108 



We find in others a prevailing tendency to calculous disorders : 

 now the same mode of causation as may render prevalent a de- 

 pravity of function or conformation in one structure, may produce 

 a similar change in another. We have even the record of a negro 

 whose skin has spontaneously become white. Here the de- 

 scendants of such a one would most probably be modified in a 

 particular which has been a characteristic of their progenitors. The 

 histories of epidemics both in men and brutes tend to the same 

 evidence. In a race which is not numerous, whether of men or 

 animals, we are supported by our present experience in the sup- 

 position that a prevalent depravity of function in the generative 

 organs might arise, and that, being continued, under many of the 

 modifications which would result from sexual intercourse, it might 

 by many approximations eventually lead to the extinction of the 

 race. But this mode of explaining a circumstance, which has 

 excited little more than the curiosity and astonishment of natu- 

 ralists, is rather foreign to my present purpose; it is sufficient for 

 this to shew, as has been done, that the rate and order of popula- 

 tion among the human species is liable to be retrograde or pro- 

 gressive, according to the operation or absence of the causes 

 enumerated; and that therefore, and for the reasons which precede 

 this enumeration, and for many other reasons, if they are required, 

 an origin of man by constitution can never be authenticated by any 

 records which a people might have preserved of the first founders of 

 their race; and it seems the less worth while to bestow more words, 

 upon this point, as no such records are even said to exist, which 

 affirm an absolute beginning in two first parents. 



18. If then neither record nor tradition can furnish us with 

 examples of the origin of man by constitution, it remains to inquire 

 whether by the laws of constitution itself we are led to such an 

 Inference? Viewed upon this ground, the question resolves itself 

 into the two following alternatives: 1st, has man existed for ever 

 or from eternity? or, 2nd, has there been a period when he began 

 to exist? 



1. It has been before said that nothing can exist without a 

 cause : how far this principle is to be admitted may be seen at 8, 

 9, 10, &c. Book I. Chap, ii.; at 2, Book I. Chap. iii. where the 

 grounds of it are stated. Now if nothing can exist without a 

 cause, it follows that the existence of every thing began at some 

 period, for the time of its causation was that at which it began to 

 exist. It will be inquired if this conclusion applies to forms 

 where there is a provision for endless perpetuity? it will be in- 

 quired whether the principle proves a first origin of the human 

 species? These questions relate to an apparent distinction be- 

 tween those parts of nature whose similitudes are propagated by 

 derivation, and those which being once formed are liable only to 

 re-combination or analysis, and which have no succession of 

 resemblances. 



