igS SYMBIOSIS 



previous normal and symbiotic to an abnormal and comparatively 

 parasitic habit of life. 



A somewhat similar convergence, only on a smaller scale, 

 was noted by Darwin in the case of domesticated pigs. To some 

 extent Darwin seems to have realised that the phenomenon is 

 due to a pathological cause. For in his Variation of Animals 

 and Plants, Vol. I., p. 90, he states that the phenomenon is due 

 " to similar causes of change acting on the several races, and 

 partly to man breeding the pig for one sole purpose, namely, 

 for the greatest amount of flesh and fat " (i.e., man is over-feeding 

 and at the same time under-exercising the creature, which is 

 certain in the long run to induce morbidity). 



On the other hand, Darwin, always open to the possibilities 

 of re-conversion, notes in the same volume (p. 95), that pigs and 

 other animals, when allowed to become feral, tend to lose their 

 monstrosity and to revert in the general shape of their bodies 

 " as might be expected from the amount of exercise which they 

 are compelled to take in search of food." 



In the case of cattle, he says that " we cannot doubt that an 

 active life, leading to the free use of the limbs and lungs, affects 

 the shape and proportion of the whole body," whence it should 

 not prove too great a step to the recognition that a definite ratio 

 of food to work, such in fact as provided by the contingencies 

 of Symbiosis, is indispensable to normal " specialisation." 



In view of the great physiological importance of this ratio, I 

 would introduce the expression f/w (^J) as a way of repre- 

 senting a norm of behaviour upon which almost everything 

 in Biology depends. 



It is also significant that Darwin compares the case of 

 monstrosity amongst cattle, e.g., the niatas, to that of the over- 

 fed pig or bulldog. Nay, he goes further, and, taking care to 

 indicate several interesting pathological stigmata, he makes a 

 comparison with the case of the gigantic extinct Sivatherium of 

 India, showing that in either case we have the lower jaw 

 projecting beyond the upper, with a corresponding upward 

 curvature, etc., etc. 



Seeing that I cannot emphasise too much the parallelism 

 between the pathology due to sluggishness, over-feeding, and 

 Parasitism in Nature, and the one induced by a perverted 

 f/w ratio in Domestication, a further digression respecting 

 Darwin's views on these matters may not be out of place. " It 



