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Emerging Perspectives 
ep.journalhosting.ucalgary.ca 

 
 

On the Capacity to Change: Exploring the Malleability of Intelligence 

Michèle P. Cheng*, Sonja Saqui 

University of British Columbia 

“Does intelligence have the capacity to change?” Addressing this question is of prime 
importance, as how we characterize intelligence can have significant consequences 
for individuals. The following paper will explore the controversy related to the 
malleability of intelligence. It will critically analyze the nature and nurture aspects of 
the debate, and suggest further research be conducted on the relationship between 
malleability and the growth mindset. 
Keywords: Intelligence, malleability, growth mindset 
Cheng, M. P. & Saqui, Sonja. (2017). On the capacity to change: Exploring the 
malleability of Intelligence. Emerging Perspectives, 1(2), 1-9. 

 
 Intelligence is a broad spectrum of differing abilities, as depicted by the Cattell-Horn-
Carroll model of cognitive abilities (Flanagan & Harrison, 2012). It has been one of the most widely 
researched constructs, yet it is still heavily debated today (Plomin & Spinath, 2004). In particular, 
there have been many objections related to the different factors that contribute to intelligence. On 
the one hand, many theorists strongly believe that genes play a predominant role in intellectual 
capacity, and that heredity is the principle, if not only, determinant of intelligence (Plomin & 
Spinath, 2004). On the other hand, many researchers believe that environmental factors contribute 
substantially to cognitive ability and can even alter genetic predisposition (Nesbitt et al., 2012; Day 
& Sweatt, 2011). The nature-nurture debate of intelligence has spurred controversy for decades, 
particularly with regards to one specific aspect: its capacity to change. The malleability of 
intelligence continues to spark fervent discussion, especially with the completion of the Human 
Genome Project, which is an international research project attempting to completely sequence 
human DNA, and the rise in research in epigenetics, which refers to changes in gene expression 
based on environmental factors (Bjorklund, 2006; Day & Sweatt, 2011). Much time and research 
has been spent in attempting to answer the important question, “Does intelligence have the capacity 
to change?” As we will see, further research should be conducted on the relationship between 
malleability and the growth mindset. 
 Addressing this question is of prime importance, as how we characterize intelligence can 
have significant consequences for individuals. For instance, we utilize tests of cognitive abilities 
to estimate an individual’s intellectual capacities in the education system to help address students’ 
academic difficulties (Kranzler & Floyd, 2013). The conclusions we draw from these tests have a 
significant impact on the solutions offered to students, as well as the students’ perspectives of their 
difficulties. If the administrator’s conclusions are based on a false interpretation of intelligence, the 

                                                        
 
* michele.p.cheng@gmail.com 



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solutions offered may have detrimental effects for the students. For example, students may believe 
that they are incapable of attaining specific grades because they are simply not as smart as other 
individuals. They may be repeatedly pushed to learn material in a specific way, when they are 
unable to grasp the material the same way as other students. Students who have a more malleable 
view of intelligence tend to put more effort in tasks and seek challenges more often than students 
who have a more fixed view of intelligence (Yeager & Dweck, 2012). The following paper will 
explore the controversy related to the malleability of intelligence. It will critically analyze the 
nature and nurture aspects of the debate and attempt to offer a solution as to whether intelligence 
has the capacity to change. 

Historical Perspective of Intelligence Malleability 

 While the malleability of intelligence has long been debated, increasing controversy 
stemmed from the publication of The Bell Curve in 1994. Within the book, the authors asserted 
that intelligence is an important predictor of many life outcomes, such as social class, social 
economic status and employment outcome (Herrnstein & Murray, 1994). Their book suggested 
that a high value for heritability, which is a correlation ranked between 0 and 1, limits the extent to 
which intelligence can be increased by a change in environment (Wahlsten, 1997). In fact, they 
asserted that intelligence remains stable and is unlikely to change. The arrival of The Bell Curve in 
1994 caused controversy within the population (Zenderland, 1997), as individuals did not want to 
believe that their own intellectual potential was predicted by their genetic predisposition and, more 
importantly, that there was nothing that could be done to change it.  

