Chapter 2

Variability of body and mind in mana€"Inheritancea€"Causes of variabilitya€"Laws of variation the same in man as in the lower animalsa€"Direct action of the conditions of lifea€"Effects of the increased use and disuse of partsa€"Arrested developmenta€"Reversiona€"Correlated variationa€"Rate of increasea€"Checks to increasea€"Natural selectiona€"Man the most dominant animal in the worlda€"Importance of his corporeal structurea€"The causes which have led to his becoming erecta€"Consequent changes of structurea€"Decrease in size of the canine teetha€"Increased size and altered shape of the skulla€"Nakednessa€"Absence of a taila€"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. 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 Australiaa€"the latter a race "probably as pure and homogeneous in blood, customs, and language as any in existence"a€"and even with the inhabitants of so confined an area as the Sandwich Islands. 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 1040 corpses how often each course prevails. The muscles are eminently variable: thus those of the foot were found by Prof. Turner not to be strictly alike in any two out of fifty bodies; and in some the deviations were considerable.

He adds, that the power of performing the appropriate movements must have been modified in accordance with the several deviations. Mr. J. Wood has recorded the occurrence of 295 muscular variations in thirty-six subjects, and in another set of the same number no less than 558 variations, those occurring on both sides of the body being only reckoned as one. In the last set, not one body out of the thirty-six was "found totally wanting in departures from the standard descriptions of the muscular system given in anatomical text books." A single body presented the extraordinary number of twenty-five distinct abnormalities. The same muscle sometimes varies in many ways: thus Prof. Macalister describes no less than twenty distinct variations in the palmaris accessorious.

The famous old anatomist, Wolff, insists that the internal viscera are more variable than the external parts: Nulla particula est quA¦ non