“Intelligence is what you do when you don't know what to do"”
Chapter 2- ABOUT INTELLIGENCE & IQ
2.1 What is Intelligence?
Intelligence of a human being is a property that is very difficult to be defined in a
clear and specific way, because usually this term has different meanings in different
people, cultures and societies. Even for the global scientific community, the term
intelligence has been, for many years, a source of controversy since its exact
definition and measurement formats of acceptance is not unanimous and general. In
popular sense, intelligence is the general mental ability of people to relate what they
know to a particular problem or situation solution.
In popular sense, intelligence is the general mental ability of people to relate what they know to a particular problem or situation solution
The meaning of human intelligence is difficult to be defined in a few words and its meaning has been changed during the years. The following are some of the more popular definitions of the term "intelligence" currently:
● "The ability to learn or to profit from experience"
● "The ability to acquire the ability"
● "Intelligence is what intelligence tests
● "A global concept
that involves an individual's ability to act intentionally,
rationally and to deal effectively with the environment"
● "Intelligence is a general factor that
crosses all kinds of performance"
"A person who possesses intelligence insofar as he had learned, or
can learn, to adjust to their environment"
cited in Sternberg, 1982, p.30)
● "Intelligence is the
adaptation to the environment"
"Intelligence is the power of the mind in the order that is perceived in a
situation that was considered messy"
(R. W. Young, quoted
in Kurzweil, 1999)
● "Intelligent activity is to capture the
essence in a given situation and respond appropriately to them"
● "Intelligence is the ability to use optimally
limited resources - including time - to achieve the objectives"
● "Intelligence is what you do when you
don't know what to do"
"Intelligence is a hypothetical concept that we define as reflected in
certain types of behavior"
2.2 General Intelligence – Factor “G”
General intelligence, also known as "G factor", refers to the existence of a common
ability that influences performance on mental ability measures. General intelligence is
based on measure of people’s performance across a variety of mental tests.
The existence of general intelligence was first described by Charles Spearman in
1904. Spearman found that those who performed well on one cognitive test tended
to perform well on other tests, while those who scored badly on one test tended to
score badly on others. He concluded that intelligence is general cognitive ability that
could be measured and numerically expressed. According to Spearman, this G
factor is responsible for overall performance on mental ability tests.
In terms of psychometrics, general intelligence can be measured and expressed by a
single number, such as an IQ (Intelligence Quotient) score. The idea is that this
underlying general intelligence influences performance on all cognitive tasks.
2.3 Measurement of Intelligence - Scale Benet
Intelligence quotient (IQ), developed in 1905 by Alfred Benet, a French psychologist
and lawyer, is the main scale used by many scientists and educators to quantify
intelligence. The initial purpose of the scale developed by Benet was to use it as a
diagnostic tool to identify students who needed special attention, based on the idea
that the intelligence of a child depending on relationship between chronological age
and mental age. For example, for a child of three years old, reciting the alphabet is a
relatively difficult task, while for a six years old would be relatively easy. As a three
year old child, what he was able to do would be considered very intelligent, while the
same thing that could not be done by a six years old would be considered less
The mental tests published by Benet were interpreted differently by the rest of the
English speaking countries, especially in England and the United States. These
tended to be a common ideology and interpretation of the results quite differently
from that of Benet in France. In the U.S., the eugenics movement sought to
demonstrate in 1908 that intelligence is inherited almost entirely, because it really
encourages that intelligence is a work environment conducive to their development,
and found useful in measuring intellectual development through test as evidence to
scientifically prove the superiority of the white race.
Professor Lewis Ternan and his team at Stanford University found the need to adapt
the test according to the parameters of education in California. The methods of
testing and outlining intelligence are established with new rules not only applicable to
teenagers, but are extended to people with older ages. The review is called Stanford-
Benet scale, which is a universally recognized and applied test to determine people's
Monitoring and studying large groups of children from poor families who have been
adopted and raised by a family with more favorable cultural and economic
environment, have established that these children fail to achieve a higher intellectual
level than those of the same origin but have been raised by their biological parents in
an alleged atmosphere of conflict and poor economic culture. These studies have
disproved the theory that had formerly under which "social class differences produce
different intrinsic aptitude, ie an" unequal intelligence "which is genetically inherited
(passed from parents to children), and is fixed and invariable." These basic
assumptions are now considered totally wrong, because intelligence really fosters an
environment conducive to the kids’ development.
