Chapter 2: The Value of Intelligence in Nature

Intelligence in Nonanimals

It is a very common assumption that intelligence is an adaptive trait that has survival value but no survival costs. Many scientists naively assume that all animals would be better off if they were smarter. As this book will show, this is just not the case. Some circumstances are favorable to advanced intelligence, but others are unfavorable. All animal species alive today made it this far because they have been successful in the past. Of course, this includes the not-so-intelligent species. We also know that the vast majority of organisms on the planet do not have brains. Not a single species from the other 5 kingdoms of life (bacteria, archaea, protists, plants, fungi) has any kind of nervous system at all. And yet, they thrive. As you can see in the table below, each of these kingdoms are more numerous, in terms of total number of individuals, total number of species, and total biomass than animals are.

Kingdom	Number of Species	Biomass in gigatons of carbon
Plants		450
Bacteria		70
Fungi		12
Archaea		7
Protists		4
Animals		2
Viruses		.2

Tabe 2.1: The biomass on Earth is 550 billion tons (gigatons) of carbon. The amount contained in each of the Kingdoms of life is listed in descending order.

In a similar way, the least intelligent animals far outnumber the most intelligent. Arthropods, such as insects and crustaceans, are the most successful animals in terms of number of species and number of individuals, but none of them have large brains. If advanced intelligence was a failsafe strategy, then all organisms would have tended toward it (or been replaced by it) during the 3.8 billion years of evolution on Earth. But it took three billion of those years for brains to even form. Intelligence is not foolproof, and much like body size, it has both benefits and costs. You may find the concept counterintuitive at first, but this book should influence you to consider how minimizing intelligence can be adaptive.

The Brains of Blind People

I don’t believe the condition of being blind was adaptive during human evolution. Only two to three out of every 10,000 newborns are blind, indicating that congenital blindness was not actively selected. Although this may not be entirely true, it is certain that blind brains are fabulous cases of neurodiverse processing. People with blindness invariably develop proficiencies that they would have never developed had they not been blind. Studies have shown that if the visual cortex is not sent visual information from the eyes, it will lend its circuits to processing information from other senses. I wish I could experience what it is like to have the visual cortex, a large and highly complex system, repurposed to more thoroughly analyze touch, hearing and other modalities. I feel that much of my thinking is dominated by vision, and it makes me wonder what it is like for blind people to have entire dimensions of thought that are unavailable to me. These dimensions contribute to the achievements of blind people. Consider blind musical prodigies such as Stevie Wonder, Nobuyuki Tsujii, Diane Schuur, Andrea Bocelli, and Ray Charles. 

It is clear that a blind animal would have much difficulty surviving in the wild. The same may be true of albinism. Albino humans are highly susceptible to severe sunburns and experience other hardships that could have seriously compromised their ability to reproduce. Consistent with the idea that these disorders were not naturally selected, their incidence is very low. Albinism occurs in only .5 per 10,000 live births. However, humans may be susceptible to blindness and albinism today because of adaptive qualities they may have conferred to a distant vertebrate ancestor.

Both blindness and albinism can be adaptive animals living today. Let’s talk about why.

Blind Cave Fish

Species of cave-dwelling animals, such as fish, salamanders, and crickets, can lose their eyesight after many years in the dark. Because the eyes are not being used, they are not needed. It is an example of when evolution tends away from complexification and toward simplification. This is not a case of “devolution” because evolution is a non-directional process. There is no reason why an animal will not trend toward simplicity if that makes it better suited to its environment. Despite this, cave blindness is often referred to as a “regressive trait” because an evolved capacity is lost.

Eyes are useless to an animal living in pure darkness and can be a disadvantage because of their energy requirements. It takes a steady supply of blood and glucose to keep eyes running. In the case of fish, blindness has evolved independently in several different species. Depending on how much time their population has spent in the dark, blind cavefish can have either smaller eyes, degenerated eyesight, or no eyes at all. It takes thousands of generations of cave life for eyes to be lost altogether. The fish also generally have no pigmentation. Again, they lose pigmentation because they don’t need it, causing them to resemble an albino. Cavefish also often lose their scales and swim bladder.

Despite the fact that cave blindness is a “regressive trait” the fish also have “constructive traits.” These include having a better olfactory sense by having taste buds covering their heads. As you might expect, cavefish brains can be different in many ways. They are often around 30% smaller than those of similar species. Again, because their niche on the food chain is simpler they can afford to have a shrunken brain which helps to save calories. However, not all brain parts shrink. Some brain areas may be larger. The Mexican cavefish has a larger teleost gustatory center which helps it make finer taste discriminations. Other senses can be enhanced, such as sensing vibrations, mouth suction echolocation, chemoreception, and electroreception. Species restricted to the cave habitat for long time periods generally show more of these specialized adaptations. Each cavefish species has evolved differently and has its own peculiarities and behavioral proclivities. A systematic comparison of their brains could enlighten the study of human neurodiversity.

Blind cavefish are often the top predators in their little ecosystems, eating a variety of small invertebrates. Deep caves are too dark for plants to grow in, so some cavefish may eat only a few weeks out of the year when seasonal floods bring in nutrients. Metabolic adaptations permit them to survive when other fish would starve. Cavefish store more fat when fed and lose less weight when food-deprived. The Mexican tetra can store four times more energy as fat than closely related fish. This allows it to cope with irregular food supplies. Some cavefish, including the Mexican tetra, have all the markings of being prone to diabetes. Their blood glucose levels remain high for long periods after eating. Chapter XX will discuss how a genetic propensity for diabetes and fat storage allows animals to put on weight and use reserves more slowly.

It is essential to point out that in some cases (notably the Mexican tetra, shortfin molly, and a few catfish), both blind cavefish and sighted, aboveground forms exist in the same species. They are referred to as different “forms” or “variants.” These are clear examples of neurodiversity within the same species and are highly analogous to human neurodiversity. Usually, these alternate forms can breed and create viable offspring. The sighted and sightless versions differ in behavior (especially regarding courtship, feeding, and sleep) and the hybrid offspring behave in ways affected by both parents.

Evolution’s knack for innovation provides unending marvels. Darwin said of blind fish:

“By the time that an animal had reached, after numberless generations, the deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and natural selection will often have effected other changes, such as an increase in the length of antennae or palpi, as compensation for blindness.”

