#74. Extended Theory of Mind [Evolution]

EV

Red, theory; black, fact.

Where is evolution going at the moment? Pretty good question. Let us look around, then. I am writing this in a submarine sandwich joint where one sandwich maker is serving two customers. The radio brings in a ballad by a lady vocalist at a tempo suggestive of sex. Now a DJ (Mauler or Rush) is amusing the listeners with some patter. The window shows that rush hour is over and only a few home-bound stragglers are in the street. If I crane my neck, I can see the green beacon on the new electric charging station. 

That will do for starters. Sandwich maker, pro singer, DJ, bureaucrat, electrician—I couldn’t do any of that. We are a society of specialists, and such societies feature differentiation with integration. So, how far back does this go? At most, nine millennia; about 450 generations. Time enough for evolution? Doesn’t matter; we want direction here, not distance.

Contemporary natural selection of humans will therefore reward differentiability and integratability.

Differentiability: vocational choices often begin in childhood with hobbies, and there is a certain frame of mind associated with hobbies called “flow.” I therefore suggest that we are being selected for a susceptibility to flow. 

Integratability: society is held together by our ability to coordinate with others, and the key ability here is thought to be “theory of mind,” or the ability to infer the mental states of those with whom we interact. Likewise, we are being selected for theory-of-mind ability.

I would like to suggest that there is something higher than theory of mind, which not everyone possesses at this time: extended theory of mind: inferring the mental states of those not present, and whose very existence is itself inferred. A society strong in this trait will appear to be communicating with one another through solid walls, as if by ESP. 

Who are these Chosen? Probably military generals, politicians, and the executive class. Go figure.

However, the human cranium is probably as voluminous as it can get and still allow childbirth, so the gray matter subserving the new ability will have to be included at the expense of some other, preferably obsolete ability, like accuracy in spearing game animals.

So challenge your mayor to a game of darts and see how he does. This theory is falsifiable.

Photo by Le Vu on Unsplash

#69. Storming South [Evolution]

EV

Red, theory; black, fact.

This is a theory of the final stages of human evolution, when the large brain expansion occurred.

At least, they did. Sorry, I don't belong to this species. The Linnaean binomial literally means "wise man." What would be the Latin for "wise guy"?

Homo sapiens: created by ice

H. sapiens appears to have arisen from Homo erectus over the last 0.8 million years due to climate instability in the apparent origin area, namely East Africa. During this time, Europe was getting glaciated every 0.1 million years because of the astrophysical Milankovitch cycle, a rhythm in the amount of eccentricity in the Earth's orbit due to the influence of the planet Jupiter.

However, I am thinking of the hominins who had settled in Europe (or Asia, it doesn't matter for this argument) during the interglacial periods (remember that H. erectus was a great disperser) and when the ice began advancing again, were now facing much worse cooling and drying than in Africa, and thus much greater selection pressures. At least during the last continental glaciation, the ice cap only extended to the Baltic Sea at the maximum, but long before the ice arrives, the land is tundra, which can support only a very thin human population. In any given glaciation, the number of souls per hectare the land could support was relentlessly declining in northern Europe/Asia, and eventually the residents had to get out of Dodge City and settle on land further south, almost certainly over the dead bodies of the former owners. This would have selected Europeans or Asians for warlike tendencies and warfaring skills, which explains a lot of human history. 

Our large brains

However, our large brains seem to be great at something else besides concocting Games of Thrones: that is, environment modification. It's a no-brainer that the first thing someone living in the path of a 2-km wall of ice needs is to keep from freezing to death, and this would have been the first really good reason to modify environments. Unlike chipping a stone axe, environment modification involves fabricating something bigger than the fabricator. Even a parka has to be bigger than you or you can't get into it. This plausibly would have required a larger brain to enable a qualitatively new ability: making something you can't see all at once when it is at working distance.

