CHAPTER XVI 1 
THEORIES AND CONCLUSIONS 
The fundamental Cuckoo problem— how and why 
her parasitic habit originated — is, of course, pro- 
bably insoluble, and I have no intention of theorising 
about it. There are, nevertheless, a number of 
interesting side-issues to the main problem, on 
many of which I think our observations throw a 
little light ; and I expatiate on them the more 
readily in the hope of stimulating other enthusiasts 
to plan and carry out campaigns of observation 
which may contribute further evidence. 
I only desire the reader constantly to bear in 
mind the caveat I have already entered, and to 
refrain from deducing a generalisation from the 
statement of a particular case. No student of 
natural history can afford to be blind to the infinite 
possibilities of variation — whether in appearance or 
in habits, whether due to permanent laws of nature 
working through the ages, or to temporary adapta- 
tion to environment and circumstance — that all 
222 
