Introduction to Stoned Ape Hypothesis

Terence McKenna was one of the first vocal proponents of this theory, which theorizes that as the North African jungles receded toward the end of the most recent ice age, giving way to grasslands, a branch of our tree-dwelling primate ancestors left the trees and took up a life out in the open - following around herds of ungulates, nibbling what they could along the way.

Among the new items in their diet were psilocybin-containing mushrooms growing in the dung of these cattle herds. The changes caused by the introduction of this drug to the primate diet were many -- McKenna theorizes, for instance, that synesthesia (the blurring of boundaries between the senses) caused by psilocybin led to the development of spoken language: the ability to form pictures in another person's mind through the use of vocal sounds. About 12,000 years ago, further climate changes removed the mushroom from the human diet, resulting in a new set of profound changes in our species as we reverted to pre-mushroomed and frankly brutal primate social structures that had been modified and/or repressed by less frequent consumption of psilocybin.

The stoned ape theory is necessarily based on much supposition interpolated between the few fragmentary facts we know about hominid and early human history. In addition, because McKenna (who describes himself as 'an explorer, not a scientist') also propounds some even more controversial suppositions, his more reasonable theories are often disregarded by the very scientists whose informed criticism is crucial for their development. In a review of his book Food of the Gods, Village Voice stated 'if only a fraction of Mckenna thoughts are true, he will someday be regarded as the Copernican for consciousness'
'The 20th century mind is nostalgic for the paradise that once existed on the mushroom-dotted plains of Africa, where the plant-human symbiosis occurred that pulled us out of the animal body and into the tool-using, culture-making, imagination-exploring creature that we are' - Mckenna

The precedent

One big explanatory challenge for evolutionary theory as it applies to modern human origins is the human neocortex. The evolution of the human neocortex has been called 'the most dramatic transformation of a major organ of a higher animal in the entire fossil record'. A review of the evolution of the human neocortex in 2009 by Pasko Rakic stated 'It is, therefore, surprising how little modern research has been done to elucidate how this human difference emerged. It appears that we are sometimes so seduced by similarities between species that we neglect the differences.'[1]

Therefore it is necessary in evolutionary theory to account for the dramatic emergence of the human neocortex in the narrow window of time of about two million years during which apes went from being higher primates, hominids, to being true humans.

Human Plant Symbiosis

Mutualistic symbiosis occurs when two distinct types of organism gain a mutual benefit from each other's company. A example would be a sucker fish that lives off of plankton on a whale's back; via this relationship both partners gain an evolutionary, survival and biological advantage; the whale gets cleaned and seems to enjoy the sensory contact aspect, and the fish gets food and protection from the huge whale. Likewise, as plants have come to depend on humans for the dispersal of seeds and other benefits, Mckenna posits that it was very likely that we in turn benefited from forest vegetation, including the psychedelic mushrooms.

It has been determined that some mushrooms do rely symbiotically on mammals to aid in spore dissemination. Some fungi and mushrooms can survive through our digestive system and germinate after being excreted, sometimes referred to as coprophilic mushrooms.

Mckenna's view is that humans have been involved in a mutualistic symbiosis with psychedelic mushrooms and other related chemical cousins for tens of thousands of years, which have been used to catalyze human imagination, spawning religions, mystical states, artwork, linguistic thinking, spirituality, introspection about the nature of consciousness not otherwise possible, the development of cultures, and many more aspects that distinguish us from other primates.[2]

Apes use of plants as medicine

Gombe Stream National Park was one of the first institutions that noticed apes sometimes persist in eating foods that they do not appear to like the taste of, and are not able to digest very well. Despite previously not enjoying this food, the apes would still selectively go looking for it [3] Eventually a redish oil was found called Rhiarubrine-A. University of British Columbia University researcher Neil Towers found that this oil kills bacteria, but just below the significant 10 in a million level that would make it clinically dangerous.[4]

Thus it seemed that even if the food they learn to eat was unpleasant, if it has a positive effect on it's well being, health or mind in some way, a chimpanzee will tend to continue eating it, thus self medicating through their choice of food selection from their surrounding natural pharmacy.[5][6][7]

Since other animals enjoy psychoactive drugs, as for example cats love catnip, and monkeys enjoy alcohol they scrounge from humans, it is only natural to expect chimps to also; and numerous studies have found that if they enjoy the medicinal effects they continue to ingest it despite unpleasant taste.[7] This is sometimes referred to zoopharmacognosy.[8][9][10] The basic premise of zoopharmacognosy is that animals utilize plant secondary compounds or other non-nutritional substances to medicate themselves. Among primatologists a major focus of concern about plant secondary compounds in the diet has been on how and why primates can cope with their presence.

