124 NATURAL INHERITANCE. [chap. 



accommodation. Evolution may produce an altogether 

 new type of vessel that shall be more efficient than the 

 old one, but when a particular type of vessel has become 

 adapted to its functions through long experience it is not 

 possible to produce a mere variety of its type that shall 

 have increased efficiency in some one particular without 

 detriment to the rest. So it is with animals. 



Variability in Fraternities. — Human Fraternities are 

 far too small to admit of their Q being satisfactorily 

 measured by the direct method. We are obliged to 

 have recourse to indirect methods, of which no less than 

 four are available. I shall apply each of them to both 

 the Special and to the R.F.F. data ; this will give 8 

 separate estimates of its value, which in the meantime 

 will be called b. The four methods are as follow : 



First method ; by Fraternities each containing the 

 same number of persons : — -Let me begin by saying that 

 I had already found in the large Fraternities of Sweet 

 Peas, that the sizes of individuals of whom they con- 

 sisted were normally distributed, and that their Q was 

 independent of the size, or of the Stature as we may 

 phrase it, of the Mid-Fraternity. We have also seen 

 that the Q is practically the same in all Co-fraternities 

 of men. Therefore it is reasonable to expect that it 

 will also be found to be the same in all their Fraternities, 

 though owino; to their small size we cannot assure our- 

 selves of the fact by direct evidence. We will assume 

 this to be the case for the present ; it will be seen that 

 the results justify the assumption. 



