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.
However, in 1993, psychologist Anders Ericsson challenged the concept of innate talent, asserting:
Individual differences, even among elite performers, are closely related to assessed amounts of deliberate practice. Many characteristics once believed to reflect innate talent are actually the result of intense practice extended for a minimum of 10 years. Analysis of expert performance provides unique evidence on the potential and limits of extreme environmental adaptation and learning.
There is no question that years of deliberate practice or intense study are required to perform at the highest levels in sport or academic enterprises. Michael Jordan’s prolonged and intense practice was certainly a key factor in his rise to elite performance. Furthermore, the research reveals that in most academic pursuits, a scholar’s best work came about 10 years after their first published work. While the speed at which a skill can be acquired draws from fluid intelligence, expertise in a particular domain is acquired through practice or study.
Some people, attempting to promote an egalitarian agenda, assert that we’re all intellectually equal at birth and the differences in intelligence when we reach adulthood are entirely attributable to environmental factors. This so-called tabula rasa (blank slate) hypothesis was advanced by John Locke in 1690 as the proletariat began a rebellion against inherited privilege. However, science in the last 100 years has revealed that the tabula rasa hypothesis is false. Genes do matter.
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.) 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.
A free downloadable chapter discussing whether talent exists or whether outstanding performance in any endeavour is merely a matter of work can be found at this link: https://www.intelligence-and-iq.com/wp-content/uploads/2021/09/Chapter-6.pdf
