IS THE THEORY OF SELECTION SUFFICIENT? 157 
point of Physiology and the Theory of Descent (Das 
Unbewusste vom Standpunkt der Physiologie and Des- 
cendenztheorie),“* has again recently observed that the 
truth of the doctrine of Descent is independent of the 
bearings and adequacy of the Darwinian theory. 
“This circumstance,” -he says, “is misunderstood by 
the majority of Darwin’s opponents ; when they adduce 
arguments for the inadequacy of natural selection in 
the struggle for life, they usually fancy they have 
adduced just as many arguments against the reliability 
of the theory of Descent. But the two have no direct 
connection with one another; for it might be possible 
that Darwin’s theory of natural selection was absolutely 
false and unserviceable, and the doctrine of derivation 
true notwithstanding ; that only the causal medium of 
the derivation of one species from another was different 
from that stated by Darwin. Similarly, it might be 
possible that, although the mediate causes of transition 
discovered by Darwin-were partially effective-—on the 
other hand, transitional phenomena existed which could 
not as yet be explained by this hypothesis ; that this 
therefore required either an auxiliary hypothesis supple- 
menting that of Darwin, or even a co-ordinating prin- 
ciple of explanation, as little discovered now as was the 
Darwinian theory twenty years ago. Such imperfect 
knowledge of the causes operating in the transition of 
one form into the other, can prejudice the general 
truth of the doctrine of Descent as little as the absence 
of intermediate forms, or the uncertainty, still exist- 
ing in many cases, of the derivation of any given form. 
If even in former times, when all knowledge of the 
causes by which transition is effected was still wanting, 
