CYCLES OF REPRODUCTION I3 



against those extremes of nature to which most other 

 species are subject, and there seems to be some reason 

 to believe that the continuance of such optimum con- 

 ditions throughout the year may tend to prolong breed- 

 ing. Certainly the reverse is true, and it is v^ell known 

 that during siege, as in the harsh conditions of the 

 German concentration camps, loss of fertility has fre- 

 quently occurred. 



However, a clearer picture of the effects ot domestica- 

 tion may be obtained from a study of the animals that 

 man has tamed. The first of these is the dog, which 

 has been with man for a very long time. Its nearest 

 wild relatives have sharply defined breeding seasons, 

 those of the various northern wolves,® like that of the 

 Australian dingo, ^^^ being in late winter and spring. 

 The English fox is more distantly related, but it too has 

 a discrete breeding season at about the end of January, 

 while the arctic fox breeds a little later in February. In 

 contrast, the domestic dog is far less precise in its breed- 

 ing habits, and indeed the male is able to mate at any 

 time. The female normally experiences two breeding 

 periods each year, and there is a tendency for one of 

 these to be in spring and the other in autumn. However, 

 both the number of periods per year and their timing are 

 highly variable. It is also interesting to note that there 

 are reports that dogs in the arctic breed only once in 

 the spring, and that conversely foxes and wolves kept in 

 zoological gardens may develop two seasons per year 

 in the manner of the domestic bitch. ^^^ 



The story of the cat is similar. The wild cat of 

 Scotland breeds only in the spring, » but with the 

 domestic animal the male can mate at all seasons while 

 the female may experience two, three or four sexual 

 periods each year which are unconnected with the 

 seasons. Similarly the domesticated rabbit, kept warm 

 and well fed, can breed all the year round, while the wild 

 rabbit has a sharply defined breeding season which in 

 Wales lasts from January to June. Brambell*^ sums up 



