The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately 7 million years, from the separation of the genus Pan until the emergence of behavioral modernity by 50,000 years ago. The first 3 million years of this timeline concern Sahelanthropus, the following 2 million concern Australopithecus and the final 2 million span the history of the genus Homo in the Paleolithic era.
Many traits of human intelligence, such as empathy, theory of mind, mourning, ritual, and the use of symbols and tools, are apparent in great apes although in less sophisticated forms than found in humans, such as great ape language.
Many traits of human intelligence, such as empathy, theory of mind, mourning, ritual, and the use of symbols and tools, are apparent in great apes although in less sophisticated forms than found in humans, such as great ape language.
History
Hominidae
The great apes (hominidae) show considerable cognitive and empathic abilities. Chimpanzees can make tools and use them to acquire foods and for social displays; they have sophisticated hunting strategies requiring cooperation, influence and rank; they are status conscious, manipulative and capable of deception; they can learn to use symbols and understand aspects of human language including some relational syntax, concepts of number and numerical sequence.
Homininae
Chimpanzee mother and baby
Around 10 million years ago, the Earth's climate entered a cooler and drier phase, which led eventually to the Quaternary glaciation
beginning some 2.6 million years ago. One consequence of this was that
the north African tropical forest began to retreat, being replaced first
by open grasslands and eventually by desert (the modern Sahara).
As their environment changed from continuous forest to patches of
forest separated by expanses of grassland, some primates adapted to a
partly or fully ground-dwelling life. Here they were exposed to predators, such as the big cats, from whom they had previously been safe.
These environmental pressures caused selection to favor bipedalism:
walking on hind legs. This gave the Homininae's eyes greater elevation,
the ability to see approaching danger further off, and a more efficient
means of locomotion.
It also freed the arms from the task of walking and made the hands
available for tasks such as gathering food. At some point the bipedal primates developed handedness, giving them the ability to pick up sticks, bones and stones and use them as weapons, or as tools for tasks such as killing smaller animals, cracking nuts, or cutting up carcasses. In other words, these primates developed the use of primitive technology. Bipedal tool-using primates form the Hominina subtribe, of which the earliest species, such as Sahelanthropus tchadensis, date to about 7 to 5 million years ago.
From about 5 million years ago, the hominin brain began to develop rapidly in both size and differentiation of function.
There has been a gradual increase in brain volume as humans progressed along the timeline of evolution, starting from about 600 cm3 in Homo habilis up to 1500 cm3 in Homo neanderthalensis. Thus, in general there's a correlation between brain volume and intelligence. However, modern Homo sapiens have a brain volume slightly smaller (1250 cm3) than neanderthals, and the Flores hominids (Homo floresiensis), nicknamed hobbits, had a cranial capacity of about 380 cm3 (considered small for a chimpanzee) about a third of that of H. erectus. It is proposed that they evolved from H. erectus
as a case of insular dwarfism. With their three times smaller brain the
Flores hominids apparently used fire and made tools as sophisticated as
those of their ancestor H.erectus. In this case, it seems that for intelligence, the structure of the brain is more important than its volume.
Homo
Roughly 2.4 million years ago Homo habilis had appeared in East Africa: the first known human species, and the first known to make stone tools, yet the disputed findings of signs of tool use from even earlier ages and from the vicinity as multiple Australopithecus fossils may put this to question its "greater intelligence when compared to earlier and more primitive Australopithecus genus".
The use of tools conferred a crucial evolutionary advantage, and
required a larger and more sophisticated brain to co-ordinate the fine
hand movements required for this task.
Our knowledge of the complexity of behaviour of Homo habilis is not
limited to stone culture, they also had habitual therapic use of toothpicks.
The evolution of a larger brain created a problem for early humans, however. A larger brain requires a larger skull, and thus requires the female to have a wider birth canal for the newborn's larger skull to pass through. But if the female's birth canal grew too wide, her pelvis would be so wide that she would lose the ability to run, which was a necessary skill 2 million years ago.
The solution to this was to give birth at an early stage of fetal
development, before the skull grew too large to pass through the birth
canal. This adaptation enabled the human brain to continue to grow, but
it imposed a new discipline. The need to care for helpless infants for long periods of time forced humans to become less mobile.
