° 1916 J Huxley, Bird-watching and Biological Scietice. 159 



The facts given above and their discussion will serve to make 

 clear some of the general principles and problems of courtship in 

 birds. Our next business is to get an insight into the interpretation 

 of observations on birds. The connected descriptions I have given 

 of the life-histories of various birds have only been made possible, 

 first by the collection of a great many facts, and secondly by the 

 interpretation of those facts; and the second is as important as 

 the first. 



It is indeed almost impossible to collect valuable facts unless 

 one has some idea of how they are to be interpreted, and to those 

 who are interested in this subject, I would say this: — remember 

 the multifarious aspects from which any fact of bird-behavior can 

 and should be looked at. 



Take the case of any elaborate courtship action, such as the 

 'shaking' of the Grebe, or the dance of the Blackcock. There are 

 two main points we want to understand; what is the meaning 

 to-day? and what has been the origin in the past? And to answer 

 these we have first to ask, and answer, the following questions : — 



First, can we see any utility in it? if so, is it of use (a) simply to 

 the species as a species, or is it of use (b) to the indi\'idual, (c) the 

 pair, or (d) the family, and so indirectly to the species? 



Secondly, can we see anything which is not of definite biological 

 utility in the character? if so, what is the reason for the presence 

 of this non-utilitarian factor? Is it (a) purely accidental? (b) 

 determined through the inheritance of characters once useful, but 

 now no longer so? (c) a matter of physiological correlation — 

 that is to say, dependent on the general structure and working of 

 the rest of the body? (d) dependent on the structure and working 

 of the mind — a matter of psychological correlation? 



Let us analyse the above examples in the light of these questions. 

 The mutual head-shaking of the Grebe is apparently of use, like 

 all the other mutual courtship actions, in keeping the pair together 

 during the breeding season. It is then of direct biological use to 

 the pair regarded as a unit of the race, and to the next generation. 

 Besides this, it may be of some slight advantage to the individuals 

 as liberating the energy of the sexual period in a harmless and 

 pleasurable manner; but as far as origin is concerned, the survival 

 value of the character — the handle bv which Mutual Selection 



