God becomes the Universe

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/God_becomes_the_Universe

The belief that God became the Universe is a theological doctrine that has been developed several times historically, and holds that the creator of the universe actually became the universe. Historically, for versions of this theory where God has ceased to exist or to act as a separate and conscious entity, some have used the term pandeism, which combines aspects of pantheism and deism, to refer to such a theology. A similar concept is panentheism, which has the creator become the universe only in part, but remain in some other part transcendent to it, as well. Hindu texts like the Mandukya Upanishad speak of the undivided one which became the universe.

Development

In mythology

Many ancient mythologies suggested that the world was created from the physical substance of a dead deity or a being of similar power. In Babylonian mythology, the young god Marduk slew Tiamat and created the known world from her body. Similarly, Norse mythology posited that Odin and his brothers, Vili and Vé defeated a frost giant, Ymir and then created the world from his skull. Chinese mythology of the Three Kingdoms era recounts the creation of elements of the physical world (mountains, rivers, the sun and moon, etc.) from the body of a creator called Pángǔ (盤古). Such stories did not go so far as to identify the designer of the world as being one as having used his or her own body to provide the material.

But, one such example exists in Polynesian myth, for in the islands of the Pacific, the idea of Supreme Deity manifests in divinities that Māori people call Rangi and Papa, Native Hawaiians Kāne, the Tongans and Samoans Tagaloa, and the peoples of the Society Islands call Ta'aroa. A native poetic definition of the Creator relates: "He was; Taaroa was his name; he abode in the void. No earth, no sky, no men. Taaroa calls, but nought answers; and alone existing, he became the universe. The props are Taaroa; the rocks are Taaroa; the sands are Taaroa; it is thus he himself is named."

Ancient philosophy

Religious studies professor, Francis Edward Peters traced this idea to the philosophy of the Milesians, who had also pioneered knowledge of pantheism, in his 1967 Greek Philosophical Terms: A Historical Lexicon, noting that "[w]hat appeared... at the center of the Pythagorean tradition in philosophy, is another view of psyche that seems to owe little or nothing to the pan-vitalism or pan-deism that is the legacy of the Milesians.

Milesian philosopher Anaximander in particular favored the use of rational principles to contend that everything in the world was formed of variations of a single substance (apeiron), which had been temporarily liberated from the primal state of the world. Friedrich Nietzsche, in his Philosophy in the Tragic Age of the Greeks, stated that Anaximander viewed "...all coming-to-be as though it were an illegitimate emancipation from eternal being, a wrong for which destruction is the only penance." Anaximander was among the material monists, along with Thales, who believed that everything was composed of water, Anaximenes, who believed it was air, and Heraclitus, who believed it to be fire.

Gottfried Große in his 1787 interpretation of Pliny the Elder’s Natural History, describes Pliny, a first-century figure, as a pandeist as well.

In the 9th century, Johannes Scotus Eriugena proposed in his great work, De divisione naturae (also called Periphyseon, probably completed around 867 AD), that the nature of the universe is divisible into four distinct classes:

Johannes Scotus Eriugena was among the first to propose that God became the universe, and did so to learn something about itself.

1. that which creates and is not created;
2. that which is created and creates;
3. that which is created and does not create;
4. that which neither is created nor creates.

The first is God as the ground or origin of all things, the last is God as the final end or goal of all things, that into which the world of created things ultimately returns. One particularly controversial point made by Eriugena was that God was "nothing", in that God could not fall into any earthly classification. Eriugena followed the argument of Pseudo-Dionysius and from neo-Platonists such as Gaius Marius Victorinus that because God was above being, God was not a being: "So supremely perfect is the essence of the Divinity that God is incomprehensible not only to us but also to Himself. For if He knew Himself in any adequate sense He should place Himself in some category of thought, which would be to limit Himself."

Eriugena depicts God as an evolving being, developing through the four stages that he outlines. The second and third classes together compose the created universe, which is the manifestation of God, God in process, Theophania; the second being the world of Platonic ideas or forms. The third is the physical manifestation of God, having evolved through the realm of ideas and made those ideas seem to be matter, and may be pantheistic or pandeistic, depending on the interference attributed to God in the universe:

[God] enters... the realm of space and time, where the ideas become subject to multiplicity, change, imperfection, and decay. In this last stage they are no longer pure ideas but only the appearances of reality, that is phenomena. ... In the realm of space and time the ideas take on the burden of matter, which is the source of suffering, sickness, and sin. The material world, therefore, of our experience is composed of ideas clothed in matter — here Eriugena attempts a reconciliation of Platonism with Aristotelean notions. Man, too, is composed of idea and matter, soul and body. He is the culmination of the process of things from God, and with him, as we shall see, begins the process of return of all things to God.

The divine system is thus distinguished by beginning, middle and end; but these are in essence one; the difference is only the consequence of man's temporal limitations. This eternal process is viewed with finite comprehension through the form of time, forcing the application of temporal distinctions to that which is extra- or supra-temporal. Eriugena concludes this work with another controversial argument, and one that had already been scathingly rejected by Augustine of Hippo, that "[n]ot only man, however, but everything else in nature is destined to return to God." Eriugena's work was condemned by a council at Sens by Honorius III (1225), who described it as "swarming with worms of heretical perversity," and by Pope Gregory XIII in 1585. Such theories were thus suppressed for hundreds of years thence.

16th century on

The ideas of Spinoza lay the foundations for pandeism.

Giordano Bruno conceived of a God who was immanent in nature, and for this very purpose was uninterested in human affairs (all such events being equally part of God). However, it was Baruch Spinoza in the 17th century who appears to have been the earliest to use deistic reason to arrive at the conception of a pantheistic God. Spinoza's God was deistic in the sense that it could only be proved by appeal to reason, but it was also one with the universe.

Spinoza's pantheistic focus on the universe as it already existed, was unlike Eriugena's. It did not address the possible creation of the universe from the substance of God, as Spinoza rejected the very possibility of changes in the form of matter required as a premise for such a belief.

Franz Wilhelm Junghuhn was the first to articulate a pantheistic deism.

18th-century British philosopher Thomas Paine also approached this territory in his great philosophical treatise, The Age of Reason, although Paine was concentrated on the deistic aspects of his inquiry. According to the Encyclopedia of American Philosophy "Later Unitarian Christians (such as William Ellery Channing), transcendentalists (such as Ralph Waldo Emerson and Henry David Thoreau), writers (such as Walt Whitman) and some pragmatists (such as William James) took a more pantheist or pandeist approach by rejecting views of God as separate from the world." It was Dutch naturalist Franz Wilhelm Junghuhn who first specifically detailed a religious philosophy incorporating deism and pantheism, in his four volume treatise, Java, seine Gestalt, Pflanzendecke, und sein innerer Bau (Images of Light and Shadow from Java's interior) released anonymously between 1850 and 1854. Junghuhn's book was banned for a time in Austria and parts of Germany as an attack on Christianity. In 1884, theologian Sabine Baring-Gould would contend that Christianity itself demanded that the seemingly irreconcilable elements of pantheism and deism must be combined:

This world is either the idea or it is the workmanship of God. If we say that it is the idea,--then we are Pantheists, if we say that it is the work, then we are Deists... But how, it may be asked, can two such opposite theories as Pantheism and Deism be reconciled,--they mutually exclude one another? I may not be able to explain how they are conciliable, but I boldly affirm that each is simultaneously true, and that each must be true, for each is an inexorably logical conclusion, and each is a positive conclusion, and all positive conclusions must be true if Christ be the Ideal and the focus of all truths.

Within a decade after that, Andrew Martin Fairbairn similarly wrote that "both Deism and Pantheism err because they are partial; they are right in what they affirm, wrong in what they deny. It is as antitheses that they are false; but by synthesis they may be combined or dissolved into truth." Ironically, Fairbairn's criticism concluded that it was the presence of an active God that was missing from both concepts, rather than the rational explanation of God's motives and appearance of absence.

In 1838, Italian phrenologist Luigi Ferrarese in Memorie Riguardanti la Dottrina Frenologica ("Thoughts Regarding the Doctrine of Phrenology") attacked the philosophy of Victor Cousin as a doctrine which "locates reason outside the human person, declaring man a fragment of God, introducing a sort of spiritual Pandeism, absurd for us, and injurious to the Supreme Being." Cousin had often been identified as a pantheist, but it was said that he repudiated that label on the basis that unlike Spinoza, Cousin asserted that "he does not hold with Spinoza and the Eleatics that God is a pure substance, and not a cause."