You are what you think, as well as what you eat

Rather than theorizing our sudden evolution was merely due to an expanded diet as our ancestors moved around, Mckenna argues there is a primary factor often overlooked, and makes the argument for a select few psychedelic foods we found, that centuries of ingesting and experimenting with set us down the road of evolving into the true humans we are today. Back then each encounter with a new food would have been thought of the same, whether it was a fruit, a drug or an insect a lot of care would at first have to be taken.

As our diets increased so did our perception of varieties of new foods and tastes, Gastronomy was born shortly after our taste for novel pharmacology, which must have preceded it, as maintenance of health and thought is a regulation of diet seen in most animals.[2]

Mckenna explains how the mental changes elicited from psychedelics may have played an even bigger role than the nutritional diet in how we evolved socially and culturally here:

The primate tendency to form dominance heirarchies was temporarily interrupted for about 100,000 years by the psilocybin in the paleolithic diet. This behavioral style of male dominance was chemically interrupted by psilocybin in the diet, so it allowed the style of socialorganization called partnership to emerge, and that that occurred during the period when language, altruism, planning, moral values, esthetics, music and so forth -- everything associated with humanness -- emerged during that period. About 12,000 years ago, the mushrooms left the human diet because they were no longer available, due to climatological change and the previous tendency to form dominance hierarchies re-emerged. So, this is what the historic dilemma is: we have all these qualities that were evolved during the suppression of male dominance that are now somewhat at loggerheads with the tendency of society in a situation of re-established male dominance.

The paleolithic situation was orgiastic and thus it was impossible for men to trace lines of male paternity. Consequently there was no concept of 'my children' for men, but rather a concept of 'our children' meaning 'we, the group.' This orgiastic style worked into the effects of higher doses of psilocybin to create a situation of frequent boundary dissolution. That's what sexuality is about , on one level, and it's what psychedelics are about, on another level. With the termination of this orgiastic, mushroom using style of existence, a very neurotic and repressive social style emerged which is now worldwide and typical of western civilization.(Terence McKenna: Mushrooms Sex and Society Interview by Philip H. Farber)

The evolutionary benefits of novel psychedelics

Mckenna comments that although his theory focuses mainly on mushrooms there is far more broader scope for a vast array of other psychoactives[2].
The mutation-inducing influence of diet on early humans and the effect of exotic metabolites on the evolution of their neurochemistry and culture is still unstudied territory. The early hominids' adoption of an omnivorous diet and their discovery of the power of certain plants were decisive factors in moving early humans out of the stream of animal evolution and into the fast-rising tide of language and culture. Our remote ancestors discovered that certain plants, when self-administered, suppress appetite, diminish pain, supply bursts of sudden energy, confer immunity against pathogens, and synergize cognitive activities. These discoveries set us on the long journey to self-reflection. Once we became tool-using omnivores, evolution itself changed from a process of slow modification of our physical form to a rapid definition of cultural forms by the elaboration of rituals, languages, writing, mnemonic skills, and technology.

Mckenna's contention is that is that greatly increased variety in physical food alone is insufficient to cause the expansion and sudden power of the human mind to evolve, and that that means various plant alkaloids would have to be involved, including DMT, Psilocybin and Harmalin. Unfortunately due it's legality only limited further tests have been done, but many subjective reports report the same at threshold dosages. If this is the case, for a species of tree dwelling primates and hunter gatherers this would provide a tremendous advantage in hunting for food and climbing trees. And they would have to come down out of the trees out of their comfort zone to do this, as the only place this miracle hunting food grew was on the floor of the forest, thus starting the human evolutionary process. The relevance of Fisher's studies have been questioned by skeptics, citing small sample size and inconclusive results. The fact that many psychotropic plants in the environment could have potentially conferred an evolutionary advantage to those members of the population that seek it out is not in dispute however (see zoopharmacognosy above).

