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Feb. 26— 62. — It is true as I said in Origin no good to creature to be sterile; but I forget that this was only means to end— To keep vars, apart highest good, as we see by man by fences &c. — In plants it is prepotency of pollen which is probably aimed at. — Though the sterility of parent & hybrids would be of good. —

In animals my difficulty is that instincts would have sufficed; but one never knows how nature will work. — Certainly instincts are not invariably strong enough to keep species apart— Hooded Crow — Black Grouse Woodpecker &c &c.

[159v]

Thus can clearly see that under general point of view good to keep vars apart — If the hybrids could breed they would drag back the new var. to primordial state. —

Hence variation so slow as structural & physiological changes have to go together. —

In all cases when animals pair & live in herd under one Lord, prepotency of semen. (if it even comes in) cannot apply.

Nature acts as a man would if

[160]

two of his best breeds united he would castrate the mongrel— As nature does in sterile — or neuter Hymenoptera & Neuroptera — Border flowers of compositæ Umbelliferæ — Hydrangeæ are rendered sterile: they perhaps in these cases due to laws of growth.

As pairing animal could not be selected, even if it varied in right way, until it chanced to evince either instinctive (& thus would not occur early enough) or physiological also aversion to unite with parent form.

Perhaps grant first a little variation & sub-race formed

[160v]

Thus would be lost, unless it were separated by sterility from parent or other races. —