Helena Petrovna Blavatsky observed this:

In the Mandukya Upanishad it is written, "As a spider throws out and retracts its web, as herbs spring up in the ground . . . so is the Universe derived from the undecaying one," Brahma, for the "Germ of unknown Darkness", is the material from which all evolves and develops, "as the web from the spider, as foam from the water," etc. This is only graphic and true, if the term Brahma, the "Creator", is derived from the root brih, to increase or expand. Brahma "expands", and becomes the Universe woven out of his own substance.

Mid-19th century German-Jewish philosopher, Philipp Mainländer theorized the world was created through "God killing himself," wherein the origin of existence can be attributed to a singularity, referred to by Mainländer as "God" in a pseudo-metaphorical sense, dispersing itself to create spatiotemporality in an attempt to elude existence, being that this singularity ("God") has an ontology of existing, and thus can only escape it through becoming entities wherein this nature is not to be found. Mainländer, inspired by Arthur Schopenhauer's will to live, theorized of the "will to death," a desire for annihilation inherent to the beings created by Mainländer's "God".

Developments from the 20th century to today

See also: Tat Tvam Asi

In the 1940s, process theologian Charles Hartshorne identified pandeism as one of his many models of the possible nature of God, acknowledging that a God capable of change (as Hartshorne insisted God must be) is consistent with pandeism. Hartshorne preferred pandeism to pantheism, explaining that "it is not really the theos that is described." However, he specifically rejected pandeism early on in favor of a God whose characteristics included "absolute perfection in some respects, relative perfection in all others" or "AR", writing that this theory "is able consistently to embrace all that is positive in either deism or pandeism." Hartshorne accepted the label of panentheism for his beliefs, declaring that "panentheistic doctrine contains all of deism and pandeism except their arbitrary negations."

In 2001, Scott Adams published God's Debris: A Thought Experiment, in which a fictional character puts forth a radical form of kenosis, surmising that an omnipotent God annihilated himself in the Big Bang, because God would already know everything possible except his own lack of existence, and would have to end that existence in order to complete his knowledge. Adams' protagonist asks about God, "would his omnipotence include knowing what happens after he loses his omnipotence, or would his knowledge of the future end at that point?" He proceeds from this question to the following analysis:

A God who knew the answer to that question would indeed know everything and have everything. For that reason he would be unmotivated to do anything or create anything. There would be no purpose to act in any way whatsoever. But a God who had one nagging question—what happens if I cease to exist?—might be motivated to find the answer in order to complete his knowledge. ... The fact that we exist is proof that God is motivated to act in some way. And since only the challenge of self-destruction could interest an omnipotent God, it stands to reason that we... are God's debris.

Adams' God exists now as a combination of the smallest units of energy of which the universe is made (many levels smaller than quarks), which Adams called "God Dust", and the law of probability, or "God's debris", hence the title. The protagonist further proposes that God is in the process of being restored not through some process such as the Big Crunch, but because humankind itself is becoming God.

The 1976 Simon Raven novel, The Survivors includes an exchange between characters where one observes, "God became the universe. Therefore the universe is God." while the other counters:

In becoming the universe God abdicated. He destroyed himself as God. He turned what he had been, his true self, into nullity and thereby forfeited the Godlike qualities which pertained to him. The universe which he has become is also his grave. He has no control in it or over it. God, as God, is dead.

Criticisms

Some theologians have criticised the notion of a Creator wholly becoming the universe. An example is William Walker Atkinson, in his Mastery of Being:

It will be seen that this fact of the Immutability of REALITY, when clearly conceived, must serve to confute and refute the erroneous theories of certain schools of Pantheism which hold that "God becomes the Universe by changing into the Universe." Thus it is sought to identify Nature with God, whereby, as Schopenhauer said, "you show God to the door." If God changes Himself into The Phenomenal Universe, then God is non-existent and we need not concern ourselves any more about Him, for he has committed suicide by Change. In such case there is no God, no Infinite, no Immutable, no Eternal; everything has become finite, temporal, separate, a mere union of diverse finite parts. In that case are we indeed adrift in the Ocean of Diversity. We have lost our Foundation of REALITY, and are but ever-changing "parts" of physical things governed by physical laws. Then, indeed, would be true the idea of some of the old philosophies that "there is No Being; merely a Becoming." Then would there, in truth, be nothing constant, the universe never the same for two consecutive moments, with no permanent ground of REALITY to support it. But the reason of man, the very essence of his mental being, refuses to so think of That-which-IS. In his heart of hearts he recognizes the existence of THAT-WHICH-CHANGES-NOT, THAT-WHICH-IS-ETERNAL, THAT-WHICH-IS-REALITY.
....
Moreover, the idea of the immutability of REALITY must, serve to confute the erroneous idea of certain schools of metaphysics which assert the existence of "an Evolving God"; that is, a God which increases in intelligence, nature, and being by reason of the change of the universe, which is an expression of Himself. This conception is that of a Supreme Being who is growing, developing, and increasing in efficiency, wisdom, power, and character. This is an attempt to combine the anthropomorphic deity and the pantheistic Nature-God. The conception is clearly anthropomorphic, as it seeks to attribute to God the qualities and characteristics of man. It defies every fact of Ultimate Principle of REALITY. It is extremely unphilosophical and will not stand the test of logical examination.

He claims that if God were evolving or improving, being an infinite being, it would have to be traceable back to some point of having "an infinitely undeveloped state and condition." But, this claim was made prior to the rise of scientific knowledge pinpointing the beginning of the universe in time, and connecting time with space, so that time would not exist as we know it prior to the universe existing. In Islam, a criticism is raised, wherein it is argued that "from the juristic standpoint, obliterating the distinctions between God and the universe necessarily entails that in effect there can be no Sharia, since the deontic nature of the Law presupposes the existence of someone who commands (amir) and others who are the recipients of the command (ma'mur), namely God and his subjects."

In 1996, Pastor Bob Burridge of the Genevan Institute for Reformed Studies wrote in his Survey Studies in Reformed Theology an essay on "The Decrees of God," also identifying the notion of God becoming the universe as incompatible with Christianity:

All the actions of created intelligences are not merely the actions of God. He has created a universe of beings which are said to act freely and responsibly as the proximate causes of their own moral actions. When individuals do evil things it is not God the Creator and Preserver acting. If God was the proximate cause of every act it would make all events to be "God in motion." That is nothing less than pantheism, or more exactly, pandeism.

Burridge disagrees that such is the case, decrying that "The Creator is distinct from his creation. The reality of secondary causes is what separates Christian theism from pandeism." Burridge concludes by challenging his reader to determine why "calling God the author of sin demand[s] a pandeistic understanding of the universe effectively removing the reality of sin and moral law."

Compatibility with scientific and philosophical proofs

Stephen Hawking's determination that the universe (and others) needed no Creator to come about inspired the response from Deepak Chopra, interviewed by Larry King, that:

He says in the book that at least 10 to the power of 500 universes could possibly exist in super position of possibility at this level, which to me suggests an omniscient being. The only difference I have was God did not create the universe, God became the universe.

Chopra insists that Hawking's discoveries speak only to the nature of God, not to its existence.

The God Theory

Physicist Bernard Haisch has published two books expressing such a model of the universe. The first was the 2006 book entitled The God Theory, in which he writes:

I offer a genuine insight into how you can, and should, be a rational, science-believing human being and at the same time know that you are also an immortal spiritual being, a spark of God. I propose a worldview that offers a way out of the hate and fear-driven violence engulfing the planet.

Haisch published a followup in 2010, The Purpose-Guided Universe. Both books reject both atheism and traditional theistic viewpoints, favoring instead a model wherein the deity has become the universe, to share in the actualized experiences therein manifested. Haisch provides as proof of his views a combination of fine tuning and mystical experiences arguments. Haisch additionally points to the peculiar capabilities of persons with autism and like defects of the brain experiencing savant syndrome, and especially having the ability to perform complex mathematical calculations. Haisch contends that this is consistent with humans being fragments of a supreme power, with their minds acting as filters to reduce that power to a comprehensible experience, and with the savantic mind having a broken filter which allows access to the use of greater capacities.

Alan Dawe's 2011 book The God Franchise, likewise proposes the human experience as being a temporarily segregated sliver of the experience of God.

Mind–body problem

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Mind%E2%80%93body_problem 

Illustration of mind–body dualism by René Descartes. Inputs are passed by the sensory organs to the pineal gland, and from there to the immaterial spirit.

The mind–body problem is a philosophical problem concerning the relationship between thought and consciousness in the human mind and body. It addresses the nature of consciousness, mental states, and their relation to the physical brain and nervous system. The problem centers on understanding how immaterial thoughts and feelings can interact with the material world, or whether they are ultimately physical phenomena.

This problem has been a central issue in philosophy of mind since the 17th century, particularly following René Descartes' formulation of dualism, which proposes that mind and body are fundamentally distinct substances. Other major philosophical positions include monism, which encompasses physicalism (everything is ultimately physical) and idealism (everything is ultimately mental). More recent approaches include functionalism, property dualism, and various non-reductive theories.