Despite the public’s disapproval, The Bell Curve nevertheless expressed an important 
aspect of intelligence: its heritability. Many researchers agreed on this component and provided 
evidence for the construct. Gottfredson (1997) conducted a survey that asked professionals in the 
field how they characterized intelligence. A main point of agreement was that intelligence was 
highly heritable and that, indeed, it changed little over time. More recently, Rushton and Jenson 
(2005), strong advocates for the heritability of intelligence, have performed multiple studies, 
suggesting that differences in intelligence might be related to genetic differences. For instance, 
they have conducted studies to investigate the causes behind group differences in mean IQ. Their 
evidence suggested that these differences were mainly due to genetic components (Rushton & 
Jenson, 2005). The more heritable a trait, the more often it is passed down from generation to 
generation, and the less likely it is to change. However, it is important to note that this research, 
though previously accepted, is highly controversial today, especially when considering how 
intelligence tests are catered to a specific subset of a population and unfairly portray other groups. 

Although many researchers supported the heritability and stability of intelligence, other 
theorists postulated a different view. In particular, Gardner (2006) believed that intelligence was 
strongly affected by individuals’ environments, as well as the culture surrounding them. His 
Multiple Intelligence theory argues that there are eight different types of intelligence, and an 
individuals’ strengths and weaknesses in terms of these abilities are strongly related to their 
environment (Gardner, 2006). In fact, if individuals were to change their environment, they would 
be able to develop and strengthen their other intelligences as well. Gardner’s theory, although 
difficult to prove, has spurred interest in the impact of the environment on intelligence. In more 
recent years, Richard Nisbett (2009), a prominent figure advocating for the malleability of 
intelligence, asserted that individual differences in intelligence are principally resulting from 
societal and cultural differences. Nisbett suggested that by bettering a student’s school 
environment, for example, through proper interventions and a positive and academically-geared 



Cheng, Saqui / Emerging Perspectives                                           3 

frame of mind, the student’s intelligence will increase. In fact, research has found that through 
proper working memory interventions, individuals also improved their fluid intelligence, that is, 
their abilities to solve novel problems through inductive and deductive reasoning (Nisbett et al., 
2012). As our environment changes, more opportunities arise to stimulate our intellectual 
capacities, and our intelligence changes as well. 

There have been many theories both to support the heritability and stability of intelligence. 
There have also been many studies to support environmental factors and the capacity of intelligence 
to change over time. The controversy surrounds the evidence that supports each claim. 

Evidence Against the Malleability of Intelligence 

 The heritability of intelligence provides evidence supporting the stability of intelligence. 
Brody (1994) found that genes influence the way in which a trait is expressed. Traits found to be 
highly developmentally stable may also be significantly heritable, in part due to strong directional 
selection (Moller & Thornhill, 1997). Additionally, a recent study examining the genetic and 
environmental contributions of intelligence found that phenotypic stability primarily resulted from 
additive genetic factors and the stability of common environment (Franic et al., 2014). This 
research provides evidence that the more heritable a trait is, the less likely it is to change over time. 
Animal, family and twin, developmental and adoption studies have all contributed to providing 
evidence to support the role of genes on intelligence, as well as the stability of this trait over time. 

Animal Studies  

Animal studies have been performed and, through genetic manipulations, have provided 
evidence for the role of heritability in intelligence. A classic experiment was conducted by Tolman 
in 1924 and repeated by Tryon in later years (1940), in which rats were bred in a specific manner 
to assess the heritability of intelligence. Rats were inbred based on their strong or weak 
performance on a maze, leading to maze-bright and maze-dull rats. Through generations of 
breeding, the researchers were able to significantly separate bright rats from dull rats in relation to 
performance on the particular maze, thereby providing evidence for the relationship between the 
specific traits and genes. These studies showed the importance of genetic input on traits related to 
cognitive ability, in this case on the performance of rats to quickly complete a maze. Further studies 
were also conducted on inbred strains of mice to investigate the contribution of genetics to 
individual differences for certain aspects of learning and intelligence (Plomin & Spinath, 2004). 
For instance, Zoubovsky et al. (2011) conducted a study in which the neural nitric oxide synthase 
gene (nNOS), which forms nitric oxide, was genetically deleted in mice. These mice then 
underwent behavioural tests, including open field test, novel object recognition test, fear 
conditioning test, Y-maze test, and delayed non-matching to place T-maze test (Zoubovsky et al., 
2011). Researchers reported that nNOS knockout (KO) mice exhibited behavioural deficits, and, 
importantly, they displayed impairments in specific cognitive abilities, such as working memory 
and mild deficits in object recognition memory (Zoubovsky et al., 2011). These animal studies 
have shown that both the presence and removal of genes have a significant impact on cognitive 
abilities, and they provide evidence for the heritability of traits related to intelligence. 

