Note 62 — APPENDIX B. An Examination by Mr. Fletcher Moulton of Mr. Wallace's Calculation touching the Possibility Of Physiological Selection ever acting alone.

His sentence, "all fertility not correlated with some useful variation has a constant tendency to effect its own elimination," still further restricts the possible action of physiological selection to cases where at least one of the other forms of homogamy with which it is associated is natural selection. Or, in other words, it is represented that physiological selection must always be associated with natural selection, even if it be likewise associated with any other form of exclusive breeding. But as this further limitation appears to me self-evidently unjustifiable (seeing that utility is not the only possible means of securing effective isolation) I here neglect it, and take the wider ground marked out above. It is needless to say that this is giving Mr. Wallace every possible advantage, by not holding him to his still narrower ground.