Measuring Intelligence?

When conducting a twin study, most experiments involve the use of fraternal and identical pairs of twins reared together as well as fraternal and identical twin pairs reared apart. The percentage of the similarities between each member in a pair is called the concordance rate, and this number tends to be higher in identical twins than fraternal. However, when the trait in question being studied can vary dramatically, such as a persons aptitude, a different method is applied; in such a case, coefficient correlations are used.

The general intelligence quotient (IQ) correlation rate between fraternal twins reared together is .60, whilst the coefficient for identical twins reared together is .86.  Meanwhile, the correlation for identical twins reared apart is .77. I can relate to this statement because sister and I, who were reared together and are identical have very similar grades and tend to excel in similar subject areas. This points to the idea that although a person's intelligence is dependent on their education, their capacity to understand relies on their genetic makeup. The fact that identical twin pairs always have higher correlations than fraternal twins, even when they are reared apart, is a clear affirmation that nature dominates over nurture in this area.

Although there isn't a standard definition of intelligence, it is accepted that identical twins have rates of concordance than fraternal twins, showcasing that a person's genes correlates with their ability to perceive.

Sigelman, C. K., & Rider, E. A. (2009). Life-span human development [ed. VI, pp. 74-79]. Retrieved from http://books.google.com/books?id=Nn8tgkPSKB4C&printsec=copyright#v=onepage&q&f=false

 Joseph, J. (2004). The gene illusion: genetic research in psychiatry and psychology under the microscope [pp. 308-311]. Retrieved from http://books.google.com/books?id=OyDQlKwRpfwC&printsec=copyright#v=onepage&q&f=false