There is another objection made by Janet which is also a very common
one. It is that the chances are almost infinite against the particular
kind of variation required being coincident with each change of external
conditions, to enable an animal to become modified by Natural Selection
in harmony with such changed conditions; especially when we consider
that, to have produced the almost infinite modifications of organic
beings, this coincidence must have taken place an almost infinite number
of times.
Now it seems to me that you have yourself led to this objection being
made by so often stating the case too strongly against yourself. For
example, at the commencement of Chapter IV. you ask if it is "improbable
that useful variations should sometimes occur in the course of thousands
of generations"; and a little further on you say, "unless profitable
variations do occur, natural selection can do nothing." Now, such
expressions have given your opponents the advantage of assuming that
_favourable_ variations are _rare accidents_, or may even for long
periods never occur at all, and thus Janet's argument would appear to
many to have great force.
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