Bicameralism[Note 1] (the condition of being divided into "two-chambers") is a controversial hypothesis in psychology and neuroscience which argues that the human mind once operated in a state in which cognitive functions were divided between one part of the brain which appears to be "speaking", and a second part which listens and obeys—a bicameral mind, and that the evolutionary breakdown of this division gave rise to consciousness in humans. The term was coined by Julian Jaynes, who presented the idea in his 1976 book The Origin of Consciousness in the Breakdown of the Bicameral Mind, wherein he made the case that a bicameral mentality was the normal and ubiquitous state of the human mind as recently as 3,000 years ago, near the end of the Mediterranean bronze age.
See also The Origin of Consciousness in the Breakdown of the Bicameral Mind
Jaynes uses governmental bicameralism as a metaphor to describe a mental state in which the experiences and memories of the right hemisphere of the brain are transmitted to the left hemisphere via auditory hallucinations. The metaphor is based on the idea of lateralization of brain function although each half of a normal human brain is constantly communicating with the other through the corpus callosum. The metaphor is not meant to imply that the two halves of the bicameral brain were "cut off" from each other but that the bicameral mind was experienced as a different, non-conscious mental schema wherein volition in the face of novel stimuli was mediated through a linguistic control mechanism and experienced as auditory verbal hallucination.
Bicameral mentality would be non-conscious in its inability to reason and articulate about mental contents through meta-reflection, reacting without explicitly realizing and without the meta-reflective ability to give an account of why one did so. The bicameral mind would thus lack metaconsciousness, autobiographical memory, and the capacity for executive "ego functions" such as deliberate mind-wandering and conscious introspection of mental content. When bicamerality as a method of social control was no longer adaptive in complex civilizations, this mental model was replaced by the conscious mode of thought which, Jaynes argued, is grounded in the acquisition of metaphorical language learned by exposure to narrative practice.
According to Jaynes, ancient people in the bicameral state of mind would have experienced the world in a manner that has some similarities to that of a person with schizophrenia. Rather than making conscious evaluations in novel or unexpected situations, the person would hallucinate a voice or "god" giving admonitory advice or commands and obey without question: One would not be at all conscious of one's own thought processes per se. Jaynes's hypothesis is offered as a possible explanation of "command hallucinations" that often direct the behavior of those afflicted by first rank symptoms of schizophrenia, as well as other voice hearers.
Jaynes built a case for this hypothesis that human brains existed in a bicameral state until as recently as 3,000 years ago by citing evidence from many diverse sources including historical literature. He took an interdisciplinary approach, drawing data from many different fields. Jaynes asserted that, until roughly the times written about in Homer's Iliad, humans did not generally have the self-awareness characteristic of consciousness as most people experience it today. Rather, the bicameral individual was guided by mental commands believed to be issued by external "gods"—commands which were recorded in ancient myths, legends and historical accounts. This is exemplified not only in the commands given to characters in ancient epics but also the very muses of Greek mythology which "sang" the poems. According to Jaynes, the ancients literally heard muses as the direct source of their music and poetry.
Jaynes asserts that in the Iliad and sections of the Old Testament no mention is made of any kind of cognitive processes such as introspection, and there is no apparent indication that the writers were self-aware. Jaynes suggests, the older portions of the Old Testament (such as the Book of Amos) have few or none of the features of some later books of the Old Testament (such as Ecclesiastes) as well as later works such as Homer's Odyssey, which show indications of a profoundly different kind of mentality—an early form of consciousness.
In ancient times, Jaynes noted, gods were generally much more numerous and much more anthropomorphic than in modern times, and speculates that this was because each bicameral person had their own "god" who reflected their own desires and experiences.
He also noted that in ancient societies the corpses of the dead were often treated as though still alive (being seated, dressed, and even fed) as a form of ancestor worship, and Jaynes argued that the dead bodies were presumed to be still living and the source of auditory hallucinations. This adaptation to the village communities of 100 individuals or more formed the core of religion. Unlike today's hallucinations, the voices of ancient times were structured by cultural norms to produce a seamlessly functioning society.
