"i] Limits to Interchangeability 73 



The detection of these limits is one of the more important 

 tasks still awaiting us. Though on this head little can yet 

 be asserted with confidence it is likely that such limitations 

 are constituted in two distinct ways : First, from all we 

 know of the capacities of animals and plants we must 

 anticipate that some characters are incompatible in the 

 same individual. For example in cattle the highest milk- 

 production is not to be found in the breeds which make the 

 best beef. Meat-production and milk-production are to some 

 extent alternative and can only be combined by compro- 

 mising one quality or both. That such an alternative 

 distribution is merely a result of allelomorphism seems on 

 the whole unlikely, though certainly not impossible. 



Then again we must surely expect that these transferable 

 characters are attached to or implanted upon some basal 

 organisation, and the attributes or powers which collectively 

 form that residue may perhaps be distinguishable from the 

 transferable qualities. The detection of the limits thus set 

 upon the interchangeability of characters would be a dis- 

 covery of high importance and would have a most direct 

 bearing on the problem of the ultimate nature of Species. 