Our rhythmic evolution

After parkas, early northerners might have evolved enough association cortex (maybe on the next glaciation cycle) to build something a little bigger, like a tent or a lean-to. On the next cycle, they might have been able to pull off a decent longhouse made of wattle. On the next, a jolly good castle surrounded by cultivated lands and drainage ditches. These structures would have delayed the moment of decision when you have to go and take on the Pleistocene-era Low-brows to the south. This will buy you time to build up your numbers, and I understand that winning battles is very much a numbers game. Therefore, environment modification skill would have been selected for in tandem with making like army ants.

Where is the fossil evidence for this theory?

Why do we not find fossil evidence of all this in Europe or Asia? <05-19-2022: Actually, we do: the Neanderthals and Denisovans, who have been difficult to account for in terms of previous theories of human origins.> My scenario can be defended against the inconvenient fossil evidence for a human origin in East Africa in general terms, by citing the well known incompleteness of the fossil record and its many biases, but, of course, I want details. Note, however, what else is in East Africa: the Suez, a land bridge to both Europe and Asia via the Arabian tectonic block, which was created by plate tectonics near the end of the Miocene, thus antedating both H. sapiens and H. erectus. Not only can hominins disperse through it to other continents during interglacials, but they can come back in, fiercer and brainier than before, when the ice is advancing again, to then deposit their fossil evidence in the Rift Valley region of East Africa. The Eurasian backflow event of 3000 years ago may be a relatively recent example of this. The Isthmus of Suez is low-lying and thus easily drowned by the sea, but the probability of this was minimal at times of continental glaciation, when sea levels are minimal. I assume that early hominins expanded like a gas into whatever continent they could access. Increasing glaciation/tundrafication of that continent would have recompressed the "gas" southward, causing it to retrace its path, partly back into Africa. 

Pleistocene selection pressures

To reiterate, this process would have been accompanied by great mortality and therefore, potentially, much selection. Moreover, during the period we are considering, temperatures were declining most of the time; the plot of temperature versus time has a saw-tooth pattern, with long declines alternating with short warming events, and it is the declines that would have been the times of natural selection of hominins living at high latitudes.

Plebius sapiens.

A limestone block in Canada showing scratches left by stones
embedded in the underside of a continental glacier.
The rock has also been ground nearly flat by the same process. Scary.

Glaciated boulder by night. Have a nice interglacial.

#64. The Drill Sergeants of the Apocalypse [evolutionary psychology, population]

EP     PO     

Red, theory; black, fact.

Seen in a hospital ward.

Updated 10-30-2024

The trickster type may really be a penetration tester. 

The type probably emerges in contexts of unequal power (Elmer Fudd has the shotgun; Bugs Bunny doesn’t). Thus, an abiding fear is the soil out of which tricksterism grows, by the following positive feedback:

A successful trick shows up the Fudds and shows them in a feckless light, which reduces the fear level of the trickster, which reinforces trick-playing. This is a short-term high that comes at the expense of worse relations with the Fudds and thus eventually even greater fear levels for the tricksters, which they try to remedy with still more tricks.

An example of an unequal power relationship is between a foreign invader and the defenders. Invasion is such a common event in history that by now, countermeasures will have evolved. Tricksterism is likely to be a tile in the mosaic of any such adaptation.

A biological precedent for penetrations testing?

Evidence for a biological precedent may be the many retroviruses integrated into the human genome. Presumably, one of these becomes active now and then at random and kills the host cell if the anti-viral defenses of the latter have become weak due to some somatic mutation. The red team-blue team strategy seems to be too good a trick for nature to miss (TGTNM).

Evolution of the trickster

09-27-2020: Modern human populations may have two (independent?) axes of political polarization: oppressor-oppressed and trickster-control freak. The first may sub serve dispersal by generating refugee groups and the second may sub serve building. Any built thing must serve in a complex world in which many constraints must be simultaneously observed. Thus, after the initial build, a long period of tweaking must typically follow. The role of the tricksters is to powerfully motivate this tweaking before the complacency of the control-freak builders leads to disaster. <03-12-2021: This may have been how engineering was done by an archaic version of Homo sapiens.><12-02-2022: The tricksters can also make mistakes, causing damage that cannot have a silver lining in any possible world, and moving to correct this is a natural role of the builders. If you are a builder, ask this: “What is the best use of my indignation?” It is to keep to a strict harm-reduction approach.><01-08-2024: Tricksterism can intensify into sadism, in which the protagonist takes pleasure in the victim’s torment and wants to make it last. Well, boy, if you make it last, you are giving the victim plenty of time and motivation to figure out solutions, like a patient old instructor giving his pupil his lessons one at a time, as he is ready for them, and this is how the wise victim will construct the situation. Such a victim will end up with information and know-how others will pay for.>

