d I should like you some time
to look at a discussion on this subject which I have introduced in the
second edition of the "Descent of Man," and which you can find (for I
have no copy here) in the list of additions. The facts have convinced me
that lessened fertility and the poor constitution of the children is one
chief cause of such decrease; and that the case is strictly parallel to
the sterility of many wild animals when made captive, the civilisation
of savages and the captivity of wild animals leading to the same result.

LETTER 416. TO ERNST KRAUSE. Down, June 30th, 1877.

I have been much interested by your able argument against the belief
that the sense of colour has been recently acquired by man. (416/1.
See "Kosmos," June 1877, page 264, a review of Dr. Hugo Magnus' "Die
Geschichtliche Entwickelung des Farbensinnes," 1877. The first part is
chiefly an account of the author's views; Dr. Krause's argument begins
at page 269. The interest felt by Mr. Darwin is recorded by the numerous
pencil-marks on the margin of his copy.) The following observation bears
on this subject.

I attended carefully to the mental development of my young children, and
with two, or as I believe three of them, soon after they had come to the
age when they knew the names of all common objects, I was startled by
observing that they seemed quite incapable of affixing the right names
to the colours in coloured engravings, although I tried repeatedly to
teach them. I distinctly remember declaring that they were colour-blind,
but this afterwards proved a groundless fear.

On communicating this fact to another person he told me that he had
observed a nearly similar case. Therefore the difficulty which young
children experience either in distinguishing, or more probably in naming
colours, seems to deserve further investigation. I will add that it
formerly appeared to me that the gustatory sense, at least in the
case of my own infants, and very young children, differed from that of
grown-up persons. This was shown by their not disliking rhubarb mixed
with a little sugar and milk, which is to us abominably nauseous; and
in their strong taste for the sourest and most austere fruits, such as
unripe gooseberries and crabapples.

(PLATE: G.J. ROMANES, 1891. Elliott & Fry, photo. Walker and Cockerell,
ph. sc.)

LETTER 417. TO G.J. ROMANES. [Barlaston], August 20th, 1878.

(417/1. Part of this letter (here omitted) is published in "Life an