RELATING TO SECONDARY SEXUAL CHARACTERS. 69 



Most of the wild species of the genus (of which about 12 are recognized) 

 have horns in both sexes, but larger in the male. There are 3 wild 

 species in which the horns are lacking in the female, according to 

 Flower and Lydekker. If these have been crossed into the domesti- 

 cated breeds the condition shown by the Merino may go back to the 

 wild state. The third condition found in domesticated races, viz, 

 hornlessness, may have appeared under domestication. Such a change 

 might have arisen in either of the two other types and would be com- 

 parable to well-known losses of characters shown by domesticated 

 animals and plants. These losses of characters are usually ascribed 

 to actual losses of genes; any lost gene in the complex of factors neces- 

 sary for the production of horns might cause such a change. But there 

 is no advantage, in fact, in ascribing the loss in the character to a loss 

 in one of the factors producing that character, for any change of any 

 kind in the factor complex might bring about the same result and the 

 evidence from multiple allelomorphs should put us on our guard 

 against the all too easy assumption that a loss in a character involves 

 necessarily loss of a factor in the real sense in which loss is used in 

 ordinary speech. 



The operative and genetic evidence for sheep shows that if the horns 

 in the male were developed through natural or sexual selection we 

 should expect them to develop also in the female. The greater develop- 

 ment in the male seems to be due to secretions from the testes which 

 probably are due to special factors that call them forth, but whether 

 such factors were also acquired to reinforce the effects being produced 

 through selection or were already present (reinforcement for horns 

 being only a by-product of their activity) can not of course be known. 

 We can suppose that special factors that suppress the development of 

 horns in the female may have arisen in the wild or in the domesticated 

 races and have been perpetuated because of some imagined benefit 

 conferred; or that in certain races factors were already present that 

 kept down the development of horns in the female. In any case such 

 factors do not cause their effects through secretions from the ovary, 

 because after ovariotomy horns do not develop; nor are they sex- 

 linked factors. Any speculation as to how natural or sexual selection 

 has brought about the evolution of the horns in sheep must reckon 

 with the conditions imposed on such speculation by the preceding 

 information. So far as I can see, it leaves the situation in this respect 

 neither better nor worse off than before. 



In deer the effects of castration are well known, but there is no 

 genetic evidence to show the kind of factors involved, since no crosses 

 have been made between species with differences in their horns. If the 

 young male deer is castrated before the antlers have appeared, no horns 

 develop. If castrated at the time when the antlers have begun to 

 develop, incomplete or imperfect development follows. The antlers 