The mind-body problem raises fundamental questions about causation between mental and physical events, the nature of consciousness, personal identity, and free will. It remains significant in both philosophy and science, influencing fields such as cognitive science, neuroscience, psychology, and artificial intelligence.

In general, the existence of these mind–body connections seems unproblematic. Issues arise, however, when attempting to interpret these relations from a metaphysical or scientific perspective. Such reflections raise a number of questions, including:

• Are the mind and body two distinct entities, or a single entity?
• If the mind and body are two distinct entities, do the two of them causally interact?
• Is it possible for these two distinct entities to causally interact?
• What is the nature of this interaction?
• Can this interaction ever be an object of empirical study?
• If the mind and body are a single entity, then are mental events explicable in terms of physical events, or vice versa?
• Is the relation between mental and physical events something that arises de novo at a certain point in development?

These and other questions that discuss the relation between mind and body are questions that all fall under the banner of the 'mind–body problem'.

Mind–body interaction and mental causation

Philosophers David L. Robb and John F. Heil introduce mental causation in terms of the mind–body problem of interaction:

Mind–body interaction has a central place in our pretheoretic conception of agency. Indeed, mental causation often figures explicitly in formulations of the mind–body problem. Some philosophers insist that the very notion of psychological explanation turns on the intelligibility of mental causation. If your mind and its states, such as your beliefs and desires, were causally isolated from your bodily behavior, then what goes on in your mind could not explain what you do. If psychological explanation goes, so do the closely related notions of agency and moral responsibility. Clearly, a good deal rides on a satisfactory solution to the problem of mental causation [and] there is more than one way in which puzzles about the mind's "causal relevance" to behavior (and to the physical world more generally) can arise.

[René Descartes] set the agenda for subsequent discussions of the mind–body relation. According to Descartes, minds and bodies are distinct kinds of "substance". Bodies, he held, are spatially extended substances, incapable of feeling or thought; minds, in contrast, are unextended, thinking, feeling substances. If minds and bodies are radically different kinds of substance, however, it is not easy to see how they "could" causally interact. Princess Elizabeth of Bohemia puts it forcefully to him in a 1643 letter:

how the human soul can determine the movement of the animal spirits in the body so as to perform voluntary acts—being as it is merely a conscious substance. For the determination of movement seems always to come about from the moving body's being propelled—to depend on the kind of impulse it gets from what sets it in motion, or again, on the nature and shape of this latter thing's surface. Now the first two conditions involve contact, and the third involves that the impelling thing has extension; but you utterly exclude extension from your notion of soul, and contact seems to me incompatible with a thing's being immaterial...

Elizabeth is expressing the prevailing mechanistic view as to how causation of bodies works. Causal relations countenanced by contemporary physics can take several forms, not all of which are of the push–pull variety.

— David Robb and John Heil, "Mental Causation" in The Stanford Encyclopedia of Philosophy

Contemporary neurophilosopher Georg Northoff suggests that mental causation is compatible with classical formal and final causality.

Biologist, theoretical neuroscientist and philosopher, Walter J. Freeman, suggests that explaining mind–body interaction in terms of "circular causation" is more relevant than linear causation.

In neuroscience, much has been learned about correlations between brain activity and subjective, conscious experiences. Many suggest that neuroscience will ultimately explain consciousness: "...consciousness is a biological process that will eventually be explained in terms of molecular signaling pathways used by interacting populations of nerve cells..." However, this view has been criticized because consciousness has yet to be shown to be a process, and the "hard problem" of relating consciousness directly to brain activity remains elusive.

Cognitive science today gets increasingly interested in the embodiment of human perception, thinking, and action. Abstract information processing models are no longer accepted as satisfactory accounts of the human mind. Interest has shifted to interactions between the material human body and its surroundings and to the way in which such interactions shape the mind. Proponents of this approach have expressed the hope that it will ultimately dissolve the Cartesian divide between the immaterial mind and the material existence of human beings (Damasio, 1994; Gallagher, 2005). A topic that seems particularly promising for providing a bridge across the mind–body cleavage is the study of bodily actions, which are neither reflexive reactions to external stimuli nor indications of mental states, which have only arbitrary relationships to the motor features of the action (e.g., pressing a button for making a choice response). The shape, timing, and effects of such actions are inseparable from their meaning. One might say that they are loaded with mental content, which cannot be appreciated other than by studying their material features. Imitation, communicative gesturing, and tool use are examples of these kinds of actions.^[9]

— Georg Goldenberg, "How the Mind Moves the Body: Lessons From Apraxia" in Oxford Handbook of Human Action

Since 1927, at the Solvay Conference in Austria, European physicists of the late 19th and early 20th centuries realized that the interpretations of their experiments with light and electricity required a different theory to explain why light behaves both as a wave and particle. The implications were profound. The usual empirical model of explaining natural phenomena could not account for this duality of matter and non-matter. In a significant way, this has brought back the conversation on the mind–body duality.

Neural correlates

Main article: Neural correlates of consciousness

The neuronal correlates of consciousness constitute the smallest set of neural events and structures sufficient for a given conscious percept or explicit memory. This case involves synchronized action potentials in neocortical pyramidal neurons.

The neural correlates of consciousness "are the smallest set of brain mechanisms and events sufficient for some specific conscious feeling, as elemental as the color red or as complex as the sensual, mysterious, and primeval sensation evoked when looking at [a] jungle scene..." Neuroscientists use empirical approaches to discover neural correlates of subjective phenomena.

Neurobiology and neurophilosophy

Main articles: Neurobiology and Neurophilosophy

A science of consciousness must explain the exact relationship between subjective conscious mental states and brain states formed by electrochemical interactions in the body, the so-called hard problem of consciousness. Neurobiology studies the connection scientifically, as do neuropsychology and neuropsychiatry. Neurophilosophy is the interdisciplinary study of neuroscience and philosophy of mind. In this pursuit, neurophilosophers, such as Patricia Churchland, Paul Churchland and Daniel Dennett, have focused primarily on the body rather than the mind. In this context, neuronal correlates may be viewed as causing consciousness, where consciousness can be thought of as an undefined property that depends upon this complex, adaptive, and highly interconnected biological system. However, it's unknown if discovering and characterizing neural correlates may eventually provide a theory of consciousness that can explain the first-person experience of these "systems", and determine whether other systems of equal complexity lack such features.

The massive parallelism of neural networks allows redundant populations of neurons to mediate the same or similar percepts. Nonetheless, it is assumed that every subjective state will have associated neural correlates, which can be manipulated to artificially inhibit or induce the subject's experience of that conscious state. The growing ability of neuroscientists to manipulate neurons using methods from molecular biology in combination with optical tools was achieved by the development of behavioral and organic models that are amenable to large-scale genomic analysis and manipulation. Non-human analysis such as this, in combination with imaging of the human brain, have contributed to a robust and increasingly predictive theoretical framework.

Arousal and content

Midline structures in the brainstem and thalamus necessary to regulate the level of brain arousal. Small, bilateral lesions in many of these nuclei cause a global loss of consciousness.

There are two common but distinct dimensions of the term consciousness, one involving arousal and states of consciousness and the other involving content of consciousness and conscious states. To be conscious of something, the brain must be in a relatively high state of arousal (sometimes called vigilance), whether awake or in REM sleep. Brain arousal level fluctuates in a circadian rhythm but these natural cycles may be influenced by lack of sleep, alcohol and other drugs, physical exertion, etc. Arousal can be measured behaviorally by the signal amplitude required to trigger a given reaction (for example, the sound level that causes a subject to turn and look toward the source). High arousal states involve conscious states that feature specific perceptual content, planning and recollection or even fantasy. Clinicians use scoring systems such as the Glasgow Coma Scale to assess the level of arousal in patients with impaired states of consciousness such as the comatose state, the persistent vegetative state, and the minimally conscious state. Here, "state" refers to different amounts of externalized, physical consciousness: ranging from a total absence in coma, persistent vegetative state and general anesthesia, to a fluctuating, minimally conscious state, such as sleep walking and epileptic seizure.

Many nuclei with distinct chemical signatures in the thalamus, midbrain and pons must function for a subject to be in a sufficient state of brain arousal to experience anything at all. These nuclei therefore belong to the enabling factors for consciousness. Conversely it is likely that the specific content of any particular conscious sensation is mediated by particular neurons in the cortex and their associated satellite structures, including the amygdala, thalamus, claustrum and the basal ganglia.

Theoretical frameworks

Different approaches toward resolving the mind–body problem

A variety of approaches have been proposed. Most are either dualist or monist. Dualism maintains a rigid distinction between the realms of mind and matter. Monism maintains that there is only one unifying reality as in neutral or substance or essence, in terms of which everything can be explained.