— Charles Darwin, Origin of Species (1859)

Did evolution select cavefish to become blind, or is their blindness attributable to sporadic mutations? “Recent studies have produced evidence that the mechanism may be direct selection,[29] or indirect selection through antagonistic pleiotropy,[30] rather than genetic drift and neutral mutation, the traditionally favored hypothesis for regressive evolution.[28]”

I think that the loss of brain and retinal tissue in blind cavefish is an excellent analogy for some forms of the loss of brain tissue in some human beings. As I will show, many neurological disorders are linked to nutrient and maternal deprivation. Being deprived of food and mothering is an environment that’s somewhat like being stuck in a dark cave. Some might think this is a stretch and ask how I can generalize from eye to brain tissue. Well, our eyes are an extension of our brains. The retinas of the eyes are an outpocketing of brain tissue. Others might ask how I can generalize from fish to humans. Well, I would like to remind them that humans, in many senses, are a type of land-dwelling fish. Also the blind cavefish is just one example. As you continue to read, I will provide many more.

Sight isn’t the only ability animals will sacrifice to save energy. There are countless examples across the five kingdoms of life. Some beetles break down their muscles during hibernation, vastly reducing the number of mitochondria in each muscle to effectively reduce their metabolism. Other insects, such as crickets and moths, break down their flight muscles to conserve energy for reproduction. For some species, a lousy winter might permanently, though adaptively, cause them to lose the ability to fly.

If a regular fish had some cavefish DNA from past interbreeding, degenerated eyes might pop up sporadically in their line of descent. If scientists didn’t know about this interbreeding, they might assume that this degeneration was merely pathological. The same is true for some of the disorders discussed in this book. They are currently classified as pathologies, but they may be evidence that our species absorbed splinter populations adapted to different environments.

You can view the human lineage as a river. Different channels branched off as they became geographically separated but then later rejoined it. Environmental barriers kept our ancestors apart, causing them to adapt to different conditions. There were many asynchronous changes in climate across different regions of Africa during early human evolution. The Sahara greened for short periods while equatorial Africa underwent drought. These kinds of changes created fluctuating barriers to reproduction while also causing isolated groups to adapt to different environmental variables. Studies of other African mammals suggest that these conditions are also responsible for their species’ diversity. The cave fish example should make us wonder what proportion of human variation has been falsely categorized as disease.

Foraging and Brain Expansion

Human brains are around three times as big as those of other apes. It is relatively rare for a species to have a much bigger brain than other closely related species. Now, insightful theories, anthropological data, and common sense have worked together to show why the human brain is so big. It seems that the most important historical difference that allowed the expansion of the human brain was a profound change in our species’ ecological niche.

Because nervous tissue consumes energy so prodigiously, most animals cannot afford to develop big brains. Chimps and other apes have a lifestyle that demands intelligence, more so than that of their smaller cousins, the monkeys. This accounts for why apes have larger brains than monkeys. Chimpanzees life makes high demands on intelligence and a capacity for insight. Chimp mothers teach their young to forage, one on one, for over a decade. This is much longer than any monkey mother. A large, energy expensive brain is necessary for young chimps to model their mother’s behavior acquiring social skills and refining foraging techniques.

Today we can see that the lifestyle of modern hunter-gatherer humans requires vast intelligence. From an early age, forager peoples are forced to learn numerous skills and methods of survival. Whereas most chimps can learn to be self-sufficient within the first decade of life, hunter-gatherer humans may take two decades and do not reach peak productivity until their mid-thirties. This is where our energy expensive brain provided an advantage. It helped us to acquire, store, update, modify, and utilize important life lessons. It allowed the creation of tools which in turn enabled us to catch large game and extract difficult-to-procure vegetative matter and other calorie dense foods to support our energetic lifestyle. In the last few decades, theorists have pointed out other factors that probably contributed to the large brains seen in our species. It is now thought that social intelligence and an aptitude for language and abstract thought allowed bigger brained humans to produce more offspring than the smaller brained humans, thus increasing the average brain size for our species.

Brain Size and Intelligence

Brain size certainly correlates with intelligence, but please keep in mind that just because one animal has a larger brain does not mean that it is smarter. For one, it is necessary to correct for body size. Larger bodies have more muscle, more nerves needed to control that muscle, and larger areas of the brain dedicated to coordinating muscle movement. Larger animals also have more skin and other tissues, so their brains need larger sensory areas to process the incoming information about touch, pain, and temperature. The average human brain is around 1,300 cubic centimeters. That is equivalent to 9 tennis balls or about 32 golf balls.

Across all vertebrates, absolute brain size varies by 5 orders of magnitude, from less than 20 mg to more than 7 kg. I believe that both mice and elephants have a form of consciousness. But consider that an elephant has 800 times more cortical neurons than a mouse. Brain size has about a 30% correlation with intelligence. But there are other neurological factors that correlate with intelligence, including brain structure and neuron density. Each animal species has a uniquely patterned brain structure because each species has a different way of getting food and finding mates. Keep these things in mind as you peruse the lists below. The first is a list of total brain size in cubic centimeters for several different animals. The second lists animals by neuron number. I include these here because it is likely that you are familiar with the behavior of many of these animals, and seeing their relative brain sizes may help you start to think about the evolutionary forces that determined them.

Animal / Species	Brain Size in Cubic Centimeters
Goldfish	.4
Eel	.6
Coelacanth	2
Rat (Norway)	2
Guinea Pig	3
Tarsier	3
Opossum	5
Marmoset	7
Armadillo	7
Alligator	10
Lemur	10
Crow	10
Koala	20
Porcupine	20
Anteater	25
Cat	30
Shark (Great White)	30
Racoon	40
Howler Monkey	50
Macaque Monkey	60
Capuchin Monkey	70
Gibbon	80
Coyote	80
Spider Monkey	100
Wolf	120
Warthog	125
Jaguar	150
Pig	180
Baboon	180
T-Rex	200
Seal	250
Lion	240
Tiger	260
Caribou	290
Orangutan	380
Cow	420
Polar Bear	507
Gorilla	500
Horse	650
Hippo	720
Walrus	1130
Human	1350
Dolphin (bottle nose)	1400
Elephant (African)	5,700
Killer Whale	6,500
Sperm Whale	7,800

