PHYSIOLOGICAL AGREEMENT. 997 



ing, upon the strictest physiological principles, for the widest of those depar- 

 tures from one common type of conformation, which we encounter in our 

 survey of the different Races of Mankind. 1 



842. Hence we are led to conclude, that, so far as regards their Anatomi- 

 cal structure, there is no such difference among them as would justify to the 

 Zoologist the assertion of their distinct origin. But further, although the 

 comparison of the structural characters of the Human races does not furnish 

 any positive evidence of their descent from a common stock, it justifies the 

 assertion that even if their stocks were originally distinct, there could have 

 been no essential difference between them ; the descendants of any one such 

 stock being able to assume the characters of another. This, as already re- 

 marked, can be proved by historical evidence in regard to a sufficient number 

 of tribes, to justify the same assertion with respect to others, whose languages, 

 customs, habits of thought, etc., have an affinity strong enough to warrant 

 us in regarding them as descendants of the same stock, whilst their physical 

 conformation is widely different. Each principal geographical area, which 

 is so isolated from others as to render it probable, a priori, that its popula- 

 tion has extended from one centre, such as the Continent of Africa, or 

 America, contains races of very diversified physical characters, whose lin- 

 guistic affinities make it almost certain that they must have had a common 

 descent ; and thus, in whatever mode the types of the principal varieties are 

 selected, they are found to be connected by so gradual a series of intermedi- 

 ate or transitional forms, that it is impossible to draw any such line of de- 

 marcation between them, as would be required by a soundly judging Natu- 

 ralist for the boundary of distinct species. 



843. A very important confirmation of this view, is afforded by the essen- 

 tial agreement which exists among the different Races of Mankind in regard 

 to their Physiological history ; the variations which they present not being 

 greater than those which we meet with between the different individuals of 

 any one race. Thus, we not only find the average duration of life to be the 

 same (making allowance for circumstances which are likely to induce disease), 

 but the various epochs of life, such as the times of the first and second den- 

 tition, the period of puberty, the duration of pregnancy, the intervals of the 

 catameuia, and the time of their final cessation, present a marked general 

 uniformity, such as does not exist among similar epochs in the lives of species 

 that are nearly allied but yet unquestionably distinct. Further, the different 

 races of Mankind are all subject to the same diseases, both sporadic, endemic, 

 and epidemic ; the only exceptions being those in which the constitution of 

 the race has grown to a certain set of influences (as that of the Negro to the 

 malaria which generate certain pernicious fevers in the European), producing 

 an hereditary immunity in the race, which is capable of being acquired by 

 individuals of other races, by a process of acclimatization commenced suffi- 

 ciently early. 2 The most important physiological test, however, of specific 



1 For a masterly digest of the analogical evidence furnished by the changes known 

 to have been thus produced among domesticated animals, and of the modifications 

 which particular tribes of men can be shown to have- undergone within the historic 

 p.-riod, see Dr. Prichard's Physical History of Mankind, and his Natural History of 

 Man; see also the summary given by the Author in the Cyclop, of Anat. and 

 Physiol , vol. iv, pp. 1301-1339"; and Darwin, The Variation of Animals and Plants 

 under Domestication, 1868. 



2 This view of the immunity of the Negro race from certain forms of fever which 

 are very fatal to Europeans, is justified, the Author believes, by all the facts known 

 upon the subject. Much may be set down, as he is assured by Dr. Daniell, to the 

 better adaptation of the Negro habits of life to their climate; and Europeans who 

 exercise due caution (especially in regard to the functions of the skin), may preserve 

 an immunity scarcely less complete. Dr. D. himself, having been taken prisoner by 



