MANNKR OF DEVELOPMENT, 26 



CHAPTER II. 



ON THE MANNER OP DBVELOPMENT OP MAN 

 PROM SOME LOWER FORM. 



Variability of body and mind in man— Inlierltanoe— Causes of varia- 

 bility — Laws of variation the same in man as in the lower animals — 

 Direct action of the conditions of life— Effects of the increased use 

 and disuse of carts- Arrested development — Reversion— Correlated 

 variation— Rate of increase — Checks to increase — Natural selection- 

 Man the most dominant animal in the world — Imporlance of his cor- 

 poreal structure — The causes which have led to his becoming erect- 

 Consequent ohang-es of structure — Decrease in size of the canine 

 teeth— Increased size and altered shape of the skull— Nakedness- 

 Absence of a tail — Defenseless condition of man. 



It is manifest that man is now subject to much variability. No 

 two individuals of the same race are quite alike. We may compare 

 millions of faces, and each will be distinct. There is an equally 

 great amount of diversity in the proportions and dimensions of 

 the various parts of the body; the length of the legs being one 

 of the most variable points.'^ Although in some quarters of the 

 world an elongated skull, and in other quarters a short skull 

 prevails, yet there is great diversity of shape even within the 

 limits of the same race, as with the aborigines of America and 

 South Australia — the latter a race "probably as pure and homo- 

 "geneous in blood, customs, and language as any in existence" — 

 and even with the inhabitants of so confined an area as the Sand- 

 wich Islands.^ An eminent dentist assures me that there is nearly 

 as much diversity in the teeth as in the features. The chief ar- 

 teries so frequently run in abnormal courses, that it has been 

 found useful for surgical purposes to calculate from 1040 corpses 



1 'Investigations in Military and Anthropolog. Statistics of American 

 Soldiers,' by B. A. Gould, 1869, p. 256. 



" "With respect to the "Cranial forms of the American aborigines," 

 see Dr. Aitken Meigs in 'Proc. Acad. Nat. Sci.' Philadelphia, May, 1868. 

 On the Australians see Huxley, in Lyell's 'Antiquity of Man,' 1863, p. 

 87. On the Sandwich Islanders, Prof. J. Wyman, 'Observations on Cra- 

 nia,' Boston, 1868, p. 18. 



