62 Froceedinr/s of the Royal Physical Society. 



his classic paper on the subject, was the first, I believe, to 

 point out the following. The bird has but a short time to 

 stay in its breeding area, and much to do in that short time. 

 " I^ature," he says, " has a call upon it to produce a numer- 

 ous progeny." Yet it is an advantage to migrate early, and 

 thus the habit of leaving the eggs to a succession of other 

 birds to incubate. 



Darwin supposed the habit to crop up. Why it should, 

 he did not inquire, but started from its occasional occurrence 

 as in the American cuckoo. The result was an advantage to 

 the parent, and also to the offspring. The former got away 

 sooner, the latter were better cared for. Those that learned 

 the trick prospered, those that didn't were eliminated, and 

 in virtue of its natural or unnatural success the device passed 

 from being exceptional to become universal, became in fact 

 an inherited specific instinct. Commenting upon this, Mr 

 Eomanes, who has made a special study of the sphere of 

 natural selection, says: — "We have here a sufficiently pro- 

 bable explanation of the raison d'etre of this curious instinct ; 

 and whether it is the true reason or the only reason, we are 

 justified in setting down the instinct to the creating influ- 

 ence of natural selection." 



Objections. — Now, while admitting with deference the 

 weight of such testimonies as the above, I wish to urge 

 a few objections. 



(a.) AVhat started the habit ? Natural selection can 

 hardly " create." Is this one of Darwin's strictly accidental 

 variations ? Was it a mere happy freak on the part of the 

 ancient progenitor of our European cuckoo ? To be successful 

 the trick must be played with some care. It is hardly on a 

 par with the casual use made by a partridge of a pheasant's 

 nest, or by a gull of an eider duck's. While allowing that 

 in its beginnings there may have been many misses before 

 the conditions of success were learned, one would like to 

 know the prompting impulses. 



(5.) Are these to be found in the advantages? Do not 

 cliese appear somewhat remote — the accelerated migration, 

 the robuster young ? Then as to the first, it does not now 

 seem at all evident why the bird should be in a hurry ; 



