CH. x] AGE AND AREA THEORY 105 



tendency to divergence caused him (DarAvin). I believe I first 

 pointed the defect out to him, at least I insisted from the first 

 on his entertaining a crude idea which held that variation was 

 a centrifugal force, whether it resulted in species or not." Huxley 

 was in the same case. For he held views of the general differentia- 

 tion of types, and his road that would lead to the discovery of 

 the causes of evolution started from the Darwinian position. 

 That road was barred to him. 



The secret of the success of Dr >Yillis is that he works with 

 limited objectives and is always free to shape his course accord- 

 ing to his results. A distant objective with a specified general 

 theory of distribution as his goal might easily have brought him 

 to the ground. As it is, he has struck a wonderful trail that 

 seems to increase in promise as he advances. But the logical 

 outcome of establishing his theorj^ successively for the species, 

 the genus, the tribe, and the family, is a general theory of 

 differentiation. In other words, it will bring him to the pre- 

 Darwinian position. Once there, he will enjoy greater freedom 

 in his choice of routes and methods, and new and unexpected 

 fields of research will be opened up all around him. This note 

 may be concluded with a brief reference to a few of the more 

 remarkable features of a theory that is still in the making. 



Though the linking up of old ideas that have been without a 

 resting place for generations is mainly incidental, it is none the 

 less significant. I gather from Dr ^Yillis that his -'alliterative 

 series," as he terms it, which began -with "Age and Area," is 

 increasing in its numbers as his work proceeds. Thus we have 

 Antiquity and Amplitude, Rank and Range, Size and Space, 

 and several others, some of them OA'erlapping, but each with 

 its own variant, and some again capable of considerable exten- 

 sion and amplification. Thus Rank and Range implies Simphcity 

 of Type and Increase of Area, a very old principle long recog- 

 nised in the theory and practice of pre-Darwinian systematists. 

 Simplicity of Type goes with Variability, another old principle. 

 If, therefore, the simplest organisms of a group are the widest 

 distributed and the most variable (ideas old enough and true 

 enough) it is among them that we ought to look for examples 

 of genera that have arisen independently in different parts of 

 their areas, as in the ease of Senecio, the most primitive form of 

 the Compositae. Incidental as such results may be, Dr Willis 

 may well claim that his materials are working for him. \Vhilst 

 he is following a definite plan, much is happening that was 



