THE CAUSATION OF DISEASE. 1 4 1 



theoretically supposing an individual to pass through life with- 

 out being exposed to such E, and we may speak of the indi- 

 vidual such as he would then be, as the strict and sole product 

 of heredity. What he is capable of becoming under particular 

 environments belongs to the region of acquisition, and every 

 such acquisition is a natural variation. There is no real differ- 

 ence between conscious education (or the conscious application 

 of a specific E to plastic organic matter, in order to induce a 

 specific variation or acquisition), and the more or less uncon- 

 scious moulding of our bodies by the agencies around us 

 — the semblance of difference lying in this : that the one 

 is done consciously and for a purpose, while the other is 

 not. And, again, between this latter kind of moulding and 

 that moulding in nature whereby distinct and well-recognized 

 variations arise, there is no distinction whatever. Both are 

 due to E. In brief, the structural states which are not 

 strictly inherited — i.e., which would not appear under our 

 theoretic negative E — are acquisitions, and all acquisitions are 

 natural variations.* 



It is therefore evident that the subtlest habit (supposing this 

 to be strictly an acquired habit) is a natural variation, since 

 fundamentally it is a structural variation wrought through 

 a peculiarity of E. Indeed, pushing the matter yet further, 

 we shall be compelled to admit that that part of our mental 

 world, which is not strictly inherent, but acquired, falls 

 under this same head of natural variation. We inherit in 

 their fulness all the so-called instincts — our simple sensations 

 and emotions — these would manifest themselves under the 



* While it is correct to say that all acquisitions are natural variations, it is 

 hardly true that all natural variations are acquisitions, or, in other words, that 

 the latter are the sole cause of variations, and this for two reasons — (i) Because 

 the union of unlike parents leads to a mean, unlike either, and this is a well- 

 recognized cause of natural variations ; nevertheless, it is only a secondary and 

 minor cause, since it would be inoperative without the other. Acquisition is 

 undoubtedly the primary cause, for if the world were peopled afresh from two 

 individuals perfectly alike in all respects, save such as depend upon sex, the 

 primary variation would be acquired. Unlikeness would thus appear, and this, 

 in course of time, would tend to marked variations. Marriage of unlike indi- 

 viduals would still further increase the variation. (2) Eeversions are natural 

 variations. These, we have seen, are very largely due to E, but they are also 

 due to the sexual union of unlike individuals. 



