employed similar constructs, such as learned helplessness, although that theory is focused on the perceived inability to escape any sort of negative stimuli rather than on social factors. Behavioral and physiological effects Social defeat is a very potent stressor and can lead to a variety of behavioral effects, like social withdrawal (reduced interactions with conspecifics), lethargy (reduced locomotor activity), reduced exploratory behavior (of both open field and novel objects), anhedonia (reduced reward-related behaviors), decreased socio-sexual behaviors (including decreased attempts to mate and copulate after defeat), various motivational deficits, decreased levels of testosterone (due to a decline in the functionality of the Leydig cells of the testes), increased tendencies to stereotyped behaviours and self-administration of drugs and alcohol (Rygula et alli, 2005; Huhman, 2006). Research also implicates that the referred behavioral effects are moderated by neuroendocrine phenomena involving serotonin, dopamine, epinephrine, norepinephrine, and in the hypothalamic-pituitary-adrenal axis, locus ceruleus and limbic systems (Bjorkqvist, 2001; Rygula et alli, 2005; Selten & Cantor-Graae, 2005; Marinia et alli, 2006; Huhman, 2006). Both animal and human studies suggest that the social environment has a strong influence on the consequences of stresses. This finding seems to be especially true in the case of social stresses, like social defeat (Bjorkqvist, 2001; Rygula et alli, 2005; de Jong et alli, 2005). In animal studies, animals housed collectively showed reduced symptoms after defeat, in comparison with those housed alone; and animals that live in more stable groups (with stable hierarchies, less intra-group aggression) exhibit reduced effects after a defeat, in comparison with those housed in a more unstable group (de Jong et alli, 2005). In separate studies, defeat behaviors can be modulated by acetylcholine (Smith et al., 2015). In human studies, individuals with greater support seem to be protected against excessive neuroendocrine activation, thereby reducing the adverse effects of stresses in general, and especially stresses of social origin. This apparent confusion, in which social defeat generates behavioral and neuroendocrine effects, both of which depending on social contextual variables, raises the question of how to interpret this data. A useful concept is the concept of “causal chain”, in which recurrent evolutionary events, in this case intra-specific competition, generates selective pressures that last for thousands of generations, influencing a whole species. This way physiological phenomena may evolve, in this case the referred neuro-endocrine phenomena, to facilitate adaptive patterns of action by individuals, in this case the referred behavioral effects. According to