4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



The majority of studies of evolution within limited groups of 

 animals emphasize single characters or single aspects, such as external 

 morphology, relatively minor changes in size, shape, or proportions, 

 or adaptation of one part or one structure to changing habits. Also, 

 the stress has been placed on characters that seem to have gone the 

 whole way from a generalized to a highly specialized condition. This 

 emphasis is understandable — it is most convincing to be able to re- 

 construct historically the path or paths followed by piecing together 

 carefully and critically all the available data. This procedure, how- 

 ever, has tended to conceal, or at least to detract attention from, the 

 fact that many organisms have evolved only "part way," and still 

 have managed to survive and to succeed. This is, of course, generally 

 implied or assumed in the stage elements of all more complete de- 

 velopments, but it is M^ell to underscore it where, as in Clamator, 

 some of the species have stopped at "part-way" stages. 



The four species of the genus Clamator form a compact group 

 that has been considered by Jourdain and Baker and other writers on 

 parasitic cuckoos as one in which adaptive evolution in egg similarity 

 to those of its usual hosts has gone as far as in any group of brood 

 parasites. Yet, two of the four species have geographic segments 

 (populations or races) that either never arrived at, or else appear to 

 have "ignored" or to have "repudiated," the results of the adaptive 

 evolution of their respective stocks, and this situation has been arrived 

 at in very different ways in the two. 



Thus, in the case of the jacobin cuckoo, Clamator jacohmus, we 

 have a species which, throughout its extensive Asiatic and part of its 

 African range, is parasitic chiefly on babbling thrushes, most of which 

 lay bluish eggs. In Asia and in northeastern Africa the eggs of 

 the jacobin are always similarly bluish or blue-green in color, but 

 in most areas south of the Sahara the resident jacobins, using some 

 of the same type of hosts, but more frequently, bulbuls and shrikes, 

 lay only pure white eggs, which contrast strikingly in appearance 

 with those of their victims. 



Turning to the great-spotted cuckoo, Clamator glandariiis, we 

 find that this species lays but one type of egg throughout its range. 

 In the Iberian peninsula and adjacent parts of northwest Africa, it is 

 almost exclusively parasitic on magpies, with the eggs of which its 

 own show extreme similarity. So great, indeed, is the resemblance, 

 that it has been cited frequently as an example of "perfected" adaptive 

 evolution, and some not uncritical collectors have had the experience 

 of collecting sets of eggs containing both species without realizing 



