1216 



HORMONAL REGULATION 



and ejaculation in bulls are inhibited l)y 

 strange surroundings, by delays in admitting 

 the bull to the cow in estrus, by pain at the 

 time of service, and by too frequent services 

 under the same conditions (Milovanov and 

 Smirnov-Ugrjumov, 1944). White Leghorn 

 cocks tend to be consistent in the frequency 

 of matings when they are not inhibited by 

 the presence of other males. When, how- 

 ever, 4 cocks raised together without con- 

 tact with hens for about 3 months were 

 placed in a pen containing 7 hens, a sup- 

 pression developed which tended to per- 

 sist after the dominant cock was removed 

 (Guhl, Collias and Allee, 1945). No clear- 

 cut difference was found between brown 

 Leghorn males reared in isolation until 

 the age of 61/9 months and males wliicli 

 had been reared with other birds (Wood- 

 Gush, 1958b). In an experiment with tur- 

 keys, birds raised in groups displayed less 

 apparent sexual behavior than the isolated 

 birds (Schein and Hale, 1959). This result 

 will be recalled when that obtained by 

 Beach (19421) on rats is described (second 

 paragraph below). 



From what was observed during a study 

 of the male dog (Beach, 1947-48), satis- 

 factory sexual relations were placed high 

 on the list of experiences augmenting sexual 

 interest in later tests. Attack or aggression 

 by a female, however, is an experience which 

 can have a depressing effect. Rosenblatt and 

 Aronson (1958a) reported that castration 

 of the male cat was followed by the eventual 

 loss of sexual behavior with copulatory re- 

 sponses dropping out first, followed some 

 time later by the loss of mounting behav- 

 ior. On the other hand, sexual experience 

 before castration retarded the loss of sexual 

 behavior for periods up to 2l/i years. 



Following a study of the rat, Beach 

 (1942i) reported (1) that the proportion of 

 copulators was highest among males raised 

 in isolation, and (2) that during tests in 

 which no copulation occurred, males raised 

 in isolation tended to be more responsive 

 to the female than males raised with fe- 

 males. The high incidence of copulations 

 among the isolated animals was attributed 

 to two factors : greater excitability resulting 

 from the novelty of contact with a second 

 animal, and greater weight. The relative 

 sexual inactivity of males raised in segrega- 



tion was attributed partially to an increase 

 in homosexual tendencies. 



In a later study (Kagan and Beach, 1953) 

 male rats were placed in individual cages 

 from the 36th day of age until the end of 

 the experiment. From day 37 to day 100 

 the animals were given different kinds of 

 experience. Males in group A were exposed 

 once a week to a receptive female, group 

 B males were exposed at weekly intervals 

 to a male, group C males were placed once 

 a week in an empty cage, and group D 

 males received no conditioning. Beginning 

 day 99 the rats were tested with a receptive 

 female. No group differed significantly with 

 respect to the number of males displaying 

 some copulatory behavior, but the complete 

 pattern including ejaculation was displayed 

 more than twice as frequently by the males 

 lacking previous contact with other rats 

 than it was by the animals which had been 

 exposed to either males or females. The 

 data are taken to indicate that patterns of 

 social behavior formed before complete 

 mating is physically possible tend to per- 

 sist and partially to inhibit the normal sex- 

 ual responses. 



The results from a recent study of rats 

 reared in isolation (Zimbardo, 1958) are at 

 variance with those reported by Beach and 

 Kagan. Except for the frequency of mounts, 

 according to Zimbardo, the differences in 

 sexual performance between males reared 

 in isolation and those reared in part-time 

 cohabitation are large and, in general, sta- 

 tistically reliable. The latter mounted faster 

 than those reared in isolation, copulated 

 sooner and with greater frequency, and had 

 a larger percentage of the total group ejacu- 

 lating. Zimbardo concluded that the sexual 

 performance of male rats reared in isolation 

 is inferior to that of rats reared in cohabita- 

 tion and that in this respect the rat is similar 

 to, rather than different from, the guinea 

 pig- 



The development of sexual behavior in 

 chimpanzees was studied by Nissen (1954). 

 Males and females, after having been raised 

 in a nursery for 2 to 3 years, were transferred 

 to large cages where they lived in sex-mixed 

 groups. Before puberty the sexes were sepa- 

 rated and placed in adjacent cages so that 

 they could still have visual and auditory 

 contact with each other. Starting well after 



