52 PHYSICAL BASIS OF CIVILIZATION 



contains. If the composition or pressure suddenly 

 changes to any great extent, then neither can perform 

 its normal functions, and serious organic disturb- 

 ances are likely to occur. 



Since, then, in the lowliest forms of life any part 

 can perform almost any of the functions ordinarily 

 falling upon other parts, the organism can adjust 

 itself easily and rapidly to sudden mutations. For 

 deficiency in or addition to the function of one part 

 is balanced by increase or decrease in kind or amount 

 of another. So that comparatively slight local or 

 temporary advantages to the organism, arising from 

 changes in the environmental constituents, may 

 easily become the transitory causes for these sudden 

 structural or functional modifications set forth in the 

 accounts of sudden mutations. But in highly spe- 

 cialized organisms, where each organ, structure, etc., 

 is exquisitely fitted and narrowly limited to its 

 specific performances, and where the health and life 

 of the whole organism and of every part of it de- 

 pends on the co-operative harmony in the function- 

 ing of all parts, and therefore an exact performance 

 of every part, a slight change in one part causes 

 so serious a general disturbance, that sudden great 

 mutations could only be conducive of equally 

 sudden fatal results. The transmission of such by 

 heredity, in highly specialized organisms, is therefore 

 impossible. Such changes in such organisms, when 

 they come at all, must obviously begin with very 

 slight modifications through variation, which then, 



