REGENERATION 61 
To know that the presence of a certain organ may lead 
to the preservation of a race is useless if we cannot tell 
how much preservation it can effect, how many indi- 
viduals it can save that would otherwise be lost ; unless 
we know also the degree to which its presence is 
harmful; unless, in fact, we know how its presence 
affects the profit and loss account of the organism.’* 
A great many other criticisms and objections have 
been brought at various times against the theory of 
the origin of adaptations by the action of natural 
selection, and many of these were considered and 
replied to by Darwin in the later editions of the ‘ Origin 
of Species.” We shall only consider here a few which 
have been put forward more or less recently. Before 
doing so it will be well to point out once more that no 
one questions the validity of natural selection as a means 
of exterminating types which are unfitted for their 
environment—there is clearly a tendency for the 
fittest types to survive once they have come into 
existence. Nor can there be any doubt that species 
in general are well adapted to the conditions which 
their environments present. But when this is admitted 
it does not necessarily follow that natural selection, 
directing the accumulation of minute differences, has 
been the method by which these adapted forms have 
originated. 
The power of regenerating a lost part must clearly 
often be of service to the creatures which possess it. 
Such a power may in many cases be considered to be 
a well-marked adaptation. But, as Morgan has well 
* W. Bateson, ‘ Materials for the Study of Variation,’ p. 12; 