A tangent about our evolutionary context

Our evolutionary forebears may have been champion dispersers for a long time <12-21-2020: i.e., Homo erectus*> before the ice age** forced some of them to become champion builders (initially, of shelters and warm clothing). <12-31-2020: "champion environment modifiers" may be closer to the mark than "champion builders"> It is an interesting fact that physically, humans exceed all other animals only in long-distance running, which can be read as dispersal ability. Our carelessness with preserving the local environments and our propensity for overpopulation can be read as typical r-selected disperser behavior. <12-21-2020: The r-selecting niche was probably big game hunting. H. erectus sites indicate consumption of medium and large meat animals. Overhunting would have occurred routinely, due to the slow reproduction rates of large animals and the high hunting efficiency of H. erectus due to tool use, so that dispersal of the hunters to new habitats would likewise have been routine.>

* H. erectus: lived 2 million years ago to 100,000 years ago. H. sapiens: earliest fossils, 300,000 years old. Evidence of behavioral modernity: 100,000–70,000 y ago.

** that is, the Pleistocene ice age, itself a sequence of 5 successive continental glaciations (by oxygen isotope evidence) separated by temperate periods, starting 2.6 million years ago and thought to be not over yet. Over the past 800,000 y, continental glaciation has happened rhythmically on a 100,000-y cycle due to astronomical factors (Milankovitch cycle). Selection for building skill may therefore have occurred in multiple successive episodes over the course of the Pleistocene.

# 59. Disaster Biology [evolution, evolutionary psychology]

EV     EP     

Red, theory; black, fact.

• The habitat is a unit of selection, leading to group selection.
• Much of evolution proceeds by an accumulation of founder effects, especially altruism in sexually reproducing species.
• Opportunities for colonization of recently-emptied habitats are ephemeral.
• Under disaster-prone conditions, this leads to selection pressure for migrant production and evolvability (i.e., a high rate of evolution, especially founder-effect evolution).
• Language diversification in humans is an evolvability adaptation.
• It works by preserving genetic founder effects from dilution by late-coming migrants, whose reproduction is held back by the difficulties of learning a new language. 
• Xenophobia and persistent ethnicity markers (PEMs) can be explained in the same way.
• The spread of linguistic and  PEM novelties in a population is predicted to be especially fast in newly colonized, previously empty habitats. <09-17-2020: Alternatively, the linguistic novelties may start as a thick patois developed by an oppressed group in the home habitat prior to becoming refugees, as a way to make plans under the noses of the oppressing group.>
•  Refugee-producing adaptations sub serving dispersal can be called "tough altruism."
• Populations producing more refugees are more likely to colonize further empty habitats, a selective advantage.
• Disaster biology may be what is conceptually missing from theories of the origin of life (abiogenesis). 01-02-2020: i.e., the forerunners of the first cells may have been spores.>
• Photo by Purnomo Capunk on Unsplash

#57. Where are All the Space Aliens? [evolution]

EV

Red, theory; black, fact.

KIRK MUST DIE! (cut to commercial.)

