9, St. Mark's Crescent N.W.
Septr. 18th. 1869
The more I think of your views as to the colours of females, the
more difficulty I find in accepting them, and as you are now
working at the subject I hope it will not interrupt you to hear
"counsel on the other side".
I have a "general" and a "special"
argument to submit
1. Female birds & insects are generally exposed to more danger
than the male, and in the case of insects their existence is
necessary for a longer period.
2. They therefore require in some way or other a special balance
3. Now if the males & female were distinct species, with
different habits & organizations, you would I think at once
admit, that a difference of colour serving to make that one less
conspicuous which evidently required more protection than the
other, had been acquired by nat.[ural] selct[io]n.
4. But you admit that varieties appearing in one
sex are transmitted (often) to that sex only.
there is therefore nothing to prevent nat.[ural]
acting on the two sexes as if they were two
6. Your objection that the same protection would to a be useful to
, seems to me
utterly unsound, & directly opposed to your own doctrine so
convincingly argued in the "Origin", "that N. Seln. never can improve an
animal beyond its needs
". So that admitting abundant
variation of colour in the male, it is impossible that he can be
brought by nat.[ural] select.[tion] to resemble the female (unless
her variations are always transmitted to him
) because this difference
of their colours is to
balance the difference
their organizations & habits,- and nat.[ural] select.[tion] can
<only balance> not give to the male <different uses,
balancing different degrees of> more than is needed to affect
that balance. <……… in selection, can not
produce the same result>
7. The fact that in almost all protected groups
perfectly resemble the males, shows I think a tendency to
transference of colour from one sex to the other when this tendency
is not injurious. Or perhaps the protection
is acquired because this
tendency exists. I admit that if there is the case of concealed
visits they habits? every have been acquired for protection
Now for the special case.
8. In the very weak flying Leptalis
both sexes mimic
9. In the much more powerful Papilio
Pieris and Diadema
it is generally the female only
10. In these cases the females often acquire more bright &
varied colours than the male. sometimes as in Pieris pyrrha
11. No single case
known of a male Papilio Pieris
Diadema or any other alone
mimicking a Danais
12. But colour
frequent in males, and variations always seem ready for
purposes of sexual or other selection.
13. The <plain explanation> fair inference seems to be that
given in pp[proposition]. 5.  of the general argument, - viz. that each species &
ch sex can only be modified by selection just as far
as is absolutely necessary, not a step farther. A male, being by
structure & habits less exposed to danger & less requiring
protection than the female cannot have more protection given to it
by nat.[ural] select[io]n.., but a female must
have some extra protection
to balance the greater danger, & she rapidly acquires it in one
way or another.
15. An objection derived from cases like male fish which seem to
require protection, yet having brighter colours, seems to me of no
more weight than is that of the existence of many white &
unprotected species of Leptalis; to Bates' theory of mimicry;- that
only one or two species of butterfly perfectly resemble leaves, or,
that the instincts or habits or colours that seem essential to the
preservation of one animal <seem> are often totally
absent in an allied species.