Human bands increasingly stayed in one place for long periods, so that
females could care for infants, while males hunted food and fought with
other bands that competed for food sources.
As a result, humans became even more dependent on tool-making to
compete with other animals and other humans, and relied less on body
size and strength.
About 200,000 years ago Europe and the Middle East were colonized by Neanderthal man, extinct by 39,000 years ago following the appearance of modern humans in the region from 40,000–45,000 years ago.
Homo sapiens
"The Lion-man", found in the Hohlenstein-Stadel cave of Germany's Swabian Alb and dated to 40,000 years ago, is associated with the Aurignacian culture and is the oldest known anthropomorphic animal figurine in the world.
Dates approximate, consult articles for details
(From 2000000 BC till 2013 AD in (partial) exponential notation)
Homo sapiens intelligence
Around 200,000 years ago, Homo sapiens first appeared in East Africa. It is unclear to what extent these early modern humans had developed language, music, religion etc. They spread throughout Africa over the following approximately 50,000 years.
According to proponents of the Toba catastrophe theory,
the climate in non-tropical regions of the earth experienced a sudden
freezing about 70,000 years ago, because of a huge explosion of the Toba
volcano that filled the atmosphere with volcanic ash for several years.
This reduced the human population to less than 10,000 breeding pairs in
equatorial Africa, from which all modern humans are descended. Being
unprepared for the sudden change in climate, the survivors were those
intelligent enough to invent new tools and ways of keeping warm and
finding new sources of food (for example, adapting to ocean fishing
based on prior fishing skills used in lakes and streams that became
frozen).
Around 80,000–100,000 years ago, three main lines of Homo sapiens diverged, bearers of mitochondrial haplogroup L1 (mtDNA) / A (Y-DNA) colonizing Southern Africa (the ancestors of the Khoisan/Capoid peoples), bearers of haplogroup L2 (mtDNA) / B (Y-DNA) settling Central and West Africa (the ancestors of Niger–Congo and Nilo-Saharan speaking peoples), while the bearers of haplogroup L3 remained in East Africa.
The "Great Leap Forward" leading to full behavioral modernity
sets in only after this separation. Rapidly increasing sophistication
in tool-making and behaviour is apparent from about 80,000 years ago,
and the migration out of Africa follows towards the very end of the Middle Paleolithic, some 60,000 years ago. Fully modern behaviour, including figurative art, music, self-ornamentation, trade, burial rites etc. is evident by 30,000 years ago. The oldest unequivocal examples of prehistoric art date to this period, the Aurignacian and the Gravettian periods of prehistoric Europe, such as the Venus figurines and cave painting (Chauvet Cave) and the earliest musical instruments (the bone pipe of Geissenklösterle, Germany, dated to about 36,000 years ago).
The human brain has evolved gradually over the passage of time; a
series of incremental changes occurred as a result of external stimuli
and conditions. It is crucial to keep in mind that evolution operates
within a limited framework at a given point in time. In other words, the
adaptations that a species can develop are not infinite and are defined
by what has already taken place in the evolutionary timeline of a
species. Given the immense anatomical and structural complexity of the
brain, its evolution (and the congruent evolution of human
intelligence), can only be reorganized in a finite number of ways. The
majority of said changes occur either in terms of size or in terms of
developmental timeframes.
Motor and sensory areas of the cerebral cortex; dashed areas shown are commonly left hemisphere dominant.
There have been studies that strongly support the idea that the level
of intelligence associated with humans is not unique to our species.
Scholars suggest that this could have, in part, been caused by
convergent evolution. One common characteristic that is present in
species of "high degree intelligence" (i.e. dolphins, great apes, and
humans - Homo sapiens) is a brain of enlarged size. Along with this, there is a more developed neocortex, a folding of the cerebral cortex, and von Economo neurons.
Said neurons are linked to social intelligence and the ability to gauge
what another is thinking or feeling and, interestingly, are also
present in bottlenose dolphins. The cerebral cortex
is divided into four lobes (frontal, parietal, occipital, and temporal)
each with specific functions. The cerebral cortex is significantly
larger in humans than in any other animal and is responsible for higher
thought processes such as: reasoning, abstract thinking, and decision
making.