Currently scientists, statisticians, psychologists, educators and researchers all agree
that intelligence or IQ (intelligence quotient) of a normal baby is determined by 60-
80% of natural genetic factors (genes inherited from mother and father) and by 20-
40% of environmental factors.
2.4 Coefficient Is Intellectual - IQ
The Intelligence Scale Stanford-Benet (SB5) is a method most commonly used to
determine the cognitive abilities of individuals aged from two to 85 years. An IQ
score represents reasoning and thinking skills. It is calculated by dividing the mental
age by chronological age and multiplying the result by 100. For example, if the
chronological age of a child is 8 years old and an intelligence test reveals that his
mental age is 10, his IQ score is more or less 10/8 = 1.25 x 100 = 125.
The mental age is determined by a series of standardized tests that measure
intelligence in five areas:- The fluid reasoning
- Quantitative reasoning
- The visual-spatial processing
- Working memory.
- Verbal scores and yield are combined to produce a score scale.
The Stanford-Benet scale suggests that the average IQ of the population is between
85 and 115. A score of 100 is considered the average IQ of the entire population. The
IQ of a genius is 140.
The factor G has a normal distribution in the general population, suggesting probably a product of several
genes that interact with the environment (Tayyari, F. 2004).
The median full scale score or the average IQ is 100.
People in the middle area of the graph with an IQ of 100 are able to obtain a
university degree. People in the IQ 110-119 or "high average" are more able to
succeed in professional activities that are intellectually demanding, like managers,
lawyers, etc. People in this range may have better memory, faster processing speeds
and superior skills of decision making. The range "superior" IQ score of 120 or higher
are those who will become doctors, scientists, academics, engineers, and the like.
In conclusion, the average IQ of the population is 100. Therefore, 68% of the
population has an IQ between 85 and 115.
- People in the 110-119 or "high average" IQ range are more capable of succeeding in professional activities that are more intellectually demanding as managers, teachers lawyers and so forth. People in this range might have better memories, faster processing speeds and higher decision-making skills.
- People in the average range with an IQ score of about 100, are capable of earning a college degree. This range fits also clerical workers, sales workers, high school graduates, skilled workers (e.g., electricians, cabinetmakers), craftsmen and foremen.
- Semi-skilled workers (operatives, service workers, including private household) are in the range of 92.
- Unskilled workers are usually in the rage of 87 and below.
2.5 Multiple Intelligences
For general purposes, a broad definition of intelligence is "a global concept that
involves an individual's ability to act intentionally, think rationally and interact
effectively with the environment." (David Wechsler, 1958).
In 1990, Salovey and Mayer coined the term emotional intelligence EI as "a form of
social intelligence that involves the ability to control one's feelings and those of
others, to discriminate among them and to use this information to guide the thoughts
and actions" (Salovey and Mayer, 1990).
For many parents and educators, the traditional IQ test (using models developed by
Benet) is a poor measure for evaluating the various forms of talents and innate
abilities that children have.
Initially psychologists and scientists began to define the term intelligence, and focused on individual cognitive aspects such as memory and problem solving in mathematics, but then many researchers acknowledged that non-cognitive aspects are also important, as the factor of emotional, personal and social. In 1983, Howard Gardner wrote his theory of multiple intelligences and proposed that interpersonal and intrapersonal intelligences are as important as the type of general intelligence as measured by IQ and related tests in life. These multiple intelligences are:
1. Logical-mathematical intelligence
(ability to solve problems that are
(ability of a person to use the word and language)
3. Visual-Spatial intelligence
(ability to create a mental model of shapes, colors and textures)
(ability to control the movement of the whole body
for physical activity)
5. Musical intelligence
(ability to create sounds,
rhythms and melodies)
6. Interpersonal intelligence
(ability to interact
and understand others)
7. Intrapersonal intelligence
we understand what we do
8. Naturalist intelligence
scientific observation of nature)
Currently, a significant percentage of educators and educational systems around the
world have adopted the theory of multiple intelligences as the basis for the education
and development of children and the planning of primary school programs.br>
Regarding psychometrics, intelligence called "G factor" in relation to "general mental
ability", which is based on measuring the performance of individuals through a series of mental tests. The factor G is normally distributed in the general population, suggesting that it is likely a product of several genes that interact with the
2.6 Emotional Intelligence
Emotional intelligence (EI)
is the ability to identify, assess, and control the emotions of oneself, of others, and of groups.
includes three skills:
1.1. Emotional awareness, including the ability
to identify your own emotions and those of others;
2. The ability to
harness emotions and apply them to tasks like thinking and problems
3. The ability to manage emotions, including the ability to
regulate your own emotions, and the ability to cheer up or calm down
another person. r>
WaWayne Payne was the first who introduced the term
emotional intelligence in his doctoral dissertation entitled "A study of
emotion: developing emotional intelligence” in 1985.
