Some people never forget a face. For the rest of us, recognizing faces is not so easy. And those with prosopagnosia can't even recognize their close friends.

Now scientists say the ability to recognize faces is inherited and separate from general intelligence or IQ.

IQ is strongly heritable. And one longstanding general thought about IQ holds that if you're smart in one area, you'll be smart in others. But some skills seem distinct. A person can be brilliant with numbers but not good with linguistics, for example. This latter reality supports a modularity hypothesis, in which the mind is like a Swiss Army knife — a general-purpose tool with special-purpose devices, researchers explained.

"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.  "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,” said co-author Nancy Kanwisher of the McGovern Institute for Brain Research at MIT.

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.

The study is detailed in the Jan. 7 issue of the journal Current Biology.

To test the ideas, 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.

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 a separate study 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.

The researchers 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.

The work was funded by the National Natural Science Foundation of China and a host of other institutions.