Another characteristic that sets humans apart from any other
species is the ability to produce and understand complex, syntactic
language. The cerebral cortex, particularly in the temporal, parietal,
and frontal lobes, are populated with neural circuits dedicated to
language. There are two main areas of the brain commonly associated with
language, namely: Wernicke's area and Broca's area.
The former is responsible for the understanding of speech and the
latter for the production of speech. Homologous regions have been found
in other species (i.e. Area 44 and 45 have been studied in chimpanzees)
but they are not as strongly related to or involved in linguistic
activities as in humans.
A big portion of the scholarly literature focus on the evolution,
and subsequent influence, of culture. This is in part because the leaps
human intelligence has taken are far greater than those that would have
resulted if our ancestors had simply responded to their environments,
inhabiting them as hunter-gatherers. (Richardson 273).
In short, the complexity and marvel of human intelligence only
emerge inside of a specific culture and history. Selection for
cooperation aided our ancestors in surviving harsh ecological conditions
and did so by creating a specific type of intelligence. An intelligence
that, today, is highly variant from individual to individual.
Models
Social brain hypothesis
The social brain hypothesis was proposed by British anthropologist Robin Dunbar,
who argues that human intelligence did not evolve primarily as a means
to solve ecological problems, but rather as a means of surviving and
reproducing in large and complex social groups.
Some of the behaviors associated with living in large groups include
reciprocal altruism, deception and coalition formation. These group
dynamics relate to Theory of Mind
or the ability to understand the thoughts and emotions of others,
though Dunbar himself admits in the same book that it is not the
flocking itself that causes intelligence to evolve (as shown by ruminants).
Dunbar argues that when the size of a social group increases, the
number of different relationships in the group may increase by orders
of magnitude. Chimpanzees live in groups of about 50 individuals whereas
humans typically have a social circle of about 150 people, which is
also the typical size of social communities in small societies and
personal social networks; this number is now referred to as Dunbar's number.
In addition, there is evidence to suggest that the success of groups is
dependent on their size at foundation, with groupings of around 150
being particularly successful, potentially reflecting the fact that
communities of this size strike a balance between the minimum size of
effective functionality and the maximum size for creating a sense of
commitment to the community.
According to the social brain hypothesis, when hominids started living
in large groups, selection favored greater intelligence. As evidence,
Dunbar cites a relationship between neocortex size and group size of
various mammals.
Criticism
Phylogenetic
studies of brain sizes in primates show that while diet predicts
primate brain size, sociality does not predict brain size when
corrections are made for cases in which diet affects both brain size and
sociality. The exceptions to the predictions of the social intelligence
hypothesis, which that hypothesis has no predictive model for, are
successfully predicted by diets that are either nutritious but scarce or
abundant but poor in nutrients. Researchers have found that frugivores tend to exhibit larger brain size than folivores.
One potential explanation for this finding is that frugivory requires
'extractive foraging,' or the process of locating and preparing
hard-shelled foods, such as nuts, insects, and fruit. Extractive foraging requires higher cognitive processing, which could help explain larger brain size.
However, other researchers argue that extractive foraging was not a
catalyst in the evolution of primate brain size, demonstrating that some
non primates exhibit advanced foraging techniques.
Other explanations for the positive correlation between brain size and
frugivory highlight how the high-energy, frugivore diet facilitates
fetal brain growth and requires spatial mapping to locate the embedded
foods.
Meerkats
have far more social relationships than their small brain capacity
would suggest. Another hypothesis is that it is actually intelligence
that causes social relationships to become more complex, because
intelligent individuals are more difficult to learn to know.
There are also studies that show that Dunbar's number is not the
upper limit of the number of social relationships in humans either.
The hypothesis that it is brain capacity that sets the upper
limit for the number of social relationships is also contradicted by
computer simulations that show simple unintelligent reactions to be
sufficient to emulate "ape politics"
and by the fact that some social insects such as the paper wasp do have
hierarchies in which each individual has its place (as opposed to
herding without social structure) and maintains their hierarchies in
groups of approximately 80 individuals with their brains smaller than
that of any mammal.