In an article published in Mensa Magazine in 1987, Keith Beasley uses the term
"emotional quotient." It has been suggested that this is the first published use of the
term. The concept of emotional intelligence is popularized in 1995, after publication
of psychologist and New York Times science writer Daniel Goleman’s book Emotional
Intelligence: Why It Can Matter More Than IQ.
According to Salovey & Mayer (1990), “the emotional intelligence could
defined as the subset of social intelligence that involves the ability to monitor
one's own and others' feelings and emotions, to discriminate among them and
to use this information to guide one's thinking and actions”
. (From “Emotional
2.7 Social Intelligence
Social intelligence is the capacity to effectively negotiate complex social relationships and environments. According with some experts, it is social intelligence,
rather than quantitative intelligence, that defines humans.
The social intelligence has been described as “a model of personality and individual
behavior in which people are presumed to be knowledgeable about themselves and
the social world in which they live” (Bar-On, 1994, p.38).
Social scientist Ross Honeywill believes that social intelligence is an aggregated
measure of self- and social-awareness, evolved social beliefs and attitudes, and a
capacity and appetite to manage complex social change. A person with a high social
intelligence quotient (SQ) is not better or worse than someone with a low SQ, but
they have different attitudes, hopes, interests and desires.
2.8 Fluid and Crystallized Intelligence
The Cattell-Horn theory of fluid and crystallized intelligence suggests that intelligence
is composed of a number of different abilities that interact and work together to
produce overall individual intelligence.
Crystallized intelligence refers to the learning, knowledge and skills that are accumulated over a lifetime
refers to the learning, knowledge and skills that are accumulated over a lifetime. This type of intelligence tends to increase with age.
or fluid reasoning is the capacity to think logically and solve
problems in novel situations, independent of acquired knowledge. This ability is
considered independent of learning, experience, and education. Examples of the use
of fluid intelligence include solving puzzles and coming up with problem-solving
strategies. Many researches suggest that fluid intelligence begins to decrease after
Fluid intelligence is the capacity to think logically and solve problems in novel situations, independent
of acquired knowledge.
Fluid and crystallized intelligences are complementary in that some learning tasks can be mastered mainly by exercising either fluid or crystallized intelligence.
2.9 Where in Human Brain Intelligence Reside?
Intelligence resides in several places, but not just one place, and not in the entire
brain. Intelligence is comprised of a network of processing centers spread throughout
very distinct parts of the brain. The left hemisphere of the brain appears to be more
related to intelligence than the right one. But the function of intelligence resides in
particular regions in the front, the back and both sides. We have been able to
pinpoint through very advanced neuroimaging technology and discreet areas within
each of the lobes where information comes together, and is processed intensively.
The brain can be divided into three major parts. The brain stem, shaped like a widening stalk, connects the spinal cord to the upper brain. It controls reflexes and
involuntary processes like breathing and heart rates. Behind the brain stem and below the upper brain is the cerebellum, which is involved in balance and
coordination. Of course, you need some parts of your brain to function in a very predictable way or you will die. Scientists are interested in identifying regions in the
brain where there is greater variability in brain activity, size, blood flow and the like, in order to locate where individual differences are most pronounced.
Most of the researches to date have been looking at gray matter - the processing
centers - of the brain. But they also have been investigating white matter, which
provides the "wiring" that links these processing centers, particularly between the
front and the back of the brain. It is the combination of gray and white matters, and
how well they work in concert that is significant to the understanding of intelligence.
Although our advanced cognitive abilities are dependent on the cerebral cortex, it is
not the only part of the brain relevant to child development. The limbic system,
located in the inner brain beneath the cortex, is a collection of small structures
involved in more instinctive behaviors like emotional reactions, stress responses, and
reward-seeking behaviors. The hippocampus is involved in memory formation and
spatial learning. The hypothalamus is the control center for one of the body’s key
stress systems, regulating the release of cortisol and other stress hormones. The
amygdala evaluates threats and triggers the body’s stress response.
