OF THE HUMAN RACE. 



221 



some of which are obvious, others of which must be conjectured, and a 

 few of which are beyond the reach of human comprehension : — but all 

 of which are common to other animals, as well as to man ; for extraor- 

 dinar}^ as these diversities may appear, they are equally to be met with in 

 the varieties of several other kinds of animals that can be proved to have 

 been produced from a single species, and, in one or tvvo instances, from a 

 single pair. 



The chief causes we are acquainted with are the four following : cli- 

 mate, food, manner of life, and hereditary diseases. 



[. The influence which climate principally produces on the animal 

 frame is on the colour of the skin and on the extent of the stature. All the 

 deepest colours we are acquainted witii are those of hot climates ; and all 

 the lightest those of coid ones. In our own country we perceive daily, 

 that an exposure to the rays of the sun turns the skin from its natural 

 whiteness to a deep brown or tan ;-and that a seclusion from the si:n keeps 

 it fair and unfreckled. In like manner the tree-frog (rana arhorea) while 

 living in the shade is of a hght yellow, but of a dark green when he is 

 obliged to shift from the shade into the sun-shine. So the nereis lacustris, 

 though whitish under the darkness of a projecting bank, is red when ex- 

 posed to the sun's rays. And that the larves of most insects that burrow 

 in the cavities of the earth, of plants, or of animals, are white, from the 

 same cause, is clear, since being confined under glasses that admit the in- 

 fluence of solar hght, they exchange their whiteness for a brownish hue. 



The same remark will apply to plants as well as to animals ; and hence 

 nothing more is necessary to bleach or whiten them, than to exclude 

 them from the light of day. Hence the birds, beasts, flowers, and even 

 fishes of the equatorial regions, are uniformly brighter or deeper tinctured 

 in their spots, their feathers, their petals, and their scales, than we find 

 them in any other part of the world. And hence, one reason at least for 

 the deep jet which, for the most part, prevails among mankind under the 

 equator ; the dark-brown and copper-colours found under the tropics ; 

 and the olive, shifting through every intermediate shade to the fair and 

 sanguine complexion, as We proceed from the tropic of Cancer northwards. 

 Hence, too, the reason why the Asiatic and African women, confined to 

 the walls of their seraglios, are as white as Europeans ; why Moorish child- 

 ren, of both sexes, are, at first, equally fair, and why the fairness continues 

 among the girls, but is soon lost among the boys. 



As we approach the poles, on the contrary, we find every thing pro- 

 gitessively whiten ; bears, foxes, hares, falcons, crows, and black-birds, all 

 assume the same common livery ; while many of them change their colour 

 with the change of the season itself. For the same reason, as also be- 

 cause they have a thinner mucous web, the Abyssinians are less deep in 

 colour than the negro race; for though their geographical chmate is 

 nearly the same, their physical climate differs essentially : the country 

 stands much higher, and its temperature is far lower. 



The immediate matter of colour, as I had occasion to observe more 

 fully in a preceding lecture, is the mucous pigment which forms the mid- 

 dle layer of the general integument of the skin ; and upon this, the sun, 

 in. hot climates, appears to act in a twofold manner ; first, by the direct 

 affinity of its colorific rays with the oxygene of the animal surface, in con- 

 sequence of which the oxygene is detached and flies oflf ; and the car- 

 bone and hydrogene being set at liberty, form a more or less perfect char- 

 coal according to the nature of their union ; and next, by the indirect in- 

 iuence which its calorific rays, like many other stimulants, produce upon 



