Darwin Correspondence Project

Royal Geographical Society | 15, Whitehall Place, S.W.

March 12 1868

My dear Mr Darwin

I have again examined a few genera of Trop. American butterflies to ascertain the gradation in divergence of sexual coloration & give you the results as promised.

1— Junonia (including G. Precis of some authors) on re-examination I think the genus is better divided into three classes, instead of four, as I gave in former letter:

1st class of species—in which there is no difference whatever in colours or pattern & both sexes are destitute of rich or strongly contrasted colours

The majority of species in this large genus come under this class

2nd class—similar colours & pattern but male richer & brighter in colour

1 Junonia Œnone— 2 J. Radama

3 Jun. clelia

3rd class  sexes quite different in colours: male having rich, deep & contrasted colours.

1 Junonia Orithya

2 " Andremiaja

2. Æneas group of Papilio, slow-flying insects abounding in Tropical American forests & highly characteristic of the fauna

1st class, both sexes having same colours & pattern, but males generally darker & richer in tint; in one species no difference of tint

at least 4 species

2nd class, sexes strongly contrasted, males with green or blue & white & crimson patches on a black ground— females simply white & crimson patches on black ground

at least a dozen species

3rd class still more strongly contrasted than class 2, the males having the crimson patches superbly glossed with opalescent shades.

—about a dozen species

4th class— contrast reaching its acme in the same direction as the gradation from 2nd to 3rd classes

Two or three species

3. Epicalia— same as described in my former letter to you. This genus illustrates the principle of females preserving a tolerably uniform type of coloration whilst the males, similar to females in some species, diverge diverge greatly in others.

I have found, however, a much better illustration of this in the genus Eubagis

4 Eubagis.— A very numerous genus abundant in Tropical America & peculiar to the fauna

Some species are alike in both sexes & their pattern is after the general type of the great group of butterflies to which the genus as well as Epicalia belongs, but in the majority of the species of Eubagis the males assume metallic colours & in some species reach a high degree of beauty, the females preserving the same plain colours. Curiously enough, in one or two species the female has a trace of metallic lustre!

I have noted a few more genera presenting similar phenomena but will not trouble you with them now, as I hope to show you them next Sunday morning.

The females of these butterflies cannot be called absolutely plain; it appears to me that in the gradual heightening of the male beauty through long ages of sexual selection the female sex has occasionally inherited some portion of the beautified colours & propagated them. I can show you cases where the male varies in ornamental colours & where selection is in all probability now going on; one case, in particular, is that of a most magnificent local variety of a common tropical American species.

I hope your health withstands the excitement of London, & that I shall see you on Sunday.

Yours sincerely | H W Bates