The next major steps for the full evolution of humankind

The main three advantages McKenna identifies as of critical importance to the survival and evolutionary success of apes are: 1) in threshold dosages, dosages where you are stimulated but not hallucinating, according to McKenna psilocybin mushrooms act as a sexual stimulator and thus result to more offspring), 2) at even higher doses psilocybin mushroom would have given humans the ability for deep introspection unique to humans, and the first truly religious experiences (which, McKenna believes, were the basis for the foundation of all subsequent religions to date), and 3) psilocybin mushrooms potency to promote linguistic thinking in the form of glossolalia; unique spoken words/sounds with an absence of meaning, which McKenna argues allowed primates to start attaching meanings that superseded the extent of their previous vocalizations.

These factors, according to McKenna, were the most important factors that promoted our evolution towards the Homo sapiens species. After this transformation took place, our species began moving out of Africa to populate the rest of the planet.[2] Mckenna points out many consciousness catalyzing effects on human development when we realized that there were opiate plants that made us not feel pain, stimulants that enabled us boundless energy, psychoactives that enabled deep states of introspection and changes to sensory acuity, tranquilizing agents to aid sleep and rest and other consciousness catalyzing efffects. The question becomes not did ancient man use such agents, that would be unavoidable, but how much various cultures used them.[2]

Sensory

Noticeable changes to the audio, visual, and tactile senses may become apparent around an hour after ingestion of psilocybin mushrooms. These shifts in perception visually include enhancement and contrasting of colors, strange light phenomena (such as auras or halos around light sources), increased visual acuity, surfaces that seem to ripple, shimmer, or breathe; complex open and closed eye visuals of form constants or images, objects that warp, morph, or change solid colors; a sense of melting into the environment, and trails behind moving objects. Sounds seem to be heard with increased clarity; music, for example, can often take on a profound sense of cadence and depth. Some users experience synesthesia, wherein they perceive, for example, a visualization of color upon hearing a particular sound.[11]

Similar psychedelics such as marijuana are used to increase visual acuity for conditions like glaucoma as well as for therapeutic use in numerous conditions, including pain, stroke, cancer, obesity, osteoporosis, fertility, neurodegenerative diseases, multiple sclerosis, and inflammatory diseases, among others, and further studies have been done on it's enhancement of visual accuracy and general benefits to the retina at night-time as well as in the day time.[12][13][14] These seem especially true when the subject is moving and not in a stationary position.[15] Adams et al. have found that static visual acuity is unaffected by alcohol or marijuana intoxication. On the other hand, the results of Brown et al.[1975] indicate a significant effect of alcohol and marijuana on dynamic visual acuity. Thus, dynamic visual acuity has been shown to be more affected by frequently present transient human states (i.e. alcohol and marijuana intoxication) than static visual acuity. Therefore, according to the present rationale, dynamic visual acuity would be rated as more critical to safe driving than static visual acuity.
Obviously, before reaching any firm conclusions, effects of other transient states on both of the skills in question would have to be ascertained, all these disparate psychedelics' medicinal values add a certain level of credence that our ancestors often made use of the plants in their convironment on a regular basis, leading to dramatic changes in their neurophysiology and the development and evolution of receptors to accommodate these various exogenous chemicals included in a primate diet.

Increased spirituality

In 2006, the United States government funded a randomized and double-blinded study by Johns Hopkins University, which studied the spiritual effects of psilocybin in particular. That is, they did not use mushrooms specifically (in fact, each individual mushroom piece can vary wildly in psilocybin and psilocin content[16]). The study involved 36 college-educated adults (average age of 46) who had never tried psilocybin nor had a history of drug use, and who had religious or spiritual interests. The participants were closely observed for eight-hour intervals in a laboratory while under the influence of psilocybin mushrooms.[17] One-third of the participants reported that the experience was the single most spiritually significant moment of their lives and more than two-thirds reported it was among the top five most spiritually significant experiences. Two months after the study, 79% of the participants reported increased well-being or satisfaction; friends, relatives, and associates confirmed this. They also reported anxiety and depression symptoms to be decreased or completely gone. Despite highly controlled conditions to minimize adverse effects, 22% of subjects (8 of 36) had notable experiences of fear, some with paranoia. The authors, however, reported that all these instances were "readily managed with reassurance."[17]

