Does genetics determines how smart you are?
Nature versus nurture, a forever hot topic in fields of life science. The debate is especially fierce when it comes to intelligence. After hundreds of years of debate, the result is still inconclusive.
Francis Galton, who devised the concept and formula for correlation with Karl Pearson, believed that intelligence is primarily a reflection of energy and the perceptual acuteness of the senses, and high intelligent people give birth to high intelligent children. (He believed in nature is more important). Whereas Alfred Binet, who famously devised the IQ test, believed that education can change IQ. In fact, for one of the many purposes, he devised the scale to test how people change in IQ across the special education program.
The most direct way to show if intelligence is genetic-based is to conduct twins’ studies. Researchers use IQ scales to measure the IQ of twins who reared together vs. reared apart. (Also, monozygotic twins vs. Dizygotic twins). The correlation between IQs of twins who are raised together is close to .90, whereas the correlation between IQs of twins who are raised apart is close to .80. (Much smaller correlation of IQ found in dizygotic twins than monozygotic twins). These evidence shows that IQ is strongly determined by genetics. However, there are other factors that may have contributed to this similarity. Firstly, adoption agencies usually try to place adoptees in homes similar to the home of biological parents. Therefore, the environment of twins growing up may be actually very similar. Secondly, parents may treat monozygotic twins much more similarly, because of their physical similarity, comparing to treat dizygotic twins. This may have contributed to the lower IQ correlations found in dizygotic twins.
The concept of ‘general intelligence’, i.e., g, is very important. Charles Spearman found that if you do well on one subset of intelligence test, you will tend to do well on others as well. He argues that general intelligence (g) is the general factor that underlines all intellectual activities. G also reflects the capacity to pay attention to information. (He concluded that mental energy determines IQ). Research shows that 80–90% of the variance in scholastic achievement is due to g. The correlation between g and SAT scores is r = 0.82. Tests of g are the best single predictors of job performance. Correlation of g with income is r = 0.40.
The most important reason scientists are very interested in this topic, from my perspective, is because there could be many practical implications once a valid result is obtained. For example, if the result is that intelligence is genetic for >90% of the variance, then many education policies may be changed, and much less of money would be invested in talent development.
The summary of various research literature is that the irritability of intelligence is 0.4–0.8. Huge variation, and not many conclusions can be drawn upon. The only conclusion we can draw is that the formation of intelligence is the interaction of nature and nurture.
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