2.10 Factors Affecting Intelligence
Various studies and investigations have identified certain circumstances and
attributes that influence a greater or lesser (but still significant) in people’s IQ
(Bouchard and Segal, 1985; Liungman, 1975).
The development of
intelligence varies positively
with the following factors:
- Birth weight
- Number of years in school
- Social Group parental home
Occupation of father (having a well-educated father is very valuable for
- Economic situation of father
- Ambition of parents
Education of mother
- Average reading books
- Confidence in accordance
with scale of measurement of attitude
- Emotional adjustment
- Age of
mother (a mother over 25 years of age is associated with higher IQ records)
- Gestational age at birth
The development of intelligence may vary negatively
- Age (negative relationship, applied only in
- Degree of authority in his parents' house
- Crime (-ve)
- Alcoholism (-ve)
- Mental Illness (-ve)
Degree of rigidity of parents (-ve)
- Child malnutrition (-ve)
Average TV Viewing (-ve)
-- Number of siblings (-ve)
It is also necessary to note that the level of intelligence that will meet an individual
in adulthood depends largely on the choices and decisions he/she makes during
his/her childhood and adolescence.
On the other hand, it is important to consider the environmental causes that
influence positively or negatively the development of intelligence. Freyer and Levitt
(2006), when testing children from eight to twelve months old, only found small
differences (SD 0.06) in IQ between black children and white children. Flynn has
argued that in the United States, the differences between the IQ of black and white
children gradually appear, suggesting environmental causes. "In just 10 months, the
average score is only one point behind. By the age of four years, it is 4.6 points
behind, and by the age of 24 years, the gap becomes 16,6 points. This could be
attributed to the genetic initially, but the steadiness after age 4 suggests something
else, which indicates about 0.6 IQ points lost every year. Similarly, genetically driven
differences, such as height differences between men and women, tend to work within
a certain age".
2.11 Children Are Smarter Every Day - Flynn Effect
In the 1980s, a scientist James Flynn, realized that IQ is increasing in all countries
most of the time, at an average rate of about 3 IQ points per decade. That is because
the average IQ worldwide has increased by 1 standard deviation (ie, 15 points) since
1945, largely due to environmental effects. As a result, they have had to adjust the
scale of intelligence tests to keep the focus on '100'.
Could it be due to the diet? Possibly, but IQ scores are increasing so rapidly in
western countries where people are fed well. Could it be the school? The education
interruptions have only temporary effects on IQ. Importantly, the best results
achieved in the tests are related to abstract reasoning.
A researcher, Ulric Neisser, suggests that the Flynn effect is due to the way that we
are being saturated with sophisticated visual images: ads, posters, video games and
television graphics, etc. - rather than written messages. He suggests that children
today live in an environment with continuous visual stimulation richer than in the
past, and this greatly helps with visual puzzle IQ tests.
2.12 The Intelligent Living Longer
Several recent studies have confirmed what has been suspected for years: intelligent
people live longer. Research conducted by Pamela Herd in 2010, University of
Wisconsin, United States, with 10,000 people who graduated high school in 1957,
found that students who finished in the top 25 of the class were healthier 50 years
later when compared to their peers with lower academic performance. This type of
work has been replicated in Australia, Denmark, England, Wales and Sweden, and the
result is the same. "The association has been found in all populations where it has
been studied," Deary wrote in the study.
Scottish researcher Ian Deary, director of the Center for Cognitive Ageing at the
University of Edinburgh, has studied extensively the fact that intelligent people live
longer that supports the theory that intelligence could predict mortality better than
other indicators such as the rate of body mass, cholesterol and blood pressure. In a
study published in 2011 in the journal Psychological Science in the Public Interest,
the researcher summarizes dozens of studies that concluded also the same:
intelligent people live longer.
One such work was done between 3654 Scottish war veterans, and the conclusion
was that those with low IQ, or normal IQ, suffered from many more diseases, from
hernias to cataract, when compared with those who showed greater alertness who
were more healthy.
2.12 Are You Smart or Just “Clever” (ready)?
For many people, a clever person is somebody who knows how to take advantage of situations.
