Chap. I. IMMUTABILITY OF SPECIES. 51 



SECTION XV. 



PERMANENCY OF SPECIFIC PECUI.IAIUTIES IN ALL ORGANIZED BEINGS. 



It was a great step in the progress of science wlieu it was ascertained that 

 species have iixcd characters, and that they do not change in the course of time. 

 But this fact, for wliich we are indebted to Cuvier,^ has acquired a still gi-eater 

 importance since it has also been established, that even the most extraordinary 

 changes in the mode of existence and in the conditions under which animals may be 

 placed, have no more influence upon their essential characters than the lapse of time. 



The facts bearing upon these two subjects are too well known now to require 

 special illustration. I will, therefore, allude only to a few points, to avoid even the 

 possibility of a misapprehension of my statements. That animals of different geo- 

 logical periods differ specifically, en masse, from those of preceding or following forma- 

 tions, is a fact satisfactorily ascertained. Between two successive geological periods, 

 then, changes have taken -place among animals and plants. But none of those pri- 

 mordial forms of life, which naturalists call species, are known to have changed 

 during an}' of these jieriods. It cannot be denied, that the species of different 

 successive periods are supposed by some naturalists to dei'ive their distinguishing 

 features from changes which have taken place in those of preceding ages ; but this 

 is a mere supposition, supported neither by physiological nor by geological evidence, 

 and the assumption that animals and plants may change in a simOar manner during 

 one and the same period, is equally gratuitous. On the contrary, it is known by 

 the evidence furnished by the Egyptian monuments, and by the most careful com- 

 parison between animals found in the tombs of Egypt with living specimens of the 

 same species ol)tained in the same countrj^, that there is not the shadow of a differ- 

 ence between them, for a period of about five thousand years. These comparisons, 

 first instituted by Cuvier, have proved, that as far as it has been possible to carry 

 back the investigation, it does not afford the beginning of an evidence that species 

 change in the course of time, if the comjiarisons be limited to the same great 

 cosmic epoch. Geology only shows that at different periods^ there have existed 



^ CuviEit, (G.,) Kceherches sur les ossements great length, each of which is characterized 1>y dit- 

 fossiles, etc., Nouv., edit. Paris, 1821, 5 vols., 4to., ferent animals, that the dirterences these animals ex- 

 fig., vol. i., sur ril>is, p. cxli. hiliit. is in itself" evidence of a change in the species. 



^ I li-iisl no rcadi T will !)(■ so ignorant of the The (incstion is, whether smy changes take place 



facts hcrr alludiil io, as to infer from the use of during one or any of tliese periods. It is almost 



the word "period" for ditlVrent eras and epochs of incredible how loosely some people will argue upon 



