192 THE DOCTRINE OF DESCENT. 
purpose? Ought it not rather to be: Every cause 
engenders a process which again works on towards 
another process? The further we go back, the deeper 
and more general is the grade, and the various ramifica- 
tions at their peripheral ends have either halted, or 
arrived at very different grades. 
An objection frequently made against this result of 
the doctrine of Descent is, that if all are pressing for- 
ward towards perfection, how is it that, besides the 
higher, so many lower members of the family are able 
to maintain themselves, and how can the lower families 
hold their own against the higher, in the struggle for 
existence? In presence of the irrefutable facts of pro- 
gress, it is enough to point out that the lower forms 
could and can continue to exist wherever they could 
find space as well as the other necessaries of life. 
While they here underwent only slight modifications, 
elsewhere the needful selection led to more profound 
metamorphoses; and on a subsequent geographical dis- 
placement, the newly transformed beings, accustomed to 
other conditions of existence, were again able to share 
sea and land with the stationary species. For as diver- 
sity is restored now by selection, and the demands for 
nutriment and other necessaries are likewise different, 
a partial remission in the struggle must take place. 
The preservation of a great many inferior organisms 
is evidently favoured by the circumstance that just be- 
cause they are simpler, their propagation is more easily 
effected. Hence although, especially in limited districts, 
amid violent competition of superior varieties, countless 
species must suffer extirpation, yet the struggle for 
existence and perfection do not exclude the existence 
