130 NATURAL HISTORY. 



latter, in proportion as the air, food, and water arf 

 gross, are clumsy, and less active and vigorous. 



From every circumstance, therefore, we may obtain 

 ii proof, that mankind are not composed of species es- 

 sentially different from each other. It appears, on 

 the contrary, that there was originally but one indi- 

 vidual species of men, which after being multiplied 

 and diffused over the whole surface of the earth, un- 

 derwent divers changes from the influence of the cli- 

 mate, from the difference of food, and of the mode of 

 living, from epidemical distempers, as also from the 

 intermixture, varied ad infiniium, of individuals more 

 or less resembling each other : at first, these alterations 

 were less considerable, and confined to individuals ; 

 but afterwards, from the continued action of the above 

 causes becoming more general, more sensible, and more 

 fixed, they formed varieties in the species. These 

 varieties have been, and are still perpetuated from 

 generation to generation, in the same manner as cer- 

 tain deformities, and certain maladies, pass from pa- 

 rents to their children. And in short, as these varieties 

 would never have been produced but by a concurrence 

 of external and accidental causes, as they would ne- 

 ver .have been confirmed and rendered permanent, but 

 by timcj and by the continued action of these causes; 

 so it is highly probable, that in time they would in 

 like manner gradually disappear, or even become dif- 

 ferent from what they at present are, if such causes 

 were no longer to subsist. 