The word intelligence comes from the Latin verb "intellegere" that means
"understanding." However, the ability to understand could be considered as "smart" -
the ability to adapt and "be ready" or "clever" which refers to the ability to adapt
creatively. In the educational context, the intelligence of a person is often equated
with their academic performance, but this is not necessarily correct.
Certainly, a person's ability to think critically, and to use the knowledge and
experience is often more important than the ability to control a large number of facts.
2.13 Fourteen Interesting Facts about Intelligence
1. IQ is associated with some simple abilities.
No one with measurable IQ has
difficulty on deciding which of the two lines is longer, or whether two pairs of letters
are identical. However, in order to perform these simple tasks, a person with an IQ below 70 may need up to five times longer than a person with a higher IQ. The
nervous systems of those with lower IQs are simply less efficient.
2. School attendance correlates with IQ
. Staying in school can elevate IQ or,
more accurately, keep it from slipping. Evidence for this dates back to the turn of the
twentieth century when the London Board of Education found that the IQs of children
in the same family decreased from the youngest to the oldest. The older children
progressively missed more school. Towards the end of the Vietnam War, a lottery
determined draft priority. Those men born on July 9, 1951 were picked first so they
tended to stay in school longer in order to avoid the draft. Those men born on July 7
were the last in the lottery and thus had no incentive to stay in school. Those men
born on July 9 had higher IQs and also earned 7 percent more money. Summer
vacations also seem to affect IQ, because with each passing month, children’s endof-
year scores decline.
3. IQ is not influenced by birth order.
The idea that birth order influences
personality and intelligence has not stood up under scrutiny. Moreover, the claim that
large families make low-IQ children may be unfounded because researchers have
found that low-IQ parents make larger families. Smart people tend to have smaller
families, but it is not smaller families per se that make people smart.
4. IQ is related to breast-feeding.
Even when researchers control factors such as
the sense of closeness of mother and child experiences through nursing, breast-fed
children appear to have an IQ of 3 to 8 points higher by age 3. 5. IQ varies by birth date.
State policies mandate the age of students entering
school as well as the age they leaving, typically 16 or 17. Those born in the final
three months of the year are more likely to enter school a year later; thus, when
they leave school, they have been attending one year less. For each year of school
completed, there is an IQ gain of approximately 3.5 points. Unsurprisingly, as a
group, those born later in the year show a lower IQ score.
6. IQ evens out with age.
Imagining, suggests Ceci, two biological siblings adopted
by two different middle class families, at age 5, and again in early adulthood. Are
their IQs more alike when younger and living in the homes of their adoptive parents,
or when they are older and living on their own? Contrary to expectation, as the
siblings go out on their own, their IQ scores become more similar. The probable
reason is that once they are away from the dictates of their adoptive parents, they
are free to let their genotypes express themselves. Because they share about 50
percent of their genes, they will become more alike because they are likely to seek
similar sorts of environments.
7. Intelligence is plural, not singular.
Regardless of their views of so-called
general intelligence, researchers agree that there are statistically independent mental abilities such as spatial, verbal, analytical, and practical intelligence. Howard Gardner,
of course, is a primary proponent of multiple intelligences theory.
8. IQ is correlated with head size.
Modern neuroimaging techniques demonstrate
that cranial volume is correlated with IQ. Evidence also comes from studies of the
helmet sizes of members of the Armed Forces whose IQs were measured during basic
training. Correlations are quite small.
9. Intelligence scores are predictive of real-world outcomes.
those with comparable levels of schooling, the greater a person’s intellectual ability,
the higher the person’s weekly earnings. Those workers with the lowest levels of
intellectual ability earn only two-thirds the amount of those with the highest level.
10. Intelligence depends on context.
In visiting racetracks, researchers found
that some men were excellent handicappers while others were not. A complex mental
algorithm that was used to convert racing data from the racing programs sold at the
track distinguished experts from nonexperts. However, the use of the algorithm was
unrelated to the men’s IQ scores. Some experts were dockworkers with IQs in the
80s, but they reasoned far more complexly at the track than all other nonexperts,
even those with IQs above 120. But, these experts performed very poorly at
reasoning outside of the track. 11. IQ is going up.
IQ has risen about 2 points with every generation, an increase
called the Flynn effect. The rise in IQ has been attributed to better nutrition, more
schooling, and better-educated parents. 12. IQ may be influenced by the school cafeteria menu.
