April 13, 1871] 

as by the pains they take to exhibit their beauties to the 
hens. The difficulty is to show the precise way in which 
the results have been attained by gradual selection. In 
two remarkable instances, the wings of the Argus phea- 
sant and the train of the peacock, Mr. Darwin succeeds in 
tracing the gradations in the same bird or the same family 
by which these wonderful and elaborate ornaments have 
been brought to their present perfection. The woodcuts 
which illustrate these gradations are unfortunately too 
numerous to be reproduced here; they are admirably 
drawn, and convey the impression of the feathers as nearly 
as is possible by the means employed. Indeed, we may here 
remark that throughout these volumes the original cuts, 
generally of details of structure, contrast very favourably 
with the figures of species taken from Brehm’s “ Thier- 
leben,” which are feebly drawn and ill-engraved. 
Sexual selection has, of course, been continually 
checked and modified by the never-ceasing influence of 
natural selection, sometimes, as in the case of the horns 
of stags, being only somewhat diverted, but often directly 
opposed, as when it produces dangerously conspicuous 
colours, and dangerously cumbersome ornaments. In 
the case of birds, Mr. Darwin holds that the usual ten- 
dency of sexual selection being to produce variation in 
males, its transmission to hen birds has been checked by 
natural selection. Mr. Wallace, on the other hand, be- 
lieves that both tendencies have generally operated to- 
gether, in opposite directions, so as to make successive 
generations of males more and more conspicuous than 
the primitive type, and those of females less so, The 
fact that, as a rule, young birds resemble hens in their 
plumage, is a strong argument for the former opinion, 
since most naturalists adinit that early characters are the 
most trustworthy guide to natural alliances, ze., to true 
genealogy. To explain the transmission in some cases of 
brilliant colours (acquired probably by sexual selection, 
and therefore properly a male character) to both sexes 
indiscriminately, Mr. Wallace has framed the ingenious 
hypothesis, that the females have been protected from 
the dull uniformity threatened by natural selection, by 
their very general habit of building covered nests. Our 
author looks at the facts in a reversed way, and supposes 
that in most cases these hen birds, having inherited 
bright colours from the males, were led to the habit of 
building covered nests for the sake of protection. 
Among mammals sexual selection has chiefly operated 
by increasing the size and strength of the males, and 
furnishing them with weapons of offence ;* but besides 
allurements to the senses of smell and hearing, this class 
offers not afew instances, especially among the Quadru- 
mana, of brilliant colouring being developed as a secondary 
sexual character. Here also we have the most striking 
instances of the production of defensive organs by the 
same process, as in the manes of lions, the cheekpads of 
some of the Swd@, and possibly the upper tusks of that 
ancient enigma, the barbirusa. Lastly, it is in the class of 
mammals that we meet with cases of what may be 
called primary sexual ornament, as in Cercopithecus 
cynosurus, which make one wonder, with a thankful 
wonder, why such apparently obvious results are ‘not 
* The very general transmission of such weapons to both sexes may, 
perhaps, be explained by the need females have of means to defend their 
young. 
NATURE 
465 

more common. We must, however, admit that such 
adornment is not more disgusting, nor that of which we 
copy a figure more ludicrous, than the personal decorations 
of savages. Sir Joshua Reynolds says that if a European 
in full dress and pigtail were to meet a Red Indian in his 
warpaint, the one who showed surprise or a disposition to 
laugh would be the barbarian.* But who could stand 
this test when meeting Semopfithecus rubicundus or 
Pithecia satanas 2 
We must admit, notwithstanding such anomalies, that, 
on the whole, birds and other animals admire the same 
forms and colours which we admire, and this, perhaps, 
may be admitted as an additional argument in favour of 
their kinship with us. Some of the ugliest creatures 
(like the hippopotamus) appear to have been quite un- 
influenced by sexual selection, while the magnificent 
plumes of pheasants and birds of paradise are undoubtedly 
due to its operation. That it has occasionally led to 
unpleasing results in birds and monkeys of aberrant 
taste, is no more strange than that all savages do not 
carve and colour as well as the New Zealanders, or that 
most Englishmen admire ugly buildings and vulgar pictures. 
The prevailing aspect of nature is beauty, and the pre- 
vailing taste of man is for beauty also. The means by 
which natural beauty has been attained are various. 
Natural selection is one, by which the healthiest, and 
therefore the most symmetrical forms survive the rest. 
Protective mimicry is another, by which fishes have 
assumed the bright colours of a coral garden and butter- 
flies the delicate venation of leaves. Flowers again have 
in many cases obtained their gay petals and fantastic 
shapes from the advantage thus gained for fertilisation 
by insects. The successive steps which have led to the 
graceful forms and brilliant tints of shells, to the intricate 
symmetry of an echinus-spine or a nummulite, these 
are as yet untraced even in imagination. 
But that many of the most striking ornaments of the 
higher animals, and almost all those which are peculiar 
to one sex, have been developed by means of sexual selec- 
tion, is a conclusion which can no longer be distrusted. 
There remain doubtless many exceptions to be accounted 
for, many modifying influences to be discovered ; but the 
existence of a new principle has been established which 
has helped to guide the organic world to its present con- 
dition. Side by side with the struggle for existence has 
gone on arivalry for reproduction, and the survival of the 
fittest has been tempered by the success of the most 
attractive. P. H. PYE SMITH 


HELMHOLTZ’S TONEMPFINDUNGEN 
Die Lehre von den Tonempfindungen, von H. Helmholtz. 
(Braunschweig: F. Vieweg. London: Williams and 
Norgate. 3rd edition. 1570.) 
HIS work traces the connection between physical 
af and physiological acoustics, on the one hand, and 
the general principles and practice of music, on the other. 
Professor Helmholtz’s qualifications for taking up this 
subject are unique. In each branch of science involved 
in the inquiry he has a reputation at least equal to that of 
any specialist in that branch. In the combination of 
eminently original mathematical power and consummate 
* Discourse delivered at the Royal Academy, December 10, 1776, 
