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carnivorous, others graminivorous; some are viviparous, others 
oviparous, &c. Yet there are certain other facts and orders of 
facts which do not seem invariable. Such notably is the case 
that, although parents produce offspring like themselves (this 
being usually a recognized law), yet they never are absolutely 
like them ; such differences as may appear in the offspring 
being due, it is said in our ignorance, to the “ laws of varia- 
tion.” This, however, is no explanation, but themselves are 
orders of facts, and therefore we are once more driven back- 
wards to find higher law or will. 
Here, then, we observe the difference between the laws of 
variation in the offspring of living beings and laws governing 
the lifeless physical phenomena of the world. The result of 
the latter can be with tolerable or perfect accuracy predicted. 
The resultant of laws of variation can never be foreseen. No 
one can tell what are the preceding forces which give rise to 
variation at all, nor in what direction the offspring may vary. 
Here, then, is the occasion where chance is apt to find a 
place in theories of specific origin ; but, as I have already 
said, taking a long and consecutive view of nature’s offspring 
we are compelled to acknowledge the presence of an over-ruling 
Law, though we cannot see it in the individual variations. 
Some of those forces which produce variation in the offspring 
have been thought to be the exercise of muscular action, an 
inherent principle of progression ; while food and external con- 
ditions acting upon the organs of reproduction is reservedly 
suggested by Mr. Darwin, though he prefers to state more 
emphatically that “ our ignorance of the laws of variation is 
profound.” ( Origin of Species, 4th edit., p. 195.) 
Now, as evolution hinges upon these so-called laws of varia- 
tion, especial attention must be paid to them: for while we can 
all recognize family likenesses, yet we can at once distinguish 
any two members of a family from each other. This may be 
a truism, but it lies at the bottom of evolution, for all that. 
If, therefore, an offspring can be different, however slight, from 
its parent, there are no a priori reasonable grounds for asserting 
that the second generation may not differ from the first as much 
as the first differs from the original parents, until at last a being 
may be produced so far different from the original parents, that 
it would (if its history were unknown) be classed by a naturalist 
as a different genus altogether. 
This, it will be remembered, has actually been done in the 
case of pigeons, as described by Mr. Darwin in his Origin of 
Species. On the other hand, some opponents of his views have 
maintained that the power of variation is limited ; if so, the 