Each of these categories contains numerous variants. The two main forms of dualism are substance dualism, which holds that the mind is formed of a distinct type of substance not governed by the laws of physics, and property dualism, which holds that mental properties involving conscious experience are fundamental properties, alongside the fundamental properties identified by a completed physics. The three main forms of monism are physicalism, which holds that the mind consists of matter organized in a particular way; idealism, which holds that only thought truly exists and matter is merely a representation of mental processes; and neutral monism, which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them. Psychophysical parallelism is a third possible alternative regarding the relation between mind and body, between interaction (dualism) and one-sided action (monism).

Several philosophical perspectives that have sought to escape the problem by rejecting the mind–body dichotomy have been developed. The historical materialism of Karl Marx and subsequent writers, itself a form of physicalism, held that consciousness was engendered by the material contingencies of one's environment. An explicit rejection of the dichotomy is found in French structuralism, and is a position that generally characterized post-war Continental philosophy.

An ancient model of the mind known as the Five-Aggregate Model, described in the Buddhist teachings, explains the mind as continuously changing sense impressions and mental phenomena. Considering this model, it is possible to understand that it is the constantly changing sense impressions and mental phenomena (i.e., the mind) that experience/analyze all external phenomena in the world as well as all internal phenomena including the body anatomy, the nervous system as well as the organ brain. This conceptualization leads to two levels of analyses: (i) analyses conducted from a third-person perspective on how the brain works, and (ii) analyzing the moment-to-moment manifestation of an individual's mind-stream (analyses conducted from a first-person perspective). Considering the latter, the manifestation of the mind-stream is described as happening in every person all the time, even in a scientist who analyzes various phenomena in the world, including analyzing and hypothesizing about the organ brain.

Christian List argues that Benj Hellie's vertiginous question, i.e. why an individual exists as themselves and not as someone else, and the existence of first-personal facts, is evidence against physicalism. However, according to List, this is also evidence against other third-personal metaphysical pictures, including standard versions of dualism. List also argues that the vertiginous question implies a "quadrilemma" for theories of consciousness. He claims that at most three of the following metaphysical claims can be true: 'first-person realism', 'non-solipsism', 'non-fragmentation', and 'one world' – and thus one of these four must be rejected. List has proposed a model he calls the "many-worlds theory of consciousness" in order to reconcile the subjective nature of consciousness without lapsing into solipsism.

Dualism

The following is a very brief account of some contributions to the mind–body problem.

Interactionism

Main article: Interactionism (philosophy of mind)

The viewpoint of interactionism suggests that the mind and body are two separate substances, but that each can affect the other. This interaction between the mind and body was first put forward by the philosopher René Descartes. Descartes believed that the mind was non-physical and permeated the entire body, but that the mind and body interacted via the pineal gland. This theory has changed throughout the years, and in the 20th century its main adherents were the philosopher of science Karl Popper and the neurophysiologist John Carew Eccles. A more recent and popular version of Interactionism is the viewpoint of emergentism. This perspective states that mental states are a result of the brain states, and that the mental events can then influence the brain, resulting in a two way communication between the mind and body.

The absence of an empirically identifiable meeting point between the non-physical mind (if there is such a thing) and its physical extension (if there is such a thing) has been raised as a criticism of interactionalist dualism. This criticism has led many modern philosophers of mind to maintain that the mind is not something separate from the body. These approaches have been particularly influential in the sciences, particularly in the fields of sociobiology, computer science, evolutionary psychology, and the neurosciences.

Avshalom Elitzur has defended interactionism and has described himself as a "reluctant dualist". One argument Elitzur makes in favor of dualism is an argument from bafflement. According to Elitzur, a conscious being can conceive of a P-zombie version of his/herself. However, a P-zombie cannot conceive of a version of itself that lacks corresponding qualia.

Epiphenomenalism

Main article: Epiphenomenalism

The viewpoint of epiphenomenalism suggests that the physical brain can cause mental events in the mind, but that the mind cannot interact with the brain at all; stating that mental occurrences are simply a side effect of the brain's processes. This viewpoint explains that while one's body may react to them feeling joy, fear, or sadness, that the emotion does not cause the physical response. Rather, it explains that joy, fear, sadness, and all bodily reactions are caused by chemicals and their interaction with the body.

Psychophysical parallelism

Main article: Psychophysical parallelism

The viewpoint of psychophysical parallelism suggests that the mind and body are entirely independent from one another. Furthermore, this viewpoint states that both mental and physical stimuli and reactions are experienced simultaneously by both the mind and body, however, there is no interaction nor communication between the two.

Double aspectism

Main article: Double aspectism

Double aspectism is an extension of psychophysical parallelism which also suggests that the mind and body cannot interact, nor can they be separated. Baruch Spinoza and Gustav Fechner were two of the notable users of double aspectism, however, Fechner later expanded upon it to form the branch of psychophysics in an attempt to prove the relationship of the mind and body.

Pre-established harmony

The viewpoint of pre-established harmony is another offshoot of psychophysical parallelism which suggests that mental events and bodily events are separate and distinct, but that they are both coordinated by an external agent: an example of such an agent could be God. A notable adherent to the idea of pre-established harmony is Gottfried Wilhelm von Leibniz in his theory of Monadology. His explanation of pre-established harmony relied heavily upon God as the external agent who coordinated the mental and bodily events of all things in the beginning.

Gottfried Wilhelm Leibniz's theory of pre-established harmony (French: harmonie préétablie) is a philosophical theory about causation under which every "substance" affects only itself, but all the substances (both bodies and minds) in the world nevertheless seem to causally interact with each other because they have been programmed by God in advance to "harmonize" with each other. Leibniz's term for these substances was "monads", which he described in a popular work (Monadology §7) as "windowless".

The concept of pre-established harmony can be understood by considering an event with both seemingly mental and physical aspects. For example, consider saying 'ouch' after stubbing one's toe. There are two general ways to describe this event: in terms of mental events (where the conscious sensation of pain caused one to say 'ouch') and in terms of physical events (where neural firings in one's toe, carried to the brain, are what caused one to say 'ouch'). The main task of the mind–body problem is figuring out how these mental events (the feeling of pain) and physical events (the nerve firings) relate. Leibniz's pre-established harmony attempts to answer this puzzle, by saying that mental and physical events are not genuinely related in any causal sense, but only seem to interact due to psycho-physical fine-tuning.

Leibniz's theory is best known as a solution to the mind–body problem of how mind can interact with the body. Leibniz rejected the idea of physical bodies affecting each other, and explained all physical causation in this way.

Under pre-established harmony, the preprogramming of each mind must be extremely complex, since only it causes its own thoughts or actions, for as long as it exists. To appear to interact, each substance's "program" must contain a description of either the entire universe, or of how the object behaves at all times during all interactions that appear to occur.

An example:

An apple falls on Alice's head, apparently causing the experience of pain in her mind. In fact, the apple does not cause the pain—the pain is caused by some previous state of Alice's mind. If Alice then seems to shake her hand in anger, it is not actually her mind that causes this, but some previous state of her hand.

Note that if a mind behaves as a windowless monad, there is no need for any other object to exist to create that mind's sense perceptions, leading to a solipsistic universe that consists only of that mind. Leibniz seems to admit this in his Discourse on Metaphysics, section 14. However, he claims that his principle of harmony, according to which God creates the best and most harmonious world possible, dictates that the perceptions (internal states) of each monad "expresses" the world in its entirety, and the world expressed by the monad actually exists. Although Leibniz says that each monad is "windowless", he also claims that it functions as a "mirror" of the entire created universe.

On occasion, Leibniz styled himself as "the author of the system of pre-established harmony".

Immanuel Kant's professor Martin Knutzen regarded pre-established harmony as "the pillow for the lazy mind".

In his sixth Metaphysical Meditation, Descartes talked about a "coordinated disposition of created things set up by God", shortly after having identified "nature in its general aspect" with God himself. His conception of the relationship between God and his normative nature actualized in the existing world recalls both the pre-established harmony of Leibniz and the Deus sive Natura of Baruch Spinoza.

Occasionalism

Main article: Occasionalism

The viewpoint of Occasionalism is another offshoot of psychophysical parallelism, however, the major difference is that the mind and body have some indirect interaction. Occasionalism suggests that the mind and body are separate and distinct, but that they interact through divine intervention. Nicolas Malebranche was one of the main contributors to this idea, using it as a way to address his disagreements with Descartes' view of the mind–body problem. In Malebranche's occasionalism, he viewed thoughts as a wish for the body to move, which was then fulfilled by God causing the body to act.