Animal / Species	Number of Neurons
Sponge	0
Tardigrade(water bear)	200
C. elegans (roundworm)	302
Jellyfish	5,600
Medicinal leech	10,000
Pond snail	11,000
Sea slug	18,000
Lobster	100,000
Fruit fly	100,000
Wandering spider	100,000
Ant	250,000
Honeybee	960,000
Cockroach	1,000,000
Carpenter bee	1,180,000
Common house gecko	3,988,000
Guppy	4,300,000
Blue-throated lizard	5,269,000
Brown water snake	5,995,000
Adult zebrafish	10,000,000
Uromastyx ornata	11,438,000
Yellow-throated lizard	11,847,000
Frog	16,000,000
Boa constrictor	19,781,000
Amboina box turtle	21,440,000
Green iguana	29,098,000
House mouse	71,000,000
Nile crocodile	80,500,000
Golden hamster	90,000,000
Common quail	117,760,000
Star-nosed mole	131,000,000
Brown rat	200,000,000
Guinea pig	240,000,000
Common treeshrew	261,000,000
Pigeon	310,000,000
Gray squirrel	453,660,000
Octopus	500,000,000
Cat	760,000,000
Common ostrich	1,620,000,000
Snowy owl	1,807,000,000
Fox	2,110,000,000
Raccoon	2,148,000,000
Raven	2,171,000,000
Domestic pig	2,220,000,000
Dog (Chihuahua)	2,510,000,000
Dog (German Shepherd)	3,530,000,000
Lion	4,667,000,000
Rhesus macaque	6,376,000,000
Brown bear	9,586,000,000
Giraffe	10,750,000,000
Chimpanzee	28,000,000,000
Orangutan	32,600,000,000
Gorilla	33,400,000,000
Human	86,000,000,000
African elephant	257,000,000,000

Fish, amphibian, reptile, and many dinosaur brains are all about equal in size when corrected for body weight. This is not true of birds and mammals, which have brains more than double the size expected from their body weight. Some scientists believe the metabolic costs of big brains became affordable when birds and mammals became warm blooded because this enabled them to engage in more rigorous foraging.

A cat’s brain is around an ounce. A Pomeranian’s brain is around .7 ounces. A human brain is about 45 ounces. “The stegosaurus brain weighed only 2.5 ounces accounting for only .004% of its body weight.)

Brain Region	Proportion by Volume (%)
	Rat	Human
Cerebral Cortex	31	77
Diencephalon	7	4
Midbrain	6	4
Hindbrain	7	2
Cerebellum	10	10
Spinal Cord	35	2
(Reference: Trends in Neurosciences, 18:471-474, 1995

There are many cases of AI software (in the form of neural networks that work much like a brain) that are bloated. They contain too many neurons (nodes) and too many connections (parameters). This causes them to waste processing resources and energy. Software engineers pare nodes and parameters down in networks inorder to maximize efficiency. Often whole sections of the network are unnecessary. Sometimes, depending on the task, only a small fraction of the processing units is needed. Often researchers build networks with too many parameters, and then cut them down so that they can complete their tasks with the bare minimum of parameters needed. This is similar to what evolution has done with the brains of animals. These reduced networks are faster, less expensive to run, and can even perform better than larger, unwieldy networks on certain benchmarks. It all depends on the requirements. For a bloated network to “look down” on a leaner network is absurd in the same way that it would be absurd for us to patronize people with smaller brains than us.

Aristotle expected that humans would exceed all other species in terms of brain size. However, elephants, dolphins, and whales all have larger brains, with an adult blue whale’s brain being roughly five times the size of an adult human brain (7kg versus 1.3 kg). Are blue whales five times smarter than we are? Probably not. Neuroscientists have determined that whales generally have neocortices that are structured more simply than those of primates. Also, whales have much larger bodies to control. In fact, the brain of the blue whale comprises only .01 percent of their body weight, whereas in humans the brain to body ratio is closer to 2 percent.

But brain to body ratio isn’t everything either. There are many small animals that have brain:body ratios that are higher than humans. Pocket mice and harvest mice, for example, have ratios close to 10 percent. Can we be the most intelligent animals if we have neither the biggest brains nor the highest brain size to body size ratio? The nonsomatic regions of the brain, that aren’t related to sensory or motor output, are also larger in larger animals, indicating that larger animals are more intelligent overall. These nonsomatic neurons that come along with larger body size can be used for intelligence rather than bodily functions.

Elephants are thought to be primitive ungulates, proboscideans.  But they have the biggest brain of any land animal, but they are ancient afrotheres.  How they became such intelligent creatures should be an amazing story, it would also be interesting to see if early stressors elicit neuropathological changes in them. This would also be an interesting thing to look for in dolphins. Interestingly, some species of dolphins are more intelligent than others and they have different cognitive specializations. Most interesting of all, their brains became large and complex millions of years before ours did.

Predictive Adaptive Responses Created by Phenotypic Plasticity

The term polyphenism refers to a case of phenotypic plasticity where a species exhibits the ability to develop into multiple distinct and reproducible body type (e.g., worker vs. queen bee). Environmental stimuli are the major triggers of polyphenisms.

When holly (Ilex aquifolium) senses that its leaves are being gnawed on by herbivores such as a deer, it activates certain genes that cause the leaves to become spiny when they grow back.

The Impact of Stress on Human Brain Development

The early environment can profoundly affect brain development in the fetus (prenatal), newborn (perinatal), and in early childhood (postnatal). Stress, in particular, can increase long-term susceptibility to neurodevelopmental and neuropsychiatric disorders in adulthood.

Today most researchers talk about early stress as a deviation from the norm, but stress and malnourishment were very common during prehistory and this is why our bodies evolved to protect our genes from them. To do this, early stress changes the way brains form, altering cell proliferation, migration, survival, differentiation (cell-type formation), communication, myelination (sheathing of nerve fibers), and even adult neuron production. Before birth, the brain produces about 250,000 cells per minute. This is disrupted in countless ways by stress, resulting in smaller over all brain volume, cortical thinning, and altered connectivity making the baby more emotional. Measures that reflect maternal stress include low birth weight, preterm birth, and elevated cortisol levels. Exposure to abuse, maltreatment or neglect.

Exposure to neurotoxins like lead, alcohol and pesticides can also produce long-term deficits in brain function. Preventable causes of cognitive impairment that we were probably not adapted to respond to include exposure to lead, pesticides, cocaine and other drugs, alcohol (fetal alcohol syndrome), meningitis, parasites, cerebral malaria, iodine deficiency, newborn asphyxia (oxygen deprivation), endocrine disorders, and traumatic brain injury.

