WCP5415

[1]

Broadstone, Dorset.

Dec[embe]^r. 13th. 1903

H. E. Howard Esq[uire].

Dear Sir

The curious change in the colour of old females of some birds was not referred to by me because I have not myself studied these physiological questions, & also because they are comparatively rare exceptions whose cause is unknown. I think it probable that the explanation you suggest may be correct, but I do not think there is any ^direct relation to the need of [2] protection being no longer required in the old & barren females. That is not a ^real cause. I should rather say that the explanation is purely physiological, depending on the internal processes by which the female has been prevented from gaining the colours of the male ^{in successive generations.} Those colours may be potentially present in all females, but kept from actually developing by some neutralising agency dependent on the normal [3] sexual functions. When these functions cease operating, the neutralising agency is removed, & the colouring matters[?] come out if the bird lives long enough.

This is a rather vague suggestion but it seems to me not improbable.

Yours very truly | Alfred R. Wallace [signature]