Historical background

The problem was popularized by René Descartes in the 17th century, which resulted in Cartesian dualism, also by pre-Aristotelian philosophers, in Avicennian philosophy, and in earlier Asian traditions.

The Buddha

See also: Gautama Buddha, Buddhism and the body, and Pratītyasamutpāda

The Buddha (480–400 B.C.E), founder of Buddhism, described the mind and the body as depending on each other in a way that two sheaves of reeds were to stand leaning against one another and taught that the world consists of mind and matter which work together, interdependently. Buddhist teachings describe the mind as manifesting from moment to moment, one thought moment at a time as a fast flowing stream. The components that make up the mind are known as the five aggregates (i.e., material form, feelings, perception, volition, and sensory consciousness), which arise and pass away continuously. The arising and passing of these aggregates in the present moment is described as being influenced by five causal laws: biological laws, psychological laws, physical laws, volitional laws, and universal laws. The Buddhist practice of mindfulness involves attending to this constantly changing mind-stream.

Ultimately, the Buddha's philosophy is that both mind and forms are conditionally arising qualities of an ever-changing universe in which, when nirvāna is attained, all phenomenal experience ceases to exist. According to the anattā doctrine of the Buddha, the conceptual self is a mere mental construct of an individual entity and is basically an impermanent illusion, sustained by form, sensation, perception, thought and consciousness. The Buddha argued that mentally clinging to any views will result in delusion and stress, since, according to the Buddha, a real self (conceptual self, being the basis of standpoints and views) cannot be found when the mind has clarity.

Plato

See also: Plato and Theory of forms

Plato (429–347 B.C.E.) believed that the material world is a shadow of a higher reality that consists of concepts he called Forms. According to Plato, objects in our everyday world "participate in" these Forms, which confer identity and meaning to material objects. For example, a circle drawn in the sand would be a circle only because it participates in the concept of an ideal circle that exists somewhere in the world of Forms. He argued that, as the body is from the material world, the soul is from the world of Forms and is thus immortal. He believed the soul was temporarily united with the body and would only be separated at death, when it, if pure, would return to the world of Forms; otherwise, reincarnation follows. Since the soul does not exist in time and space, as the body does, it can access universal truths. For Plato, ideas (or Forms) are the true reality, and are experienced by the soul. The body is for Plato empty in that it cannot access the abstract reality of the world; it can only experience shadows. This is determined by Plato's essentially rationalistic epistemology.

Aristotle

Main article: Hylomorphism § Body–soul hylomorphism

For Aristotle (384–322 BC) mind is a faculty of the soul. Regarding the soul, he said:

It is not necessary to ask whether soul and body are one, just as it is not necessary to ask whether the wax and its shape are one, nor generally whether the matter of each thing and that of which it is the matter are one. For even if one and being are spoken of in several ways, what is properly so spoken of is the actuality.

— De Anima ii 1, 412b6–9

In the end, Aristotle saw the relation between soul and body as uncomplicated, in the same way that it is uncomplicated that a cubical shape is a property of a toy building block. The soul is a property exhibited by the body, one among many. Moreover, Aristotle proposed that when the body perishes, so does the soul, just as the shape of a building block disappears with destruction of the block.

Medieval Aristotelianism

Working in the Aristotelian-influenced tradition of Thomism, Thomas Aquinas (1225–1274), like Aristotle, believed that the mind and the body are one, like a seal and wax; therefore, it is pointless to ask whether or not they are one. However, (referring to "mind" as "the soul") he asserted that the soul persists after the death of the body in spite of their unity, calling the soul "this particular thing". Since his view was primarily theological rather than philosophical, it is impossible to fit it neatly within either the category of physicalism or dualism.

Influences of Eastern monotheistic religions

Main articles: Dualistic cosmology and Gnosticism

In religious philosophy of Eastern monotheism, dualism denotes a binary opposition of an idea that contains two essential parts. The first formal concept of a "mind–body" split may be found in the divinity–secularity dualism of the ancient Persian religion of Zoroastrianism around the mid-fifth century BC. Gnosticism is a modern name for a variety of ancient dualistic ideas inspired by Judaism popular in the first and second century AD. These ideas later seem to have been incorporated into Galen's "tripartite soul"  that led into both the Christian sentiments expressed in the later Augustinian theodicy and Avicenna's Platonism in Islamic Philosophy.

Descartes

René Descartes (1596–1650) believed that mind exerted control over the brain via the pineal gland:

My view is that this gland is the principal seat of the soul, and the place in which all our thoughts are formed.

— René Descartes, Treatise of Man

[The] mechanism of our body is so constructed that simply by this gland's being moved in any way by the soul or by any other cause, it drives the surrounding spirits towards the pores of the brain, which direct them through the nerves to the muscles; and in this way the gland makes the spirits move the limbs.

— René Descartes, Passions of the Soul

His posited relation between mind and body is called Cartesian dualism or substance dualism. He held that mind was distinct from matter, but could influence matter. How such an interaction could be exerted remains a contentious issue.

Kant

Main article: Immanuel Kant

For Immanuel Kant (1724–1804) beyond mind and matter there exists a world of a priori forms, which are seen as necessary preconditions for understanding. Some of these forms, space and time being examples, today seem to be pre-programmed in the brain.

...whatever it is that impinges on us from the mind-independent world does not come located in a spatial or a temporal matrix,...The mind has two pure forms of intuition built into it to allow it to... organize this 'manifold of raw intuition'.

— Andrew Brook, Kant's view of the mind and consciousness of self: Transcendental aesthetic

Kant views the mind–body interaction as taking place through forces that may be of different kinds for mind and body.

Huxley

Main article: Thomas Henry Huxley

For Thomas Henry Huxley (1825–1895) the conscious mind was a by-product of the brain that has no influence upon the brain, a so-called epiphenomenon.

On the epiphenomenalist view, mental events play no causal role. Huxley, who held the view, compared mental events to a steam whistle that contributes nothing to the work of a locomotive.

— William Robinson, Epiphenomenalism

Whitehead

Main article: Alfred North Whitehead

Alfred North Whitehead advocated a sophisticated form of panpsychism that has been called by David Ray Griffin panexperientialism.

Popper

Main article: Karl Popper

For Karl Popper (1902–1994) there are three aspects of the mind–body problem: the worlds of matter, mind, and of the creations of the mind, such as mathematics. In his view, the third-world creations of the mind could be interpreted by the second-world mind and used to affect the first-world of matter. An example might be radio, an example of the interpretation of the third-world (Maxwell's electromagnetic theory) by the second-world mind to suggest modifications of the external first world.

The body–mind problem is the question of whether and how our thought processes in World 2 are bound up with brain events in World 1. ...I would argue that the first and oldest of these attempted solutions is the only one that deserves to be taken seriously [namely]: World 2 and World 1 interact, so that when someone reads a book or listens to a lecture, brain events occur that act upon the World 2 of the reader's or listener's thoughts; and conversely, when a mathematician follows a proof, his World 2 acts upon his brain and thus upon World 1. This, then, is the thesis of body–mind interaction.

— Karl Popper, Notes of a realist on the body–mind problem

Ryle

Main article: Gilbert Ryle

With his 1949 book, The Concept of Mind, Gilbert Ryle "was seen to have put the final nail in the coffin of Cartesian dualism".

In the chapter "Descartes' Myth," Ryle introduces "the dogma of the Ghost in the machine" to describe the philosophical concept of the mind as an entity separate from the body:

I hope to prove that it is entirely false, and false not in detail but in principle. It is not merely an assemblage of particular mistakes. It is one big mistake and a mistake of a special kind. It is, namely, a category mistake.

Searle

Main article: John Searle

For John Searle (1932-2025) the mind–body problem is a false dichotomy; that is, mind is a perfectly ordinary aspect of the brain. Searle proposed biological naturalism in 1980.

According to Searle then, there is no more a mind–body problem than there is a macro–micro economics problem. They are different levels of description of the same set of phenomena. [...] But Searle is careful to maintain that the mental – the domain of qualitative experience and understanding – is autonomous and has no counterpart on the microlevel; any redescription of these macroscopic features amounts to a kind of evisceration, ...

— Joshua Rust, John Searle

Evolution of the brain

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Evolution_of_the_brain

Evolution of the brain from ape to man

The evolution of the brain refers to the progressive development and complexity of neural structures over millions of years, resulting in the diverse range of brain sizes and functions observed across different species today, particularly in vertebrates.

