It has certainly been an immense
relief to my mind; for I have been stumbling over the subject for years,
dimly seeing that some relation existed between the various classes of
facts. I now hear from H. Spencer that his views quoted in my footnote
refer to something quite distinct, as you seem to have perceived.
I shall be very glad to hear, at some future day, your criticisms on the
causes of variability.
Indeed, I feel sure that I am right about sterility and Natural
Selection. Two of my grown-up children who are acute reasoners have two
or three times at intervals tried to prove me wrong, and when your
letter came they had another try, but ended by coming back to my side. I
do not quite understand your case, and we think that a word or two is
misplaced. I wish some time you would consider the case under the
following point of view. If sterility is caused or accumulated through
Natural Selection, then, as every degree exists up to absolute
barrenness, Natural Selection must have the power of increasing it. Now
take two species, A and B, and assume that they are (by any means)
half-sterile, i.
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