THEORIES AND CONCLUSIONS 233 
type, but is the egg of a Robin Cuckoo insufficiently 
dominant to secure an ideal depository, or perhaps 
of a dominant Robin Cuckoo diverted by some 
accident from her normal prey. Whatever the 
cause, the result is clearly that an egg conspicuously 
different from the foster bird’s eggs runs a greater 
risk of causing desertion, and so failing to achieve 
the object for which it was laid, than does an egg 
which resembles them. 
If we postulate the truth of the theory, which 
for my part I confidently hold, that a female Cuckoo 
bred in (say) a Robin’s nest is not only herself the 
descendant on the maternal side of generations of 
Robin Cuckoos, but has an inherited instinct to 
seek out Robins’ nests and make Robins, so to 
speak, her preferential victims, it ceases to surprise 
us that the respective eggs of Robin and Robin 
Cuckoo should exhibit a marked similarity. What 
has been the law of the survival of the fittest, from 
the Cuckoo’s point of view, throughout the ages of 
evolution, is thus dovetailed with the line of least 
resistance on the part of the Robin. 
But I frankly admit that this theory must fail 
to the ground, if it is a fact that the influence of 
the male parent-bird is at least as potent, if not 
more so, as that of the female parent on the off- 