The evolution of the brain has exhibited diverging adaptations within taxonomic classes, such as Mammalia, and even more diverse adaptations across other taxonomic classes. Brain-to-body size scales allometrically. This means that as body size changes, so do other physiological, anatomical, and biochemical connections between the brain and body. Small-bodied mammals tend to have relatively large brains compared to their bodies, while larger mammals (such as whales) have smaller brain-to-body ratios. When brain weight is plotted against body weight for primates, the regression line of the sample points can indicate the brain power of a species. For example, lemurs fall below this line, suggesting that for a primate of their size, a larger brain would be expected. In contrast, humans lie well above this line, indicating they are more encephalized than lemurs and, in fact, more encephalized than any other primate. This suggests that human brains have undergone a larger evolutionary increase in complexity relative to size. Some of these changes have been linked to multiple genetic factors, including proteins and other organelles.

Early history

Main article: Evolution of nervous systems

Unsolved problem in biology

How and why did the brain evolve?

More unsolved problems in biology

One approach to understanding overall brain evolution is to use a paleoarchaeological timeline to trace the necessity for ever-increasing complexity in structures that allow for chemical and electrical signaling. Because brains and other soft tissues do not fossilize as readily as mineralized tissues, scientists often look to other structures as evidence in the fossil record to get an understanding of brain evolution. This, however, leads to a dilemma as the emergence of organisms with more complex nervous systems with protective bone or other protective tissues that can then readily fossilize occur in the fossil record before evidence for chemical and electrical signaling. Evidence from 2008 showed that the ability to transmit electrical and chemical signals existed even before more complex multicellular lifeforms.

Fossilization of brain tissue, as well as other soft tissue, is nonetheless possible, and scientists can infer that the first brain structure appeared at least 521 million years ago, with fossil brain tissue present in sites of exceptional preservation.

Another approach to understanding brain evolution is to look at extant organisms that do not possess complex nervous systems, comparing anatomical features that allow for chemical or electrical messaging. For example, choanoflagellates are organisms that possess various membrane channels that are crucial to electrical signaling. The membrane channels of choanoflagellates' are homologous to the ones found in animal cells, and this is supported by the evolutionary connection between early choanoflagellates and the ancestors of animals. Another example of extant organisms with the capacity to transmit electrical signals would be the glass sponge, a multicellular organism, which is capable of propagating electrical impulses without the presence of a nervous system.

Before the evolutionary development of the brain, nerve nets, the simplest form of a nervous system developed. These nerve nets were a sort of precursor for the more evolutionarily advanced brains. They were first observed in Cnidaria and consist of a number of neurons spread apart that allow the organism to respond to physical contact. They are able to rudimentarily detect food and other chemicals, but these nerve nets do not allow them to detect the source of the stimulus.

Ctenophores also demonstrate this crude precursor to a brain or centralized nervous system, however they phylogenetically diverged before the phylum Porifera (the Sponges) and Cnidaria. There are two current theories on the emergence of nerve nets. One theory is that nerve nets may have developed independently in Ctenophores and Cnidarians. The other theory states that a common ancestor may have developed nerve nets, but they were lost in Porifera. While comparing the average neuron size and the packing density the difference between primate and mammal brains is shown.

A trend in brain evolution according to a study done with mice, chickens, monkeys and apes concluded that more evolved species tend to preserve the structures responsible for basic behaviors. A long term human study comparing the human brain to the primitive brain found that the modern human brain contains the primitive hindbrain region – what most neuroscientists call the protoreptilian brain. The purpose of this part of the brain is to sustain fundamental homeostatic functions, which are self regulating processes organisms use to help their bodies adapt. The pons and medulla are major structures found there. A new region of the brain developed in mammals about 250 million years after the appearance of the hindbrain. This region is known as the paleomammalian brain, the major parts of which are the hippocampi and amygdalas, often referred to as the limbic system. The limbic system deals with more complex functions including emotional, sexual and fighting behaviors. Of course, animals that are not vertebrates also have brains, and their brains have undergone separate evolutionary histories.

The brainstem and limbic system are largely based on nuclei, which are essentially balled-up clusters of tightly packed neurons and the axon fibers that connect them to each other, as well as to neurons in other locations. The other two major brain areas (the cerebrum and cerebellum) are based on a cortical architecture. At the outer periphery of the cortex, the neurons are arranged into layers (the number of which vary according to species and function) a few millimeters thick. There are axons that travel between the layers, but the majority of axon mass is below the neurons themselves. Since cortical neurons and most of their axon fiber tracts do not have to compete for space, cortical structures can scale more easily than nuclear ones. A key feature of cortex is that because it scales with surface area, more of it can be fit inside a skull by introducing convolutions, in much the same way that a dinner napkin can be stuffed into a glass by wadding it up. The degree of convolution is generally greater in species with more complex behavior, which benefits from the increased surface area.

The cerebellum, or "little brain," is behind the brainstem and below the occipital lobe of the cerebrum in humans. Its purposes include the coordination of fine sensorimotor tasks, and it may be involved in some cognitive functions, such as language and different motor skills that may involve hands and feet. The cerebellum helps keep equilibrium. Damage to the cerebellum would result in all physical roles in life to be affected. Human cerebellar cortex is finely convoluted, much more so than cerebral cortex. Its interior axon fiber tracts are called the arbor vitae, or Tree of Life.

The area of the brain with the greatest amount of recent evolutionary change is called the neocortex. In reptiles and fish, this area is called the pallium and is smaller and simpler relative to body mass than what is found in mammals. According to research, the cerebrum first developed about 200 million years ago. It is responsible for higher cognitive functions—for example, language, thinking, and related forms of information processing. It is also responsible for processing sensory input (together with the thalamus, a part of the limbic system that acts as an information router). The thalamus receives the different sensations before the information is then passed onto the cerebral cortex. Most of its function is subconscious, that is, not available for inspection or intervention by the conscious mind. The neocortex is an elaboration, or outgrowth, of structures in the limbic system, with which it is tightly integrated. The neocortex is the main part controlling many brain functions as it covers half of the whole brain in volume. The development of these recent evolutionary changes in the neocortex likely occurred as a result of new neural network formations and positive selections of certain genetic components.

Role of embryology

Further information: Embryology and Brain development timelines

In addition to studying the fossil record, evolutionary history can be investigated via embryology. An embryo is an unborn/unhatched animal and evolutionary history can be studied by observing how processes in embryonic development are conserved (or not conserved) across species. Similarities between different species may indicate evolutionary connection. One way anthropologists study evolutionary connection between species is by observing orthologs. An ortholog is defined as two or more homologous genes between species that are evolutionarily related by linear descent. By using embryology the evolution of the brain can be tracked between various species.

Bone morphogenetic protein (BMP), a growth factor that plays a significant role in embryonic neural development, is highly conserved amongst vertebrates, as is sonic hedgehog (SHH), a morphogen that inhibits BMP to allow neural crest development. Tracking these growth factors with the use of embryology provides a deeper understanding of what areas of the brain diverged in their evolution. Varying levels of these growth factors lead to differing embryonic neural development which then in turn affects the complexity of future neural systems. Studying the brain's development at various embryonic stages across differing species provides additional insight into what evolutionary changes may have historically occurred. This then allows scientists to look into what factors may have caused such changes, such as links to neural network diversity, growth factor production, protein- coding selections, and other genetic factors.

Randomizing access and increasing size

Some animal phyla have gone through major brain enlargement through evolution (e.g. vertebrates and cephalopods both contain many lineages in which brains have grown through evolution) but most animal groups are composed only of species with extremely small brains. Some scientists^[who?] argue that this difference is due to vertebrate and cephalopod neurons having evolved ways of communicating that overcome the scalability problem of neural networks while most animal groups have not. They argue that traditional neural networks fail to improve their function when scaled up because filtering based on previously known probabilities creates self-fulfilling prophecy-like biases. These biases generate false statistical evidence, producing a completely inaccurate worldview. In contrast, randomized access can overcome this problem, allowing brains to scale to more discriminating conditioned reflexes. This, in turn, can lead to new worldview-forming abilities once certain thresholds are reached. This means when neurons scale in a non randomized fashion that their functionality becomes more limited due to their neural networks being unable to process more complex systems without the exposure to new formations. This is explained by randomization allowing the entire brain to eventually get access to all information over the course of many shifts even though instant privileged access is physically impossible. They cite that vertebrate neurons transmit virus-like capsules containing RNA that are sometimes read in the neuron to which it is transmitted and sometimes passed further on unread which creates randomized access, and that cephalopod neurons make different proteins from the same gene which suggests another mechanism for randomization of concentrated information in neurons, both making it evolutionarily worth scaling up brains.

