Origin of Species Variorum

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 had been of great importance to the young cuckoo to have received as much food as possible during the first few days after birth, I can see no especial difficulty, if it possessed sufficient strength, in its gradually acquiring, during successive generations, the habit (first, perhaps, through mere unintentional restlessness) and the structure best fitted for ejecting its foster-brothers; for those young cuckoos which had such habits and structure would have been 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 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 variation 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 together with the whole theory of natural selection.