l6 The Descent of Man. Paex L 



CHAPTER II. 



On the Manner of Development of Man from some 



Lower Form. 



Variability of body and mind in man — Inheritan< e — Causes of variability 

 — 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 parts — Arrested development — Reversion — Correlated variation — 

 Rate of increase — Checks to increase — Natural selection — Man the most 

 dominant animal in the world — Importance of his corporeal structure — 

 The causes which have led to his becoming erect — Consequent changes 

 of structure — Decrease in size of the canine teeth — Increased size and 

 altered shape of the skull — Nakedness — Absence of a tail — Defenceless 

 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. 1 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 homogeneous in blood, customs, and language as any 

 " in existence " — and even with the inhabitants of so confined 

 an area as the Sandwich Islands. 2 An eminent dentist assures 

 me that there is nearly as much diversity in the teeth as in the 

 features. The chief arteries so frequently run in abnormal 

 courses, that it has been found useful for surgical purposes to 

 calculate from 1010 corpses how often each course prevails. 3 

 The muscles are eminently variable : thus those of the foot 

 were found by Prof. Turner 4 not to be strictly alike in any two 

 out of fifty bodies ; and in some the deviations were considerable. 



1 'Investigations in Military and Huxley, in Lyell's 'Antiquity of 

 Anthropolog. Statistics of American Man,' 1863, p. 87. On the Sand- 

 Soldiers,' by B. A. Gould, 1869, p. wich Islanders, Prof. J. Wy.nan, 

 256. ' Observations on Crania,' Boston, 



2 With respect to the "Cranial 1868, p. 18. 



forms of the American aborigines," 3 'Anatomy of the Arteries,' by 



see Dr. Aitken Meigs in ' Proc. R. Quain. Preface, vol. i. 1844. 

 Acad. Nat. Sci.' Philadelphia, May, 4 'Transact. Royal Soc. Edin 



1868. On the Austialians, *ee burgh,' vol. xxiv. pp. 175, 189. 