Brain re-organization

With the use of in vivo Magnetic resonance imaging (MRI) and tissue sampling, different cortical samples from members of each hominoid species were analyzed. In each species, specific areas were either relatively enlarged or shrunken, which can detail neural organizations. Different sizes in the cortical areas can show specific adaptations, functional specializations and evolutionary events that were changes in how the hominoid brain is organized. In early prediction it was thought that the frontal lobe, a large part of the brain that is generally devoted to behavior and social interaction, predicted the differences in behavior between hominoid and humans. Discrediting this theory was evidence supporting that damage to the frontal lobe in both humans and hominoids show atypical social and emotional behavior; thus, this similarity means that the frontal lobe was not very likely to be selected for reorganization. Instead, it is now believed that evolution occurred in other parts of the brain that are strictly associated with certain behaviors. The reorganization that took place is thought to have been more organizational than volumetric; whereas the brain volumes were relatively the same but specific landmark position of surface anatomical features, for example, the lunate sulcus suggest that the brains had been through a neurological reorganization. There is also evidence that the early hominin lineage also underwent a quiescent period, or a period of dormancy, which supports the idea of neural reorganization.

Dental fossil records for early humans and hominins show that immature hominins, including australopithecines and members of Homo, have a quiescent period (Bown et al. 1987). A quiescent period is a period in which there are no dental eruptions of adult teeth; at this time the child becomes more accustomed to social structure, and development of culture. During this time the child is given an extra advantage over other hominoids, devoting several years into developing speech and learning to cooperate within a community. This period is also discussed in relation to encephalization. It was discovered that chimpanzees do not have this neutral dental period, which suggests that a quiescent period occurred in very early hominin evolution. Using the models for neurological reorganization it can be suggested the cause for this period, dubbed middle childhood, is most likely for enhanced foraging abilities in varying seasonal environments.

Genetic factors in recent evolution

Genes involved in the neuro-development and in neuron physiology are extremely conserved between mammalian species (94% of genes expressed in common between humans and chimpanzees, 75% between humans and mice), compared to other organs. Therefore, few genes account for species differences in the human brain development and function.

Development of the human cerebral cortex

Main differences rely on the evolution of non-coding genomic regions, involved in the regulation of gene expression. This leads to differential expression of genes during the development of the human brain compared to other species, including chimpanzees. Some of these regions evolved fast in the human genome (human accelerated regions). The new genes expressed during human neurogenesis are notably associated with the NOTCH, WNT and mTOR pathways, but are also involved ZEB2, PDGFD and its receptor PDGFRβ. The human cerebral cortex is also characterized by a higher gradient of retinoic acid in the prefrontal cortex, leading to higher prefrontal cortex volume. All these differential gene expression lead to higher proliferation of the neural progenitors leading to more neurons in the human cerebral cortex. Some genes are lost in their expression during the development of the human cerebral cortex like GADD45G and FLRT2/FLRT3.

Another source of molecular novelty rely on new genes in the human or hominid genomes through segmental duplication. Around 30 new genes in the hominid genomes are dynamically expressed during human corticogenesis. Some were linked to higher proliferation of neural progenitors: NOTCH2NLA/B/C, ARHGAP11B, CROCCP2, TBC1D3, TMEM14B. Patients with deletions with NOTCH2NL genes display microcephaly, showing the necessity of such duplicated genes, acquired in the human genomes, in the proper corticogenesis.

MCPH1 and ASPM

Bruce Lahn, the senior author at the Howard Hughes Medical Center at the University of Chicago and colleagues have suggested that there are specific genes that control the size of the human brain. These genes continue to play a role in brain evolution, implying that the brain is continuing to evolve. The study began with the researchers assessing 214 genes that are involved in brain development. These genes were obtained from humans, macaques, rats and mice. Lahn and the other researchers noted points in the DNA sequences that caused protein alterations. These DNA changes were then scaled to the evolutionary time that it took for those changes to occur. The data showed the genes in the human brain evolved much faster than those of the other species. Once this genomic evidence was acquired, Lahn and his team decided to find the specific gene or genes that allowed for or even controlled this rapid evolution. Two genes were found to control the size of the human brain as it develops. These genes are Microcephalin (MCPH1) and Abnormal Spindle-like Microcephaly (ASPM). The researchers at the University of Chicago were able to determine that under the pressures of selection, both of these genes showed significant DNA sequence changes. Lahn's earlier studies displayed that Microcephalin experienced rapid evolution along the primate lineage which eventually led to the emergence of Homo sapiens. After the emergence of humans, Microcephalin seems to have shown a slower evolution rate. On the contrary, ASPM showed its most rapid evolution in the later years of human evolution once the divergence between chimpanzees and humans had already occurred.

Each of the gene sequences went through specific changes that led to the evolution of humans from ancestral relatives. In order to determine these alterations, Lahn and his colleagues used DNA sequences from multiple primates then compared and contrasted the sequences with those of humans. Following this step, the researchers statistically analyzed the key differences between the primate and human DNA to come to the conclusion, that the differences were due to natural selection. The changes in DNA sequences of these genes accumulated to bring about a competitive advantage and higher fitness that humans possess in relation to other primates. This comparative advantage is coupled with a larger brain size which ultimately allows the human mind to have a higher cognitive awareness.

ZEB2 protein

ZEB2

ZEB2 is a protein- coding gene in the Homo sapien species. A 2021 study found that a delayed change in the shape of early brain cells causes the distinctly large human forebrain compared to other apes and identify ZEB2 as a genetic regulator of it, whose manipulation lead to acquisition of nonhuman ape cortical architecture in brain organoids.

NOVA1

In 2021, researchers reported that brain organoids created with stem cells into which they reintroduced the archaic gene variant NOVA1 present in Neanderthals and Denisovans via CRISPR-Cas9 shows that it has a major impact on neurodevelopment and that such genetic mutations during the evolution of the human brain underlie traits that separate modern humans from extinct Homo species. They found that expression of the archaic NOVA1 in cortical organoids leads to "modified synaptic protein interactions, affects glutamatergic signaling, underlies differences in neuronal connectivity, and promotes higher heterogeneity of neurons regarding their electrophysiological profiles". This research suggests positive selection of the modern NOVA1 gene, which may have promoted the randomization of neural scaling. A subsequent study failed to replicate the differences in organoid morphology between the modern human and the archaic NOVA1 variant, consistent with suspected unwanted side effects of CRISPR editing in the original study.

SRGAP2C and neuronal maturation

Less is known about neuronal maturation. Synaptic gene and protein expression are protracted, in line with the protracted synaptic maturation of human cortical neurons so called neoteny. This probably relies on the evolution of non-coding genomic regions. The consequence of the neoteny could be an extension of the period of synaptic plasticity and therefore of learning. A human-specific duplicated gene, SRGAP2C accounts for this synaptic neoteny and acts by regulating molecular pathways linked to neurodevelopmental disorders. Other genes are deferentially expressed in human neurons during their development such as osteocrin or cerebelin-2 .

LRRC37B and neuronal electrical properties

Even less is known about molecular specificities linked to the physiology of the human neurons. Human neurons are more divergent in the genes they express compared to chimpanzees than chimpanzees to gorilla, which suggests an acceleration of non-coding genomic regions associated with genes involved in neuronal physiology, in particular linked to the synapses. A hominid-specific duplicated gene, LRRC37B, codes for a transmembrane receptor that is selectively localized at the axon initial segment of human cortical pyramidal neurons. It inhibits their voltage-gated sodium channels that generate the action potentials leading to a lower neuronal excitability. Human cortical pyramidal neurons display a lower excitability compared to other mammalian species (including macaques and marmosets) which could lead to different circuit functions in the human species. Therefore, LRRC37B whose expression has been acquired in the human lineage after the separation from the chimpanzees could be a key gene in the function of the human cerebral cortex. LRRC37B binds to secreted FGF13A and SCN1B and modulate indirectly the activity of SCN8A, all involved in neural disorders such as epilepsy and autism. Therefore, LRRC37B may contribute to human-specific sensitivities to such disorders, both involved defects in neuronal excitability.

Genome repair

The genomic DNA of postmitotic neurons ordinarily does not replicate. Protection strategies have evolved to ensure the distinctive longevity of the neuronal genome. Human neurons are reliant on DNA repair processes to maintain function during an individual's life-time. DNA repair tends to occur preferentially at evolutionarily conserved sites that are specifically involved with the regulation of expression of genes essential for neuronal identity and function.

Other factors

Many other genetics may also be involved in recent evolution of the brain.

