It’s a familiar pattern in science, the more we learn about something, the more variations we see in the details. Take, for example, the human brain and its memory capacity. “Memory” used to be considered a unitary capability, that is, the ability to remember things was thought to be all part of the brain’s area that holds memory. Then it was learned that many different parts of the brain contribute to memory. Likewise, the thinking was that various memory skills, such as languages and image retention, were functions of a generalized memory capability. New research, conducted at Beijing Normal University (China), is now showing that at least in some areas, memory skills are specialized.

The question in the Beijing study was whether the ability to retain images of people’s faces was a matter of heredity – and a function of IQ – or something else. Retaining images of human faces is a ‘survival skill,’ meaning that our capacity to analyze and remember faces is part of our ability to discern danger or threat. (There are, of course, positive aspects as well, such as the ability to detect visual signs of love or friendship, which come to think of it is part of survival too.)

Using 102 pairs of identical twins (sharing 100% of their genome) and 71 pairs of fraternal twins (sharing 50% of the genome), both groups were shown 20 different facial images. Thereafter, they were shown 20 images and scored on their ability to remember if they had seen any of them before. 37% of the identical twins identified exactly the same score, whereas only 5% of the fraternal twins matched scores. This was an indication that facial recognition has a hereditary component. Similar tests were done with facial images that were upside down or offset in odd ways; this resulted in similar scores for both groups and showed that general image retention is different than memory of faces.

To examine the relationship of facial image retention to IQ, all the twins were given a standardized IQ test (Raven’s Matrices). It turned out twins that shared the ability to remember facial images did not share IQ scores. This confirmed facial recognition as a skill separate from other cognitive skills that make up IQ.

The implication of the study was that besides a generalized memory function, we have evolved other specialized memory skills – some of which are hereditary.

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.
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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.

[Source: Scientific American]