Roland Griffiths has conducted pioneering research at John Hopkins university showing that the correct dose of psilocybin mushrooms can cause mystical type experiences that have substantial and sustained personal meaning and spiritual significance.[17] At 2 months, the volunteers rated the psilocybin experience as having substantial personal meaning and spiritual significance and attributed to the experience sustained positive changes in attitudes and behavior consistent with changes rated by community observers. These effects were still apparent even 14 months after taking the ingesting the psilocybin.[18][19] Obviously for evolving apes a plant/fungi that produces such a drastic change that the effects are still felt 14 months after ingestion would have produced huge interest and effected their long term physiology. Other studies by Griffiths have also shown that these mystical experiences occasioned by the hallucinogen psilocybin lead to increases in the personality domain of openness, which would greatly effect the perspective of habit forming apes in prehistory.[20]

As Medicine

There have been calls for medical investigation of the use of synthetic and mushroom-derived psilocybin for the development of improved treatments of various mental conditions, including chronic cluster headaches, following numerous anecdotal reports of benefits.[21]There are also several accounts of psilocybin mushrooms sending both obsessive-compulsive disorders (OCD) and OCD-related clinical depression (both being widespread and debilitating mental health conditions) into complete remission immediately and for up to months at a time, compared to current medications which often have limited efficacy.[22][23] The effect of mushrooms to break OCD habits when applied to primates would be a lot more apparent, as animals operate on habits and instincts with less conscious introspection than humans do; psychedelics could have played a role in snapping us out of our previously rigid and primitive behaviour patters that we were stuck in.
Developing drugs that are more effective and faster acting for the treatment of OCD is of utmost importance and until recently, little hope was in hand. A new potential avenue of treatment may exist. There are several reported cases concerning the beneficial effects of hallucinogenic drugs (psilocybin and LSD), potent stimulators of 5-HT2A and 5-HT2C receptors, in patients with OCD (Brandrup and Vanggaard, 1977, Rapoport, 1987, Moreno and Delgado, 1997) and related disorders such as body dysmorphic disorder (Hanes, 1996).[24]

Emotional evolution

As with other psychedelics such as DMT or LSD, the psilocybin experience or trip is strongly dependent upon set and setting. A negative environment could likely induce a bad trip and frequent undesirable side-effects, whereas a comfortable and familiar environment would allow for a pleasant experience. Many users find it preferable to ingest the mushrooms with friends, people they're familiar with, or people that are also 'tripping', although neither side of this binary is without exception.[23] [24] This would make users more socially aware of who they are emotionally close to, and give an amount of introspection into their emotions, actions, feelings, fears and community they would not have any insight into without the use of the psychedelics.

Archeological evidence

There is some archaeological evidence for their use in ancient times. Several mesolithic rock paintings from Tassili n'Ajjer (a prehistoric North African site identified with the Capsian culture) have been identified by author Giorgio Samorini as possibly depicting the shamanic use of mushrooms, possibly Psilocybe.[25] Hallucinogenic species of Psilocybe have a history of use among the native peoples of Mesoamerica for religious communion, divination, and healing, from pre-Columbian times up to currently.[26] Mushroom stones and motifs have been found in Mayan temple ruins in Guatemala, though there is considerable controversy as to whether these objects indicate the use of hallucinogenic mushrooms or whether they had some other significance with the mushroom shape being simply a coincidence.[27] More concretely, a statuette dating from ca. 200 AD and depicting a mushroom strongly resembling Psilocybe mexicana was found in a west Mexican shaft and chamber tomb in the state of Colima. Hallucinogenic Psilocybe were known to the Aztecs as teonanácatl (literally "divine mushroom" - agglutinative form of teó (god, sacred) and nanácatl (mushroom) in Náhuatl) and were reportedly served at the coronation of the Aztec ruler Moctezuma II in 1502. Aztecs and Mazatecs referred to psilocybin mushrooms as genius mushrooms, divinatory mushrooms, and wondrous mushrooms, when translated into English.[27] Bernardino de Sahagún reported ritualistic use of teonanácatl by the Aztecs, when he traveled to Central America after the expedition of Hernán Cortés.
At present, hallucinogenic mushroom use has been reported among a number of groups spanning from central Mexico to Oaxaca, including groups of Nahua, Mixtecs, Mixe, Mazatecs, Zapotecs, and others.[27][28]

