Physicists are not particularly well known for never forgetting a face, while some politicians are. Physicists tend to have higher IQs than politicians, but politicians have probably been evolving longer. So, is facial recognition just the general factor of intelligence in action once again, or is there a specifically evolved cognitive mechanism for it?

One of the more intriguing epistemological questions of recent decades has been over the prevalence of a g or General Factor of intelligence versus specific "mental modules."

The dominance of the "blank slate" theory of social conditioning was undermined beginning in 1958 by linguist Noam Chomsky's observation that children seemed to be particularly good at learning and speaking their native tongue, better than the existing behaviorist / Pavlovian worldview would suggest, which implied that humans have what Steven Pinker called in 1994 a "language instinct."

Although Chomsky remained agnostic over whether natural selection could account for this instinct, a school of evolutionary psychology grew up late in the century, exemplified by John Tooby and Leda Cosmides's 1992 book, that hypothesized the existence of multitudinous inherited mental modules for skills besides language.

Psychometricians, such as Arthur Jensen and Chris Brand (in 1998 books both entitled The g Factor) suggested that the very old (Spearman 1904) concept of a general factor of intelligence could account for quite a bit of the hypothesized mental modules. This seems particularly likely for mental demands that people only recently encountered, such as understanding quantum mechanics. It seems implausible that humans evolved a specific mental module for, say the Physics BC Advanced Placement test. Instead, people seem to rely for that upon the general factor plus some specific factors such as three-dimensional imagination.

Therefore, evolutionary psychologists have tended to focus their hypothesizing on cognitive skills that would have been useful in navigating the social life of a low tech tribe, such as learning a language or recognizing faces.

From an MIT press release adapted in Science Daily:

Recognizing faces is an important social skill, but not all of us are equally good at it. Some people are unable to recognize even their closest friends (a condition called prosopagnosia), while others have a near-photographic memory for large numbers of faces. Now a twin study by collaborators at MIT and in Beijing shows that face recognition is heritable, and that it is inherited separately from general intelligence or IQ.This finding plays into a long-standing debate on the nature of mind and intelligence. The prevailing generalist theory, upon which the concept of IQ is based, holds that if people are smart in one area they tend to be smart in other areas, so if you are good in math you are also more likely to be good at literature and history. IQ is strongly influenced by heredity, suggesting the existence of "generalist genes" for cognition.

Yet some cognitive abilities seem distinct from overall IQ, as happens when a person who is brilliant with numbers or music is tone-deaf socially or linguistically. Also, many specialized cognitive skills, including recognizing faces, appear to be localized to specialized brain regions. Such evidence supports a modularity hypothesis, in which the mind is like a Swiss Army knife — a general-purpose tool with special-purpose devices.

"Our study provides the first evidence supporting the modularity hypothesis from a genetic perspective," said lead author Jia Liu, Professor of Cognitive Neuroscience at Beijing Normal University in China of the study published in the Jan. 7 issue of Current Biology. "That is, some cognitive abilities, like face recognition, are shaped by specialist genes rather than generalist genes."

"Our finding may help explain why we see such disparities of cognitive abilities within the same person in certain heritable disorders," added co-author Nancy Kanwisher of the McGovern Institute for Brain Research at MIT, where Liu studied before moving to Beijing. In dyslexia, for example, a person with normal IQ has deficits in reading, while in Williams Syndrome, people have low IQ but excellent language skills.

For the study, Liu and his colleagues recruited 102 pairs of identical twins and 71 pairs of fraternal twins aged 7 to 19 from Beijing schools. Because identical twins have 100 percent of their genes in common while fraternal twins have just 50 percent, traits that are strongly hereditary are more similar between identical twins than between fraternal twins. (Identical twins still show variability because of the influence of environmental factors.)

Participants were shown black-and-white images of 20 different faces on a computer screen for one second per image. They were then shown 10 of the original faces mixed with 20 new faces and asked which ones they had seen before. The scores were more closely matched between identical twins than fraternal twins, and Liu attributed 39 percent of the variance between individuals to genetic effects. Further tests confirmed that these differences were specific to face recognition, and did not reflect differences in sharpness of vision, general object recognition abilities, memory or other cognitive processes.

In an independent sample of 321 students, the researchers found that face recognition ability was not correlated with IQ, indicating that the genes that affect face recognition ability are distinct from those that affect IQ. Liu and Kanwisher are now investigating whether other cognitive abilities, such as language processing, understanding numbers, or navigation, are also heritable and independent from general intelligence and other cognitive abilities.

Generally speaking, language is so central to human thought that the ten question vocabulary test in the annual General Social Survey can be used as a rough proxy for IQ, so I don't think "language processing" is likely to pan out as heritable and terribly independent from general intelligence. There are presumably, however, specific language-related skills (such as, say, noticing when you are being insulted) that are less correlated with IQ than general language processing.

Even though vocabulary correlates closely with g, the Chomskyan idea of a language instinct seems fairly reasonable, since the vast majority of human beings who are not suffering an obvious organic problem (such as deafness or severe retardation) learn to speak a native tongue well enough to pass the famous Turing Test that has proven so difficult for artificial intelligence technologists.

In contrast, many other skills are much more widely distributed, such as singing on key.

Researchers at the Beijing Normal University and Graduate University of the Chinese Academy of Sciences contributed to this research: Qi Zhu, Yiying Song, Siyuan Hu, Xiaobai Li, Moqian Tian, Zonglei Zhen and Qi Dong.

In addition to providing new insight into the structure of the mind, this work could shed light on the underlying causes of developmental disorders like autism and dyslexia. "The heritability of these cognitively specific diseases suggests that some genes have specific cognitive effects, but it's a big mystery how genes produce cognitively specific effects," said Kanwisher.

Here's the abstract:

Heritability of the Specific Cognitive Ability of Face Perception

What makes one person socially insightful but mathematically challenged, and another musically gifted yet devoid of a sense of direction? Individual differences in general cognitive ability are thought to be mediated by ”generalist genes” that affect many cognitive abilities similarly without specific genetic influences on particular cognitive abilities [1]. In contrast, we present here evidence for cognitive ”specialist genes”: monozygotic twins are more similar than dizygotic twins in the specific cognitive ability of face perception. Each of three measures of face-specific processing was heritable, i.e., more correlated in monozygotic than dizygotic twins: face-specific recognition ability, the face-inversion effect [2], and the composite-face effect [3]. Crucially, this effect is due to the heritability of face processing in particular, not to a more general aspect of cognition such as IQ or global attention. Thus, individual differences in at least one specific mental talent are independently heritable. This finding raises the question of what other specific cognitive abilities are independently heritable and may elucidate the mechanisms by which heritable disorders like dyslexia and autism can have highly uneven cognitive profiles in which some mental processes can be selectively impaired while others remain unaffected or even selectively enhanced.