44 BIRDS OF THE PLAINS 



than in the ordinary cocks, and it is this that attracts 



the hens. 



We must also bear in mind that abnormal variations 

 have a strong tendency to perpetuate themselves. If 

 a white cock mates with an ordinary peahen, the 

 majority of the offspring are pure white. 



If there be such a thing as sexual selection, and 

 if it be, as I believe, the strongest, the most mettle- 

 some individuals, those in which the sexual instincts 

 reach the highest development, that attract the opposite 

 sex, then the question arises : is there any connection 

 between these characteristics and the size and colour 

 of their possessor ? We are not in possession of 

 sufficient data to answer this question in the affirmative. 

 Nevertheless I believe that such a relation does exist. 



The researches of Professor Pearson seem to point to 

 the fact that there exists a definite relation between 

 variation and fertility. For every species there is a 

 mode or typical size and form, and from this there are 

 deviations in all directions, and, speaking generally, the 

 greater the deviation from the mode the less the fertility 

 of the individual. 



If this be a general law we have here a very potent 

 factor tending to make species stable. Those indi- 

 viduals which deviate least from the common type are 

 the most fertile ; they produce the most offspring ; 

 moreover, they are the most numerous, hence they, by 

 sheer force of numbers, keep a species stable. The 

 abnormal individuals are comparatively few in number, 

 and they beget comparatively few of their kind, so have 

 no chance of establishing themselves and crushing out 



