INDEFINITELY FROM THE ORIGINAL TYPE. 37 
main preponderant in numbers, and under adverse 
physical conditions again alone survive. But this 
new, improved, and populous race might itself, in 
course of time, give rise to new varieties, exhibiting 
several diverging modifications of form, any of which, 
tending to increase the facilities for preserving ex- 
istence, must, by the same general law, in their 
turn become predominant. Here, then, we have 
progression and continued divergence deduced from the 
general laws which regulate the existence of animals 
in a state of nature, and from the undisputed fact 
that varieties do frequently occur. It is not, how- 
ever, contended that this result would be invariable; 
a change of physical conditions in the district might 
at times materially modify it, rendering the race 
which had been the most capable of supporting ex- 
istence under the former conditions now the least so, 
and even causing the extinction of the newer and, 
for a time, superior race, while the old or parent 
species and its first inferior varieties continued to 
flourish. Variations in unimportant parts might 
also occur, having no perceptible effect on the life- 
pteserving powers; and the varieties so furnished 
might run a course parallel with the parent species, 
either giving rise to further variations or returning 
to the former type. All we argue for is, that cer- 
tain varieties have a tendency to maintain their 
existence longer than the original species, and this 
tendency must make itself felt ; for though the doc- 
trine of chances or averages can never be trusted to 
. 