It is important not to scare or worry pregnant mothers into thinking that minor stress will affect their baby, and it is known that a mother’s biological response to stress is dampened during gestation. Some stress is likely good for the baby. It is sustained, intense toxic stress and massive deprivation that we consider here. Excessive exposure to psychosocial stressors during pregnancy, such as domestic violence, intense anxiety, or the loss of a loved one can impose delayed mental and motor development, difficult temperament, and impaired cognitive performance on the baby. It will be important for researchers to determine during which critical periods these conditions exert their greatest impact. This is important because this can affect quality of life, educability, and future economic productivity.

Predispositions to cope with the demands of adverse environments, such as the enhancement of predator detection and avoidance.  

Prenatal Forms of Risk Exposure to Developmental Insult	Postnatal Forms of Stress
Stress / Adversity	Maltreatment
Cortisol, Stress Hormones	Abuse
Inflammation	Neglect
Low Birth Weight	Limited social partners
Poor relationship satisfaction	Negative social interactions
Reduced access to healthcare	Lack of parental warmth
Genetics, family history	Poor parental caregiving quality
Poor Diet and lifestyle choices	Lack of environmental enrichment
Lack of vitamins, B12 and Folate	Insensitive parenting
Lack of exercise	Unresponsive parenting
Lack of social support	Lack of parental stroking and touch
Low socioeconomic status	Lack of skin-to-skin contact
Poor sleep hygiene	Lack of language exposure
Low parental education	Lack of novel toys, books, and objects

Table 2.1: (Buss et al., 2012, Nolvi et al., 2023)

Neurological Outcomes Associated with Developmental Stress	Psychological Outcomes Associated with Developmental Stress
Neurodevelopmental disorders	Psychological disorders
Neuropsychiatric disorders	Delayed motor development
Reduced synapse development	Delayed mental development
Reduced neurotrophic growth factors	Reduced cognitive performance
Reduced myelination	Difficult temperament
Reduced gray matter volume	Impaired executive functioning
Reduced cortical thickness	Impaired self-regulation
Reduced hippocampal volume	Intellectual disability
Cortical thinning	Emotional disturbances
Reduced dendritic length	Oppositional defiant disorder
Reduced neurogenesis	Conduct disorder
Reduced neural proliferation, cell survival, and differentiation	Personality disorders
Reduced high frequency brain waves	Psychopathy
Increased cortisol reactivity	Antisocial personality disorder
Reduced oxytocin levels	Schizophrenia
Compromised amygdala–prefrontal connectivity	ADHD
Reduced connectivity in frontolimbic circuits	Dementia and Alzheimer’s

Table 2.2: (Buss et al., 2012, Nolvi et al., 2023)

Nolvi, S. et al., 2023. Prenatal stress and the developing brain: Postnatal Environments Promoting Resilience. Biological Psychiatry. 93:942-952.

Buss, C., Entringer, S., Swanson, J. M., & Wadhwa, P. D. (2012). The Role of Stress in Brain Development: The Gestational Environment’s Long-Term Effects on the Brain. Cerebrum : the Dana forum on brain science, 2012, 4.

Genetics loads that gun, epigenetics (gene-environment interactions) pulls the trigger.

Epigenetic processes adapt mental competencies to local conditions. Adaptive developmental plasticity responds to environmental variability (sensitivity to context) to create individual differences rather than following a single species-typical cognitive architecture. These alternate body types develop under continuous and bidirectional gene-environment interactions that emerge over time. These alternate body types can be triggered by false cues and thus mismatched with their environment. This happens when a strategy that is optimal in one environment may be sub-optimal in another.

Exposure to violence, harsh child rearing, environmental unpredictability, frequent moving, unstable family composition,

Maternal Deprivation, Neglect, and Romanian Orphanages

In Romania in the 1960s abortion and contraception were made illegal because it was believed that population growth would lead to economic growth. The increased number of births resulted in many children being abandoned in orphanages along with people with mental illnesses. These vulnerable groups were subjected to severe institutionalized neglect. Electricity and heat in the orphanages was intermittent. Children were often washed with cold water and a broom. Sometimes several infants would be crammed into the same crib. Food was often scarce and many starved to death. It was common to see children confined to cages with metal bars lying in urine and feces. Children were tied naked to their cots. 10 year olds would sit together at tables without talking or interacting, just rocking back and forth. Many of these children had delayed cognitive development and did not know how to feed themselves. Studies of these children showed that basic human contact is just as vital as nutrition. The lack of external stimulation led to self stimulation such as hand flapping and rocking. Because they had no primary caregiver in infancy, these children struggled to form emotional attachments to others for the rest of their lives. MRI studies revealed that these children developed smaller brains.

“According to the research, the longer the time the Romanian adoptees spent in the institutions, the smaller the total brain volume in adulthood, with each additional month of deprivation associated with a 0.27% reduction in total brain volume. Deprivation related changes in brain volume were associated with lower IQ and more symptoms of attention deficit hyperactivity disorder (ADHD).” They also had higher rates of depression and anxiety. The right medial prefrontal cortex (an area that plays a role in executive functions) was reduced. The right inferior temporal gyrus an area involved in auditory and visual processing was actually larger then expected.

Psychosocial Short Stature

Extreme emotional deprivation or stress can create a syndrome caused psychosocial short stature in people between 2 and 15. It is a growth disorder characterized by very short stature and weight that is inappropriate for the height. Even if the child receives adequate nutrition, they fail to thrive and meet normal developmental milestones. It is caused when constant stress causes a severe decrement in growth hormones. It also effects cognition, and as long as the child is left in the stressful environment their cognitive abilities continue to deteriorate. However, regular growth resumes once the source of stress is gone. Although rare it is common in feral children and in cases of severe neglect, confinement, or deprivation. Essentially, it is another example of when brain development can be arrested due to stress.

Encephalization

Cephalization is an evolutionary trend in which, animals tend to have the mouth, sensory organs, and nerve ganglia (brain matter) concentrated at the front end, producing a head.

There are three groups of animals thought to have highly sophisticated brains, namely the arthropods, cephalopod molluscs, and vertebrates.

Encephalization is an evolutionary increase in the relative size or complexity of the brain. In mammals this often corresponds in a shift of function from subcortical parts of the brain to the cortex.

The concept of encephalization begs us to consider the phenomenon of decephalization.

Domestication results in smaller brain size. In some senses dogs are microcephalic wolves.