Reduction in aggression
Another theory that tries to explain the growth of human intelligence is the reduced aggression theory (aka self-domestication
theory). According to this strand of thought what led to the evolution
of advanced intelligence in Homo sapiens was a drastic reduction of the
aggressive drive. This change separated us from other species of monkeys
and primates, where this aggressivity is still in plain sight, and
eventually lead to the development of quintessential human traits such
as empathy, social cognition and culture.
This theory has received strong support from studies of animal
domestication where selective breeding for tameness has, in only a few
generations, led to the emergence of impressive "humanlike" abilities.
Tamed foxes, for example, exhibit advanced forms of social communication
(following pointing gestures), pedomorphic physical features (childlike
faces, floppy ears) and even rudimentary forms of theory of mind (eye contact seeking, gaze following).
Evidence also comes from the field of ethology (which is the study of
animal behavior, focused on observing species in their natural habitat
rather than in controlled laboratory settings) where it has been found
that animals with a gentle and relaxed manner of interacting with each
other – like for example stumptailed macaques, orangutans and bonobos –
have more advanced socio-cognitive abilities than those found among the
more aggressive chimpanzees and baboons. It is hypothesized that these abilities derive from a selection against aggression.
On a mechanistic level these changes are believed to be the
result of a systemic downregulation of the sympathetic nervous system
(the fight-or-flight reflex). Hence, tamed foxes show a reduced adrenal
gland size and have an up to fivefold reduction in both basal and
stress-induced blood cortisol levels. Similarly, domesticated rats and guinea pigs have both reduced adrenal gland size and reduced blood corticosterone levels. It seems as though the neoteny
of domesticated animals significantly prolongs the immaturity of their
hypothalamic-pituitary-adrenal system (which is otherwise only immature
for a short period when they are pups/kittens) and this opens up a
larger "socialization window" during which they can learn to interact
with their caretakers in a more relaxed way.
This downregulation of sympathetic nervous system reactivity is
also believed to be accompanied by a compensatory increase in a number
of opposing organs and systems. Although these are not as well specified
various candidates for such "organs" have been proposed: the
parasympathetic system as a whole, the septal area over the amygdala, the oxytocin system, the endogenous opioids and various forms of quiescent immobilization which antagonize the fight-or-flight reflex.
Social exchange theory
Other
studies suggest that social exchange between individuals is a vital
adaptation to the human brain, going as far to say that the human mind
could be equipped with a neurocognitive system specialized for reasoning
about social change. Social Exchange is a vital adaptation that evolved
in social species and has become exceptionally specialized in
humans.This adaption will develop by natural selection when two parties
can make themselves better off than they were before by exchanging
things one party values less for things the other party values for more.
However, selection will only pressure social exchange when both parties
are receiving mutual benefits from their relative situation; if one
party cheats the other by receiving a benefit while the other is harmed,
then selection will stop. Consequently, the existence of cheaters—those
who fail to deliver fair benefits—threatens the evolution of exchange.
Using evolutionary game theory, it has been shown that adaptations for
social exchange can be favored and stably maintained by natural
selection, but only if they include design features that enable them to
detect cheaters, and cause them to channel future exchanges to
reciprocators and away from cheaters. Thus, humans use social contracts
to lay the benefits and losses each party will be receiving (if you
accept benefit B from me, then you must satisfy my requirement R).
Humans have evolved an advanced cheater detection system, equipped with
proprietary problem-solving strategies that evolved to match the
recurrent features of their corresponding problem domains. Not only do
humans need to determine that the contract was violated, but also if the
violation was intentionally done. Therefore, systems are specialized to
detect contract violations that imply intentional cheating.
One problem with the hypothesis that specific punishment for
intentional deception could coevolve with intelligence is the fact that
selective punishment of individuals with certain characteristics selects
against the characteristics in question. For example, if only
individuals capable of remembering what they had agreed to were punished
for breaking agreements, evolution would have selected against the
ability to remember what one had agreed to.
Though this becomes a superficial argument after considering the
balancing positive selection for the ability to successfully 'make ones
case'. Intelligence predicts the number of arguments one can make when
taking either side of a debate. Humans who could get away with
behaviours that exploited within and without-group cooperation, getting
more while giving less, would overcome this.
