Pain as an evolutionary necessity.

The proposed title "Pain as an evolutionary necessity" could lead to a broad debate with implications covering many chapters of the medicine and particularly of clinical neurology. In the present perspective, the discussion will focus on migraine and cluster headache chosen as elective examples of biological and not only clinical conditions, that unveil the bond between pain and necessity. Migraine, cluster headache, and perhaps other primary headaches begin to be depicted in terms of recurrent activation of innate bio-behavioral specific patterns, with a crucial and highly conserved evolutionarily adaptive significance. The pan-mammalian sickness behavior and the fight or flight response, selectively activated by different kinds of pain, are here proposed as paradigmatic of migraine and cluster headache attacks associated behaviors, allowing to reformulate these forms as the inappropriate recurrent presentation of coordinated allostatic processes, modeled along million of years of natural evolution. In this light, all the multifaceted characteristics of migraine and cluster headache attacks can be reinterpreted as complex and integrated allostatic defensive reactions to an inescapable or to an escapable pain, respectively aimed to the restoration of biologic homeostasis through a temporary disengagement from active interaction with environment (migraine associated sickness behavior) or, on the contrary, to promote the coordinated biological changes preparatory to emergency and defensive behaviors (cluster headache-related fight or flight response).