Family and Twin Studies 

Family and twin studies have been conducted to investigate the role of heredity in 
intelligence and have shown a greater stability in cognitive abilities. A study of more than 10,000 
monozygotic and dizygotic twins showed that the heritability of intelligence in monozygotic twins 



Cheng, Saqui / Emerging Perspectives                                           4 

is approximately 0.86 in correlation and the heritability of intelligence in dizygotic twins is 
approximately 0.60 in correlation (Plomin, DeFries, McClearn, & McGuffin, 2001). These studies 
demonstrate that the more genes individuals have in common with one another, such as with 
monozygotic twins, the greater the similarities in their levels of intelligence. Further studies have 
also shown that variation in total gray matter, which is related to cognitive functioning, and total 
white matter, which is related to processing speed, in adult human brains is 70-80% genetically 
determined (Baaré, 2001; Pennington et al., 2000; Pfefferbaum et al., 2000). Cross-trait and cross-
twin correlations were also assessed, and evidence showed a strong genetic component in the 
neuronal network for human intelligence, that is, the circuit of neurons that fire when cognitive 
processes are engaged (Hulshoff et al., 2006). Finally, a within-family association study was 
performed to investigate the presence of the CHRM2 gene, which is thought to be related to, among 
other things, neuronal excitability, synaptic plasticity, and cognitive processes such as learning and 
memory (Gosso et al., 2006). Results showed a significant association between the CHRM2 gene 
and intelligence and a strong presence of the gene within families. In sum, these family and twin 
studies have shown a significant genetic impact on intelligence, thereby providing evidence for its 
heredity. Furthermore, intelligence was unlikely to change throughout the lifespan, despite the 
unshared environment between family members. Indeed, the more heritable a trait, the less likely 
it will be affected by surrounding environment and the more stable it will be over time. 

Developmental Studies 

The heritability of intelligence has been shown to increase until adulthood. Indeed, studies 
show that the difference between monozygotic and dizygotic twin correlations increases slightly 
from early to middle childhood and then dramatically into adulthood (McGue, Bouchard, Iacono, 
& Lykken, 1993), resulting in a greater heritability for intelligence. Because there have been 
relatively few twin studies regarding intelligence that have included adults, summaries of 
intelligence data mainly provide evidence for the heritability of intelligence in childhood (Plomin 
& Spinath, 2004). However, results from a 20-year longitudinal adoption study support the view 
of increasing heritability (Plomin, Fulker, Corley, & DeFries, 1997), as results indicate that adopted 
children more closely resembled their biological parents’ intelligence scores as they became older. 
In sum, although intelligence has a high degree of heritability in childhood, studies have found that 
this trait increases in heritability in adulthood, making it less subject to change. 

Adoption Studies  

Finally, adoption studies were examined to determine the role of genetics and environment 
on intelligence. According to these studies, biological parents and their children who were given 
up for adoption, siblings that were adopted apart, and monozygotic twins adopted apart all 
presented substantial genetic influence (Plomin & Spinath, 2004). In fact, there are adoption studies 
of contrasted environments (Locurto, 1990), wherein the biological family’s socioeconomic status 
is considerably different from the adopted family’s socioeconomic status and provides better 
chances for environmental effects.  These studies provided malleability estimates that were modest, 
suggesting a more stable view of intelligence. The high levels of heredity in intelligence scores 
suggest little effect of environmental factors and provide strong evidence to support the stability of 
intelligence. 
 In sum, heritability is an important factor related to intelligence and there is strong evidence 
for its stability over time (Moller & Thornhill, 1994). Support for the heritability of intelligence 
and the role of genes in cognitive abilities was shown through animal studies, family and twin 



Cheng, Saqui / Emerging Perspectives                                           5 

studies, developmental studies and, finally, through adoption studies. Further studies supported the 
argument that trait heritability is a contributing factor to trait stability (Moller & Thornhill, 1994). 

