April 20, 1871 | 
NATURE 
489 

Persons who have read his book say that he does dwell with 
considerable force upon these very matters, but it is easy to see 
from the Reviewer’s tone that they are mistaken, and that such 
inyestigations have been sacrificed to a glance or two at things 
on the surface. This is the more to be grieved and wondered at, 
because in his monograph on the Fossil Cirripedes and in his 
work on the Fertilisation of Orchids, Mr. Darwin showed an 
uncommon aptitude at ‘‘a thoroughly scientific clairvoyance.” 
The Reviewer thinks it perfectly reasonable that the hand of a 
man and the foot of a horse, the flipper of a seal and the wing 
of a bat, should have all been formed upon the same general plan, 
without any connection bya common ancestry. It would be ex- 
tremely gratifying to an inquiring mind, if he would explain upon 
this reasonable plan, the vast succession of creatures unveiled 
by geological research, Why have innumerable species been 
created and then destroyed? When did the creation begin, and 
when did it end? What causes, or if there were no causes pro- 
perly so called, what caprice brought about the extinction of the 
mammoth, and led to the introduction of the modern species of 
elephant? Has the creative power been at last exhausted, or do 
sudden creations still occur, only in a shy sort of way, when no 
one is looking on? The Reviewer very sensibly censures Mr. 
Darwin and his followers for not specifying the year B.c. when 
the process of evolution first began. It is with the less diffi- 
dence, therefore, that a question is propounded above as to the 
date of the creation. The solution of this point of chronology 
_ will be awaited by many with extreme impatience, as different 
nations give very different accounts, and the Hebrews, who 
have a very ancient record, are by no means at one with them- 
selves in the Hebrew and Greek editions of it. The number of 
years required for the process of evolution is confessedly indefi- 
nite, and as the whole hypothesis must, therefore, be destitute of 
any scientific value, it is no doubt quite fair on the Reviewer’s 
art, to represent an indefinite number of years as equivalent to 
‘infinite time.” But the steps required for the process are also 
an indefinite number, and on this point he is less clear than 
elsewhere, for, referring to the old sophism respecting Achilles 
and the tortoise, he tells us, from Sir Isaac Newton, that 
‘quantities ultimately coincide which may be proved to 
approach each other indefinitely, within a finite time.” From 
this it would seem that, if Darwinians could be content with the 
boundaries of geological time, the genealogies of men and 
apes might ultimately coincide. To avoid this miserable and 
preposterous conclusion, we are told that the solution of the 
sophism by Diogenes, ‘‘is the only true one,” solvitur ambu- 
Jando. We are further obligingly informed that this solution 
is identical with Newton’s. And as Mr. Darwin cannot trans- 
form one species into another under our eyes, the eminently un- 
practical character of his speculations is triumphantly exhibited. 
It will be very impertinent if any one suggests that the instan- 
taneous creation of a species has never yet been witnessed, and 
that those who believe in such occurrences ought, on the so/vi- 
tur ambulando principle, to favour the world with, at least, one 
such exhibition. Captious persons may find fault with the 
Reviewer's opinion that the poetic faculty has received no deve- 
lopment since Homer, and the religious sentiment none since the 
book of Genesis. They may call to mind that Moses and 
Socrates, and St. Paul and Luther, were guilty, like Mr. Darwin, 
of laying before popular audiences dangerous and ‘‘disintegrat- 
ing” speculations ; they may fancy that truth is worth discover- 
ing, even when it seems to involve some contradiction to our 
pride and some loss of comfort to our finer feelings, but such 
persons must be very captious, and the Reviéwer will, doubtless, 
know how to deal with them. 
Torquay, April 15 Tuomas R. R. STEBBING 
Sexual Selection 
In the first volume of ‘The Descent of Man,” at page 396, 
Mr. Darwin says, referring to butterflies, that ‘the lower sur- 
face (of the wings) generally affords to entomologists the most 
useful character for detecting the affinities of the various species.’ 