Astronomical observations and the Fermi paradox

Contemporary exoplanet research keeps turning up extra-solar-system planets that seem to be promising abodes of life of the Earthly variety (never mind the completely weird biochemistries that may exist on other planets). In the habitable exoplanets catalogue (HEC), kept by the Planetary Habitability Laboratory (University of Puerto Rico) at Arecibo, the list of planets found orbiting in the conservative habitable zone now has 17 entries, and a 2013 paper by Petigura et al. ("Prevalence of Earth-size planets orbiting Sun-like stars") placed the percentage of stars in our galaxy with potentially habitable planets at 22 ± 8. Accumulating evidence suggests that life is common in our galaxy, yet SETI research—the search for extraterrestrial civilizations that send out radio signals that bear some stamp of intelligence—has drawn a complete blank, as far as I know. (And if it did find something, it would make such a sensation in the media that no-one could help knowing.) So I ask you: where are all the space aliens? (This question is generally attributed to 20th-century physicsmeister Enrico Fermi and has since become known as the Fermi Paradox.)

My hypothesis is this:

Life is one thing; intelligent life is quite another. This is a form of the Rare Earth hypothesis, which is one of the avenues that has been explored through the years in the search for a resolution of the Fermi Paradox.

Biospheres may not be permanent 

No doubt there are many, many planets in our part of the galaxy that have some form of primitive life, and many, many more "graveyard planets" that once had life but are now sterile. Mars may well be an example of this kind of planet in our own solar system.

Biochallenge!

I conjecture that if we seem to be alone in this part of the galaxy, based on the negative SETI evidence, it is because we are, and this is because we have evolved to the level of intelligence first in this galactic neighborhood, because evolution on the Earth is egregiously rapid. It has taken us four billion years to get this far, which doesn't sound so fast, but everything is relative. This rapid evolution is plausibly a response to challenges: all the various natural disasters we are subject to here on Earth, examples being bolide (meteor) crashes, continental glaciations, drifting continents, droughts, earthquakes, floods, hurricanes, long climatic warm spells, tornadoes, tsunamis, volcanism, wild weather, wildfires, and winter.

Sept 23, 2018: Tornadoes knock out primary transformer station in Ottawa.

Case in point: a large bolide strike is believed to have triggered the extinction of the dinosaurs, making way for the rise of the mammals, and we ourselves are the descendants of those mammals. <03-21-2020: The bolide may have killed the dinosaurs indirectly, by touching off a climate shift in our dangerously unstable world. This would explain the temporary presence of dinosaur fossils above the Cretaceous/Tertiary iridium anomaly, which has been a problem for the bolide hypothesis.>

Case in point: the rise of modern humans seems to have coincided with the end of the last continental glaciation. The rigorous, cold-climate conditions prevailing then might have selected our ancestors for high ability in building shelters and sewing protective clothing. These skills might have required the rapid evolution of a high ability to process spatial information, which we then leveraged into the building of civilizations upon the return of temperate climatic conditions. (See: #24, "The Pictures in Your Head," this blog.)

To contrive a planet that is so challenging and difficult, yet has not succeeded in destroying life altogether in four billion years, may require a very rare combination of parameters (e.g., our distance from the sun, the size and composition of the Earth, the presence of the asteroid belt, the presence of the Oort cloud), and this rarity has led to our emerging into intelligence before it happened anywhere else in this part of the galaxy.

01-08-2020: These parameters may well have special values at which critical behavior occurs, such as the onset of positive feedbacks leading to heating or cooling. Earth may be simultaneously close to several of these critical points, a rare circumstance, but one that does not require extreme, atypical values of any given variable.

My take on the Rare Earth hypothesis therefore emphasizes what are called "evolutionary pumps" (e.g., glaciations, bolide crashes, etc.) in discussions of this hypothesis, as well as the anthropic principle.

August 28, 2011: An Ottawa sunset inflamed by a recent hurricane in the USA.

Evil-ution

I further conjecture that the difficulties of our past have left their mark on us, and we call it "evil." (Some will deny that this concept has any construct validity, saying, "It's not a thing," but I think that it is an approximate version of something that does, which I term "dispersalism" in this blog.) This is because a basic strategy for surviving disasters is dispersal, which I have previously linked to evil in these pages (See: #35, "The Pilgrim and the Whale," and #37, "Two Kinds of War," this blog).