Jaynes inferred that these "voices" came from the right brain counterparts of the left brain language centres; specifically, the counterparts to Wernicke's area and Broca's area. These regions are somewhat dormant in the right brains of most modern humans, but Jaynes noted that some studies show that auditory hallucinations correspond to increased activity in these areas of the brain.
Jaynes notes that even at the time of publication there is no consensus as to the cause or origins of schizophrenia. Jaynes argues that schizophrenia is a vestige of humanity's earlier bicameral state. Recent evidence shows that many schizophrenics do not just hear random voices but experience "command hallucinations" instructing their behavior or urging them to commit certain acts.
As support for Jaynes's argument, these command hallucinations are little different from the commands from gods which feature prominently in ancient stories. Indirect evidence supporting Jaynes's theory that hallucinations once played an important role in human mentality can be found in the recent book Muses, Madmen, and Prophets: Rethinking the History, Science, and Meaning of Auditory Hallucination by Daniel Smith.
Jaynes theorized that a shift from bicameralism marked the beginning of introspection and consciousness as we know it today. According to Jaynes, this bicameral mentality began malfunctioning or "breaking down" during the 2nd millennium BCE. He speculates that primitive ancient societies tended to collapse periodically: for example, Egypt's Intermediate Periods, as well as the periodically vanishing cities of the Mayas, as changes in the environment strained the socio-cultural equilibria sustained by this bicameral mindset.
The Bronze age collapse of the 2nd millennium BCE led to mass migrations and created a rash of unexpected situations and stresses which required ancient minds to become more flexible and creative. Self-awareness, or consciousness, was the culturally evolved solution to this problem. This necessity of communicating commonly observed phenomena among individuals who shared no common language or cultural upbringing encouraged those communities to become self-aware to survive in a new environment. Thus consciousness, like bicamerality, emerged as a neurological adaptation to social complexity in a changing world.
Jaynes further argues that divination, prayer, and oracles arose during this breakdown period, in an attempt to summon instructions from the "gods" whose voices could no longer be heard. The consultation of special bicamerally operative individuals, or of divination by casting lots and so forth, was a response to this loss, a transitional era depicted, for example, in the book of 1 Samuel. It was also evidenced in children who could communicate with the gods, but as their neurology was set by language and society they gradually lost that ability. Those who continued prophesying, being bicameral according to Jaynes, could be killed. Leftovers of the bicameral mind today, according to Jaynes, include mental illnesses such as schizophrenia and the hallucinations present in patients with split brain syndrome.
The Origin of Consciousness was financially successful, and has been reprinted several times. It remains in print, with digital and audio editions appearing in 2012 and 2015.
A new edition, with an afterword that addressed some criticisms and restated the main themes, was published in the United States in 1990 and in the United Kingdom (by Penguin Books) in 1993, re-issued in 2000.
Philip K. Dick, Terrence McKenna, and David Bowie all cited the book as an influence.
Jaynes's hypothesis remains controversial. According to Jaynes, language is a necessary but not sufficient condition for consciousness: language existed thousands of years earlier, but consciousness could not have emerged without language. The idea that language is a necessary component of subjective consciousness and more abstract forms of thinking has gained the support of proponents including Andy Clark, Daniel Dennett, William H. Calvin, Merlin Donald, John Limber, Howard Margolis, Peter Carruthers, and José Luis Bermúdez.
Gary Williams defends the Jaynesian definition of consciousness as a social–linguistic construct learned in childhood, structured in terms of lexical metaphors and narrative practice, against Ned Block's criticism that it is "ridiculous" to suppose that consciousness is a cultural construction, while the Dutch philosophy professor Jan Sleutels offers an additional critique of Block.
Moffic  questioned why Jaynes' theory was left out of a discussion on auditory hallucinations by Asaad & Shapiro. The author's published response was: ... Jaynes' hypothesis makes for interesting reading and stimulates much thought in the receptive reader. It does not, however, adequately explain one of the central mysteries of madness: hallucination.
The new evidence for Jaynes' model of auditory hallucinations arising in the right temporal-parietal lobe and being transmitted to the left temporal-parietal lobe that some neuroimaging studies suggest was discussed by various respondents For further discussion, see Marcel Kuijsten (2007).
