Intelligence quotient (IQ) is a measure of cognitive abilities, such as reasoning, logic, memory and problem-solving skills. There has been much debate around whether IQ can change over time, especially as we age. Some studies have found that IQ is stable across the lifespan, while others suggest it can grow. Here we review the evidence on both sides of this discussion.
The stability of IQ
The prevailing view among psychologists for many years was that IQ remains relatively stable from late adolescence onwards. This notion stems from research by psychologists including Lewis Terman, who followed a group of high IQ participants from childhood into adulthood. He found that their IQ scores changed very little over this time, strengthening the idea that intelligence is fixed.
More recent longitudinal studies, where the same individuals are tracked over many years, also provide evidence for the stability of IQ. For example, one study followed the same group from ages 12 to 79 and found high correlations between IQ scores taken at different ages. This suggests each person’s intelligence ranking changed little relative to others over nearly 70 years.
There are several reasons why IQ may remain steady throughout life:
- Genetics – Intelligence has a strong hereditary component that does not change.
- Brain plasticity declines – The brain’s ability to change and reorganize itself reduces with age.
- Cognitive abilities peak – Different cognitive skills like reasoning and spatial ability are thought to peak at different ages.
Overall, the relative stability of IQ among individuals over time has led many to believe it cannot be increased substantially through effort and practice. Proponents of this view argue you cannot teach an old dog new tricks when it comes to intelligence.
Evidence that IQ can grow with age
Despite the common belief that intelligence is fixed, some studies have found IQ scores can actually improve over time. For example, research tracking IQ from age 11 to 90 found scores gradually increased into late adulthood, before declining in the oldest age groups. Gains of around 5 to 10 IQ points from adolescence to late middle age were observed.
There are several possible explanations for these observed IQ increases:
- Improved test-taking skills – Familiarity with tests may inflate scores over time.
- Environmental influences – Better education and mental stimulation may bolster cognitive abilities.
- Brain plasticity remains – The brain can generate new neurons and build new connections later in life through learning.
This research suggests intelligence is not completely stable and elements of it can continue developing with age. However, others argue apparent IQ gains with age are mostly down to methodological issues, like practice effects, rather than genuine increases in cognitive skills. Disentangling these factors remains an ongoing area of study.
The Flynn effect
One of the most widely discussed phenomena around increasing IQ is the Flynn effect. This refers to the observation that average IQ scores have steadily increased over the 20th century. For example, someone who scored 100 (average) on an IQ test in 1900 may have scored closer to 70 on a test normed for today’s population.
This effect has been consistently observed across many countries. Proposed explanations include:
- Improved education and access to information.
- Better nutrition and healthcare.
- More mentally stimulating environments.
- Increasing test familiarity over time.
Crucially though, the Flynn effect represents rises in average population IQ – it does not necessarily mean individual IQ increases over time. While environmental effects may have boosted group averages, there is less evidence the same factors systematically raise an individual’s IQ across their lifespan.
Does getting a higher education increase IQ?
Many wonder if pursuing higher education, such as attending college or university, can directly increase cognitive abilities. Several studies have investigated this question.
In one longitudinal study, researchers found that students who went to college gained around 4 IQ points more over 4 years than less educated groups of the same age. Similar results have been noted in other cohorts tracked over time.
Of course, individuals who seek higher education tend to differ from the general population in many ways. Factors like motivation, parental influences and peer groups make it difficult to isolate the effect of education alone. Improvements may also reflect developing test-taking skills over time in education.
Nonetheless, some experts argue the enriched environments and mental stimulation of higher education can directly strengthen certain cognitive abilities. Things like learning new fields of knowledge, reading challenging texts and critical thinking may all help exercise the brain. The development of ‘crystallized intelligence’ – accumulated knowledge and skills – is thought to be particularly sensitive to education through adulthood.
Can the aging brain increase IQ?
Natural age-related declines in some cognitive functions are well documented. Processing speed, working memory and long-term recall tend to degrade as we get older. But do these changes affect IQ and abstract reasoning abilities?
Some argue IQ tests are impervious to cognitive decline in healthy adults because they tap into more durable ‘crystallized abilities’ built up over many years. Vocabulary size and general world knowledge tend to remain intact with age.
However, others contend IQ tests also rely on skills like working memory, attention and mental agility that do decline. One study found adults over 60 scored worse on some IQ test items like digit span recall compared to younger adults.
Physical changes in brain structure and function as we age may also impact IQ. Grey matter and neural connectivity decrease over time, while inflammatory processes can impair cognition.
Interestingly, one study found engaging in mentally stimulating leisure activities, like reading and puzzles, was associated with improved IQ performance in older adults. This highlights the potential to boost cognitive skills through life.
Can IQ be increased at any age?
The accumulation of knowledge and crystallized abilities may allow IQ gains well into old age. But can other cognitive skills be enhanced at any age?
