the pres- 

 ent day, to date back the earth's history only a few thousand years. 

 Geology teaches that hundreds of thousands of years do not limit 

 the period of the earth's existence as an abode for living organ- 

 isms. In the early days of geological science, the numerous gaps 

 in the record of fossil forms would have been a strong argument 

 against the theory of Darwin; certain species seemed to become 

 extinct and new ones to appear without connecting links ; but, as 

 page after page of this geological record has been discovered, tho 

 gaps become less numerous and less abrupt, and the intermediate 

 torms are gradually being added to form the continuous series. 



