Origin of Species Variorum

Comparison with 1866

believe, that the young thus reared would be apt to follow by inheritance the occasional and aberrant habit of their mother, and in their turn would be apt to lay their eggs in other birds' nests, and thus be successful in rearing their young. By a continued process of this nature, I believe that the strange instinct of our cuckoo could be, and has been, generated. I may add that, according to Dr. Gray and to some other observers, the European cuckoo has not utterly lost all maternal love and care for her own offspring. ↑

It has been objected by some authors that I have not noticed other related instincts and points of structure in the cuckoo, which are falsely spoken of as necessarily co-ordinated. But in all cases, speculation on any instinct or character known in only a single species, is useless, for we have no facts to guide us. Until quite recently the instincts of the European and of the non-parasitic American cuckoo alone were known; now, owing to Mr. E. Ramsay's observations, we know something about three Australian species, which lay their eggs in other birds' nests. The chief points referred to are three: firstly, that the cuckoo, with rare exceptions, lays only one egg in a nest, so that the large and voracious young cuckoo receives ample food. Secondly, that the egg is so remarkably small, that it does not exceed in size that of the skylark,—a a bird not more than one-fourth of the size of the cuckoo; that this is a real case of adaptation we may infer from the fact of the non-parasitic American cuckoo laying eggs of full size proportionally with her body. Thirdly and lastly, that the young cuckoo, soon after birth, has the instinct, the strength, and a properly shaped back for ejecting its foster-brothers, which then perish from cold and hunger. This, it has been boldly maintained, is beneficently designed, in order that the young cuckoo may get sufficient food, and that its foster-brothers may perish, before, as it is supposed, they have acquired much feeling!

Turning now to the Australian species; though these birds generally lay only one egg in a nest, it is not rare to find two and even three eggs of the same species of cuckoo in the same nest. In the Bronze cuckoo the eggs vary greatly in size, from eight to ten lines in length. Now if it had been of any advantage to this species to have laid eggs even smaller than those now laid by her, so as to have deceived certain foster-parents, or, as is more probable, to have been hatched within some shorter period (for it is asserted that there is a relation between the size of eggs and the period of incubation), then there is no difficulty in believing that a race or species might have been formed which would have laid smaller and smaller eggs; for these would have been more safely hatched and reared. Mr. Ramsay remarks that

believe, that the young thus reared would be apt to follow by inheritance the occasional and aberrant habit of their mother, and in their turn would be apt to lay their eggs in other birds' nests, and thus be more successful in rearing their young. By a continued process of this nature, I believe that the strange instinct of our cuckoo ... has been generated. ↑ It has, also, recently been ascertained on sufficient evidence, by Adolf Müller, that the cuckoo occasionally lays her eggs on the bare ground, sits on them, and feeds her young. This rare event is probably a case of reversion to the long-lost, aboriginal instinct of nidification.

It has been objected ... that I have not noticed other related instincts and adaptations of structure in the cuckoo, which are .. spoken of as necessarily co-ordinated. But in all cases, speculation on an instinct known to us only in a single species, is useless, for we have hitherto had no facts to guide us. Until .. recently the instincts of the European and of the non-parasitic American cuckoo alone were known; now, owing to Mr. .. Ramsay's observations, we have learnt something about three Australian species, which lay their eggs in other birds' nests. The chief points to be referred to are three: first, that the common cuckoo, with rare exceptions, lays only one egg in a nest, so that the large and voracious young bird receives ample food. Secondly, that the eggs are remarkably small, ... not exceeding those of the skylark,—a a bird about one-fourth as large as the cuckoo. That the small size of the egg is a real case of adaptation we may infer from the fact of the non-parasitic American cuckoo laying full-sized eggs. Thirdly, .. that the young cuckoo, soon after birth, has the instinct, the strength, and a properly shaped back for ejecting its foster-brothers, which then perish from cold and hunger. This .. has been boldly called a beneficent arrangement, in order that the young cuckoo may get sufficient food, and that its foster-brothers may perish before they had acquired much feeling!

Turning now to the Australian species; though these birds generally lay only one egg in a nest, it is not rare to find two and even three eggs in the same ... neSt. In the Bronze cuckoo the eggs vary greatly in size, from eight to ten lines in length. Now if it had been of an advantage to this species to have laid eggs even smaller than those now laid, .. so as to have deceived certain foster-parents, or, as is more probable, to have been hatched within a shorter period (for it is asserted that there is a relation between the size of eggs and the period of their incubation), then there is no difficulty in believing that a race or species might have been formed which would have laid smaller and smaller eggs; for these would have been more safely hatched and reared. Mr. Ramsay remarks that