Compared to their body size, the koala brain, at 20 cubic centimeters, is very small. In fact, koalas have one of the smallest brain to body ratios of any mammal at 1:400 (brain:body). The ratio for the average mammal is 1:180 and for humans this number is 1:40. Your brain is around 70 times larger than a koala’s. As we discussed, many scientists point out that brain size is not the most important factor when assessing intelligence. Rather surface folding and brain structure are the factors that matter. Koalas score low in this regard as well as their brains have little cortical folding with a cortical surface that is fairly smooth, typical for a “primitive” animal. But why is their brain so small? Koalas are not good runners, not good fighters, and are not very smart. They don’t have to be. Because they can subsist on eucalyptus leaves alone, they are highly toxic to other predators, and thus experience very little predation. A less demanding place in the food chain has bequeathed koalas very small brains. In other words, their brain size is an adaptation to a very calorie deficient diet, lack of predators, and lack of competition for their food source.

After the asteroid (Cretaceous–Paleogene (K-Pg) extinction event) that wiped out the non-avian dinosaurs, 65 million years ago, mammal brains shrunk. Or at least their brain to body size ratio (encephalization quotient) shrunk. In that barren postapocalyptic world it was better to invest in size than intelligence. Mammals put brawn before brains. These findings prompted specialists to wonder what ecological pressures could have led to this. The asteroid impact at the end of the Cretaceous caused a sudden mass extinction of three-quarters of the plant and animal species on Earth. Before this mass extinction mammal brains were much smaller than present day mammal brains. But their brains shrank even more as the planet recovered. As you know, brain tissue uses about an order of magnitude more energy than other body tissues and having to fuel a larger brain, can reduce an organism’s ability to survive and reproduce. They had proportionately, smaller brains without any major changes in structure, or the addition of new features. It took about 10 million years for the mammalian encephalization quotient to increase. Ecosystems recovered, and new food webs and ecological niches emerged, and mammals needed more intelligence to take advantage of them. Brain structure started to change as well. Brain areas associated with smell, shrank, such as the olfactory bulb, and areas associated with vision, eye, movement, and balance increased. And the neo cortex volume increased. There is no inevitable linear progression towards high intelligence. That an apocalypse would cause brains to shrink is another line of evidence suggesting that stressful times are not conducive to higher-order intelligence.

Intelligence May Create Too Many Degrees of Freedom

Humans, and apes in general, have very mobile shoulder joints which allowed our ancestors to swing among branches. This activity is known to primatologists as brachiation. The shoulder joints in apes are more flexible than they are in most other animals, and this is due to their reliance on branch swinging and tree climbing. Because apes use their feet when they climb, the same goes for their hip joint. Humans and most monkeys have a ligament that straps down our hip joint and constrains movement. The ligament holds the ball of the femur (thigh bone) tightly into the hip socket of the pelvis. This ligament is absent in the orangutan. For orangs movement in the hip is unrestricted allowing it to position its legs any way it deems fit to reach for and grasp branches. They often sit up in the tops of trees like “spiders” or “acrobats” in contorted ways.

This much flexibility in the positioning of the limbs would be maladaptive in most other mammals. Imagine an infant cat or dog or mouse that had this kind of mobility in their hips and shoulders. After flailing about in their first few weeks after birth they might never learn to walk or run properly because their limb movement is so unrestricted. The confining ligaments in a cat’s body place it on a direct path to learning how to organize its legs into striding, jumping, and running efficiently.

Highly complex conceptual thinking and detail-oriented behavior would hinder and endanger many, more simplistic animals. These animals analyze situations on a superficial level. They then react to them using a small number of inflexible behavioral responses. Bigger brains would render these animals less receptive to external stimuli and less responsive to their environment. In other words, many animals have not been, and will not be, selected to be more intelligent.

Plants cannot afford neurons. Plants are immobile, so they cannot forage or hunt for the energy needed to power neurons. They probably wouldn’t benefit from making an effort to evolve neurons and muscles because they wouldn’t be able to out-compete animals, which already move very well. So, they are stuck using hormones to send messages from one part of the body to the next. We see them as “stuck” but they are probably very “content” where they are.

In much the same way, too much flexibility in thought and behavior can be dangerous. Having a large cortex is a lot like having limbs that are too flexible. Having a small brain that emphasizes rigid instincts is safe because of its simplicity. It regulates and restrains the animal so that it stays in line with its innate tendencies. It makes the animal’s behavior simplistic, but effective, whereas a large brain can create inefficient, unnecessarily complex behavior. Analysis paralysis takes place when overanalyzing or overthinking can cause decision-making to become “paralyzed” or too slow to react. Of course, this is the opposite of the phrase “extinct by instinct” which is when a hasty reaction causes death.

Intelligence Is Inseparable from Inhibition

All animals with large brains have a preponderance of inhibitory neurons. These inhibitory neurons take up huge amounts of energy. And yet, they don’t help us to act as much as they help us stop ourselves from acting. Inhibitory neurons inhibit impulses from excitatory neurons. The ability to veto basic and instinctual actions allows us to do things that are more difficult and complex instead. Compared to most animals, humans have an unnaturally high, almost paralyzing, abundance of interneurons.

A human brain would be totally unappealing to a worm. It would be a death sentence in terms of both movement and metabolism. Of course, the weight of a three-pound brain would render a worm (and most animals for that matter) completely immobile. Moreover, the metabolic requirements of a human brain would deplete all the energy stored in the worm’s body in seconds. But even if it was weightless and made no energy draw, a human brain would not increase a worm’s survival or reproductive success. A worm’s life is simple, but it must respond to its environment quickly and unerringly. The only reason our brain works for us because humans inhabit a rarified and specialized niche. There are a few examples of ludicrous energy drains in nature, like a blue whale’s size or a peacock’s tail. When they exist, they do so for very specific reasons.

There are times when brain injury can create positive attributes. There have been several documented cases where people with traumatic brain injuries gain fantastic skills, such as “acquired savant syndrome.” For example, there are dozens of reported cases of people with little musical talent, who have woken up from concussions to becoming piano virtuosos. In other cases, people have gained artistic, mathematical, or memory abilities. Because it would it be impossible for an injury to create all the memory traces necessary for these skills, they are not created as much as they are unlocked. Essentially, these are abilities that are disinhibited. I will discuss how I benefitted from disinhibition from severe stress in Chapter 5. Anytime someone has some form of brain injury their brain will demonstrate compensatory neural plasticity. This by necessity creates new and different modes of thinking. Thus, there are possible positive sides to every form of brain disorder. This book looks to explore them.

