120 INTRODUCTION TO EVOLUTION 



pines appeared in the Old World and in South America in Oligocene times 

 but that none lived in North America until the Pliocene (p. 137). If the 

 porcupines had a common origin how did some of them reach South 

 America and others Africa without passing through North America? While 

 it is possible, as suggested by Darlington (1957), that both they and 

 monkeys may have passed through North America without leaving fossil 

 evidence as yet discovered, the question remains a troublesome one. Land 

 bridges from Africa to South America, rafting across the Atlantic Ocean, 

 and island-hopping via Antarctica have all been invoked in attempting to 

 explain this peculiar distribution. 



But perhaps the African and American porcupines are not closely re- 

 lated at all. Perhaps they both evolved independently from rodents known 

 to be widely distributed before the first porcupines appeared (Wood, 

 1950). If so, we may expect that they would be quite unlike serologically. 

 Moody and Doniger (1956) investigated the question, using (1) antisera 

 formed against North American porcupine serum, and (2) antisera 

 formed against African porcupine serum. All tests agreed in indicating 

 that the porcupines are but distantly related to each other, as distantly as 

 either is to guinea pig and agouti, in fact. Apparently, then. New World 

 and Old World porcupines developed their quills independently by parallel 

 evolution. Quills are modified hairs; various other relatively unrelated 

 mammals have developed quills and spines from hair (e.g., the European 

 hedgehog, and the spiny anteater of Australia, Fig. 12.2, p. 262). 



Musk Ox 



The musk ox, shaggy denizen of Arctic regions, is obviously a member 

 of the family of artiodactyls to which cattle, bison, buffaloes, sheep, and 

 goats belong: Family Bovidae. But is it more closely related to cattle and 

 bison or to sheep and goats? On the one hand, it has sometimes been re- 

 garded as an arctic bison, and hence closely related to cattle. On the other 

 hand, fossil evidence seems to indicate that it is more closely related to 

 goats than to cattle and their allies. Serological tests (Moody, 1958) indi- 

 cate that its relationship is to sheep and goats rather than to cattle. Fig. 6.5 

 indicates this and also demonstrates the value of reciprocal tests in serologi- 

 cal studies. An antimusk-ox serum gave a large reaction with sheep and 

 goat sera, little with beef and bison sera. An antigoat serum gave large re- 

 action with musk-ox serum, thus confirming the test with antimusk-ox 

 serum. Finally, an antibeef serum gave small reaction with musk-ox serum, 

 thereby confirming the small reaction given by the antimusk-ox serum 