I think, also, that this lower surface might afford another link in 
the chain of argument by which Mr. Darwin supports his theory 
of Sexual Selection. Thus, for example, to speak of British 
species only, in the cabbage butterflies, the under surface of the 
wings is alike in both sexes of Pieris Brassica. The black spots, 
however, which appear on both surfaces of the fore wing of the 
female vanish from the upper surface of that of the male, 
probably because the female has some dislike to them. Thereis 
no difference in food-plant, habit, or need of protection here ; 

the only explanation seems to be a whim of the female or a 
whim of nature, and we have lately discarded all thought of 
nature being freakish. In ?. Rafe and P. Nafi a similar difference 
prevails, though less constant and ina degree less marked. In 
the allied Anthocharis Cardamines the under surface of both 
sexes is alike, notwithstanding the vast difference of their upper 
surfaces. When these butterflies alight and close their wings, 
the under surfaces of the Aind wings are alone visible, and these 
are, apparently, the parts of the insect modified for the sake of 
protection. The simple yellow in Brassice and Rafa, the green- 
veined yellow in Vai, the green marbling in Cardamines, of the 
under sides of the hind wings, are well fitted to conceal those 
insects as they settle on the wild flowers which they prefer. 
Again in Aipparchia Fanira the light brown patch so con- 
spicuous on the upper surface of the fore wing of the female 
vanishes from that of the male; and in /7. 7ithonus and H. 
hyperanthus a tendency to decrease the quantity of light colour 
on the upper surface of the male butterfly prevails. So is it 
also with one of the Hair Streaks, Zhecla Betule, the under sur- 
face still remaining alike in both sexes of these different species. 
In this case the female butterflies would seem to wish their 
partners to be of a duskier hue than it is granted to themselves 
to be. The differences mentioned above are so slight that Mr. 
Darwin says at page 317, ‘‘ With those (butterflies) which are 
plain-coloured, as the meadow-browns (//iffarchie) the sexes 
are alike.” But it will be admitted that though these differences 
are slight they are yet important, as showing a tendency, more 
or less marked, to follow the rule which Mr. Darwin has laid 
down ; and every sign of such a tendency strengthens his case. 
In Afgatura Jris the under surface of both sexes is alike, 
though the male has his upper surface glorified with purple for 
the delight of his plain brown wife. Inthe blues, Polyommatus 
Alexis, P. Corydon, P. Adonis, and P. 42gon, the under surface of 
both sexes is also alike, though in the males the blue and in the 
females the brown of the upper surface forms the background 
of the spotty design. The blue blood is very strong in these 
butterflies, and will show itself sometimes even in the females ; 
who, if powerless over their own decoration, have at least suc- 
ceeded in bringing out the innate splendour of their handsome 
husbands. With the blues, as with the cabbage butterflies, the 
under’surface of the hind-wings seems specially adapted for 
protective purposes ; every butterfly-hunter knows how difficult 
it is to distinguish the common blue when it is siitting, shut up, 
on a scabious flower. It is the same with the small copper 
butterfly, which has its under surface dotted very similarly. But 
burnished copper and dazzling blue are not colours for protection, 
surely. We may give the under surface to Mr. Wallace, but 
we must yield the upper surface to Mr. Darwin. 
At page 399, speaking of the ghost moth (/Zepialus humuli) 
and others of the moth kind, Mr. Darwin says, ‘‘ It is difficult 
to conjecture what the meaning can be of these differences be- 
tween the sexes of darkness or lightness ; but we can hardly 
suppose that they are the results of mere variability, with 
sexually-limited inheritance, independently of any benefit thus 
derived.”” The female ghost moth follows Mr. Darwin’s rule, 
that females are most conservative of the features of kinship. 
In her colouring she closely resembles the other Hepialidz, And 
the male, notwithstanding his shining shroud, keeps to the same 
sober under-colouring as his mate. Now //. humuli is more 
nocturnal in its habits than any of the other species in the genus 
Hepialus ; Vhave caught H. hectus and H. lupulinus flymg in 
bright sunshine, but I have never seen the ghost moth until dusk 
was far advanced. May it not be that sexual selection has come 
into play here by the female preferring the zw/i¢est male, he being 
the most distinguished when all colour has faded into dimness ? 
She could not decide between differing patterns of gold and 
amber at that hour, but a snow-white surface would then be quite 
visible. The fact mentioned at page 402, that ‘‘in the Shetland 
Islands males (of 7% Aumuli) are frequently found which closely 
resemble the females” (I have seen similarly varied males in 
Peterhead collections), would seem to confirm this theory ; for 
the twilight of the north, at the season when the ghost-moth 
abounds, is so bereft of dusk that whiteness would not be needed 
to render the males visible. 
It is possible that those acquainted with the habits of the 
other moths, of which Mr. Darwin speaks, may be able to recon- 
cile their appearance with the rules of Sexual Selection which he 
has laid down so clearly and illustrated so fully in his last great 
work. GEORGE FRASER 
169, Camden Road, London, N.W. 
