January 7, 2010 | 4
Some people seem to have it all, mentally speaking—strong math and verbal skills, a keen memory and good spatial sense. This gift could be chalked up to good "generalist genes," or genes that affect many cognitive abilities and, broadly speaking, determine intelligence. The downside of generalist genes is that, because their functions overlap, someone who falters at understanding algebra may also be more likely to have trouble learning a foreign language.
But good news for Mensa rejects comes in a study published in the January 7 issue of Current Biology. Scientists identified the first high-level cognitive skill—the ability to recognize faces—that is independent of IQ-related skills. By studying pairs of identical and fraternal twins, the researchers found that, unlike cognitive abilities such as verbal and spatial understanding, the inheritance of facial recognition does not correlate with IQ inheritance.
The finding supports a Swiss Army knife metaphor for the mind, says Jia Liu, a neuroscientist at Beijing Normal University in China and lead author of the study. According to this thinking, the mind is a general-purpose tool that handles IQ-related skills and lower level tasks such as reacting to a stimulus, but that also has specialized tools. One of these, Liu’s study suggests, is facial recognition. As he points out, the ability to distinguish a friend from a stranger is a fundamental skill for social animals like humans. There are, however, shades of gray in that some people can recognize strangers, for example, better than others.
To study the inheritance of facial recognition ability, Liu’s group worked with 102 pairs of identical twins and 71 pairs of fraternal twins that were recruited from elementary and middle schools in Beijing. Because identical twins have the same genome while fraternal twins share 50 percent of their genes, hereditary traits such as IQ are more likely to be similar among identical than fraternal twins. But traits like IQ still vary among identical twins because they are also influenced by environmental factors.
By conducting a facial recognition test, Liu’s group found that the ability to recognize faces was also more similar among identical than fraternal twins and, thus, hereditary. For this experiment, participants first looked at black-and-white pictures of 20 different faces on a computer screen for 1 second per image. Then, in the test trial, the researchers showed the participants 10 of these faces intermixed with 20 new faces and asked them to identify the ones they had already seen. Thirty-seven percent of the pairs of identical twins had the same score in this test, compared with only 5 percent of fraternal twin pairs
The researchers took into account the ability of participants to recognize other types of images. Additional series of tests were done where participants were asked to remember pictures of either inverted or misaligned faces. Even though these images have the same visual content as unaltered faces, they are not recognized as faces. Liu’s group found no difference between the ability of identical and fraternal twins to recognize these images, indicating that it is the ability to recognize faces, not just visual images, which is hereditary.
To determine if facial recognition ability is inherited under the same umbrella as intelligence-related traits, the researchers tested the intelligence of the participants using a popular multiple-choice IQ test called the Raven’s Matrices. Liu’s team found that the pairs of twins that shared similar IQs were in many cases not the same pairs that shared facial recognition ability.
Because facial recognition is inherited independently of the IQ-related cognitive skills, the authors suggest that specialist, rather than generalist, genes are responsible for this skill. "This finding raises the question of what other specific cognitive abilities are independently heritable," they wrote. Because children with autism can have normal IQs, Liu thinks that autism disorders might be controlled by specialist genes. Other candidates for specialized cognitive abilities are dyslexia and certain aspects of language comprehension, the latter of which Liu’s group plans to study next.
The image shows two of the unaltered and inverted face pictures that were used in the facial recognition test. The image is courtesy of Zhu et al., State Key Laboratory of Cognitive Neuroscience and Learning