Yes, research has revealed that some people do, indeed, have higher intelligence than others. This was established unequivocally by Bouchard and others during the 1990’s in their study of identical twins who were raised in different environments. Since the twins in Bouchard’s 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. In the years that followed, many researchers conducted similar studies with similar results establishing that the contribution of genetics to intelligence is incontestable, although the size of its importance varies across individuals.
In 2011, a large group of researchers published the results of a genome-wide analysis of 549,692 single nucleotide polymorphisms (SNPs) involving 3511 unrelated adults. (An SNP represents a difference in a single DNA building block, called a nucleotide.) (See: Davies, G., A. Tenesa, A. Payton, J. Yang, S.E. Harris, D. Liewald, et al. 2011. “Genome-wide association studies establish that human intelligence is highly heritable and polygenic.” Molecular Psychiatry. 16. pp. 996–1005.) They reported:
Our results unequivocally confirm that a substantial proportion of individual differences in human intelligence is due to genetic variation, and are consistent with many genes of small effects underlying the additive genetic influences on intelligence. … [Furthermore] purely genetic (SNP) information can be used to predict intelligence.
This research estimated the heritability of IQ to be about 0.5, confirming the results of the studies involving identical twins. Its conclusion that general intelligence is polygenic, i.e., it derives from a combination of many genes supports the concept of intelligence as a multi-faceted characteristic.
Research has also shown that IQ can be increased, especially during the formative years, by appropriate environmental factors such as education and other forms of intellectual stimulation. IQ tests remain the best instrument for estimating intelligence, but they do not test curiosity, creativity and long-term problem solving abilities that are vital components of intelligence. The short answer to your question is that your DNA sets your highest potential intelligence, but your environmental experiences determine the extent to which you reach that potential.
While genetics play a significant role your fluid intelligence, i.e., the speed and efficiency of your neural processes, experiences are the major contributor to your crystallized intelligence. Your crystallized intelligence is the sum total of all your acquired knowledge and concepts derived from life experiences including your education and your observations. Even those of average fluid intelligence can enhance their total intelligence by intense involvement in learning, observing, theorizing and thinking. These activities, especially during the formative years, stimulate the production of neurons and the formation of neural structures on which advanced concepts can be built. Many people of relatively average IQ have been high achievers in demanding cognitive areas by immersion in cognitive engagements over an extended period of time.
