76 THE FOUR SEGREGATIVE PRINCIPLES. 



kind, one mother-bird might fail of doing her share of the task of 

 incubation or of feeding the young, and still be represented by de- 

 scendants, a result that would, in the next generation, slightly lower 

 the average standard in the instincts that secure faithful service. 

 Man may perhaps be able to devise more than one method of fore- 

 stalling the degeneracy that tends to arise from communal methods 

 of providing for the young; but for the simple-minded Ani there 

 would seem to be no possible way by which it may prevent the slowly 

 increasing decay of parental instincts. The probability is that in the 

 course of a few hundred generations the cooperative method of incu- 

 bation and of providing for the young will break down through the 

 general tendency to shirk the task ; and the more degenerate mem- 

 bers, who have heretofore imposed on their own kindred, will find it 

 equally easy to lay their eggs in the nests of other species and so estab- 

 lish the method that has already been reached by at least two species. 



I am informed by Prof. Lynds Jones of an irregularity in the habit 

 of two species of American cuckoos which may throw some light on 

 the possible steps by which the greater degeneracy of the Old World 

 cuckoo has been reached. The yellow-billed cuckoo and the black- 

 billed cuckoo are clearly marked species, both found nesting in 

 Eastern North America. Usually a nest of either species contains 

 only the eggs or young of that species, but occasionally an interloper 

 of the other species is found. If a delinquent individual of either of 

 these species sometimes lays an egg in the nest of another species, is 

 it not probable that it has failed to build any nest of its own and is 

 leaving all its eggs for the season to the care of other birds, usually 

 laying them in the nests of birds of the same species and thus escaping 

 the inquisitive impertinence of the ornithologist, who finds the eggs 

 all of one color, and passes without suspicion? At any rate, the faith- 

 ful workers of the species seem to have no method of dealing with the 

 delinquents or of preventing the blending of their descendants with 

 the descendants of the faithful. There is, therefore, some reason to 

 fear that these two species have entered on a path that will lead to 

 extinction, unless, like the Old World cuckoo, they succeed in shifting 

 the work of raising their young ones on to other species of more sturdy 

 instincts. 



Whether the change in the Old World cuckoo came by sudden 

 mutation or by gradual accumulation of individual variations, it was 

 certainly a regressive process, undoing instincts that had been inheri- 

 ted for countless generations. 