Evidence to Support the Malleability of Intelligence 

 In opposition to this research, environmental factors have also been studied and provide 
evidence to support the capacity of intelligence to change over time. Specific scientific fields have 
provided evidence on the malleability of intelligence. In particular, neuroplasticity, epigenetics, 
and the presence of a growth mindset all support the malleable property of intelligence. 

Neuroplasticity Studies 

Studies have shown that through our environment, our brains have the ability to adapt our 
neural pathways and strengthen them through myelination, thereby affecting our cognitive capacity 
(Lee, Yan, & Lu, 2012; Takeuchi et al., 2012; Landon-Murray & Anderson, 2013). Myelination is 
the process through which an insulation layer surrounds the axon of the neuron to accelerate 
communication between different parts of the brain and body. The strengthening of neural 
pathways, known as neuroplasticity, has been studied extensively in the last few decades and 
studies and case studies have supported this concept. For instance, Lee, Yan and Lu (2012) 
published a case study on a boy who survived a major stroke at 40 days old. Despite his 
intracerebral hemorrhagic stroke, which resulted in his hospitalization for tremors and weaknesses, 
the young boy almost completely recovered his motor abilities. Furthermore, his intelligence 
appeared unaffected, with the predominant hypothesis being the neuroplastic potential of the 
human brain (Lee et al., 2012). Another study investigated the way in which the internet and other 
related technologies change the way individuals engage information and the changes these 
technologies make to cognitive functioning (Landon-Murray & Anderson, 2013). Results showed 
that these technologies have affected organization in the brain and have allowed individuals more 
focused and disciplined thinking, which is a key component in many cognitive abilities. Neuronal 
circuits in the brain have the capacity to adapt and strengthen, thus increasing cognitive ability and 
therefore intelligence. Takeuchi et al. (2012) investigated whether cognitive abilities in the elderly 
could be improved upon with certain activities. They found that processing speed training, in which 
participants are instructed and able to practice speeded tasks, improves performance on novel 
untrained processing speed tasks. Training is also associated with changes in the gray matter 
structures of the brain, neural changes associated with speeded cognitive processes, and functional 
activity related to simple cognitive processes. In other words, processing speed training has led to 
neuroplastic changes in the brain, thereby affecting cognitive processes. These studies provide 
evidence to support the ability of intelligence to increase throughout the lifespan through 
neuroplasticity. 

Epigenetics Studies  

Although there have been multiple studies advocating for the effect of genes on intelligence, 
growing research in epigenetics, that is, the change in genetic expression due to environmental 
factors, suggest that our environment may play a role in the expression of certain genes over others, 
thus advocating for the impact of environmental factors on the genetic expression of intelligence. 
A change in environment may lead to a change in genetic expression, which would result in a 
change in intelligence over time. In particular, one study suggested that long-term behavioural 
change may be associated with epigenetic regulation of transcription in the central nervous system 
(Day & Sweatt, 2011). Environmental factors have been found to either increase or decrease DNA 



Cheng, Saqui / Emerging Perspectives                                           6 

methylation in genes (the addition of methyl groups to DNA to monitor the gene’s activity), thus 
affecting their level of expression. In fact, evidence suggests that changes in DNA methylation 
contribute to memory formation and maintenance, a predominant component of certain cognitive 
abilities (Day & Sweatt, 2011). In other words, through cognitive epigenetics, DNA methylation 
for genes related to memory may be increased or decreased, thus affecting the expression of the 
gene and the individual’s performance on memory tasks. This study on DNA methylation has 
provided evidence for epigenetic components relative to cognitive abilities; a change in 
environment could lead to a change in gene expression and a decrease in the heritability and 
stability of intelligence. 

