92 TEST CASES [ch. x 



fourteen. The relative proportions of widely and of narrowly 

 distributed species were not well known at that time, nor the 

 relative proportions of the genera in a family, both shown in the 

 hollow curves. Nor was it realised that no boundary could be 

 fixed dividing endemic species or genera from non-endemic. A 

 mere glance at the hollow curves will show this, or at a contour 

 map (chap, xiii, case 27). Even the big genera consist largely or 

 even principally of local or endemic species. 



As an actual case, we may take the Monimiaceae, already de- 

 scribed upon p. 33. There are two large genera and thirty small. 

 What is selection going to do with these latter, which contain 

 30, 25, 15, 15, 11, 7, 6, 5, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 

 1, 1, 1, 1, 1, 1, 1, species respectively? The ones will presumably 

 disappear first on the whole, and the family should logically be 

 reduced ultimately to the two large genera of 107 and 75 species, 

 most of which again are relics in the sense that they only occupy 

 small areas. It is clear that natural selection, working upon the 

 lines usuallv laid down for it, would result in a tremendous dimi- 

 nution. And not only do the numbers of species in the genera 

 follow the law of Age and Area — the hollow curves — but so do 

 the areas that they occupy. The diameters of areas occupied by 

 genera of one or two species average about 560 miles, with three 

 to five species about 830, with six to eleven 1766, with fifteen to 

 thirty about 2310, and the two large genera about 5500 miles. 

 One can draw no lines of distinction. If the ultimate end of 

 natural selection is to be a small number, why begin with so large 

 a one? Whence did thev all come, and whv were thev evolved at 

 all? Under differentiation expansion is the rule, for each one may 

 ultimately give two, and there is no necessary reason for the 

 older ones to die out as they must under natural selection. Once 

 established in a small way, if there is no necessary difference in 

 adaptational value between one morphological form and another 

 nearly allied to it from which it may even have arisen, a species 

 may go on indefinitely, though by reason of the presence of 

 barriers to spread — physical, climatic, ecological, etc. — it may 

 never be able to expand over very large areas of country. 



The same results as are shown by the Monimiaceae are shown 

 by any other family that one may take, especially if it be of fairly 

 reasonable size. The Cruciferae, with 350 genera, begin higher up 

 (with larger genera than the Monimiaceae) and end with 56 twos 

 and 145 ones. The Compositae end with 148 twos and 446 ones 

 (old figures). 



