154



On Red-breasted Starlings, etc.



In spite of the total dissimilarity of their bills, it is evident

that Ridgway regards Trzipialis and Leistes as still nearly related ;

if so their divergence from a common ancestor may have been

comparatively recent in the unthinkable ages of avian evolution ;

and I see no more difficulty in the retention of a certain type of

colouring for a million years than for ten thousand, provided that

it is suited to the conditions of its wearer.


I feel certain that many supposed instances of what has

been called mimicry are nothing more than inherited resem¬

blances between genera which had a common origin, some of

which like Trupialis and Leistes have inherited also certain

similarities in habits.


Nature has not a free hand in the development of colour,

although her resources seem to be unlimited : for instance, one

cannot believe it possible for a blue species to be developed direct

from a yellow; I believe the colouring must either pass through

the black stage, or else be gradually modified from yellow through

orange, crimson and purple as in the rainbow. We constantly

find tawny, black and yellow in a single individual; blue, black,

green and yellow; tawny, black and crimson, and so on; but

in a single instance which I recall in which yellowish-white,

bluish grey and blood red species occur in one genus, there is

some trace of black remaining, and a smoky brown type in a

transition stage between the dissimilar colours: I think it is

true in this respect, if not in all, that Natura non facit saltum.

As black is a combination of all colours, we may conclude that

it is capable of producing them all : on the other hand white,

being the absence of colour, should be capable of producing

none. When therefore white changes to yellow, we must con¬

clude that it reverts to a previous condition. Blue seems to be

the first colour produced from black, and when one sees a pale

blue belt in conjunction with a white one, there is pretty certain to

be black close to it, and often at the extremities of the blue belt.

But I fear I am wandering somewhat from my point, which was

to show that similar types of colouring are to be expected in

related forms, inasmuch as Nature works most smoothly in the

direction of the least resistance.



