442 PHYSICAL DETERIORATION & MICROBIC DISEASE 



good, and where they are defective, the effects and the remedy 

 are obvious. It follows, since human diet, consisting as it does 

 of certain essential constituents, cannot be greatly varied, since 

 nutriment penetrates to all parts of the individual, since the supply 

 of nutriment is usually sufficient, and since instinct prompts to 

 the consumption of about the right kind and quantity of nutriment, 

 that we cannot hope to improve materially such a people as the 

 English by altering its nutritive supply. Especially we cannot 

 hope to improve its inborn traits its capacities for development, 

 and those characters which arise under the stimulus of nutriment. 

 If, therefore, we wish to alter them, the only conceivable method 

 is selection. Probably, however, no one would wish to use a 

 method so difficult to manage rightly, so destructive of liberty, 

 so fraught with suffering to the innocent as selection, merely to 

 change the shapes and sizes of such physical structures as ears, 

 eyes, lungs, and the like, and no one who understands the functions 

 of the instincts would lightly wish to tamper with these exquisite 

 mental adaptations. It would be excellent, of course, if we 

 exalted the potential physical and mental powers of Englishmen 

 by increasing their innate capacity to develop under the stimulus 

 of use and experience ; but it is so much easier, so much more 

 within the range of practical politics, to alter stimuli by changing 

 the conditions of life than to alter capacities by selection that, 

 before attempting the latter, we should, as I have indicated in 

 general terms, be very sure that the conditions under which the 

 British dwell are such as ensure the utmost development and the 

 best kind of development possible. Only after we have ascer- 

 tained beyond reasonable doubt that nothing more is achievable 

 by altering the conditions can selection be desirable. 



725. The different parts of the human body develop under the 

 stimulus of use on lines almost as rigidly fixed as those on which 

 they develop under the stimulus of nutriment. Indeed, the physical 

 growth made under the former stimulus is usually a mere exten- 

 sion of that made under the latter. For example, a human limb 

 develops after birth on lines very similar to those on which it 

 developed before. When the direction or character of the growth 

 is changed it is usually by injury, not by use. But while nutri- 

 ment penetrates to all parts of the body and is thus, except as to 

 the quantity consumed, largely beyond control, we are able to 

 regulate in great measure the extent to which the different parts 

 of our bodies are used. Thus we may lead a hard laborious life 

 as that of a navvy or hunter, or a sedentary one as that of a clerk 



