In his fantastic anthropological books “Cows, Pigs, Wars, and Witches”, and “Cannibals and Kings”, Marvin Harris provides descriptions of the Yanomamo people.
The Yanomamo are a people who live in the forests along the border between Brazil and Venezuela near the headwaters of the Orinoco and the Rio Negro rivers. They are continually at war with one another. Male bravado and supremacy rule the Yanomamo culture. Polygyny, frequent wife beating, and gang rape of captured female enemies are a normal way of life. Women serve their men’s every needs. Female infanticide is common, with the sex ratio of male to female children being distorted by as much as 260:100 in some particularly war-like tribes.
It seems the Yanomamo are always fighting about something. The men regularly get into fights over their women, in fact they regard fights over women as their primary cause of wars. One third of Yanomamo male deaths are caused by wounds received in battle. Fighting is a normal way to resolve disputes, and villages regularly erupt into punch-ups over trifling matters that are usually resolved by thwacking each other violently with long wooden poles until someone falls down bloodied, injured, or even dead.
Things have not always been this way. The Yanomamo used to be distant forest tribes that survived by hunting in the peripheries, whilst the Orinoco and Rio Negro rivers were occupied by civilised river Indians like the Arawak and Carib groups, whose sophisticated dwellings stretched for miles and miles along the edges of the rivers. The river Indians lived largely by fishing. But white traders bringing infections, invaders and a reduced food supply killed this civilisation off, leaving the land empty for the Yanomamo to occupy.
Unlike the river Indians, the Yanomamo never learned to fish. Their population only took off about a hundred and fifty years ago when they began to obtain steel axes and machetes from contact with other Indians and white traders. Most Amazonian Indians traditionally relied on manioc (cassava) for their starchy carbohydrate supply, but the Yanomamo learned how to cultivate bananas and plantains, which entered the new world from Asia and Africa in the post-Columbian period. Banana and plantain cultivation has taken over from manioc, perhaps because they produce a more abundant crop, or require less post-harvest processing (manioc must be carefully cooked to ensure that the cyanogenic glycosides in it are neutralised – they turn into cyanide in the presence of linamarase, a naturally occuring enzyme in the plant).
The Yanomamo men regularly gather and imbibe hallucinogenic and other psychoactive drugs from the plants in the forest. Psychoactive drugs produce behavioural problems, including aggression, anger, and irritability as a matter of course, and the Yanomamo are very good at taking psychoactive drugs.
The Yanomamo diet is made up of at least 90% bananas and plantain. Hunting in the forests is very scarce. Harris reports that the average animal protein intake per capita per day for tropical-forest village groups averages 35 grams, and the Yanomamo appear to get even less than this due to population pressure. Is 35 grams of protein per day sufficient? I am an individual of small size and weight, and my RDA for protein is around 50 grams. Whilst 35 grams is enough to prevent outright clinical deficiency, is it enough for optimal development? Protein deficiency, it has been observed, produces aggression and even cannibalism in otherwise good-tempered, gentle animals. Even mice become aggressive and kill and eat each other when fed a diet of nothing but fruit.
Bananas and plantains are extremely low in protein and fat, and extremely high in carbohydrate. An average 7″ banana contains around one gram of protein, and bananas are low in every single essential amino acid with the exceptions of glutamic acid, aspartic acid and histidine, which is present in vast quantities. Bananas also contain the biogenic amines, histamine, tyramine, serotonin, and dopamine – neurotransmitters that can produce a variety of mental effects. Nutritionally a diet of bananas is a recipe for disaster. Glutamic acid and aspartic acid are used as excitatory neurotransmitters in the brain. The high quantities of histidine break down into the pro-inflammatory compound histamine as the fruit ripens. The carbohydrates present are digested quickly, impact blood sugar, and are not kept in check by protein, fat, or fibre. The diet is high in phytosterols, lacks vitamins A, most B complex (but is grotesquely high in B6 including the b6 blockers pydridoxine glycosides), D, E, calcium, iron, selenium, zinc, sodium, and essential fatty acids.
In short – the Yanomamo, who are considered the most aggressive, violent tribe in the world, are also on the diet most likely to produce aggression and violence. It would be interesting to see how different the Yanomano diet is from the diet of the worst deprived, most criminally inclined groups in Western society.