In one large study, one
million students enrolled in the New York City school system were examined before
and after preservatives, dyes, colorings, and artificial flavors were removed from
lunch offerings. The investigators found a 14% improvement in IQ after the removal.
Improvement was greatest for the weakest students.
13. SMART WOMEN ARE THE MOST WHO HAVE DECIDED NOT TO HAVE
A study made in 2013 by the London School of Economics, concluded
that the higher female intelligence, the lower the maternal desire. According to the
psychologist Satoshi Kanazawa at the School of Economics and Political Science,
London, who led the study said that “this act goes against the human evolutionary
sense. They are avoiding their biological destiny and thus the least intelligent
mothers will have less intelligent children, and this can have drastic implications for
the CI of the population," he warns.
14. The IQ varies with the age.
The maximum IQ of a person is reached
approximately between 20 and 30 years of age. Fluid intelligence peaks in
adolescence and begins to decline progressively beginning around age 30 or 40. It is
unclear whether any lifestyle intervention can preserve fluid intelligence into older
ages. Cross-sectional studies usually show that especially fluid intelligence peaks at a
relatively young age (often in the early adulthood), while longitudinal data mostly
show that intelligence is stable until the mid-adulthood or later. Subsequently,
intelligence seems to decline slowly.
Real People & IQ
There's tremendous variability in human intelligence, ranging from profound mental
retardation to genius. In humans, the average IQ is between 90 and 109, which
accounts for about half of the population. Only 25 percent of the population has IQs
at 110 or above, and this number goes down rapidly as IQ increases: 10 percent
have IQs 120 or above, 2 percent are 130 or above, and less than half of 1 percent
are at an IQ of 140 or above.
To see this fact in a real perspective, people in the average range with an IQ score
of about 100, are capable of earning a college degree. People in the 110-119 or
"high average" IQ range are more capable of succeeding in professional activities
that are more intellectually demanding - managers, lawyers and so forth. People in
this range might have better memories, faster processing speeds and higher
decision-making skills. When we go up to the "superior" range, an IQ score of 120
and above, that's when you get into medical doctors, scientists, academics,
engineers and the like.
That isn't to say that you can't be a professor with an IQ of 100. In fact, you could
very well be a great professor. It just means that it may be somewhat harder to
attain this level of education than it is for someone with an IQ of 120. Other factors
besides IQ play significant roles in each of these careers, including interpersonal
skill, creativity, opportunity, and so on.
2.14 Famous People and their IQ Scores.
The following is a list of former U.S. presidents and famous people, and it is a list of IQ scores
Source: Some of these estimated IQ scores are taken from "The Calculated IQ
Estimates for 301 Historic Geniuses" published by Catherine Cox Miles,
American Psychologist- See more at:
● In the popular sense, intelligence is the general mental ability of the people to relate what they know
in order to act and solve a particular problem or situation.
● The general intelligence or “g factor” can be measured and
expressed by a single number, such as an IQ score.
● Emotional intelligence (EI) is the ability to identify, assess, and control
the emotions of oneself, of others, and of groups.
● The social intelligence can be described as “a model of personality and individual behavior in which people are presumed to be knowledgeable
themselves and the social world in which they live.”
● IQ is associated with some simple abilities. The nervous systems of those with lower IQs are simply less efficient.
● Howard Gardner was the proponent of multiple intelligences theory that is today widely accepted. These multiple intelligences are: Logicalmathematical,
visual-spatial intelligence, kinesthetic intelligence, musical
intelligence, intrapersonal intelligence, intrapersonal intelligence and naturalist intelligence.
● School attendance correlates with IQ. Staying in school can elevate IQ or, more accurately, keep it from slipping.
● IQ is not influenced by birth order. Smart people tend to have smaller families, but it
is not smaller families per se that make people smart.
● IQ is related to breast-feeding. Breast-fed children appear to have an IQ of 3 to 10 points higher by age 3.
● IQ is going up. IQ has risen about 20 points with every generation, an increase called the Flynn effect.
● Both types of intelligence, Crystallized and Fluid, increase throughout childhood and adolescence.
● Fluid intelligence peaks in adolescence and begins to decline progressively beginning around age 30 or 40.
● Crystallized intelligence continues to grow throughout adulthood.