- A twin study found that both intelligence and rationality are highly heritable, suggesting strong genetic influences.
- There is no separate “rationality gene”—rational thinking appears to be an extension of general intelligence.
- People who score lower on intelligence tests tend to make more irrational decisions, linking cognitive ability with decision-making skills.
- These findings suggest that IQ tests may need to incorporate rationality assessments to better measure cognitive potential.
- Understanding rationality’s genetic basis could inform artificial intelligence design, improving machine decision-making.
A groundbreaking study on twins has revealed that intelligence and rational decision-making may be more intertwined than previously thought. Researchers found that rationality—our ability to make logical choices and avoid cognitive biases—is strongly influenced by genetics and closely tied to overall intelligence. This challenges the idea that rationality is a separate skill, instead suggesting that making sound decisions is simply a reflection of general cognitive abilities.
Defining Intelligence and Rationality
Before diving into the genetic connections, it’s important to differentiate between intelligence and rationality.
- Intelligence refers to a person’s ability to process, understand, and apply knowledge. It includes skills like problem-solving, reasoning, and pattern recognition. Intelligence is typically measured through IQ tests, which assess verbal abilities, mathematical reasoning, and spatial awareness.
- Rationality is about making logical, well-reasoned decisions based on available evidence. It encompasses critical thinking, resistance to cognitive biases, and the ability to override automatic yet incorrect assumptions. Unlike intelligence, rationality focuses on the quality of choices people make rather than their raw cognitive ability.
Historically, some experts believed these were distinct cognitive traits. They argued that intelligence was about knowledge and reasoning, whereas rationality involved overriding intuitive, impulsive thought patterns—a skill not captured by traditional IQ tests. Others speculated that rational thinking was simply an extension of general intelligence and dependent on the same cognitive resources.
Investigating the Genetic Link Between Intelligence and Rationality
To understand how intelligence and rationality are connected, researchers turned to the Brisbane Adolescent Twin Study. This study aimed to separate genetic influences from environmental factors using twin participants.
Why Twin Studies Matter in Psychological Research
Twin studies are a powerful tool for investigating genetic influences. The key advantage lies in the comparison
- Identical twins (monozygotic) share nearly 100% of their DNA.
- Fraternal twins (dizygotic) share about 50% of their DNA, similar to regular siblings.
By analyzing how similarly identical and fraternal twins perform on intelligence and rationality tests, scientists can estimate how much of these abilities stem from genetics versus environmental factors like upbringing and education.
How the Study Was Conducted
- 1,570 teenage twins participated, split between identical and fraternal twins.
- Intelligence was assessed using cognitive tests measuring vocabulary, numerical reasoning, and pattern recognition.
- Rational decision-making was evaluated using the Cognitive Reflection Test (CRT), designed to measure how well people override their initial intuitive responses with logical reasoning.
One of the classic CRT questions is
“A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost?”
Many people instinctively answer “10 cents”—an incorrect response driven by fast, intuitive thinking. The correct answer, “5 cents,” requires a second layer of logical reasoning, demonstrating cognitive reflection.
By comparing twins’ performance on intelligence and CRT tests, researchers were able to determine how much rationality and intelligence share a genetic basis.
Key Findings of the Twin Study
The research yielded compelling results about the nature of rational decision-making and its link to genetic intelligence.
Rationality is Highly Heritable
Both intelligence and rational decision-making were found to be strongly influenced by genes. This suggests that rationality isn’t just a learned skill—it has deep genetic roots. While education and training can improve decision-making, the study shows that some people are naturally predisposed to think more rationally due to genetic factors.
No Separate “Rationality Factor”
When researchers tested whether rational thinking could be measured separately from intelligence, they found no evidence supporting a distinct rationality factor. Instead, rational thinking scores heavily overlapped with intelligence scores. This implies that rationality is not an independent mental trait but rather a subset of general intelligence.
Irrationality and Lower Intelligence Are Linked
The study also showed that people who struggle with logical decision-making tend to have lower general intelligence. This finding suggests that many irrational choices aren’t due to a lack of reasoning practice but rather a lower baseline of cognitive ability.
What This Means for Our Understanding of Rational Thinking
If rationality is simply an expression of intelligence, this has important implications
Should IQ Tests Measure Rationality?
Traditional IQ tests focus on problem-solving, memory, and processing speed. However, given this research, IQ assessments might be missing an important component of intelligence—decision-making skills. Incorporating questions that measure rational thought and bias resistance could improve intelligence testing.
Can Rational Thinking Be Trained?
If rationality is at least partly genetic, does that mean people with lower natural ability cannot improve? Not necessarily. Education, cognitive training, and self-awareness exercises can help people recognize and resist biases. Critical thinking courses could be a valuable way to enhance rational decision-making, even for those without a strong genetic predisposition.
Could AI Benefit from These Findings?
Artificial Intelligence (AI) systems face similar challenges to humans when making decisions—avoiding bias, processing complex probabilities, and distinguishing intuitive versus logical responses. Understanding that rationality is deeply linked to intelligence may help refine AI algorithms to better mimic human judgment.
Implications for Psychology, AI, and Cognitive Science
These findings have groundbreaking implications across multiple disciplines
- Education: Schools could integrate rational thinking exercises into general intelligence training, teaching students how to resist cognitive biases.
- Artificial Intelligence: AI models may need to incorporate logical reflection mechanisms to better simulate human decision-making.
- Mental Health & Therapy: Recognizing irrational decision-making as a function of lower cognitive abilities could lead to more effective psychological interventions.
Limitations and Directions for Future Research
Despite its valuable contributions, this study has limitations that need further investigation
- Scope of rationality assessment: The study relied on the Cognitive Reflection Test, which only measures a few aspects of rational thinking. Future research should include broader real-world decision-making scenarios like financial planning or risk assessment.
- Cultural and Age-related Variations: The participants were adolescents from a single study population. Expanding this research to different age groups and cultures could reveal how rationality develops and varies across environments.
- Environmental Influences: Though genetics play a major role, education, motivation, and personal experiences are also crucial in shaping a person’s rational thinking abilities. More studies should explore how training and education can improve decision-making.
Final Thoughts
This study strongly suggests that intelligence and rationality are closely linked, largely due to genetic factors. Rather than being a separate cognitive skill, rationality appears to stem from general intelligence, reinforcing the idea that irrational mistakes reflect cognitive limitations. These findings have major implications for education, AI, and psychological research, paving the way for a deeper understanding of human reasoning.
Interested in Learning More?
The full study by Professor Timothy C. Bates is available in the journal Intelligence.
Citations
- Bates, T. C. (2024). Cognitive rationality is heritable and lies under general cognitive ability. Intelligence. Retrieved from ScienceDirect.