To recapitulate, our planet's predilection for disaster has deeply ingrained dispersal tendencies into most species here, by the mechanism of natural selection. Humans now get their food from agriculture. However, agriculture requires a settled existence and is therefore in opposition to dispersal, so the plot thickens.

This characteristic of agriculture results in the psychological pressure for dispersal relentlessly building, pressure-cooker fashion, across time, until a destructive explosion occurs (war or revolution), thereby accomplishing the long-delayed dispersal.

May 21, 2022 derecho-storm damage in Ottawa.

Wildfire smoke seen in Ottawa, Jun 2023.

#53. Advanced Human Depopulation Model [Population, Evolutionary Psychology]

Picture 1: A four-stage model of a human depopulation event. C = cycle; growth = growth phase; depop = depopulation

PO     EP     

Red, theory; black, fact

I present in Picture 1 a four-stage model of human depopulation events that is intended to account for more data. The same two emotional programs, the anger cycle and the sadness cycle (see post #41), occur in two "generations," with the second generation having greater violence and using modified signals.

• Stage 1: depopulation by emigration; accomplishes dispersal of the human species; coordinated by an exchange of anger signals;
• Stages 2-4: depopulation by mass murder: accomplishes long-term population density confinement within limits;
• Stage 2: coordinated by an asymmetric exchange of contempt and sadness signals; has similarities with cannibalism;
• Stage 3: total war program; coordinated by an exchange of anger signals with mimicry added;
• Stage 4: loss of civilization; triggered by a repudiation of the social contract by trusted elites with grudges: coordinated by increasing paralysis on the part of victims and increasing cynicism on the part of perpetrators. May be too recent an evolutionary development to have an efficient halting signal.

Nevertheless, the modes of worship of Islam are the best place to look for such a signal (06-02-2019: or other remedy) if it exists. 

In this connection, the Islamic prayer discipline has extraordinary potential to alter brain physiology, based on variations in blood flow to this organ, known to be highly sensitive to same. The variations would come about as a result of the highly regimented posture changes occurring during Islamic prayer. I have coded these postures according to the probable effect on blood pressure measured at the brain, and the result looks like this:

Picture 2. The inferred brain physiology of Islamic prayer. Source of data: YouTube, "Time to pray with Zacky," accessed 05-23-2019.

 Shown are my inferred variations in brain oxygenation during two rakat, or units of prayer. Bowing is coded the same as sitting, namely 1. Prostration is coded as 2 and standing is coded as 0. Some forms of Islam prescribe up to 19 rakat per day. Special procedures (Sujud Sahwi) exist for fixing prayers performed erroneously due to "forgetfulness" but this "forgetfulness" I find suggestive of temporary brain dysfunction due to lack of oxygen from getting up too quickly, possibly at about minute 2, above.

06-02-2019: Unprompted revision for clarity and sensitivity: The above observation is to help establish that Islamic prayer manipulates a variable that matters, always an important issue at the outset of a research project. You don't want to waste taxpayer money blindly researching variable after variable and concluding at great expense merely that none of them was relevant.

#51. A Theory of Christianity [Evolutionary Psychology, Population]

EP     PO     

Red, theory; black, fact.

My gut told me that there is more to be said about Christianity than what I wrote or implied in Post #50. My doubts about the completeness of my work began with this statement by Saint Paul:

“And if Christ be not risen, then is our preaching vain, and your faith is also vain.”

1 Corinthians 15:14, KJV

I was struck by the clarity and insistence of this impossible claim. What is going on here? We as theoreticians need to drill down here.

“Risen” means having come back from the dead, which is still an impossibility for modern medicine. However, Paul explains that what dies is a “natural body,” whereas what rises, or is “resurrected,” is a “spirit body,” which is “incorruptible.” The word “resurrection” does not appear in the Old Testament (Hebrew Bible), making its first appearance in Matthew, the first book of the New Testament. All things considered, the concept is obviously central to Christianity.

Postulate 1: Resurrection theology is an approximate theory, and as such, is allowed to contain an impossibility.

