50 THE COURTSHIP OF ANIMALS 



are not to be lost sight of. In the first place, horns, at 

 any rate, are confined to the hoofed animals. That the 

 various types of hoofed animals, living and extinct, have 

 had a common ancestry, no one at the present day will 

 probably call in question. The relationship, however, 

 of the various living types, one to another, is by no means 

 always apparent : the missing links are to be sought in 

 the records of the rocks. 



When the whole of the evidence comes to be surveyed, 

 and not till then, it becomes apparent that this wonderful 

 diversity is the result of complex factors. That the con- 

 ditions of existence have controlled the results is beyond 

 question ; but it is equally certain that these conditions 

 have been merely controlling and not causative. In 

 other words, we must regard each of these different groups 

 or types — Deer, Antelopes, Horses, Elephants, Swine, and 

 so on — as witnesses of what we call " Heredity." They 

 are so many " Diathetic types." That is to say, the 

 forms, or individuals, belonging to each type have inherited 

 certain peculiarities in common ; they display a " Diathesis" 

 as the doctors call it : an inherent, inborn tendency, or 

 habit of growth, in a definite direction : a tendency which, 

 ever and anon, develops new qualities, takes new direc- 

 tions. And thus it is that we get Oxen — using this term 

 in its widest sense and not in its special sense — Antelopes, 

 Goats and Sheep, for example. These have, among other 

 things, a " diathesis " in the direction of horn production, 

 and each, too, of a different type. What is meant by 

 this apparently mystifying term " diathesis " will perhaps 

 be made clear by taking the case of the Ox and the Sheep. 

 While very different in appearance, these live on pre- 

 cisely similar food ; yet no one has any difficulty in 

 discriminating between the taste of beef and mutton. In 



