Notes on Sexual Selection.



24 r



e.g . the guinea-fowl’s feet tend to become orange instead of black,

and the Muscovy drake’s face, naturally mostly black, becomes

more, or altogether, red.


Structural decorations may appear, like the knob on the

beak of the Chinese Goose (Cygnopsis cygnoides') which is often

orange, contrasting with the normal black of the bill, and

common ducks and pigeons assume crests.


Sometimes these alterations are sex-limited, e.g. cinnamon

in canaries and blue in budgerigars, tend to be female colours,

while white in common geese tends to be a male colour.


We can see, then, that even without selection decorative

plumage and appendages, &c. tends to appear; it is true that

such peculiarities are irregular, not constant as in wild species,

but in the latter natural selection may come into play to limit

variation. For instance, white feathers are usually soft, and so

we find few birds are all white or have even white quills, easily-

abraded quills being a dangerous possession for a wild bird. It

is particularly noticeable that in the only wild bird which varies

widely like an unselected domestic one—the Ruff (.Pavoncella

pugnax ) the variation (except in the rare white-necked variety)

is confined to the breeding season, and the Ruff, to be able to

carry his cumbrous decorations at all, must surely be able to defy

natural selection on his breeding-grounds at any rate.


If decorations are the result of the withdrawal of the

pressure of some form of natural selection we can see why they

are so often concealed in repose ; so long as a bird has the

tips of the quills, for instance, dark and tough, the concealed

part may be of any colour that variation gives, provided that

colour is correlated with a strong constitution—for no character

can escape constitutional selection, but must always go along

with power of resistance to climate, a good digestion, or what

not.


The nine-days-wonder of a grey thoroughbred winning

the Derby this year shows how important is the principle of

correlation, for if grey horses had high speed u 7 e should hear more

about their doings. I think myself that the force of variation,


* We would point out that these instances given by Mr. Finn are all those of ‘ weaker’

■colours, whereas ‘brighter’ colours generally imply ‘strength.’— Ed.