Sexual selection
This model, which invokes sexual selection, is proposed by Geoffrey Miller who argues that human intelligence is unnecessarily sophisticated for the needs of hunter-gatherers
to survive. He argues that the manifestations of intelligence such as
language, music and art did not evolve because of their utilitarian
value to the survival of ancient hominids. Rather, intelligence may have
been a fitness indicator. Hominids would have been chosen for greater intelligence as an indicator of healthy genes and a Fisherian runaway positive feedback loop of sexual selection would have led to the evolution of human intelligence in a relatively short period.
In many species, only males have impressive secondary sexual characteristics
such as ornaments and show-off behavior, but sexual selection is also
thought to be able to act on females as well in at least partially monogamous species. With complete monogamy, there is assortative mating
for sexually selected traits. This means that less attractive
individuals will find other less attractive individuals to mate with. If
attractive traits are good fitness indicators, this means that sexual
selection increases the genetic load
of the offspring of unattractive individuals. Without sexual selection,
an unattractive individual might find a superior mate with few
deleterious mutations, and have healthy children that are likely to
survive. With sexual selection, an unattractive individual is more
likely to have access only to an inferior mate who is likely to pass on
many deleterious mutations to their joint offspring, who are then less
likely to survive.
Sexual selection is often thought to be a likely explanation for
other female-specific human traits, for example breasts and buttocks far
larger in proportion to total body size than those found in related
species of ape.
It is often assumed that if breasts and buttocks of such large size
were necessary for functions such as suckling infants, they would be
found in other species. That human female breasts (typical mammalian
breast tissue is small) are found sexually attractive by many men is in agreement with sexual selection acting on human females secondary sexual characteristics.
Sexual selection for intelligence and judging ability can act on
indicators of success, such as highly visible displays of wealth.
Growing human brains require more nutrition than brains of related
species of ape. It is possible that for females to successfully judge
male intelligence, they must be intelligent themselves. This could
explain why despite the absence of clear differences in intelligence
between males and females on average, there are clear differences
between male and female propensities to display their intelligence in
ostentatious forms.
This absence of difference is now known to exist at the middle of
distributions. Average intelligence doesn't differ much between
genders, but because female selection is restricted more towards males
at the top end of male-male hierarchies or those increasingly above
average in physical attractiveness, male trait distributions often have
longer tails; that is to say the lowest and highest intelligences (and
many more traits) in male populations extend further out into the lowest
and highest values of the distribution than for female traits. This is
because it paid to be a highly variable male, as average males would
have consistently low opportunity, but variable males had a chance of
falling on the preferred side of the trait distribution.
Critique
The
sexual selection by the disability principle/fitness display model of
the evolution of human intelligence is criticized by certain researchers
for issues of timing of the costs relative to reproductive age. While
sexually selected ornaments such as peacock feathers and moose antlers
develop either during or after puberty, timing their costs to a sexually
mature age, human brains expend large amounts of nutrients building myelin
and other brain mechanisms for efficient communication between the
neurons early in life. These costs early in life build facilitators that
reduce the cost of neuron firing later in life, and as a result the
peaks of the brain's costs and the peak of the brain's performance are
timed on opposite sides of puberty with the costs peaking at a sexually
immature age while performance peaks at a sexually mature age. Critical
researchers argue that this means that the costs that intelligence is a
signal of reduce the chances of surviving to reproductive age, does not
signal fitness of sexually mature individuals and, since the disability
principle is about selection for disabilities in sexually immature
individuals that evolutionarily increase the offspring's chance of
surviving to reproductive age, would be selected against and not for by
its mechanisms. These critics argue that human intelligence evolved by
natural selection citing that unlike sexual selection, natural selection
have produced many traits that cost the most nutrients before puberty
including immune systems and accumulation and modification for increased
toxicity of poisons in the body as a protective measure against
predators.
Intelligence as a disease-resistance sign
The number of people with severe cognitive impairment caused by childhood viral infections like meningitis, protists like Toxoplasma and Plasmodium, and animal parasites like intestinal worms and schistosomes is estimated to be in the hundreds of millions.
