ON THE VALUE OF SPECIFIC DISTINCTIONS. 81 



we must look in part to the original constitution of the species, and in part 

 to the influence of external conditions. As already mentioned, there is a 

 marked difference among various species of animals (even those nearly allied, 

 such as the Domestic Cat and the Tiger), in regard to their respective capa- 

 cities for variation. And among the peculiarities of conformation which oc- 

 casionally present themselves in the Human and other most variable species, 

 there are several, which cannot be in any way attributed to the modifying 

 influence of external conditions; such, for example, as the development of 

 additional fingers or toes, the alteration in the number of the vertebra in the 

 tail, the unusual consolidation or separation of the toes, &c. But it cannot 

 be doubted, when the known history of the domesticated races is fairly con- 

 sidered, that a change of external circumstances is capable of exerting a very 

 decided influence upon the physical form, upon the habits and instincts, and 

 upon various functions of life. The variations thus induced, extend to con- 

 siderable modifications in the external aspect, such as the colour, the texture, 

 and the thickness of the external covering ; to the structure of limbs, and the 

 proportional size of parts ; to the relative development of the organs of the 

 senses and of the psychical powers, involving changes in the form of the cra- 

 nium; and to acquired propensities, which, within certain limits (depending, it 

 would appear, on their connection with the natural habits of the species), may 

 become hereditary. 



4. On the Extremes of Variation among the Races of Men. 



72. We have now to inquire, in the third place, how far the same influ- 

 ences might be expected to operate in the Human race ; and whether the ex- 

 treme varieties, which we encounter among Mankind, are really greater than 

 those, which we meet with m the races of domesticated animals, known to 

 have had a common ancestry. It must be admitted by every one, that both 

 of the conditions just noticed as favouring the origination of peculiarities, ope- 

 rate to their fullest extent in Man. There is no other species of animals, in 

 which an equal tendency to variation exists. The different individuals of the 

 same breed of Dogs, for example, resemble each other far more closely in 

 physical and mental characters, than the individual men of one nation ; and 

 there is no species of animals, which possesses an equal power of maintain- 

 ing life in the remote extremes of climate, atmospheric pressure, &c., which 

 are encountered at different parts of the earth's surface, and at different ele- 

 vations above it. Again, we should expect to find these varieties in external 

 circumstances, together with the change of habits induced by civilization 

 (which is far greater than any change effected by domestication in the condi- 

 tion of the lower animals), producing still more important alterations in the 

 physical form and constitution of the Human body, than those effected in 

 brutes by a minor degree of alteration. And it may be reasonably antici- 

 pated, that, as just now explained, there would be a greater tendency to the 

 perpetuation of these varieties, in other words, to the origination of distinct 

 races, during the earlier ages of the history of the race, than at the present 

 time, when, in fact, by the increasing admixture of races which have long 

 been isolated, there is a tendency to \hefusion of all these varieties, and to a 

 return to a common type. Now, when the extreme varieties which are pre- 

 sented by the different races of Man are carefully compared together, it is 

 found that their differences are all of the same kind as those, which present 

 themselves among the breeds of domesticated animals; and do not by any 

 means exceed them (perhaps not even equalling them in degree. This will 

 be shown in detail hereafter. 



73. It appears, then, that the analogical argument derived from the pheno- 



