226 NUG.E ETH.VOLOr.ICAE. 



deny the unity of the human species may be divided into two classes 

 holding opposite extremes of opinion. The one, struck with the multi- 

 tudinous evidences of the plastic power of nature, the potency of the 

 affinities of matter, and the surprising eflects of those imponderable es- 

 sences which defy our keenest scrutiny, making themselves known only 

 by their mighty energies, have concluded that the ordinary forces of the 

 material world are competent to the development of organized from un- 

 organized matter. This assumption once granted, it is easy to arrive at 

 the conclusion that the organization thus effected, may be perfected by 

 the same forces which originated it. The production of a man from 

 brute matter by the operation of ordinary laws then ceases to be unrea- 

 sonable, and may soon be asserted unequivocally. This school may be 

 denominated the natural Jdstorical. The first traces of its theory are 

 found in the Phenician and other ancient oriental cosmogonies, it is 

 taught by Virgil (Georg. lib. IV.) and Lucretius, (De Rer. Nat. v. 803,) 

 and has been maintained with more or less distinctness by all who con- 

 tended for what has been called equivocal or spontaneous generation. 

 The boldest of its modern defenders has been Lamarck, and it has re- 

 cently been set forth in a popular form by the author of the "Vestiges 

 of the Natural History of Creation." The other class, in endeavoring 

 to avoid Scylla have fallen upon Charybdis. They may be styled the 

 historical school. Their starting point is the permanency of the known 

 varieties under many diverse influences and for immense periods of time. 

 Tracing back the historical evidence of the existence of the varieties 

 now known, at a period which the ordinarily received chronology makes 

 the infancy of the race, they expect that the causes which could have 

 produced them in the previous era would necessarily have prevented 

 their permanency from that date to the present. The inference then is, 

 that they must have been either original or efl'ected by a miraculous 

 agency. This school limits the power of the ordinary forces of matter 

 as much as the other extends it. Now the truth appears to me to be 

 between these two extremes. We know that the forces mentioned do 

 produce very important changes in the structure, color, &c. of organized 

 beings — quite as great, as before remarked, as any existing between the 

 varieties of men. On the other hand, I think it can be shown that this 

 eflect never extends so far as the destruction of the original specific type. 

 The force exists, but within bounds. It may cause varieties but it can 

 never effect a mutation of the sj^ecies. Even were this granted, the case 

 would not be entirely clear, for we might rest on the assertion that it 

 cannot commute genera. The procreation, although it is of hybrids, 

 which takes place between individuals of dilferent species in the same 