Even more people live with moderate mental damages, such as inability
to complete difficult tasks, that are not classified as 'diseases' by
medical standards, may still be considered as inferior mates by
potential sexual partners.
Thus, widespread, virulent,
and archaic infections are greatly involved in natural selection for
cognitive abilities. People infected with parasites may have brain
damage and obvious maladaptive behavior in addition to visible signs of
disease. Smarter people can more skillfully learn to distinguish safe
non-polluted water and food from unsafe kinds and learn to distinguish
mosquito infested areas from safe areas. Smarter people can more
skillfully find and develop safe food sources and living environments.
Given this situation, preference for smarter child-bearing/rearing
partners increases the chance that their descendants will inherit the
best resistance alleles, not only for immune system
resistance to disease, but also smarter brains for learning skills in
avoiding disease and selecting nutritious food. When people search for
mates based on their success, wealth, reputation, disease-free body
appearance, or psychological traits such as benevolence or confidence;
the effect is to select for superior intelligence that results in
superior disease resistance.
Ecological dominance-social competition model
A predominant model describing the evolution of human intelligence is ecological dominance-social competition (EDSC), explained by Mark V. Flinn, David C. Geary and Carol V. Ward based mainly on work by Richard D. Alexander.
According to the model, human intelligence was able to evolve to
significant levels because of the combination of increasing domination
over habitat
and increasing importance of social interactions. As a result, the
primary selective pressure for increasing human intelligence shifted
from learning to master the natural world to competition for dominance among members or groups of its own species.
As advancement, survival and reproduction within an increasing
complex social structure favored ever more advanced social skills, communication
of concepts through increasingly complex language patterns ensued.
Since competition had shifted bit by bit from controlling "nature" to
influencing other humans, it became of relevance to outmaneuver other
members of the group seeking leadership or acceptance, by means of more advanced social skills. A more social and communicative person would be more easily selected.
Intelligence dependent on brain size
Human
intelligence is developed to an extreme level that is not necessarily
adaptive in an evolutionary sense. Firstly, larger-headed babies are
more difficult to give birth to and large brains are costly in terms of nutrient and oxygen requirements.
Thus the direct adaptive benefit of human intelligence is questionable
at least in modern societies, while it is difficult to study in
prehistoric societies. Since 2005, scientists have been evaluating
genomic data on gene variants thought to influence head size, and have
found no evidence that those genes are under strong selective pressure
in current human populations. The trait of head size has become generally fixed in modern human beings.
While decreased brain size has strong correlation with lower
intelligence in humans, some modern humans have brain sizes as small as
Homo Erectus but normal intelligence (based on IQ tests) for modern
humans. Increased brain size in humans may allow for greater capacity
for specialized expertise.
Expanded cortical regions
The two major perspectives on primate brain evolution are the concerted and mosaic approaches.
In the concerted evolution approach, cortical expansions in the brain
are considered to be a by-product of a larger brain, rather than
adaptive potential. Studies have supported the concerted evolution model by finding cortical expansions between macaques and marmosets are comparable to that of humans and macaques. Researchers attribute this result to the constraints on the evolutionary process of increasing brain size. In the mosaic approach, cortical expansions are attributed to their adaptive advantage for the species. Researchers have attributed hominin evolution to mosaic evolution.
Simian primate brain evolution studies show that specific
cortical regions associated with high-level cognition have demonstrated
the greatest expansion over primate brain evolution. Sensory and motor regions have showcased limited growth. Three regions associated with complex cognition include the frontal lobe, temporal lobe, and the medial wall of the cortex. Studies demonstrate that the enlargement in these regions is disproportionately centered in the temporoparietal junction (TPJ), lateral prefrontal cortex (LPFC), and anterior cingulate cortex (ACC). The TPJ is located in the parietal lobe and is associated with morality, theory of mind, and spatial awareness. Additionally, the Wernicke's area is located in the TPJ. Studies have suggested that the region assists in language production, as well as language processing. The LPFC is commonly associated with planning and working memory functions. The Broca's area, the second major region associated with language processing, is also located in the LPFC. The ACC is associated with detecting errors, monitoring conflict, motor control, and emotion.
