SEXUAL BEHAVIOUR 89 



Strength, age, sex, and season are probably all important 

 factors in determining the position of an individual in 

 the peck order. The first experimental analysis of the 

 problem was that of Allee and his co-workers- who 

 attempted to change the peck order by means of hormone 

 treatment. Since then it has become obvious that 

 personal aggressiveness and effectiveness in combat are 

 in direct proportion to the amount of male hormone 

 present in the body, and that this is the most important 

 single factor determining an individual's position in the 

 peck order. Experimentally the effects of injections of 

 testosterone propionate are once again extremely 

 dramatic so that low-ranking hens can be made to rise 

 rapidly to the top of the order. The same result has been 

 obtained in experiments with many diverse species, and 

 in all cases the treated animals showed an increase in 

 bodily vigour and in willingness to fight. No similar effect 

 is induced by the female hormones, and it would there- 

 fore appear that dominance within a flock is due mainly 

 to the degree of maleness of the various individuals. 

 This conclusion can be applied to females as well as to 

 males since it will be remembered that the normal 

 ovary secretes male hormone. 



Most of these observations and experiments have been 

 made with domesticated or caged animals. It seems 

 probable that among wild animals, such as the starling, 

 which live a social life during their non-breeding season, 

 it is the increase in aggressiveness and intolerance 

 accompanying the growth of the gonads that causes the 

 breakup of the flocks at the beginning of the breeding 

 season.^*' 120 



As usual it is dangerous to apply these conclusions 

 directly to man himself. While aggressiveness and social 

 dominance among both men and women may bear some 

 relation to the hormone testosterone, it is obvious that 

 other factors, psychological and social, are also involved. 



Investigations involving the injection of a female 

 hormone, such as oestradiol, into female vertebrates 