Postulate 2: Christianity is focused on taming a third stage of depopulation that follows the anger cycle and the sadness cycle if neither of these has returned population density to the reset value after a certain time (See Post #50 for explanations of these terms.). This is the total war stage, and it takes place on an international scale. Examples are WWI and WWII, which would be the international phases of national conflicts between a central-European majority and Serbs and Jews, respectively. Total war is arguably altruistic because each of two alliances or countries is helping the other with their population problem. The required signaling cycle seems to be that of the anger cycle but with the exchanged signals doing double duty as liquidation tactics. This is not just a fight, where the only consideration is what would be the shrewdest blow; there is a strong tendency to ape the opponent’s latest gambit, as expected in an exchange of signals "designed" to lock non-altruists out of the process. This psychology is called “sending back the bullet” in battlefield situations and “poetic justice” in everyday life. It is satisfying and it is a signal and it is illegal in peacetime, no matter that the other guy started it. In peacetime, you have to search elsewhere for your solutions than in mimicry and cooperation with a dangerous emotional program.

Furthermore, if you allow yourself to be drawn into a vendetta, you just wrote an “ = “ between yourself and the person you take exception to.

05-06-2022: The old, skeptical explanation of the resurrection, namely that the crucifixion was a fraud, deserves mention here. The New Testament mentions particular Romans and Pharisees sympathetic to Jesus. Extrapolating, I posit a pro-Jesus faction spanning all segments of that society and including many influential Romans and Pharisees, who would have had the resources necessary to pull off such a deception, but who could not openly interdict the crucifixion for lack of the necessary influence. Thus, the seeming miraculousness of the resurrection would in reality be a measure of the power of the illusion that groups identified as “The Enemy” are implacable and unitary. 

The total war program is well known for its destructiveness to the infrastructures of civilization, which suggests that the program evolved recently and is still being refined by natural selection. It may not even be older than agriculture, the last quantum leap in our ability to increase our numbers. That new ability may have generated the selection forces that brought forth the total war program.

Christian theology works a rational override on the anger cycle (See Post #41) by reassuring believers that they will be resurrected and therefore need not fear death. Since anger is fear in disguise, this reassurance undercuts the anger-cycle-like dynamics of the total war program.

Postulate 3: the corresponding exact theory of Christianity is that depopulation events always leave survivors and Christianity enhances your probability of being one of them. When population density has declined to the reset value, this should trigger a dramatic turnaround in the Zeitgeist from death-producing attitudes to nurturing ones, to start the population-density curve on its next long, slow upward climb. The resurrection of “spirit bodies” may refer to the re-establishment of life-valuing attitudes in Society.

03-25-2019: It follows that the human race is being selected for a predisposition to Christianity, and probably other religions as well.

The book of Revelation, the last book in the New Testament, appears to describe the sudden depopulation event that ends the population-density cycle. This is wrongly identified as the end of time/history, but remember that we deal here with an approximate theory.

Christian worship activities revolve around the Eucharist, a communal sharing and consumption of bread and wine. Its purpose is to eradicate the deepest roots of the fear of death, a fear that leads to the hatreds of the total-war emotional program. How does it work?

The Eucharist pacifies people by exposing them to the halting signal of the total war program. So, it halts. How did the consumption of bread and wine come to be the halting signal? Because they are made by people “playing with their food,” for the sake of variety, one imagines. However, this comes at the cost of caloric content (not caloric density) because the yeast always takes its cut. This practice will only make sense under conditions of plenty, which return with sufficient depopulation. Thus, alcohol (which I assume to be the active signaling ingredient) and leavened bread now signal to the human limbic system the return of abundance. I conjecture that these signals have a subtle pacifying effect, making it easier to resist tit-for-tat total-war signalling.

03-02-2024: Alternatively, Jesus may have been medicating the disciples with food and alcohol to keep their arousal level out of the panic zone at a time of peak emotion so that they could continue to function adaptively.

#45. The Denervation-supersensitivity Theory of Mental Illness [neuroscience, evolution, genetics]

NE     EV     GE     

Red, theory; black, fact.