In 1931 a man named Winthrop Kellogg began to raise young female chimpanzee along with his son Donald. The Kelloggs raised the two as brother and sister for nine months, dutifully recording many aspects of their development. To make a story short, he found that the chimpanzee progressed impressively in learning everyday human behaviors. In fact, she learned many things faster than his son Donald did. She performed ahead of Donald at many tasks including responding to simple commands, recognizing people, drinking from a cup, and eating with a spoon. Simple things can be more easily understood and mastered by simple, uninhibited brains.

Neurons Are Highly Energetically Expensive

Energy is the fuel of life and all lifeforms have been optimized to expend it efficiently. Competition for limited energy resources, streamlining of metabolism, and hardiness to nutrient deprivation were driving forces of evolution. Of course, this metabolic penny pinching also applies to the organ of thought. The metabolic costs of neural tissue act as an evolutionary break on brain complexity (Reser, 2006).

Neurons don’t contract to move parts of the body like muscles cells do. Neurons stand still. But nevertheless, consume lots of oxygen and fuel (in the form of glucose). Most of this energy performs work at a microscopic scale, driving the numerous membrane pumps found in every neuron. These pumps actively pump sodium, calcium, and water out of the cell and potassium into the cell. This creates a charge (ionic gradient across the cell membrane) allowing neurons to send electrical messages to each other. When sufficiently triggered by other neurons, it is this charge that allows a neuron to create an action potential to send a message to other neurons. During the action potential the neuron lets the ions it has been pumping flow backward (depolarization is excitatory, hyperpolarization is inhibitory). These ions rush toward equilibrium, collapsing the ionic gradients and sending a fast message down the neuron’s axon.

Time, memory, attention, and energy are basic constraints pressing organisms toward simplicity. Sustained firing itself, is heavily metabolically expensive because of the high cost of action potentials (Mongillo et al., 2008).

The heart pumps between two-thirds of a pint and two whole pints of blood around the brain each minute (Rempp, Brix, Wenz, 1994). The blood passes through arteries at speeds up to 80 cm per second (Saito, Yoshokawa, Nishihara, 1995) and in children it can be as high as 240 cm/sec (Pegelow, Wang, Granger, 2001).

Mongillo G, Barak O, Tsodyks M. 2008. Synaptic theory of working memory. Science. 319: 1543-1546.

Intelligence Requires Increased Metabolic Costs

Bioenergetic studies show that in comparison with a resting state, the brain’s glucose use increases only about 5% in response to simple tasks, but up to 12% in conditions of mental stress (Madsen et al., 1995).

We naturally don’t want to use our brains more than we have to. The literature recognizes that all humans are “cognitive misers.” Some tasks require more glucose than others, in tests or in foraging, we must have been selected to find these onerous, so that we could minimize expenditure. We all seek fast, adequate solutions to problems rather than laborious, well-considered ones. We use mental shortcuts when we make judgments and draw inferences because we don’t want to have to do unnecessary mental work in the same way that we balk at unnecessary physical work. This tendency is surely adaptive.

Madsen PL et al. 1995. Persistent resetting of the cerebral oxygen/glucose uptake ratio by brain activation: evidence obtained with the Kelly-Schmidt technique. Journal of Cerebral Blood Flow and Metabolism. 15, 485-491.

An average brain draws about 15 watts of energy, six times less than that common 100-watt bulb in the ceiling. So, your brain is more like an energy saving LED bulb. Given that a standard electrical outlet can provide about 1,500 watts, you could potentially run around 100 of your brains from just one circuit in your home.  

We are all descended from winners. If so, then why aren’t we stronger and smarter? There is one answer to this question: thrift is part of being a winner. Frugality, austerity

The brain consumes about 16 percent of the energy consumption of the entire body (making the total resting energy output of the body around 100 watts). The digestive tract is the only organ in the body that consumes more energy. Your gut registers at about 70 percent of the entire body’s energy supply.

Leslie Aiello and Peter Wheeler introduced the “expensive tissue hypothesis” which proposed that for an animal to evolve a large brain without a large increase in basal metabolic rate, it must use less energy in other energy-expensive organs. In the cause of humans, we were able to develop brains three times larger than our closest ancestors (apes) due to the shrinkage of our gut.  Our gastrointestinal tract is only 60% of what you would expect in a primate of our size. Like neurons, intestinal cells require lots of energy. Through mathematical analyses they showed that the smaller relative size of the human digestive tract almost completely compensates for the metabolic costs of increased brain size. But they took this even further, stating that a larger brain would enable more complex foraging behavior and the acquisition of higher quality, more easy-to-digest foods, which would then allow the gut to shrink further, making more energy available to the brain. Further research is ongoing, but studies have shown negative correlations between brain and gut size in various species. They have also shown that species economize the expense of tissues and behaviors when metabolic stinginess is necessary.

Ecological Niche

It often happens that animals are introduced into new habitats they have not evolved to interact with. Successful newcomers, in both mammals and birds are usually those species with the largest brains. Bigger brains are better at general problem solving and generating behavioral strategies that can aid in survival. High intelligence has allowed humans to conform to various climates. Today (and 30,000 years ago) we can make our homes in the desert or on the ice. Our cerebral cortex allows us to wire ourselves for the ecological niche we find, rather than being born preadapted to one niche. Less intelligent animals die outside of the ecosystem their ancestors evolved to be specialized for. We can make new connections giving us the potential to survive in a wider range of environments.

Omnivorous species are generally assumed to be more flexible and intelligent than specialized feeders. There are exceptions though. Although gorillas are herbivores, they keep track of as many as 100 different plant species and must remember how to locate and identify these according to the season and they must also know how to collect and process them before eating.

this ms interprets certain types of syndromic retardation as “meat-adaptive” balanced polymorphisms.  After analyzing epidemiological, bio-energetic, life-history and neuro-physiological data I conclude that many of these syndromes may represent an evolved, r-strategic phenotype that would have adopted an alternate food procurement strategy.

