The study of height and intelligence examines correlations between human height and human intelligence. Some epidemiological research on the subject has shown that there is a small but statistically significant positive correlation between height and intelligence after controlling for socioeconomic class and parental education. One such theory argues that since height strongly correlates with white and gray matter volume, it may act as a biomarker for cerebral development which itself mediates intelligence. Competing explanations for the correlation between height and intelligence include that certain genetic factors may influence both height and intelligence, or that both height and intelligence may be affected in similar ways by adverse environmental exposures during development. Measurements of the total surface area and mean thickness of the cortical grey matter using a magnetic resonance imaging (MRI) revealed that the height of individuals had a positive correlation with the total cortical surface area. This supports the idea that genes that influence height also influence total surface area of the brain, which in turn influences intelligence, resulting in the correlation. Other explanations further qualify the positive correlation between height and intelligence, suggesting that because the correlation becomes weaker with higher socioeconomic class and education level, environmental factors could partially override any genetic factors affecting both characteristics.
Previous studies First inquiries into the correlation of height and intelligence came within the study of development in schoolchildren. William Porter was the first person to conduct a study to find a relationship between the physiology of children and their intelligence. The motive for this research was to attempt to predict the potential "dullness" or "precocity" of children based on simple measurements teachers could make. He did in fact find a correlation between body size and the learning level of children, but did not focus specifically on height. More recent studies have continued the research into a correlation between height and intelligence, but again were often not directly related to height and intelligence. Some of the earlier large studies cited for height and intelligence are the Scottish Mental Surveys in 1932 and 1947. However, the studies were largely meant to analyze the genetic and environmental contributions to cognitive ability differences. Height (and weight) were added to provide a multivariate analysis. In an effort to better understand this association, numerous other studies were thus carried out. These studies either expanded upon the association or sought to find an explanation. A study by Douglas, et al. (1965) addressed the Scottish study and sought to test if the association reflected a linkage between development of the brain and/or emotional development and the development of the rest of the body. Similarly, in 1986, Wilson et al. wanted to study if there is a longitudinal relation between height and intelligence. Nonetheless, as these studies were unable to provide satisfying results and explanations for the correlation, interest in it persists in the 21st century. In 2014, another study was carried out by a team of researchers at Edinburgh University, Scotland, motivated by the understanding that both height and intelligence test scores are predictors of better health outcomes and mortality. The study was constructed to better identify if there are any shared phenotypic and genetic influences from height and intelligence in determining health outcomes and mortality.(Be aware of the difference between genetic correlation and phenotypic correlation since the former means the proportion of heritability that two traits share while the latter just means the term that describes animals with high values for one phenotype also tending to have high (or low) values for another phenotype so to discuss over the correlation between measured height and intelligence, phenotypic correlation is what should be discussed.)
Definition of intelligence
Human intelligence can be measured according to an extensive number of tests and criteria, ranging from academic, social, and emotional fields. While there is no clear consensus on a definition of human intelligence, there are common themes among those that exist, summarized generally as "Intelligence measures an agent's ability to achieve goals in a wide range of environments". There are several theories that define different categories of intelligence and associate traits, instead of a single general ability. In most of the studies, intelligence quotient (IQ) tests were used to measure a subject's mental age, which was checked for possible correlation with height. While the use of IQ tests are highly debated among scientists as an accurate measurement of intelligence, they provide a quantitative and normal distribution to compare cognitive abilities among people. Intelligence cannot be strictly defined, and it has been cautioned that intelligence has many different facets. Regardless, studies conducted to compare height with intelligence frequently use the Wechsler Adult Intelligence Scale (WAIS) which measures verbal and performance abilities for individuals over the age of 16 (WISC for those under 16) years through the following tests: information, general comprehension, memory span, arithmetical reasoning, similarities, vocabulary, picture arrangement, picture completion, block design, object assembly, and a digit symbol test. Many of the studies performed on the relationship between physical stature and intelligence used one of these tests in order to gauge relative cognitive ability based on the age of the participants. In addition to IQ tests, some of the studies that were performed on children use academic performance as a measure of intelligence through standardized tests such as the Wide Range Achievement Test.
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