on the Direction of Evolution. 181


makes it a wholly new character, and its bearer a new species.

To the mutationist the bars of Columba livia, both as a whole

and in their component elements, would be viewed as essentially

fixed units. As we look at the character in the mature state, it

seems a perfect picture of immutability. To reach such a definite-

ly localized and apparently rigid character, it might seem that

evolution had come to a halt, that the character was caught in a

mutation trap, from which there could be no escape. But even

while we are looking at this picture, the self-same process that pro-

duced it may be preparing another picture to appear after a moult

in more or less different guise. Can a single individual mutate

from plumage to plumage, i.e., become a new species?


When we look around among allied species and see these

same bars reduced to about half dimensions in the Rock Pigeons

of Manchuria (C. rupestris), reduced to mere remnants of two to

six spots in the Stock Dove(C cenas), carried to complete obso-

letion or to a few shadowy reminiscences in the secondaries in

C. rufi?ia of Brazil, gone past return in some of our domestic

breeds and in many of the wild Columbse — when we see all these

stages multiplied and varied through some four to five hundred

wild species and one to two hundred domestic breeds, and in

general tending to the same goal, we begin to realize that they

are not to be regarded as permanent halts, but rather as slowly

passing phases in the progress of an orthogenetic process of

evolution, which seems to have no fixed goal this side of an

immaculate monochrome — possibly none short of complete

albinism.


Even in cases where natural selection has probably played

a conspicuous part in modifying and beautifying these marks,

e.g., in the Crested Pigeon of Australia (Ocyphaps lophotes), we

find that the reducing process has not been brought to standstill.

Indeed, a careful comparison of the juvenal and adult plumages

in both sexes, shows that differentiation has been gradual and

continuous, and that it is still in progress in the bar of the long

coverts, the homologue of the anterior bar in the Rock Pigeons.

What we now see going on in this bar, has already been achieved

in the White-bellied Plumed Dove* (Lophophaps leticogaster^oi


* A good picture of this dove was given by Mr. D. Seth -Smith, in the December

number of the Avicultural Magazine.



