1358 



HORMONAL REGULATION OF BEHAVIOR 



suckling behavior. Beagle puppies, on the 

 other hand, can be replaced with the moth- 

 ers as late as 2 to 4 weeks of age, and de- 

 velop normal suckling. Note that the guinea 

 pig is normally much more precocious in 

 its development than the puppy. Neverthe- 

 less, Levy (1934) found that dogs removed 

 from their mothers at birth and returned 

 to them at about 13 days of age had con- 

 siderable difficulty in establishing suckling. 



The licking of newborn young by the 

 mother is, in many species of mammals, 

 an essential condition for the establish- 

 ment of urination and defecation. Reyniers 

 (1953) found that baby rats isolated at 

 birth die within a few days because they do 

 not urinate, but that the survival of the 

 animals can be assured by stroking the 

 genitals, which reflexly elicits urination; 

 after a few such experiences, urination oc- 

 curs normally without stimulation by the 

 keeper. Similarly, newborn polecats (Eibl- 

 Eibesfeldt, 1955b) and wood rats (Richard- 

 son, 1943) are stimulated to urinate and 

 defecate for the first time by the mother's 

 licking. 



In herd-living animals, the experience 

 of the young animal with its mother during 

 very early life apparently plays a vitally 

 important role in enabling it to become in- 

 tegrated with the herd. Scott (1945) took 

 two lambs from their mothers at birth and 

 bottle-fed them for 8 or 9 days, then re- 

 turned them to the flock. These animals 

 showed little tendency to play with other 

 lambs, and little tendency to stay with 

 the flock while grazing. Similar observations 

 have been made on a foal by Grzimek 

 (1945). Murie (1944) observed that a Dall 

 sheep reared by human beings from a few 

 hours of age later showed no interest in join- 

 ing nearby sheep. Altmann (1952, 1958) ob- 

 served that the nursing interactions between 

 baby elks and moose and their mothers form 

 strong conditioned attachments between 

 mother and calf which persists even after 

 weaning. In this connection, Denniston 

 (1956) found that moose calves which lose 

 their mothers at the age of 7 or 8 months 

 have a lower survival rate than do calves 

 which continue to live with their mothers, 

 even though weaning occurs at about 2 

 months of age. He suggests that protection 



by the mother is an important factor in en- 

 suring the calf's access to foraging places. 



It is well known that the early experi- 

 ences of animals, including experiences with 

 the parents, have substantial effects on their 

 behavior in later life. Beach and Jaynes 

 (1954) have reviewed most of the literature 

 on this subject, and we need make only a 

 few comments here. Mice reared in isola- 

 tion are, when adults, more aggressive to- 

 ward other mice than are those reared by 

 their mothers (Kahn, 1954). It has now 

 been demonstrated many times that han- 

 dling of rats during infancy causes them to 

 develop into adults showing less signs of 

 ''emotionality," and less organic damage 

 under severe stress, than animals reared 

 without such handhng (Weininger, 1956; 

 see also Levine, 1959, I960). Seitz (1954) 

 found that rats reared in small litters and 

 those reared in large litters differed in many 

 significant respects in adulthood. Animals 

 from small litters tended to eat more and 

 to go after food more quickly when hungry 

 than those raised in large litters. The ani- 

 mals raised in large litters hoarded more 

 food in adulthood than those from small 

 litters. Those reared in small litters re- 

 acted to new experiences with less "anxiety" 

 and more exploratory behavior in adult- 

 hood than those from larger litters. A 

 number of other differences were observed, 

 undoubtedly stemming from the differences 

 in relationships between mother and young, 

 and among the young, which are character- 

 istic of the different litter sizes. In a later 

 paper, Seitz (1959) described the effect 

 on the behavior of cats, when adults, of 

 separating them from their mothers at vari- 

 ous ages. Kittens separated from their 

 mothers at 2 weeks of age developed into 

 adults which were more active, more dis- 

 turbed by novel situations, more aggressive, 

 and slower to learn simple routines, than 

 were kittens which remained with their 

 mothers for 6 or 12 weeks. 



Harlow and his students (Harlow and 

 Zimmermann, 1958, 1959; Harlow, 1959) 

 have succeeded in rearing young rhesus 

 monkeys from birth with artificial mothers 

 from which the young could suckle. How- 

 ever, in later (unpublished) observations at 

 the University of Wisconsin, Dr. Harlow 