Current research

Although not often framed in the psycho-pharmacological context of psychedelic consuming humans in prehistory, the ever evolving field of epigenetic inheritance of behavioural traits might add some plausibility to the stoned ape theory previously unnoticed by genetic determinism based ideologies. The extent to which behavioural traits are based on changes to gene expression, from states of mind and perception, is still a matter of scientific contention. The most concrete example of this effect to date is the inheritance of PTSD found from witnesses to the 9/11 world trade centre attacks although there exist many others.[29]
In Animals and psychedelics: The natural world and the instinct to alter consciousnes, one of the only books on the topic by an evolutionary biologist, Giorgio Samorini, examines the effects of psychedelic plants on animals rather than humans.[30] Samorini "[o]ffers a completely new understanding of the role psychedelics play in the development of consciousness in all species. [...] Rejecting the Western cultural assumption that using drugs is a negative action or the result of an illness, Samorini opens our eyes to the possibility that beings who consume psychedelics--whether humans or animals--contribute to the evolution of their species by creating entirely new patterns of behavior that eventually will be adopted by other members of that species."

Criticism

Many people have accused the theory of only focusing on psilocybin, when there are numerous other psychedelic candidates that could satisfy the same criterion. For example, Andy Letcher, Author of Shroom: A Cultural History of the Magic Mushroom, comments on his blog:

There’s a danger here that if we don’t question ourselves we’ll end up ossifying into a kind of entheogism, replete with its own mythology, founding fathers, saints, orthodoxies and cherished truths. I’m with the brothers McKenna: it behoves us to question.

So, to restate my position: that these strange, daubed figures might indeed depict psilocybin mushrooms, used within a shamanistic context, remains a possibility but one that is far from proven and which rests on several unsupported assertions.[31]
Other criticisms of the stoned aped hypothesis focus on the relative lack of scientific evidence for many of McKenna's claims. For example many have questioned the interpretation of the effects of even low dose psilocybin mushrooms on visual acuity. It isnt clear that the evidence speaks in favour of vision being improved by the inclusion of such drugs in the human diet nor that any increased acuity is of a robust enough nature to confer any evolutionary advantage on mushroom eaters.
Furthermore, McKenna's other assertions about the evolutionary advantages conferred by the hypothesized addition of psychedelic mushrooms have been claimed to be unsupported by evidence and even contrary to the best current scientific thinking about these matters. For example, there is not a lot of evidence that psychedelic mushrooms increase libido generally, that if they do the result would have been more offspring, nor even if more offspring result that this confers any evolutionary advantage. Indiscriminate mating could just as easily be contrary to the fitness of the human species depending on what sort of reproductive strategies were available and what the environment most favoured.
Additionally, it is not at all clear that a culture or religion involving use of psychedelic drugs is the kind of harmonious happy culture McKenna appears to believe it must have been. Examples such as the Aztec culture which both used psychedelic mushrooms and practiced human sacrifice spring to mind, as does the notably ego-enhancing and non-sexism-free psychedelic Western culture of the late twentieth century.

References

1. ^Rakic. P. Evolution of the neocortex: Perspective from developmental biology. Nat Rev Neuroscience. 2009 October; 10(10): 724–735.
2. ^ a b c d eTerence McKenna (1999) 'Food of the gods: the search for the original tree of knowledge: a radical history of plants, drugs, and human evolution - Medical Book Publication
3. ^Huffman, Michael (2007) Current evidence for self-medication in primates: A multidisciplinary perspective - YEARBOOK OF PHYSICAL ANTHROPOLOGY 40:171–200.
4. ^G. H. Neil Towers (1996) 'Leaf-swallowing by chimpanzees: A behavioral adaptation for the control of strongyle nematode infections' - International Journal of Primatology August 1996, Volume 17, Issue 4, pp 475-503.
   
