Benoist Schaal

Testosterone, Physical Aggression, Dominance, and Physical Development in Early Adolescence

The associations among testosterone, physical development, social dominance, and antisocial behaviour during early adolescence were assessed in a sample of boys followed from 6 to 13 years. Saliva testosterone level was positively correlated with height, and uncorrelated with measures of fatness, including the body mass index. Physical aggression and social dominance were not significantly correlated. Regression analyses revealed that testosterone level and body mass additively predicted social dominance, whereas only body mass predicted physical aggression. Thus, early adolescents with high levels of testosterone were more likely to be socially dominant, especially if they had a large body mass. Those who had a large body mass were more likely to be physically aggressive, independently of their testosterone level. The observed pattern of correlations between testosterone, body mass, dominance, and physical aggression offers an interesting example of the complex hormone-physique-behaviour relations at puberty. They support the hypothesis that testosterone level and social dominance are related, and that the association between testosterone level and physical aggression is probably observed in contexts where physical aggression leads to social dominance.

Psychobiological functions of the mammary pheromone in newborn rabbits

Lactating female rabbits (Oryctolagus cuniculus) nurse once daily for 5 min. The pups are thus forced to localize the nipples quickly. The females emit multiple chemosignals to guide them, among which are common odors derived from dietary aromas and one identified pheromone. Thus, the mammary pheromone (MP) released in rabbit milk is highly behaviorally active: it is a potent releaser of suckling-related behaviors in pups. The MP also acts as a strong reinforcer for early odor learning. Both of these functions of the MP are active right after birth and are thus in a position to play a central role in neonatal adaptation. However, the releasing function and the reinforcing functions of the MP follow different time-courses, suggesting that they are controlled by different underlying mechanisms. These data illustrate how a same chemical signal can carry distinct functions in a newborn mammal.