CHAPTER V 



SEXUAL BEHAVIOUR 



I. INTRODUCTION 



FOR a very long time it has been clearly understood 

 that a close connexion exists between the state of 

 the reproductive system and the behaviour in which an 

 animal indulges. It is obvious to any layman that as an 

 animal reaches maturity its activities and interests 

 change, and similar changes are also strikingly obvious 

 during the course of a reproductive cycle which is 

 characterized by alternating periods of gonad growth 

 and regression. As regards the oestrous cycle, changes 

 are evident in the behaviour of a bitch when it comes on 

 to heat, and as regards the seasonal cycle an example can 

 be given in the sudden urge to nest-building that seizes 

 a bird when its gonads are nearing maturity. Conversely 

 it will be remembered that throughout the whole of 

 recorded history the striking effects of castration on 

 both beasts and men have been widely understood, and 

 even as regards the female Aristotle could write 2,000 

 years ago that 'the ovaries of sows are excised with the 

 view of quenching their sexual appetites'.^^* 



Of course, the behaviour shown by an animal is simply 

 the outward sign of an internal activity of the nervous 

 system, and therefore cyclical behaviour changes must be 

 regarded as reflections of cyclical changes in the nervous 

 state. So while towards the end of the last chapter the 

 effects of nervous activity on breeding condition were 

 discussed, it is now necessary to reverse the process and 

 to examine the effects of breeding condition on nervous 

 activity. Although this is a relatively modern study, 

 striking results have already been obtained, and 



