Intelligence, like most other traits, is due in part both to nature and nurture. The nurture aspect regarding the development of intelligence, however, must account for the nature aspect. Thus, research on intelligence from the field of behavioral genetics is important because it may ultimately help us understand which aspects of the environment are important to bring out each individualâs intelligence and broader array of cognitive abilities to the fullest. There are two approaches being used: first, investigating the extent to which genes contribute to intelligence differences (known as quantitative genetics, often using twins and siblings), and, second, investigating which are the specific genes in the DNA that, when they differ among people, cause intelligence differences (known as molecular genetics). To date, an enormous amount of evidence has accumulated surrounding the heritability of intelligence using twin samples; however, there is now headway in the molecular genetics area when studying intelligence (for comprehensive reviews, see Plomin & Deary, 2014; Plomin & von Stumm, 2018). Suffice it to say, the evidence has accumulated such that intelligence is in part due to nature as well as nurture.
The Significant Correlates of Intelligence
General intelligence, or g, has been called a ârosetta stoneâ or a crucial key given its broad links to many phenomena of interest in psychology, social science, and society ( Jensen, 2006). Large amounts of data spanning the last century have indicated links between intelligence and numerous outcomes of consequence, including educational achievement, occupational success, income, mortality, and others (e.g., for reviews, see Gottfredson, 2003b; Haier, 2016; Hunt, 2011; Jensen, 1998; Ritchie, 2015). To offer some illustrations, higher intelligence has been linked to positive health-related habits, such as exercising more, eating better, and smoking less (e.g., see Gottfredson, 2003b; Gottfredson & Deary, 2004). People with higher intelligence are less likely to have medical issues such as heart disease, obesity, or hypertension, and this is found for both physical and mental health (Wraw, Deary, Gale, & Der, 2015). Higher intelligence has also been linked to lower mortality or death risk (Batty, Gale, Tynelius, Deary, & Rasmussen, 2009). Higher intelligence has even been linked to higher creativity (Mosing, Pedersen, Madison, & UllĂ©n, 2014; Nusbaum & Silvia, 2011; Wai, Lubinski, & Benbow, 2005). Intelligence has also been linked to political preferences and religion, among an array of other outcomes (for an extensive list of correlations between g and many outcomes, see Jensen, 1998; Strenze, 2015).
However, for the purposes of this review, two sets of outcomes are most relevant. First, general intelligence has been linked to many educational outcomes. A very large and representative sample from the United Kingdom (Deary, Strand, Smith, & Fernandes, 2007) examined the scores of over 13,000 students at age 11 and correlated those scores with educational achievement at age 16. The researchers found that the correlation between g and the overall exam score was r = .81. This correlation is very high, especially in relation to what is typically found in social science, and indicates the importance of general intelligence for educational achievement.
In the United States, the entire range of SAT scores (which, as noted earlier, also measure g) were discovered to be linearly related to college grade point average (GPA; Cullen, Hardison, & Sackett, 2004). In addition, SAT scores are associated with a wide variety of outcomes, including graduate school performance (Berry & Sackett, 2009). Kuncel, Hezlett, and Ones (2004) conducted a major meta-analysis illustrating that g as tapped by the Miller Analogies Test (MAT) predicted a range of graduate student academic criteria. General intelligence predicted GPA, comprehensive examination scores, time to degree completion and attainment, faculty ratings, and research productivity.
Studies of intellectually precocious youths who have participated in a 7th-grade US talent searchâwhere students complete the SAT before age 13âprovide...