Specifically, researchers have found that the ACC in humans is
disproportionately expanded when compared to the ACC in macaques.
Studies on cortical expansions in the brain have been used to examine the evolutionary basis of neurological disorders, such as Alzheimer's disease.
For example, researchers associate the expanded TPJ region with
Alzheimer's disease. However, other researchers found no correlation
between expanded cortical regions in the human brain and the development
of Alzheimer's disease.
Cellular, genetic, and circuitry changes
Human brain evolution involves cellular, genetic, and circuitry changes. On a genetic level, humans have a modified FOXP2 gene, which is associated with speech and language development. The human variant of the gene SRGAP2, SRGAP2C, enables greater dendritic spine density which fosters greater neural connections. On a cellular level, studies demonstrate von Economo neurons (VENs) are more prevalent in humans than other primates. Studies show that VENs are associated with empathy, social awareness and self-control. Studies show that the striatum plays a role in understanding reward and pair-bond formation. On a circuitry level, humans exhibit a more complex mirror neuron system,
greater connection between the two major language processing areas
(Wernicke's area and Broca's area), and a vocal control circuit that
connects the motor cortex and brain stem. The mirror neuron system is associated with social cognition, theory of mind, and empathy.
Studies have demonstrated the presence of the mirror neuron system in
both macaques in humans; However, the mirror neuron system is only
activated in macaques when observing transitive movements.
Group selection
Group selection
theory contends that organism characteristics that provide benefits to a
group (clan, tribe, or larger population) can evolve despite individual
disadvantages such as those cited above. The group benefits of
intelligence (including language, the ability to communicate between
individuals, the ability to teach others, and other cooperative aspects)
have apparent utility in increasing the survival potential of a group.
In addition, the theory of group selection is inherently tied to
Darwin's theory of natural selection. Specifically, that "group-related
adaptations must be attributed to the natural selection of alternative
groups of individuals and that the natural selection of alternative
alleles within populations will be opposed to this development".
Between-group selection can be used to explain the changes and
adaptations that arise within a group of individuals. Group-related
adaptations and changes are a byproduct of between-group selection as
traits or characteristics that prove to be advantageous in relation to
another group will become increasingly popular and disseminated within a
group. In the end, increasing its overall chance of surviving a
competing group.
However, this explanation cannot be applied to humans (and other
species, predominantly other mammals) that live in stable, established
social groupings. This is because of the social intelligence that
functioning within these groups requires from the individual. Humans,
while they are not the only ones, possess the cognitive and mental
capacity to form systems of personal relationships and ties that extend
well beyond those of the nucleus of family. The continuous process of
creating, interacting, and adjusting to other individuals is a key
component of many species' ecology.
These concepts can be tied to the social brain hypothesis,
mentioned above. This hypothesis posits that human cognitive complexity
arose as a result of the higher level of social complexity required from
living in enlarged groups. These bigger groups entail a greater amount
of social relations and interactions thus leading to a expanded quantity
of intelligence in humans.
However, this hypothesis has been under academic scrutiny in recent
years and has been largely disproven. In fact, the size of a species'
brain can be much better predicted by diet instead of measures of
sociality as noted by the study conducted by DeCasien et. al. They found
that ecological factors (such as: folivory/frugivory, environment)
explain a primate brain size much better than social factors (such as:
group size, mating system).
Nutritional status
Diets deficient in iron, zinc, protein, iodine, B vitamins, omega 3 fatty acids, magnesium and other nutrients can result in lower intelligence
either in the mother during pregnancy or in the child during
development. While these inputs did not have an effect on the evolution
of intelligence they do govern its expression. A higher intelligence
could be a signal that an individual comes from and lives in a physical
and social environment where nutrition levels are high, whereas a lower
intelligence could imply a child, its mother, or both, come from a
physical and social environment where nutritional levels are low. Previc
emphasizes the contribution of nutritional factors, especially meat and
shellfish consumption, to elevations of dopaminergic activity in the brain, which may have been responsible for the evolution of human intelligence since dopamine is crucial to working memory, cognitive shifting, abstract, distant concepts, and other hallmarks of advanced intelligence.
