Neurobiological aspects of shamanism and sacrifice

According to Winkelman, humans skilled in “soul yourneys” are termed as “shamans”: they are religious practitioners found in foraging societies around the world with antiquity at least as far back as the Middle/Upper Paleolithic transition. Shamans are able to enter into an “ecstatic” state of consciousness that is produced by drumming, chanting, dancing and a variety of other procedures including plant drugs. Altered states of consciousness must be understood in relation to biological capacities, as those related to endogenous neurotransmitters which also have external analogues, such as opioids/opiates and serotonin–like analogues. Recent findings in neurobiological studies support the role of human transmitters systems in religious activities. Proceding from gathering to agricultural societies, it has been noted the absence of sacrificial rites in hunting and gathering societies, and their presence in agricultural societies. This is in accordance with Burkert’ conception of animal sacrifice as ritualistic rendering of the hunt. Yet, agricultural societies might face problems due to the amino acid composition of vegetable proteins. Neuronal synthesis of serotonin depends on the plasma “trp/Large Neutral Amino Acids” ratio, because of competition made by LNAAs against tryptophan for neuron access, since they use the same carrier to cross the blood-brain barrier. “trp/LNAAs” ratio value, in turn, tends to be correlated with amino acid composition of the diet: So a low “trp/LNAAs” ratio diet lowers brain serotonin synthesis. Precursor dependency of catecholamines (dopamine and noradrenaline) in the brain is coupled to the firing rate of the tyrosine hydroxylase containing neurons. Foods rich in their precursor (tyrosine, that in liver can be also obtained from phenylalanine) can provoke an excessive catecholaminergic tone in stressing situations: this, in turn, lowers serotonergic activity, particularly if serotonergic tone is barely sufficient. Vegetable proteins often are rich in phe or tyr and poor in trp, so vegetable based diets, in stressing situations, may cause the appearing of behaviors typical of serotonin deficiency. Serotonin deficiency involves several behavioural consequences such as tendency towards aggressive behaviour, increase of intraspecific competition, increase of magic thought (i. e. obsessive-compulsive disorder) or religious fanaticism, temporal lobe epilepsy, and attraction for fire. Among cereals utilised for human feeding, maize has a very low “trp/LNAAs” value. Maize was firstly and largely utilised by Native American peoples. Among them, above-mentioned behavioural consequences appear, as a rule, positively correlated with maize alimentary dependence. This is particularly interesting in the study of the Aztec human sacrifice/cannibalism complex: historical data reveal that cannibalism occurred in period of the year when maize dependence was greater, supporting the hypothesis of Ernandes and co-workers that serotonin deficiency among the Aztecs might have accentuated their religious and aggressive behavior patterns on the one hand, and on the other it might have led them, unconsciously, towards anthropophagy in order to attenuate it (rising trp/LNAAs value by means of human proteins) when it became too strong. In “Tristes Tropiques” Levi-Strauss described the Aztecs as suffering from “a maniacal obsession with blood and torture”. We may expound Levi-Strauss’ affirmation: the Aztecs were unconscious as to the basis of their behavior, and must be therefore considered the guiltless victims of an awful natural experiment.