Research seems to indicate that intelligence is acquired through a combination of two factors: genetic inheritance (nature) and environmental experiences (nurture) We have little control over our genetic inheritance, but much more control over our environmental experiences.
Research Pertaining to the Your Genetic Inheritance
In 1990, Thomas J. Bouchard et al. published a seminal article titled, Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart in which he and his research team assembled 100 sets of identical twins who were separated early in life and raised apart. All participants in the study completed about 50 hours of medical and psychological assessment.
Since identical twins come from a single fertilized egg, they share virtually 100% of their alleles and can be considered to be genetically identical. Furthermore, since they were raised apart, the differences in their IQ, when tested at the end of their separation could be entirely attributable to environmental factors.
Since the twins in the Minnesota study were raised apart, no part of the correlation in the IQ scores of twins could be attributed to shared experiences. Hence, Bouchard et al. were able to estimate the difference in IQ attributable to genetics, using the correlation in the IQ scores of the twins. The researchers reported “about 70% of the variance in IQ was found to be associated with genetic variation.” The authors cautioned that this finding did not imply that IQ cannot be enhanced by rich experiences. However, the contribution of genetics to intelligence was incontestable.
Research Pertaining to the Your Environmental Experiences
The reason that we humans have reached the top of the food chain can be attributed to our ability to learn and adapt to our environment. During our formative years, our brain passes through periods of brain growth, producing neurons at a prodigious rate and purging those that aren’t used. It is during these periods, in particular, that we can increase our intelligence through intellectual stimulation. This can take the form of reading, doing mathematics, learning science and other academic or artistic disciplines. As Einstein once observed, “The value of a college education is not the learning of many facts, but the training of the mind to think.”
Recent research indicates that while the average IQ of those in the same age cohort is relatively stable over a span of several years, the IQ of an individual can change significantly during the teenage years. In a longitudinal study, 33 teenagers of average age 14.1 years were administered an IQ test and a structural brain scan in 2004 and then again in 2007, when their average age was 17.7 years. It was found that during this period, the average IQ of the group had changed very little; however about 20% of the participants showed a positive or negative change in IQ of at least 15 points (one standard deviation). Furthermore, magnetic resonance imaging (MRI) revealed that positive changes in IQ corresponded to increased gray matter in sections of the brain associated with those cognitive functions. Summarizing their findings, the researchers reported: (see Ramsden, Sue. et al. 2011. “Verbal and non-verbal intelligence changes in the teenage brain.” Nature. Vol. 479. pp. 113-116.”)
You can find more information on the brain and its growth spurts at: How can I improve my intelligence/IQ, problem solving skills, logical and critical thinking as a teenager? – Intelligence and IQ
