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Ritual behaviour, intended as a specific, repetitive and rigid form of action flow, appears both in social and non-social environmental contexts, representing an ubiquitous phenomenon in animal life including human individuals and cultures. The purpose of this contribution is to investigate an evolutionary continuum in proximate and ultimate causes of ritual behavior. A phylogenetic homology in proximal mechanisms can be found, based on the repetition of genetically programmed and/or epigenetically acquired action patterns of behavior. As far as its adaptive significance, ethological comparative studies show that the tendency to ritualization is driven by the unpredictability of social or ecological environmental stimuli. In this perspective, rituals may have a "homeostatic" function over unpredictable environments, as further highlighted by psychopathological compulsions. In humans, a circular loop may have occurred among ritual practices and symbolic activity to deal with a novel culturally-mediated world. However, we suggest that the compulsion to action patterns repetition, typical of all rituals, has a genetically inborn motor foundation, thus precognitive and pre-symbolic. Rooted in such phylogenetically conserved motor structure (proximate causes), the evolution of cognitive and symbolic capacities have generated the complexity of human rituals, though maintaining the original adaptive function (ultimate causes) to cope with unpredictable environments., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The effects of chronic intra-peritoneal administration of 10 mg/kg (t.i.w., for 5 weeks) of sildenafil on competitive aggression, sexual behaviour and body weight gain was tested in CD1 subordinate male mice in two experimental contexts: 1) "low levels of aggression", i.e. housing in dyads of siblings 2) "high levels of aggression", i.e. exposure to a model of chronic psychosocial stress with an unfamiliar mice. Subordinate mice in both experimental contexts were injected with sildenafil or saline. After 2 weeks of sildenafil administration, a subgroup of subordinates exposed to "high levels of aggression" began to counterattack their dominant counterparts at higher rates than saline-injected subordinates. This effect was essentially similar but faster in subordinates subjected to "low levels of aggression". As far as sexual behaviour is concerned, in both experimental contexts, sildenafil-injected subordinated mice showed significant lower latencies to mount a proceptive female when compared to saline-injected subjects. Furthermore, in the "high levels of aggression" context, Sildenafil reduced stress-induced body weight gain. Sildenafil showed no effects in individually housed males serving as controls. In conclusion, chronic Sildenafil treatment counteracts the inhibitory effects of social subordination on male competitive aggression, sexual behaviour and body weight gain. Overall our data suggests that sildenafil could be acting in the central nervous system to modulate sexual and agonistic motivation., (Copyright © 2010 Elsevier B.V. All rights reserved.)