Introduction

The views on the role that hormones play in the control of behaviour have changed progressively with time. Hormones were classically seen as causal agents of behaviour, acting directly on the display of a given behaviour. This view was mainly supported by early studies of castration and hormone-replacement therapy, which showed that some behaviours were abolished by castration and restored by exogenous administration of androgens (Nelson, 2001). Later this view shifted towards a more probabilistic approach and hormones started to be seen more as facilitators of behaviour than as deterministic factors (Simon, 2002). According to this new view, hormones may increase the probability of the expression of a given behaviour by acting as modulators of the neural pathways underlying that behavioural pattern. For example, the effects of androgens on the expression of aggressive behaviours in mammals are mediated by modulatory effects on central serotonergic and vasopressin pathways (Simon, 2002). Yet, it is also known that the social environment (i.e. network of interacting individuals) also feeds back to influence hormone levels (Wingfield et al., 1990), suggesting a twoway type of interaction between hormones and behaviour. In this chapter, I will develop the hypothesis that social modulation of androgens is an adaptive mechanism through which individuals adjust their motivation according to the social context that they are facing. Thus, the social interactions within a given social network would stimulate the production of androgens in the individuals and the individual levels of androgens would be a function of the perceived social status and the stability of the social environment in which the animal is living.