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.
Adding to the complexity of interpreting the percentage of intelligence attributable to genes is the fact that intelligence is polygenic, meaning that it is determined by a huge number of individual genes and is therefore manifest in different forms. See: What is intelligence? Is it measurable? – Intelligence and IQ
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.) Genome-wide association studies establish that human intelligence is highly heritable and polygenic – Molecular Psychiatry. 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.
Recent research in epigenetics suggests that environments can “switch on” and “switch off” certain genes, and this adds more complexity to the role of environment on intelligence at the individual level. While we must be cautious in how we express the contributions of environment and genetics to our intelligence, we do know that genetics play a very strong role in cognitive performance, especially when allowed to interact with a stimulating environment.
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. It’s the intellectual version of the “Hare and the Tortoise” allegory.