People get mental illness but animals seemingly do not, or at least not outside of artificial laboratory models such as the unpredictable, mild-stress rodent model of depression. A simple theory to account for this cites the paleontological fact that the human brain has been expanding at breakneck speed over recent evolutionary time and postulates that this expansion is ongoing at the present time, and that mental illness is the price we are paying for all this brain progress.

In other words, the mentally ill carry the unfavorable mutations that have to be selected out during this progress, and the mutation rate in certain categories of mutation affecting human brain development is elevated in modern humans by some sort of "adaptive" hot-spot system. "Adaptive" is in scare quotes here to indicate that the adaptation inheres in changes in the standard deviation of traits, not the average, and is therefore not Lamarkian.

In brain evolution, the growth changes in the various parts very probably have to be coordinated somehow. I conjecture that there is no master program doing this coordination. Rather, I conceive of the human brain as comprising scores of tissue "parcels," each with its own gene to control the final size that parcel reaches in development. (This idea is consistent with the finding of about 400 genes in humans that participate in establishing body size.) All harmonious symmetry, even left-right symmetry, would have to be painstakingly created by brute-force selection, involving the early deaths of millions of asymmetrical individuals. This idea was outlined in post 10.

Assuming that left and right sides must functionally cooperate to produce a fitness improvement, mutations affecting parcel growth must occur in linked, left-right pairs to avoid irreducible-complexity paradoxes. I have previously conjectured in these pages that the crossing-over phenomenon of egg and sperm maturation serves to create these linked pairs of mutations, where the two mutations are identified with the two ends of the DNA segment that translocates. (See "Can Irreducible Complexity Evolve?")

Most of the evolutionary expansion of the human brain appears to be focused on association cortex, which I conjecture implements if-then rules, like those making up the knowledge bases familiar from the field of artificial intelligence. The "if" part of the rule would be evaluated in post-Rolandic cortex, i.e., in temporal and parietal association cortices, and the "then" part of the rule would be created by the pre-Rolandic association cortex, i.e., the prefrontal cortex. The white matter tracts running forward in the brain would connect the "if" part with the "then" part, and the backward running white-matter tracts would carry priming signals to get other rules ready to "fire" if they are commonly used after the rule in question.

Due to such tight coordination, I would expect that the ideal brain will have a fixed ratio of prefrontal cortex to post-Rolandic association cortex. However, the random nature of the growth-gene bi-mutations (perhaps at mutational hot-spots) permitting human brain evolution will routinely violate this ideal ratio, leading to the creation of individuals having either too much prefrontal cortex or too much temporal/parietal cortex. In the former case, you will have prefrontal cortex starved of sensory input. In the latter case, you will have sensory association cortex starved of priming signals feeding back from motoric areas.

Denervation supersensitivity occurs when the normal nerve supply to a muscle is interrupted, resulting in a rapid overexpression of acetylcholine receptors on the muscle. This can be seen as an attempt to compensate for weak nerve transmission with a tremendous re-amplification of the signal by the muscle. Analogous effects have been found in areas of the cerebral cortex deprived of their normal supply of sensory signals, so the effect seems to be quite general.

In cases of genetically-determined frontal-parietal/temporal imbalance, I conjecture that the input-starved side develops something like denervation supersensitivity, making it prone to autonomous, noise-driven nervous activity.

If the growth excess is in sensory association cortex, this autonomous activity will manifest as hallucinations, resulting in a person with schizophrenia. If the growth excess is in the prefrontal cortex, however, the result of the autonomous activity will be mania or a phobia. Depression may originally have been an adaptation to the presence of a man-eating predator in the neighborhood, but in civilized contexts, it can get activated by the unpredictable (to the sufferer) punishments resulting from manic activity. If the mania is sufficiently mild to co-exist with depression, as in type II bipolar disorder, then the overall effect of the depressive component may be like a band-aid on the mania.

The non-overgrown association cortex might even secondarily develop the opposite of denervation supersensitivity as the result of continual bombardment with autonomous activity from the other side of the Rolandic fissure. This could account for the common observation of hypoprefrontality in cases of schizophrenia.