ch are sufficient for Natural Selection to work with,
could be SEXUALLY selected. We seem to require a series of bold and
abrupt variations. How can we imagine that an inch in the tail of the
peacock, or 1/4-inch in that of the Bird of Paradise, would be noticed
and preferred by the female.")

In regard to sexual selection. A girl sees a handsome man, and without
observing whether his nose or whiskers are the tenth of an inch longer
or shorter than in some other man, admires his appearance and says she
will marry him. So, I suppose, with the pea-hen; and the tail has been
increased in length merely by, on the whole, presenting a more gorgeous
appearance. J. Jenner Weir, however, has given me some facts showing
that birds apparently admire details of plumage.

LETTER 432. TO F. MULLER. March 28th [1868].

I am particularly obliged to you for your observations on the
stridulation of the two sexes of Lamellicorns. (432/1. We are unable
to find any mention of F. Muller's observations on this point; but
the reference is clearly to Darwin's observations on Necrophorus and
Pelobius, in which the stridulating rasp was bigger in the males in the
first individuals examined, but not so in succeeding specimens. "Descent
of Man," Edition II., Volume I., page 382.) I begin to fear that I am
completely in error owing to that common cause, viz. mistaking at first
individual variability for sexual difference.

I go on working at sexual selection, and, though never idle, I am able
to do so little work each day that I make very slow progress. I knew
from Azara about the young of the tapir being striped, and about young
deer being spotted (432/2. Fritz Muller's views are discussed in the
"Descent of Man," Edition II., Volume II., page 305.); I have often
reflected on this subject, and know not what to conclude about the loss
of the stripes and spots. From the geographical distribution of the
striped and unstriped species of Equus there seems to be something very
mysterious about the loss of stripes; and I cannot persuade myself
that the common ass has lost its stripes owing to being rendered more
conspicuous from having stripes and thus exposed to danger.

LETTER 433. TO J. JENNER WEIR.

(433/1. Mr. John Jenner Weir, to whom the following letters are
addressed, is frequently quoted in the "Descent of Man" as having
supplied Mr. Darwin with information on a variety of subjects.)

Down, February 27th [1868].

I must thank you fo