Down, April 6th [1868].
I have been considering the terrible problem.

Let me first say that no man could have more earnestly wished for the success of Natural Selection in regard to sterility than I did; and when I considered a general statement (as in your last note) I always felt sure it could be worked out, but always failed in detail.

The cause being, as I believe, that Natural Selection cannot effect what is not good for the individual, including in this term a social community.

It would take a volume to discuss all the points, and nothing is so humiliating to me as to agree with a man like you (or Hooker) on the premises and disagree about the result.
I agree with my son's argument and not with the rejoinder.

The cause of our difference, I think, is that I look at the number of offspring as an important element (all circumstances remaining the same) in keeping up the average number of individuals within any area.