Humans and Ecology

A Tendency to Produce Fewer Anabolic Hormones

Anabolic

           Growth hormone

           IGF 1 and other insulin-like growth factors

           Insulin

           Testosterone

           Estrogen

Catabolic

           Cortisol

           Glucagon

           Adrenaline

           Cytokines

The r and K Strategy Continuum Relates Intelligence to Reproductive Strategy

Each species on the earth employs a different reproductive strategy to ensure that they leave offspring behind before they die. There are two types of fundamental reproductive strategy, and they are the K strategy and the r strategy.  K strategists are often said to be “K-selected” and r strategists are said to be “r-selected.” Organisms can be differentiated from one another in terms of their relative reliance on one strategy over the other. Examples of r-selected species include bacteria, insects, and fish. Highly K-selected species include elephants, apes, and whales.

r                                                                                                                                       K __._________._________._______.________.__________._________.________.___ bacteria      mollusks      insects      fish      amphibians      reptiles      mammals     apes

The r/K continuum is a spectrum with two opposing reproductive strategies. All animal species sit somewhere on this line with r on one side and K on the other. R-selected organisms produce many offspring at once, offer little to no parental or protective care, gestate quickly, and reach reproductive maturity quickly. Generally, this is how the least intelligent animals with the least complex nervous systems operate. K-selected animals are more intelligent, produce only a few, large well-developed offspring, offer parental care, exhibit long gestations, slow growth, and delayed maturation.

An oyster is an example of an r-selected species. The females can release 50 to 100 million eggs into the water in a single season. They don’t teach their babies anything and often do not ever encounter them. Without parenting, they have relatively little to learn and thus have very small nervous systems. Chimpanzees are an example of an extremely K-selected species. Females generally have one baby every five years, for a total of two to three raised to adulthood. Those babies stay with her and learn from her for around 10 years each. Compared to chimps many mammals are r-selected.

Comparison of r & K Selected Organisms

Characteristics of r Selection	Characteristics of K Selection
Energy used to create offspring is low	Energy used to create offspring is high
Many offspring created at a time	Few offspring created at a time
Most offspring don’t survive to reach maturity	Most offspring reach near maximum lifespan
Early maturity and sexual maturation	Late maturity and sexual maturation
Unstable, unreliable environment	Stable, reliable environment
Short life expectancy	Long life expectancy
Parents don’t teach offspring	Parents instruct offspring
Behavior is instinctual	Behavior is learned
Brains are smaller	Brains are larger

Table X: This table lists traits that have been hypothesized to correspond to r and K-selected strategies.

Many animals can get up and walk around shortly after birth. Humans are stuck floundering in a cradle for 10 to 18 months. A wildebeest can run from a hyena an hour after it is born. A two-month-old mouse is sexually mature and can become a grandparent at just four months of age. Compare this to humans who cannot run until they reach around 24 months, and are not capable of having babies until well after 10 years old. In some ways, delaying reproduction for so long, and relying so much on parenting is a very tenuous strategy. A human baby requires tremendous sunken costs and is, in effect, an 18-year risk. So you can see how a single oyster baby is a much less risky proposition.  

This axis of variation is also known as the fast-slow continuum. Fast, r species show high mortality, early maturation, early reproduction, and high fertility. Slow, K species mature later, live longer, and produce fewer offspring.

It is commonly assumed in the literature that life history strategies show adaptive plasticity and that faster, r strategies are adaptive in harsh or unpredictable environments. It is also accepted that there is variation on this continuum found within the human species and that some examples of psychopathology may map onto r-selected traits. And even that harsh early conditions may predispose individuals to r-selected strategies which may be specialized into different forms of mental pathology. These include disorders such as, conduct disorder, oppositional-defiant disorder, social anxiety disorder, generalized anxiety disorder, avoidant personality disorder, schizotypal, schizoaffective,

In biology, r/K selection theory relates to the natural selection of traits that trade off between quantity and quality of offspring. The r strategy is associated with having lots of young but not providing them with parental investment and the K strategy is the opposite. It is sometimes referred to as the fast/slow or cheap/expensive continuum. Unstable or unsafe environments encourage species to use the r strategy because the likelihood offspring will live to adulthood is slim. Under these conditions, current reproduction is prioritized over future reproduction. It is important to note that the same environmental setting may be unstable for one species but stable for another, especially if the second species has the intelligence to understand and control the unstable elements. The life-history paradigm has largely replaced the r/K paradigm, although it incorporated many of its important concepts.

Many offspring, low probability of surviving to adulthood. High fecundity, small body size, early maturity onset, short generation time, shorter life expectancies,  ability to disperse offspring widely (like a dandelion). Many organisms do not follow the r/K pattern. For instance, sea turtles are large organisms, with long lifespans that produce large numbers of offspring that they do not care for after hatching.

r-selected Psychological Traits	K-selected Psychological Traits
Impulsivity, disinhibition, present orientation, risk-taking, sensation seeking, precocious sexuality, uncommitted sex with multiple partners, unrestricted sociosexuality, antagonism, defensiveness, antisocial, distractibility, impatient urgency,	Conscientiousness, self-control, risk aversion, honesty, humility, low threshold for moral disgust, low threshold for sexual disgust, couple stability, stable romantic attachments agreeableness, discipline, deference, patience,

Table X: This table lists human psychological traits that have been hypothesized to correspond to r and K-selected strategies.

R strategists do not focus on passing down memes, units of cultural information, to their young. Instead, the behavior of the young is determined by their genes. The young are “precocial,” meaning that they can make it on their own with little instruction or supervision from their parents. Larger brains create more autonomy which requires more learning, more mothering, and longer developmental periods. A similar word is “nidifugous” which is an adjective describing a young bird or other animal that is capable of leaving the nest shortly after birth.

K strategists are very different in that they attempt to ensure the survival of their offspring by investing time in them instead of investing in lots of them. It is a reproductive strategy that focuses on quality over quantity. K strategists have relatively few offspring and try at being good parents. Their young are “altricial” meaning they cannot survive on their own. The offspring are also relatively intelligent so that they can internalize the lessons from their parents.  Humans are perhaps the most K-selected because they usually only produce one offspring at a time. Also, those young are truly helpless, they necessitate a full two decades of parental care and tutelage.

The r strategy is by far the more robust strategy. The behavior of an r strategist is dictated by its genes which are naturally selected over geological time. This means that r strategists are self-sufficient and their behavior rarely goes wrong. The behavior of a K strategist on the other hand is completely dependent on the lessons from its parents and so extreme K strategy is very risky. 

