Can butterflies be polygamous?—­i.e. will one male impregnate more than one female?

Forgive me troubling you, and I daresay I shall have to ask your forgiveness again, and believe me, my dear Wallace, yours most sincerely,

CH.  DARWIN.

P.S.—­Baker has had the kindness to set the Entomological Society discussing the relative numbers of the sexes in insects, and has brought out some very curious results.

Is the orang polygamous?  But I daresay I shall find that in your papers in (I think) the Annals and Magazine of Natural History.

* * * * *

The following group of letters deals with the causes of the sterility of hybrids (see note in “More Letters,” p. 287).  Darwin’s final view is given in the “Origin,” 6th edit., 1900, p. 384.  He acknowledges that it would be advantageous to two incipient species if, by physiological isolation due to mutual sterility, they could be kept from blending; but he continues:  “After mature reflection, it seems to me that this could not have been effected through Natural Selection.”  And finally he concludes (p. 386):  “But it would be superfluous to discuss this question in detail; for with plants we have conclusive evidence that the sterility of crossed species must be due to some principle quite independent of Natural Selection.  Both Gaeartner and Kolreuter have proved that in genera including numerous species a series can be formed from species which, when crossed, yield fewer and fewer seeds, to species which never produce a single seed, but yet are affected by the pollen of certain other species, for the germen swells.  It is here manifestly impossible to select the more sterile individuals, which have already ceased to yield seeds; so that this acme of sterility, when the germen alone is affected, cannot have been gained through selection; and from the laws governing the various grades of sterility being so uniform throughout the animal and vegetable kingdoms, we may infer that the cause, whatever it may be, is the same or nearly the same in all cases.”

Wallace still adhered to his view (see “Darwinism,” 1889, p. 174, also p. 292 of “More Letters,” note 1, and Letter 211, p. 299).  The discussion of 1868 began with a letter from Wallace, written towards the end of February, giving his opinion on the “Variation of Animals and Plants”; the discussion on the sterility of hybrids is at p. 185, Vol.  II., 1st edit.

* * * * *

(Second and third sheets of a letter from Wallace, apparently of February, 1868.)