• For instance, scientists showed experimentally, with brain organoids grown from stem cells, how differences between humans and chimpanzees are also substantially caused by non-coding DNA (often discarded as relatively meaningless "junk DNA") – in particular via CRE-regulated expression of the ZNF558 gene for a transcription factor that regulates the SPATA18 gene. SPATA18 gene encodes a protein and is able to influence lysosome-like organelles that are found within mitochondria that eradicate oxidized mitochondrial proteins. This helps monitor the quality of the mitochondria as the disregulation of its quality control has been linked to cancer and degenerative diseases. This example may contribute to illustrations of the complexity and scope of relatively recent evolution to Homo sapiens.
• A change in gene TKTL1 could be a key factor of recent brain evolution and difference of modern humans to (other) apes and Neanderthals, related to neocortex-neurogenesis. However, the "archaic" allele attributed to Neanderthals is present in 0.03% of Homo sapiens, but no resultant phenotypic differences have been reported in these people. Additionally, as Herai et al. contend, more is not always better. In fact, enhanced neuron production "can lead to an abnormally enlarged cortex and layer-specific imbalances in glia/neuron ratios and neuronal subpopulations during neurodevelopment." Even the original study's authors agree that "any attempt to discuss prefrontal cortex and cognitive advantage of modern humans over Neandertals based on TKTL1 alone is problematic".
• Some of the prior study's authors reported a similar ARHGAP11B mutation in 2016.
• Epigenetics also play a major role in the brain evolution in and to humans.

Recently evolved traits

Language

A genome-wide association study meta-analysis reported genetic factors of, the so far uniquely human, language-related capacities, in particular factors of differences in skill-levels of five tested traits. It e.g. identified association with neuroanatomy of a language-related brain area via neuroimaging correlation. The data contributes to identifying or understanding the biological basis of this recently evolved characteristic capability.

Human brain

Further information: Cranial capacity and Brain-to-body mass ratio

One of the prominent ways of tracking the evolution of the human brain is through direct evidence in the form of fossils. The evolutionary history of the human brain shows primarily a gradually bigger brain relative to body size during the evolutionary path from early primates to hominids and finally to Homo sapiens. Because fossilized brain tissue is rare, a more reliable approach is to observe anatomical characteristics of the skull that offer insight into brain characteristics. One such method is to observe the endocranial cast (also referred to as endocasts). Endocasts occur when, during the fossilization process, the brain deteriorates away, leaving a space that is filled by surrounding sedimentary material over time. These casts, give an imprint of the lining of the brain cavity, which allows a visualization of what was there. This approach, however, is limited in regard to what information can be gathered. Information gleaned from endocasts is primarily limited to the size of the brain (cranial capacity or endocranial volume), prominent sulci and gyri, and size of dominant lobes or regions of the brain. While endocasts are extremely helpful in revealing superficial brain anatomy, they cannot reveal brain structure, particularly of deeper brain areas. By determining scaling metrics of cranial capacity as it relates to total number of neurons present in primates, it is also possible to estimate the number of neurons through fossil evidence.

Facial reconstruction of a Homo georgicus from over 1.5 Mya

Despite the limitations to endocasts, they can and do provide a basis for understanding human brain evolution, which shows primarily a gradually bigger brain. The evolutionary history of the human brain shows primarily a gradually bigger brain relative to body size during the evolutionary path from early primates to hominins and finally to Homo sapiens. This trend that has led to the present day human brain size indicates that there has been a 2-3 factor increase in size over the past 3 million years. This can be visualized with current data on hominin evolution, starting with Australopithecus, a group of hominins from which humans are likely descended. After all of the data, all observations concluded that the main development that occurred during evolution was the increase of brain size.

However, recent research has called into question the hypothesis of a threefold increase in brain size when comparing Homo sapiens with Australopithecus and chimpanzees. For example, in an article published in 2022 compiled a large data set of contemporary humans and found that the smallest human brains are less than twice that of large brained chimpanzees. As the authors write '...the upper limit of chimpanzee brain size is 500g/ml yet numerous modern humans have brain size below 900 g/ml.' (Note that in this quote, the unit g/ml is to be understood not in the usual way as gram per millilitre but rather as gram or millilitre. This is consistent because brain density is close to 1 g/ml.) Consequently, the authors argue that the notion of an increase in brain size being related to advances in cognition needs to be re-thought in light of global variation in brain size, as the brains of many modern humans with normal cognitive capacities are only 400g/ml larger than chimpanzees. Additionally, much of the increase in brain size - which occurs to a much greater degree in specific modern populations - can be explained by increases in correlated body size related to diet and climatic factors.

Australopiths lived from 3.85 to 2.95 million years ago with the general cranial capacity somewhere near that of the extant chimpanzee—around 300–500 cm³. Considering that the volume of the modern human brain is around 1,352 cm³ on average this represents a substantial amount of brain mass evolved. Australopiths are estimated to have a total neuron count of ~30-35 billion.

Progressing along the human ancestral timeline, brain size continues to steadily increase (see Homininae) when moving into the era of Homo. For example, Homo habilis, living 2.4 million to 1.4 million years ago and argued to be the first Homo species based on a host of characteristics, had a cranial capacity of around 600 cm³. Homo habilis is estimated to have had ~40 billion neurons.

A little closer to present day, Homo heidelbergensis lived from around 700,000 to 200,000 years ago and had a cranial capacity of around 1290 cm³ and having around 76 billion neurons.

Homo neaderthalensis, living 400,000 to 40,000 years ago, had a cranial capacity comparable to that of modern humans at around 1500–1600 cm³on average, with some specimens of Neanderthal having even greater cranial capacity. Neanderthals are estimated to have had around 85 billion neurons. The increase in brain size topped with Neanderthals, possibly due to their larger visual systems.

It is also important to note that the measure of brain mass or volume, seen as cranial capacity, or even relative brain size, which is brain mass that is expressed as a percentage of body mass, are not a measure of intelligence, use, or function of regions of the brain. Total neurons, however, also do not indicate a higher ranking in cognitive abilities. Elephants have a higher number of total neurons (257 billion) compared to humans (100 billion). Relative brain size, overall mass, and total number of neurons are only a few metrics that help scientists follow the evolutionary trend of increased brain to body ratio through the hominin phylogeny.

In 2021, scientists suggested that the brains of early Homo from Africa and Dmanisi, Georgia, Western Asia "retained a great ape-like structure of the frontal lobe" for far longer than previously thought – until about 1.5 million years ago. Their findings imply that Homo first dispersed out of Africa before human brains evolved to roughly their modern anatomical structure in terms of the location and organization of individual brain regions. It also suggests that this evolution occurred – not during – but only long after the Homo lineage evolved ~2.5 million years ago and after they – Homo erectus in particular – evolved to walk upright. What is the least controversial is that the brain expansion started about 2.6 Ma (about the same as the start of the Pleistocene), and ended around 0.2 Ma.

Evolution of the neocortex

Further information: Neocortex

In addition to just the size of the brain, scientists have observed changes in the folding of the brain, as well as in the thickness of the cortex. The more convoluted the surface of the brain is, the greater the surface area of the cortex which allows for an expansion of cortex. It is the most evolutionarily advanced part of the brain. Greater surface area of the brain is linked to higher intelligence as is the thicker cortex but there is an inverse relationship—the thicker the cortex, the more difficult it is for it to fold. In adult humans, thicker cerebral cortex has been linked to higher intelligence.

The neocortex is the most advanced and most evolutionarily young part of the human brain. It is six layers thick and is only present in mammals. It is especially prominent in humans and is the location of most higher level functioning and cognitive ability. The six-layered neocortex found in mammals is evolutionarily derived from a three-layer cortex present in all modern reptiles. This three-layer cortex is still conserved in some parts of the human brain such as the hippocampus and is believed to have evolved in mammals to the neocortex during the transition between the Triassic and Jurassic periods. After looking at history, the mammals had little neocortex compared to the primates as they had more cortex. The three layers of this reptilian cortex correlate strongly to the first, fifth and sixth layers of the mammalian neocortex. Across species of mammals, primates have greater neuronal density compared to rodents of similar brain mass and this may account for increased intelligence.

Theories of human brain evolution

Explanations of the rapid evolution and exceptional size of the human brain can be classified into five groups: instrumental, social, environmental, dietary, and anatomo-physiological. The instrumental hypotheses are based on the logic that evolutionary selection for larger brains is beneficial for species survival, dominance, and spread, because larger brains facilitate food-finding and mating success. The social hypotheses suggest that social behavior stimulates evolutionary expansion of brain size. Similarly, the environmental hypotheses suppose that encephalization is promoted by environmental factors such as stress, variability, and consistency. The dietary theories maintain that food quality and certain nutritional components directly contributed to the brain growth in the Homo genus. The anatomo-physiologic concepts, such as cranio-cerebral vascular hypertension due to head-down posture of the anthropoid fetus during pregnancy, are primarily focused on anatomic-functional changes that predispose to brain enlargement.

No single theory can completely account for human brain evolution. Multiple selective pressures in combination seems to have been involved. Synthetic theories have been proposed, but have not clearly explained reasons for the uniqueness of the human brain. Puzzlingly, brain enlargement has been found to have occurred independently in different primate lineages, but only human lineage ended up with an exceptional brain capacity. Fetal head-down posture may be an explanation of this conundrum because Homo sapiens is the only primate obligatory biped with upright posture.