Memetics

“When you plant a fertile meme in my mind you literally parasitize my brain, turning it into a vehicle for the meme’s propagation in just the way that a virus might parasitize the genetic mechanism of a host cell.”

N.K. Humphrey

So, the r strategy typified by simple organisms is mostly reliant on the transference of genes and their accompanying instincts. The K strategy is reliant on the transference of memes. Memes are units of cultural or social information, and they are passed from parent to child. The human condition is especially reliant on memes, as without language, knowledge, and skills humans usually will not survive in a natural environment. Bacteria, plants, and many other organisms have no use for memes. All the behavior that they need to reproduce is already contained in their bodies at birth.

Most mammals do not share solid food with their young. They only provide breast milk. If the young want to eat, they must learn to hunt or forage by watching the mother. Young monkeys sit in their mother’s lap watching their mother feed herself. Crumbs fall around the young monkey, and they learn to grab them and place them in their own mouths. Memes leap from brain to brain in the form of imitation.

Perceiving False Patterns

Have you even seen a face in a cloud? If so, you have experienced apophenia. Apophenia is a general term for interpreting patterns or meaning in meaningless data. This involves any kind of information, including visual, auditory, or others. The term pareidolia refers to an apophenic experience that focuses on visual information like seeing a figure in the clouds.

Cognitive Noise

One question that assesses advanced intelligence is asking, “is this animal smart enough to create behavior that doesn’t increase its reproductive success.” If an animal is all survival machine, then there is no room for thoughts that run contrary to the genes’ interests. But if the animal can become more than an instinctive automaton then it demonstrates real intelligence.

A certain proportion of an animal’s thoughts do not increase its reproductive prospects. Some of this thinking may be misguided but some of it will be false. When this happens the animals brain is generating plasticity to nothing. This “junk learning” is learning that is not adaptive.

You might call it “cognitive entropy” when cognition tends toward disorder. The Second Law of Thermodynamics states that entropy is the tendency of all closed systems to drift toward a state of disorder rather than order. Only highly balanced biological systems can counteract entropy, and when this balance is offset, the organism dies, succumbing to the disorganizing tendency of thermodynamics. Thermodynamics may also be the antagonistic force in cognitive entropy as well, increasing disorder in cognitive systems unless they are in some kind of neuroecological balance. Intelligent animals learn and internalize valuable schemas but are likely to misapply a known schema to a new situation because of a false association. When this happens they are liable to make a life-threatening mistake. Cognition, like everything else in the universe is affected by entropy. Cognitive noise is just an example of thoughts tendency toward disorder. Cellular metabolic pathways allow matter and energy to act orderly when their tendency is to be disordered. Generational resource and meme flows help cognition to act orderly when its natural tendency is for disorder.

Trained animals often revert to instinctual behavior. Racoons can be trained to deposit coins into a bank. After a while though, such racoons are likely to retrieve the deposited coin, dip it into the bank several times, and rub the coin with their paws. Because depositing the coin is similar to their natural feeding behavior it can trigger the instinctual response of washing the item in water and then rubbing it clean with their paws. Instinctive drift happens when an animal abandons learned behaviors and goes back to automatic and unconscious ones that correspond with evolutionary contingencies. When trained animals revert to instinctive behaviors, this is called instinctual drift. I see cognitive noise as a form of drift as well, however in this case, it is drifting away from instinct. Because animal thought can be broken down into instinct and insight, I see cognitive noise as “insightful drift.” Except the insights are not always helpful in nature. Intelligence is often overrated.

Using intense concentration while in a hostile situation would not be helpful. It would likely cause the animal to zone out and be inattentive to the pressing variables. Environmental awareness and defensive responses are blunted leaving the animal vulnerable. Many carnivorous mammals such as wolverines and honey badgers don’t overthink, they rush in brashly and chaotically. In one of my favorite panels, the comic book character Wolverine is running with his claws unsheathed toward a troop transport where several soldiers are opening fire on him. As he jumps at them he says to himself, “this won’t work if I think about it.” I often feel this way especially when performing physically or athletically. Professional golfers claim that after the golf swing is thoroughly mastered, the best thing to do is NOT to think about it, just let it happen. Throwing a football, shooting a basketball, and much more fall into this domain. Thinking can be a disturbance, a nuisance, and a hinderance.  

Cognitive Parsimony

The more cosmopolitan your world view the easier it is to determine the relative strength and weakness of individual causal forces and thereby make accurate predictions. But r selected animals don’t need fine distinctions in their predictions, they are fine just using their instincts.

The more intelligent you are the further the limbic is removed from the cortex.  Less intelligent organisms are curious about things that evoke emotion, whereas the smarter you get, generally the further removed your interests are from emotion. The ability to be interested in and learn about things that are not strongly emotionally arousing is something that is very dangerous. It is always important for an animal to learn about things that are very upsetting or very rewarding. But most other things are just not important.

It’s common to see dogs in internet videos doing stupid things, acting clueless, and making ridiculous mistakes. Cats often don’t make the same kinds of mistakes even though their brains are significantly smaller than dogs on average. Cats, although, intelligent mammals, operate on a lower level than dogs (at least in some ways), and so may not have the capacity for some of the high-level accidents, goofy behavior, and absence of instinct.

Having fingers and prehensile thumbs helps us put our higher-order thoughts to good use. Other animals don’t have nimble fingers capable of grasping. The way most animals’ bodies are structured leaves them unable to create complex tools, build structures, or perform any kind of manual labor. If a wildcat, for instance, was blessed with higher cognitive abilities, much of its thinking couldn’t find productive implementation. He might even fall prey to other more survival-dedicated animals. Every species’ brain has a complexity threshold, beyond which increased complexity produces not just diminishing returns, but maladaptivity.

All of this neuropathology is evidence of the maladaptive properties of excessive memory (hypermnesia). The implicitization of behavior that does not improve reproductive success is the most scary of all of the mistakes that can be made. To form memories about occurrences that don’t matter, and then to form memories about additional subjective interpretations about these memories is dangerous. The subjective interpretations are likely to be wrong, unless the animal is very knowledgeable. For memories that are secondary to instinct to inform behavior in an implicit, automatic or procedural way is fine. But for memories that are tertiary to instinct to inform behavior in this way is very risky.

For example, a decrease in working memory span may increase creative and spontaneous thought, facilitate reaction time, and increase attentiveness to the environment. On the other hand, an increase in working memory capacity may necessitate a higher degree of prior network training to produce adaptive behavior.