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admit that all bodies act in the same manner under similar 
circumstances? If we were so compelled, we know that we 
should be wrong, and that we should ultimately find our law 
confronted with certain bodies which do not contract on cooling. 
Similarly, we are not compelled by any necessity of the case 
either to apply the doctrine of evolution to all animals and 
plants alike, or to deny its existence and operation altogether. 
On the contrary, we are perfectly at liberty if we choose, and 
the facts will bear us out, to believe that some sort or kind of 
evolution has taken place, and that some animals and plants 
have been produced out of other pre-existent forms, whilst 
others have been differently produced, and ow r e their peculiari- 
ties to some other cause. It is perfectly open to us, to put the 
case in a concrete form, to believe that certain groups of allied 
species have been evolved each from a common ancestor; but 
we may at the same time consistently believe that the origin 
and production of these ancestro.l types has been conditioned 
and controlled by some totally different law. There are plenty 
of instances, in point of fact, in which one law continues to act 
regularlywithin certain limits, and then has its operation super- 
seded by some higher law. 
In the same way, with regard to the Darwinian hypothesis, 
it cannot reasonably be maintained, that we are either bound 
to suppose that all varieties of animal and vegetable life have 
been produced by the action of natural and sexual selection, or 
that we are shut up, as our only alternative, to the denial that 
natural selection is a vera causa at all. It is impossible to 
doubt the operation of “natural selection ” within certain 
limits; but the question remains as to what these limits are ; 
and we are certainly not justified in concluding that because it 
operates in certain cases, therefore all the peculiarities of the 
structure of living beings can be explained as due to this, aloue 
or combined with “ sexual selection.” 
Lastly, we have one extremely important consideration to 
bear in mind, and that is that very different meanings may be 
attached to the term “ evolution.” Supposing ground should 
appear for believing that certain forms of life have been 
evolved from other different forms, we have to admit the 
partial operation of “ evolution ” in its real and strict sense ; 
but it still remains to gauge the quality and significance of this 
process, as well as to assign the causes by which it was brought 
about. To some minds, “ evolution ” appears to convey little or 
no notion of definite law and order, and the whole process 
appears to present itself as a kind of chance-medley operation, 
one species becoming converted into another, not along certain 
