Willis.— The Evolution of Species in Ceylon , 
10 
The mere fact that the numbers representing rarities come out with 
such simple arithmetical relations seems enough to show that whatever cause 
is operative in causing such relations it cannot be Natural Selection. So 
simple an explanation of evolution is impossible, though a more ‘ mechanical ’ 
explanation of its more obvious features than is Natural Selection is 
called for. 
[All the tables of rarity given in my previous paper show the same 
thing, varying in almost purely ‘mechanical’ ways. Table VI shows that 
the rarity of the endemics is much the same for all, taken family by 
family. Table IX shows much the same thing for genera, and if analysed 
gives the following figures : 
Table XI . 1 
Rarity 
i 
-2 
2-1-3 
3 *i -4 
4 *i -5 
5*1-6 
spp. 
Spp. 
spp. 
spp. 
Spp. 
Genera, per 
Genera, per 
Genera, per 
Genera, per 
Genera, per 
genus. 
genus. 
genus. 
gemis. 
genus. 
Endemic 
5 
I *2 
6 
2*0 
GO 
OO 
•<r 
26 , 
K 6*6 
^ 2*6 
Ceyl.-P.-I. 
18 
i '5 
16 
T° 
i_ 24 f 2 *i 
Ts 
3 
i *3 
Wide 
19' 
f 
i-4 
, 6*o 
14 | 6-o 
5 
2-0 
2 
1*0 
The regularity of the numbers according to the ordinary rules of trial 
and error is too great to be explicable on any hypothesis of other than 
a mechanical cause. The larger genera come nearer to the means. 
Table XV shows equal mechanical regularity coming out in the 
distribution of species according to the zones they live in. Tables XVII, 
XVIII show that endemic genera obey the same rules as endemic species. 
Table XIX is even more striking, as showing the same rule coming out 
within each of the single endemic genera Doona and Stemonoporus , ] 
When we come to look at these tables, it is evident that the distribution 
of the endemic species of Ceylon obeys a simple law which determines that 
there shall be, family by family, and genus by genus, some species under 
all the heads of classification of rarity from VR up to VC, but that the 
number shall be a decreasing one, there being ten times as many VR as 
VC. In every family or larger genus there are usually species under VR, 
R, and RR, but a few get no higher than this, more stop at RC, yet more 
at C, and very few reach to VC at all. The law is quite clear from the 
figures, though of course, like Mendel’s Law, it is followed with the usual 
variations due to the operations of the laws of trial and error. 
At the same time, the distribution in Ceylon of the species which are 
also common to Peninsular India, and that of the species of yet wider 
distribution, obey exactly similar laws, but in each of these cases the 
maximum is not at VR, but at C, in the first case with only slight falling 
off towards VR, in the second case with a very marked decrease. 
1 Maxima underlined. 
