1214 



HORMONAL REGULATION 



would help us in our analysis of the basis 

 for the differences between individuals. 



The possibility that differences in re- 

 activity of the soma are associated with age, 

 inherent rhythms in the tissues, seasonal 

 changes, and the nutritional level is dis- 

 cussed by Young (1941) . More recently, new 

 information bearing on the influence of age 

 (Hooker, 1942; Price and Ortiz, 1944; Price, 

 1947; Thung, Boot and Mlihlbock, 1956), 

 season (Bates and Riddle, 1941; Quin and 

 Van Der Wath, 1943; Bradbury, 1944; Mc- 

 Cormack and Elden, 1945; Phillips, Fraps 

 and Frank, 1946; Lyman and Dempsey, 

 1951; Denniston, 1957; Michael and Scott, 

 1957; Harris, Michael and Scott, 1958; Kaw- 

 akami and Sawyer, 1959a), and inherent 

 rhythms (Emmens, 1939; del Castillo and 

 di Paola, 1942; Jones and Astwood, 1942; 

 Clark, 1947; Gillman and Gilbert, 1948) 

 has been presented, but as we noted in 1941, 

 when animals are homogeneous with respect 

 to these factors, all can be eliminated. 



An effect of abnormal thyroid activity in 

 the male guinea pig can be discounted by 

 the demonstration that the strength of 

 sexual behavior can be so different in in- 

 dividuals in which the level of thyroid ac- 

 tivity is so nearly the same. Some limiting 

 action was demonstrated by Riss (1955) 

 and by Riss and Goy (1957), but not even 

 in the rigorous tests they gave was evidence 

 found that oxygen consumption fixes the 

 strength of sexual behavior. In the female, 

 on the other hand, the level of thyroid ac- 

 tivity seems to be important for the main- 

 tenance of normal responsiveness (Innes, 

 Young and Webster, 1947; Peterson, Web- 

 ster, Rayner and Young, 1947 ; Peterson and 

 Young, 1955; Hoar, Goy and Young, 1957), 

 but as with age, seasonal changes, and the 

 nutritional level, deviations from the mean 

 can easily be detected and controlled. This 

 leaves us with little to fall back on except 

 the genetical factor and experience, possi- 

 bilities that must be considered separately. 



The assumption that genetical factors are 

 influential in determining the character of 

 the soma is based on many observations. 

 An impaired sexual behavior was encoun- 

 tered in inbred rats in which demonstrable 

 defects in folliculogenesis and germ cells 

 did not exist (Evans, 1928; Craig, Casida 



and Chapman, 1954). Evidence that differ- 

 ences in the running activity of rats are in- 

 herited is presented by Rundquist (1933) 

 and Brody (1942). Rasmussen (1952) esti- 

 mated the strength of sex drive of male and 

 female rats tested in a modified Columbia 

 obstruction apparatus and conducted se- 

 lective breeding for five generations. In the 

 first generation of selection the differences 

 in the number of crossings were not great, 

 but in the F5 generation male and female 

 offspring of parents with high sex drive 

 crossed about six times as frequently as the 

 offspring of parents with low sex drive. 

 Symptoms of heat vary in breeds of cattle 

 (Lagerlof, 1951). The Simmenthaler cows 

 in Switzerland, the Telemark cows in Nor- 

 way, and the Swedish Highland breed have 

 as a rule intense and pronounced heat symp- 

 toms. In the Swedish red cattle the heat is 

 often so weak that in winter it is detected 

 with difficulty. Three triplet Shorthorn bulls 

 raised in the same environment were alike 

 in their lack of interest in serving (Olson 

 and Petersen, 1951 ) . The mating behavior 

 of six pairs of twin bulls was followed from 

 IY2 to 7 years. During this time the indi- 

 vidual pairs were extraordinarily alike, but 

 the differences between the pairs were very 

 great (Bane, 19541. Differences in libido in 

 the brown Leghorn cock are under genetical 

 control (Wood-Gush and Osborne, 1956). 

 In a breeding experiment it was revealed 

 that the females had made a significant con- 

 tribution to the genetical variance (Wood- 

 Gush, 1958a). 



The highly inbred guinea pigs (strains 2 

 and 13) in the colony at Kansas exhibit 

 significant differences in their patterns of 

 behavior. Males in strain 2 nibble and nuz- 

 zle more actively, whereas the frequency of 

 mounting, intromission, and ejaculation is 

 greater in strain 13 (Valenstein, Riss and 

 Young, 1954) . Their rates of sexual matura- 

 tion are slower than that of males from the 

 genetically heterogeneous stock. The differ- 

 ences were not overcome by injecting ani- 

 mals castrated soon after birth with large 

 amounts of androgen (Riss, Valenstein, 

 Sinks and Young, 1955). The possibility 

 that quantitative or qualitative nutritional 

 factors in the mother's milk or some feature 

 of the care might account for the differences 



