Schizophrenia is found in all known populations in all continents and has a similar prevalence and outcome in each. This indicates that genetic rather than environmental factors are the principal cause, but if this is so we must ask the question what adaptive function does schizophrenia serve? Horrobin (1998) proposed that during the course of human evolution specific biochemical alterations led to changes in metabolism which enabled the human brain to expand in size and function more efficiently. He points out that a large brain per se does not automatically lead to creativity or intelligence as our ancestors did possess large brains, but for many millions of years showed no evidence of using them. Around 35-50,000 years ago there was a sudden burst of intellectual and creative achievement leading to religion, war, art, transport, complex culture and an agricultural revolution. If brain size was not the principal factor, then Horrobin argues that connectivity was the key.
Neural connectivity is determined largely by the availability of phospholipids, which make up 60% of the brain, and in particular the connections between neurons are made by phospholipid-rich axons and dendrites. These rely on a supply of the essential fatty acids (arachidonic acid, and docosahexaenoic acid) and the essential amino acids, which are vital for cell-function and neuronal signalling and can only be obtained from a diet rich in animal protein (meat, fish, eggs).
Horrobin points out that the sudden rise in creativity paralleled dietary changes as hominids moved from eating vegetation and fruit, to eating meat and fish. While these changes led to improvements in brain function, they may also have had a side effect ? schizophrenia. This disorder is typically seen in families who were distinguished in many other fields (art, leadership etc), families in which one member is schizophrenic clearly show other behaviours that are referred to as ?schizotypal?:
Excess of suspiciousness.
Trace of paranoia.
Difficulty in making social contact.
Increased interest in religion and mysticism.
Interestingly, schizophrenics have been found to have reduced levels of phospholipids, there is increased activity of the phospholipases which removes the fatty acids from membranes. Membrane activity is thus affected and neuronal conductivity suppressed. This will not be a problem provided that the diet is rich in fatty acids (as it was during that part of our evolution when creativity and intelligence boomed). However, modern diets are severely lacking in the essential fatty acids and are replaced with saturated fatty acids, modern farming and agricultural techniques and contributed to this.
Horrobin proposes that biochemical alterations caused by dietary changes increased brain size, improved neural connectivity and led to creative intelligence, but also produced a series of behaviour patterns such as paranoia, visual artistic skills, mild sociopathy, religious experiences which were kept in check by sufficient dietary levels of the essential fatty acids. As these levels have dropped in modern society, the very behaviours that made us human are expressed in more extreme behaviours of schizophrenia and manic depression. Schizophrenia has certainly increased over the past few hundred years, it has a higher incidence in cultures with a high rate of dietary non-essential fatty acids, and is reduced in patients who increase their intake of essential fatty acids.
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