THE ORIGIN AND RELATIONSHIP OF THE ROCK-PIGEONS. 55 



The two posterior rows of chequers, which have been preserved in this genus 

 and raised to a state of brilliant iridescence, are the exact homologues of the two 

 black bars of Columba livia. The starting-point is then again found in general 

 chequers, and evolution has advanced by a definitely directed reduction of pigment, 

 proceeding from before backward, 9 in the same direction as that of embryonic 

 development. That this is the direction of evolution, and that there is no possi- 

 bility of reading the conditions in the opposite direction, becomes still clearer when 

 we discover that a closely allied genus (Lophophaps) has taken a step in advance 

 of Ocyphaps, in that it has acquired the narrow bars in the place of chequers in 

 the row of long coverts, leaving but a single row of chequers on the secondaries. 

 That Lophophaps occupies the higher plane is obvious in other modifications seen 

 in the head, breast, and wing-pattern. 



If the testimony of juvenal patterns be extended to species having chequers 

 so closely agreeing in form, color, and distribution with those of the chequered 

 rock-pigeon that no shadow of doubt can remain as to their homology, we shall 

 get only additional confirmatory evidence that the process of evolution in color- 

 patterns has been a sweeping one, involving the whole surface and taking the same 

 general direction. The stages reached are various, ranging all the way from the 

 full-chequered to the wholly unchequered state; from chequers and bars combined 

 in different proportions to bars alone; from many bars to three, two, one, a remnant, 

 or none; and in all shades of brown, black, gray, red, to pure white. Nowhere in 

 this field of variations do we find any indications that chequers originated in the 

 form of bars at the posterior end of the wing and then spread from behind forward. 



The wild passenger-pigeon (Ectopistes) bears chequers closely resembling those 

 of the chequered rock-pigeon. 10 There can be no mistake here as to the direction 

 in which the phenomena are to be read. The direction is as certain as that the 

 adult male stands in advance of the adult female, and still more in advance of 

 the young bird. The significance of the case lies mainly in the fact that it is not 

 an isolated or exceptional one. Many other species tell more or less perfectly 

 the same story. 



A parallel case, only carried still farther in the same direction, is found in the 

 mourning-dove (Zenaidura). The adult male (see pi. 19, Vol. II) and female differ 

 but slightly, each having about a dozen chequers visible on each side. These are 

 confined to the scapulars and to a few feathers at the posterior upper edge of the 

 wing. In the young (pi. 7) they are more numerous, but less so than in the young 

 passenger-pigeon. The middle and fore parts of the wing in the adult have no 

 visible chequers, but a few concealed ones which may be seen on lifting the over- 

 lying feathers. These concealed chequers and other differences between old and 

 young show that the species had its origin in a chequered stock and that its history 

 has been analogous to that of the passenger-pigeon. The reduction has not been 

 carried out in a way to leave bars, but the location and the clean-cut outlines of 

 the spots, as well as their intensity of color, suggest that some influence may have 

 operated to preserve and then intensify them in a region suited to their most 

 effective display. 



9 Just the reverse of the contention of Eimer and his school, that evolution in color-marks progresses in a postero- 

 anterior direction. 



10 These have been described and illustrated in Chapter II. — Ed. 

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