5. ^Dale H. Clayton Nathan D. Wolfe (1998)The adaptive significance of self-medication Volume 8, Issue 2, February 1993, Pages 60–63.
6. ^Andrew Fowler, Yianna Koutsioni, Volker Sommer (2007) Leaf-swallowing in Nigerian chimpanzees: evidence for assumed self-medication January 2007, Volume 48, Issue 1, pp 73-76.
7. ^ a bHarold Altshuler (1975) 'Intragastric self-administration of psychoactive drugs by the rhesus monkey' Volume 17, Issue 6, 15 September, Life Sciences Pages 883–890
8. ^Huffman, A (2001) 'Self-Medicative Behavior in the African Great Apes: An Evolutionary Perspective into the Origins of Human Traditional Medicine 'BioScience 51(8):651-661. 2001
9. ^Huffman MA et al. (1994) 'The diversity of medicinal plant use by chimpanzees in the wild.' Chimpanzee Cultures. Cambridge, MA: Harvard University Press, pp. 129–148.
10. ^Rodriguez E et al (1993) Zoopharmacog 'The use of medicinal plants by animals. In KR Downum, JT Romeo, and H Stafford' Recent Advances in Phytochemistry, vol. 27: Phytochemical Potential of Tropic Plants. New York: Plenum, pp. 89–105.
11. ^D.M. Turner Psilocybin Mushrooms: The Extraterrestrial Invasion Of Earth? The Essential Psychedelic Guide - By D. M. Turner, First Printing - September 1994, Panther Press ISBN 0-9642636-1-0
12. ^Ben Amar M (2006) Cannabinoids in medicine: A review of their therapeutic potential (2006) Journal of Ethno-Pharmacology 2006 Apr 21;105(1-2):1-25
13. ^ Stephen Yazull (2009) Endocannabinoids in the retina: From marijuana to neuroprotection Progress in Retinal and Eye Research 27 (2008) 501–526
14. ^ Stephen Yazulla (2006) Cannabis improves night vision: a case study of dark adaptometry and scotopic sensitivity in kif smokers of the Rif mountains of northern Morocco Survey of Ophthalmology Volume 46, Issue 1, July–August 2001, Pages 43–5.
15. ^Michael Sivak Human Factors and Highway-Accident Causation: Some Theoretical Considerations Acrid Anal & Prw.. Vol 13. pp 614.
16. ^ Stafford PJ. (1992). Psychedelics Encyclopedia. Berkeley, California: Ronin Publishing. ISBN 0-914171-51-8
    
17. ^ a b c Griffins et al Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance. Psychopharmacology187(3):268-83. August 2006.
18. ^Griffiths, Roland R., et al. Mystical-type experiences occasioned by psilocybin mediate the attribution of personal meaning and spiritual significance 14 months later; Journal of Psychopharmacology 22.6 (2008): 621-632.
19. ^Griffiths, Roland R., et al. Psilocybin occasioned mystical-type experiences: immediate and persisting dose-related effects. Psychopharmacology 218.4 (2011): 649-665.
20. ^MacLean, Katherine A., Matthew W. Johnson, and Roland R. Griffiths. Mystical experiences occasioned by the hallucinogen psilocybin lead to increases in the personality domain of openness. Journal of Psychopharmacology 25.11 (2011): 1453-1461.
21. ^Arran Frood (2007) Cluster Busters NATURE MEDICINE VOLUME 13 | NUMBER 1 | JANUARY 2007, Paper endorsed and made public by MAPS.
22. ^Christopher Wiegand, M.D (2060)Safety, Tolerability, and Efficacy of Psilocybin in 9 Patients With Obsessive-Compulsive Disorder J Clin Psychiatry. 2006 Nov;67(11):1735-40.
23. ^ a bStamets, Paul (1996)Psilocybin Mushrooms of the World. Ten Speed Press. ISBN 0898158397.
24. ^ a bSimon G.Powell The Psilocybin Solution:Prelude To A Paradigm Shift
25. ^Giorgio Samorini (1992) The oldest Representations of Hallucinogenic Mushrooms in the World. Integration, vol. 2/3, pp. 69-78,
26. ^John M. Allegro.The Sacred Mushroom And The Cross. Gnostic Media Research & Publishing; 40 Anv edition (12 Nov 2009)
27. ^ a b cStamets, Paul (1996) [1996]. Psilocybin Mushrooms of the World. Ten Speed Press. p. 11. ISBN 0898158397.
28. ^Johnson, Jean Bassett (1939). The Elements of Mazatec Witchcraft. Gothenburg, Sweden: Ethnological Studies, No. 9.
29. ^ Yehuda, Rachel, and Linda M. Bierer. Transgenerational transmission of cortisol and PTSD risk. Progress in brain research 167 (2007): 121-135.
30. ^Samorini, Giorgio. Animals and psychedelics: The natural world and the instinct to alter consciousness. Park Street Press, 2002.
31. ^ http://andy-letcher.blogspot.co.uk/2011/07/selva-pascuala-mushroom-mural-or-not.html

The_Adaptive_Significance_of_Self-nedication.pdf

TerenceMckenna-FoodOfTheGods.pdf