Working memory and fluid reasoning are generally thought to peak in young adulthood before declining. However, emerging research suggests working memory training programs can yield improvements in older adults by altering brain activity patterns.
Engaging in new learning over a lifetime also seems crucial for building cognitive reserve and brain resilience against aging. Mastering a foreign language or musical instrument in adulthood, for example, provides the brain with new challenges.
Some small intervention studies have shown cognitive training activities, like logic puzzles and memory games, may boost IQ test performance to some degree. But far transfer effects to overall intelligence remain debated.
In summary, active mental stimulation across adulthood can at least help maintain cognitive skills, even if baseline IQ remains stable. But more research is still needed on whether fundamental problem-solving abilities can be enhanced late in life.
Role of brain plasticity
For many years, a dogma in neuroscience was that the adult brain could not grow new neurons. It was thought no new brain cells could be produced after early development had finished.
However, research over the past few decades has completely overturned this view. The discovery of neurogenesis – the growth of new neurons from neural stem cells – in the adult brain has changed perspectives on its malleability through life.
Parts of the brain like the hippocampus retain the capacity to regenerate neurons in response to experiences like learning. This adds to the system’s plasticity – its ability to continually reorganize neural networks and forge new connections.
Studies in animals and humans suggest cognitive stimulation and learning new skills may promote neurogenesis. The increased neural connectivity this supports may underpin gains in memory, attention and other cognitive abilities key to IQ.
Research on cognitive training indicates it may work in part by strengthening existing neural pathways and relationships. While the brain loses plasticity over time, it seems a capacity for change is retained well into maturity.
Genetic contributions
Twin studies have found high genetic contributions to intelligence, suggesting IQ is strongly heritable. But recent genetics research also proposes interesting links between IQ and environment over time.
One landmark study found genetic factors actually accounted for increasing amounts of individual differences in IQ with age. Environmental factors like education explained more variance earlier in development.
This illustrates a dynamic relationship between genetics and experience. Early education environments may help maximize genetic cognitive potential that later remains stable. The brain capacity to respond to learning is innate, but also requires stimulation to reach its potential.
Other cognitive changes
It is worth noting that aspects of cognition that decline with age, like processing speed and memory, are distinct from general problem-solving intelligence measured by IQ tests. Simple reaction time slows as we get older for example, but vocabulary knowledge remains steady.
These dissociations suggest that while some cognitive faculties degrade, core reasoning abilities may persist. Vocabulary size, cultural knowledge and expertise built up over a lifetime can balance declines in other areas.
However, others contend that fluid intelligence operations like working memory, abstract reasoning and attention are integral for expressing knowledge. According to this view, aging-related declines in these executive functions necessarily impact overall IQ performance.
Potential barriers
There are a few factors that may hinder potential IQ increases over the lifespan:
- Fixed mindsets – Believing intelligence is immutable may discourage engagement in cognitive growth.
- Mental illness – Conditions like depression can obstruct motivation and learning.
- Poor education – Early disadvantage limits foundations for later cognitive development.
- Social isolation – Stimulating mental engagement with others facilitates intellectual growth.
- Head injuries – Brain trauma and dementia can impair cognitive potential.
While IQ gains may be possible, certain environmental and psychological factors can obstruct opportunities for growth. Access to education and mental stimulation throughout life likely allows abilities to reach their peak.
The debate
There are good arguments on both sides of the debate around whether IQ can grow with age:
For IQ stability:
- High IQ test score correlations from adolescence to old age.
- IQ is strongly genetically influenced with limited malleability.
- Brain plasticity and neurogenesis decline over the lifespan.
For IQ growth:
- Average population IQ scores have increased substantially over the 20th century.
- Higher education is associated with IQ gains.
- Mental stimulation may boost cognitive reserve against aging declines.
There is truth on both sides – early IQ potential is shaped by genetics and adolescent enrichment, but growth seems possible through active cognitive engagement throughout life.
Conclusion
The development of IQ over the lifespan remains debated. While innate cognitive potential is genetically shaped, it also requires appropriate stimulation through development and education early in life to reach its peak.
IQ is generally thought to stabilize in adulthood, but factors like higher education and ongoing mental stimulation may still sharpen cognitive skills and effective intelligence expression. There is potential for growth via the brain’s retained plasticity, though limits likely exist.
To summarize:
- IQ appears mostly stable from adolescence based on longitudinal studies tracking individuals over time.
- Environmental influences like education and mental stimulation may boost IQ to some degree over the lifespan.
- Higher education is associated with modest IQ gains, potentially reflecting enriched experience.
- Working memory training may benefit older adults, but effects on general intelligence are less clear.
- Continued cognitive engagement through life seems crucial for building reserves against aging declines.
In the right circumstances, IQ retention or growth seems possible into maturity and old age through active mental stimulation. But gains are thought to be modest, and fundamental cognitive potential remains anchored in genetics and early development.