Growth Mindsets 

A possible explanation for the stability of intelligence is the fixed mindset, in which 
individuals believe that their abilities are given at birth and no amount of effort will lead to 
improved outcomes in performance. In contrast to the fixed mindset, simply believing that 
intelligence has the capacity to change may result in an increase in an individual’s cognitive 
abilities and increase his or her performance in academic disciplines as well (Blackwell, 
Trezesniewski, & Dweck, 2007). A longitudinal study in adolescents explored the impact of the 
growth mindset, in which people believe that the more effort you put into a task, the better the 
results will be (Blackwell et al., 2007). Results showed that when individuals were encouraged to 
believe that intelligence was changeable rather than fixed, they performed higher academically and 
their scores on tests increased. However, when individuals believed that intelligence was a fixed, 
unchangeable concept, their performances remained stable. This study also explored the 
relationship between mindset and income. The research suggests that students from lower-income 
families may be less likely to hold a growth mindset compared to higher-income peers. However, 
when they do hold a growth mindset, they are less prone to the effects of poverty on achievement 
(Blackwell et al., 2007). Academic achievement is not an explicit measurement of intelligence. 
However, research has shown that performance on IQ tests is a reasonable predictor of grades at 
school, performance at work, and aspects of success in life, including income (Gottfredson, 2004). 
These results suggest that having a growth mindset may alter an individual’s performance on 
measures or outcomes related to intelligence. However, further research is recommended to explore 
the direct relationship between intelligence and the growth mindset. 
 In sum, evidence from neuroplasticity, epigenetics, and the growth mindset suggests that 
environmental factors may play a role in intelligence. In fact, when an individuals’ environment 
has changed, their academic and intellectual output have been shown to change as well. 

Discussion 

 The controversy related to the malleability of intelligence is ongoing. There has been much 
evidence both to support the stability of intelligence and to advocate for its capacity to change. On 
the one hand, some studies support the idea that intelligence is highly heritable, and therefore less 
conducive to change. On the other hand, studies have found that certain environmental factors may 
also play a role in intelligence, thus supporting the malleability of intelligence. The studies that 
were analyzed provide support for both sides of the argument. However, an important theory that 
should be highlighted is that simply believing in the malleability of intelligence may result in better 
performance on intelligence tasks. Indeed, a study showed that the belief in intelligence 
malleability may actually increase an individual’s performance on test of cognitive abilities 
(Blackwell et al., 2007). Furthermore, the belief that intelligence is unchangeable may be the reason 



Cheng, Saqui / Emerging Perspectives                                           7 

why intelligence has remained stable in populations (Aronson, Fried, & Good, 2002). Another 
theory is that by believing that cognitive abilities can be improved, individuals have an increased 
motivation to apply effort to tasks that are cognitively challenging. Conversely, by believing that 
intelligence is heritable and unchangeable, individuals might have a “why bother” approach to 
intellectual obstacles, thus preventing them from increasing their effort to overcome these 
impediments. Therefore, it is plausible that the malleability of intelligence is predicated by 
individual belief on whether intelligence can change. Further research should be conducted in this 
area to determine whether growth mindset impacts the malleability of intelligence. 

Conclusion 

 The nature-nurture debate of intelligence has spurred much controversy, particularly in 
regard to the capacity of intelligence to change. Indeed, much research has been conducted to 
determine the malleability of intelligence. On the one hand, animal, family, twin, developmental 
and adoption studies have found that intelligence is highly heritable and therefore highly stable. 
On the other hand, studies in neuroplasticity, epigenetics and different mindsets support the role of 
environmental factors in the malleability of intelligence. However, one particular theory behind the 
abundance of evidence supporting both the stability and malleability of intelligence pertains to the 
growth mindset and the belief that intelligence can change. Indeed, primary research suggests that 
simply believing in the malleability of intelligence can increase an individual’s motivation and 
effort, and subsequently improve cognitive performance on ability tests, though further research is 
warranted in this area. It is therefore suggested that more research be conducted on the relationship 
between the malleability of intelligence and the growth mindset.  

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