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Genetics play a crucial role in determining our maximum IQ, with heritability increasing with age and specific genes and brain structures being implicated in cognitive abilities. However, environmental factors, including socioeconomic status, also significantly influence intelligence. Understanding the interplay between genetics and environment is essential for a comprehensive view of intelligence.
The question of whether our maximum IQ is determined by our genetics has intrigued scientists for decades. Intelligence, a core construct in differential psychology and behavioral genetics, is one of the most heritable behavioral traits. This article explores the genetic underpinnings of intelligence, examining the extent to which our genes influence our cognitive abilities and the implications of these findings.
Genetic Influence on Intelligence
Heritability of Intelligence
Research indicates that the heritability of intelligence increases with age. In infancy, genetic factors account for about 20% of the variance in intelligence, but this figure can rise to as much as 80% in later adulthood1 4. This suggests that as individuals age, genetic factors play a more significant role in determining intelligence.
Genetic Correlation with Cognitive Abilities
Intelligence captures genetic effects on diverse cognitive and learning abilities. These abilities, which phenotypically correlate at about 0.30 on average, show a much higher genetic correlation of about 0.60 or higher1. This indicates that the same genes may influence various cognitive skills, reinforcing the idea that intelligence is a broad and genetically influenced trait.
Assortative Mating and Genetic Variance
Assortative mating, where individuals with similar intelligence levels are more likely to pair up, contributes to the high heritability of intelligence. Spouse correlations for intelligence are around 0.40, significantly higher than for other traits such as personality or physical characteristics1. This phenomenon pumps additive genetic variance into the population, further enhancing the genetic influence on intelligence.
Genetic Studies and Findings
Genome-Wide Association Studies (GWAS)
Recent advancements in genome-wide association studies (GWAS) have identified specific genes and neuronal cell types associated with intelligence. For instance, genes linked to intelligence implicate pyramidal neurons of the somatosensory cortex and CA1 region of the hippocampus, as well as midbrain embryonic GABAergic neurons2. These findings provide new hypotheses for neuroscience experiments and suggest that specific brain regions and cell types play crucial roles in cognitive function.
Twin Studies
Twin studies have been instrumental in understanding the genetic basis of intelligence. These studies reveal that the influence of shared environment decreases while the influence of heritability increases across development6. Non-shared environmental factors contribute to changes in intelligence over time, but the genetic influence remains stable and significant.
Brain Structure and Intelligence
Genetic influences on brain morphology are closely linked to intelligence. Studies using sophisticated brain-mapping techniques have shown that cognitive abilities are associated with specific cortical patterns, which are under strong genetic control9. This suggests that the genetic links to intelligence are partly mediated by brain structure.
Environmental and Socioeconomic Factors
While genetics play a significant role in determining intelligence, environmental factors cannot be ignored. Socioeconomic status (SES) interacts with genetic influences on intelligence, with genetic effects being more fully realized under conditions of socioeconomic advantage5. This highlights the importance of considering both genetic and environmental factors in understanding intelligence.
Is our maximum IQ determined by our genetics?
Casey Pfluger has answered Extremely Unlikely
An expert from University of Queensland in Neurobiology, Neurology
Our maximum IQ is not entirely determined by genetics but genetics does play a role in intelligence in general. The genetics of intelligence is still poorly understood and needs more research to fully understand which genes/gene combinations contribute to increased intelligence. IQ results can be improved by basic training in certain types of logic. This is demonstrated by increasing IQ scores for each generation in developed countries. This is not an increase in intelligence but is instead an increased ability to apply logic and reason to problems such as those posed in IQ tests. Test results for IQ are influenced by many factors such as genetics, socioeconomic status, nutrition, exposure to certain infectious agents, education, exposure to environmental pollutants such lead or mercury etc. Intelligence can be divided into many aspects such as social cognition, spacial cognition, auditory cognition etc. Many of these aspects of intelligence are not assessed by IQ testing.
Is our maximum IQ determined by our genetics?
David Eccles has answered Extremely Unlikely
An expert from Malaghan Institute of Medical Research in Genetics, Genomics, Bioinformatics, Biostatistics, Data Science
This is a difficult question to answer. We are created and changed both by what we are (i.e. our genes) and what we experience (i.e. our environment). Every trait we have has an environmental component and a genetic component to its appearance and its variation.
To drill deeper into that needs a lot of conditional statements. Genetics and environment interact with each other and change us in ways that can’t be predicted by a study of one or the other on its own. The environment we live in can both hide the way in which we are changed by our genes, and make those changes more glaringly obvious. As an example, there are genes that have a strong influence on your ability to see different colours as different (i.e. colour blindness). If you were blinded in an accident, then those genes don’t matter. If your job depends on your ability to tell colours apart (e.g. a clothing designer), then the impact of those genes is made a lot more obvious.
IQ is further complicated in that it can’t be defined precisely, i.e. the people and cultures that decide what constitutes the components of IQ have different opinions. Where there is agreement, the non-cultural aspects of intelligence may be less relevant for everyday life. Considering the environmental component, there may be specific, unpredictable environmental situations that cause an individual to have a lower IQ assessment or a higher IQ assessment at any given time. Statements are quite easily misinterpreted by people with a different understanding of IQ than that of the person who made the statement.
Additionally, a common definition of IQ is based on an expected normal distribution of abilities within a population. Assuming this is carried out continuously (which it isn’t), then the mean/median IQ would remain constantly at 100, and each standard deviation from the mean would be 15 IQ points. This puts a statistical limit on the maximum IQ that is largely independent of genetic or environmental factors, and I expect that where there is some wiggle room, the differences in IQ score would fit within the range of natural variation in assessed IQ.