Brian J. McVeigh, a graduate student of Jaynes, maintains that many of the most frequent criticisms of Jaynes' theory are either incorrect or reflect serious misunderstandings of Jaynes' theory, especially Jaynes' more precise definition of consciousness. Jaynes defines consciousness—in the tradition of Locke and Descartes—as "that which is introspectable". Jaynes draws a sharp distinction between consciousness ("introspectable mind-space") and other mental processes such as cognition, learning, sensation, and perception. McVeigh argues that this distinction is frequently not recognized by those offering critiques of Jaynes' theory.
Richard Dawkins in The God Delusion (2006) wrote of The Origin of Consciousness in the Breakdown of the Bicameral Mind: "It is one of those books that is either complete rubbish or a work of consummate genius; Nothing in between! Probably the former, but I'm hedging my bets."
The philosopher Daniel Dennett suggested that Jaynes may have been wrong about some of his supporting arguments – especially the importance he attached to hallucinations – but that these things are not essential to his main thesis: "If we are going to use this top-down approach, we are going to have to be bold. We are going to have to be speculative, but there is good and bad speculation, and this is not an unparalleled activity in science. ... Those scientists who have no taste for this sort of speculative enterprise will just have to stay in the trenches and do without it, while the rest of us risk embarrassing mistakes and have a lot of fun." — Daniel Dennett
Gregory Cochran, a physicist and adjunct professor of anthropology at the University of Utah, wrote: "Genes affecting personality, reproductive strategies, cognition, are all able to change significantly over few-millennia time scales if the environment favors such change—and this includes the new environments we have made for ourselves, things like new ways of making a living and new social structures. ... There is evidence that such change has occurred. ... On first reading, Breakdown seemed one of the craziest books ever written, but Jaynes may have been on to something."
Author and historian of science Morris Berman writes: "[Jaynes's] description of this new consciousness is one of the best I have come across."
Danish science writer Tor Nørretranders discusses and expands on Jaynes's theory in his 1991 book The User Illusion, dedicating an entire chapter to it.
Iain McGilchrist proposes that Jaynes's hypothesis was the opposite of what happened: "I believe he [Jaynes] got one important aspect of the story back to front. His contention that the phenomena he describes came about because of a breakdown of the 'bicameral mind' – so that the two hemispheres, previously separate, now merged – is the precise inverse of what happened." However, Kuijsten maintains that McGilchrist mischaracterized Jaynes's theory.
As an argument against Jaynes's proposed date of the transition from bicameralism to consciousness, some critics have referred to the Epic of Gilgamesh. Early copies of the epic are many centuries older than even the oldest passages of the Old Testament, and yet it describes introspection and other mental processes that, according to Jaynes, were impossible for the bicameral mind.
Jaynes noted that the most complete version of the Gilgamesh epic dates to post-bicameral times (7th century BCE), dismisses these instances of introspection as the result of rewriting and expansion by later conscious scribes, and points to differences between the more recent version of Gilgamesh and surviving fragments of earlier versions: "The most interesting comparison is in Tablet X.":252 His answer, however, does not deal with the generally accepted dating of the "Standard Version" of the Gilgamesh epic to the later 2nd millennium BCE, nor does it account for the introspection characteristic of the "Standard Version" being thoroughly rooted in the Old Babylonian and Sumerian versions, especially as historians' understanding of the Old Babylonian poem improves.
Jaynes's proposal does not explain how bicameralism could have been lost at the same time across the entire human species. The indigenous Australian culture was completely separated from the rest of the world from 4000 BCE to 1600 CE, yet appears today to be both historically unchanged and self-conscious.
Divination is also considerably older than that date and the early writings he claims show bicamerality: The oldest recorded Chinese Writing was on oracle bones, meaning that divination arose at the same time or even earlier than writing in Chinese society.
The Julian Jaynes Society was founded by Marcel Kuijsten in 1997, shortly after Jaynes's death.
The society has published a number of books on Julian Jaynes's theory, including:
The society also maintains a member area, with articles, lectures, and interviews on Jaynes's theory.
Brian J. McVeigh (one of Jaynes' graduate students) expand on Jaynes' theory: