A study by Michael Fisher, Rudolph Nager and Pat Monaghan on the effects of malnourishment on birds' intelligence showed that birds fed less nutritionally valuable food took longer to learn a new task in adulthood. Although their growth sped up when they were switched to a good diet, they still took longer to solve an associated learning task. Similar results were found in human infants, but the precise reason for this phenomenon is unknown.
Researchers from the University of Illinois found that breast-fed children score higher on average on IQ tests than non breast-fed children. A variant of the FADS2 gene causes the link between breastfeeding and IQ test scores and is related to the fatty acids available only in breast milk. The researchers ruled out other causes for this discrepancy, including the mother's IQ, social class and gene exposure.
Many people suggest that IQ tests are culturally biased, testing only a Western model of intelligence. For example, some intelligence tests assume that people read pieces of classic literature or are familiar with the types of questions that are asked on intelligence tests. Robert Serpell, Ph.D., studied the idea of intelligence across rural African communities beginning in the 1970s and found that the line between intelligence and social competence is blurred. Robert Sternberg, president of the American Psychological Society, studied the Luo people in rural Kenya and found similar results. The Luo see intelligence in four parts, and only one of those parts, Reiko, matches the Western definition of intelligence. Sternberg found that children who could identify and explain the effects of medicinal herbs, which is a form of practical intelligence, scored poorly on academic intelligence tests.
East Asians perform, on average, about six points better than Caucasians on IQ tests, according to a News Medical website article. African Americans score an average of 15 points lower than Caucasians, and blacks living in Africa score about 15 points lower than African Americans. The data seem to suggest both a cultural and a racial difference in IQ scores, although exceptions exist and other factors and circumstances may relate.