Origin of Species Variorum

Comparison with 1869

two of the Australian cuckoos, when they lay their eggs in an open or not domed nest, manifest a decided preference for nests containing eggs similar to their own. The European species certainly manifests some tendency towards a similar instinct, but not rarely departs from it, as is shown by her laying her dull and pale-coloured eggs in the nest of the Hedge-warbler with its bright greenish-blue eggs: had she invariably displayed the above instinct, it would assuredly have been added to those which it is assumed must all have been acquired together. The eggs of the Australian Bronze cuckoo vary, according to Mr. Ramsay, in an extraordinary manner in colour; so that in this respect, as well as in size, natural selection assuredly might have secured and fixed any advantageous variation. ↑

With respect to the last point insisted on—namely, of the young European cuckoo ejecting its fosterbrothers—it must first be remarked that Mr. Gould, who has paid particular attention to this subject, is convinced that the belief is an error; he asserts that the young foster-birds are generally ejected during the first three days, when the young cuckoo is quite power less; he maintains that the young cuckoo exerts, by its hunger-cries, or by some other means, such a fascination over its foster-parents, that it alone receives food, so that the others are starved to death, and are then thrown out, like the egg-shells or the excrement, by the old birds. He admits, however, that the young cuckoo when grown older and stronger may have the power, and perhaps the instinct, of ejecting its foster-brothers, if they happen to escape starvation during the first few days after birth. Mr. Ramsay has arrived at a similar conclusion with respect to the Australian species, which he especially observed: he states that the young cuckoo is at first a little helpless fat creature, but, "as it grows rapidly, it soon fills up the greater part of the nest, and its unfortunate companions, either smothered by its weight, or starved to death through its greediness, are thrown out by their parents." Now, if it were of great importance to the young cuckoo to receive as much food as possible soon after birth, I can see no special difficulty ... in its gradually acquiring during successive generations, the habit (perhaps through mere unintentional restlessness) the strength and the structure best fitted for ejecting its foster-brothers; for those young cuckoos which had such habits and structure would be the best fed and most securely reared. ↑ I can see no more difficulty in this, than in young birds acquiring the instinct and the temporary hard tips to their beaks for breaking through their own shells;—or than in the young snake having in its upper jaw, as Owen has remarked, a transitory sharp tooth for cutting through the tough egg-shell. For if each part is liable to individual variations at any age, and the variations tend to be inherited at a corresponding age,— propositions which cannot, as we shall hereafter see, rightfully be disputed, — then the instincts and structure of the young can be slowly modified as well as those of the adult, and both cases must stand or fall .. with the whole theory of natural

two of the Australian cuckoos, when they lay their eggs in an open ... nest, manifest a decided preference for nests containing eggs similar in colour to their own. The European species apparently manifests some tendency towards a similar instinct, but not rarely departs from it, as is shown by her laying her dull and pale-coloured eggs in the nest of the Hedge-warbler with .. bright greenish-blue eggs. Had our cuckoo invariably displayed the above instinct, it would assuredly have been added to those which it is assumed must all have been acquired together. The eggs of the Australian Bronze cuckoo vary, according to Mr. Ramsay, to an extraordinary degree in colour; so that in this respect, as well as in size, natural selection .. might have secured and fixed any advantageous variation.

In the case of the European cuckoo, the offspring of the foster-parents are commonly ejected from the nest within three days after the cuckoo is hatched; and as the latter at this age is in a most helpless condition, Mr. Gould was formerly inclined to believe that the act of ejection was performed by the foster-parents themselves. But he has now received a trustworthy account of a young cuckoo which was actually seen, whilst still blind and not able even to hold up its own head, in the act of ejecting its foster-brothers. One of these was replaced in the nest by the observer, and was again thrown out. ↑ With respect to the means by which this strange and odious instinct was acquired, if it were of great importance for the young cuckoo, as is probably the case, to receive as much food as possible soon after birth, I can see no special difficulty in its having gradually acquired, during successive generations, the blind desire, the strength, and structure necessary for the work of ejection; for those young cuckoos which had such habits and structure best developed would be the most securely reared. The first step towards the acquisition of the proper instinct might have been mere unintentional restlessness on the part of the young bird, when somewhat advanced in age and strength; the habit having been afterwards improved, and transmitted to an earlier age. I can see no more difficulty in this, than in the unhatched young of other birds acquiring the instinct to break through their own shells;—or or than in young snakes acquiring in their upper jaws, as Owen has remarked, a transitory sharp tooth for cutting through the tough egg-shell. For if each part is liable to individual variations at all ages, and the variations tend to be inherited at a corresponding or earlier age,— propositions which cannot ... be disputed,— then the instincts and structure of the young could be slowly modified as surely as those of the adult; and both cases must stand or fall together with the whole theory of natural