Compared with notable successes in the genetics of basic sensory transduction, progress on the genetics of higher level perception and cognition has been limited. We propose that investigating specific cognitive abilities with well-defined neural substrates, such as face recognition, may yield additional insights. In a twin study of face recognition, we found that the correlation of scores between monozygotic twins (0.70) was more than double the dizygotic twin correlation (0.29), evidence for a high genetic contribution to face recognition ability. Low correlations between face recognition scores and visual and verbal recognition scores indicate that both face recognition ability itself and its genetic basis are largely attributable to face-specific mechanisms. The present results therefore identify an unusual phenomenon: a highly specific cognitive ability that is highly heritable. Our results establish a clear genetic basis for face recognition, opening this intensively studied and socially advantageous cognitive trait to genetic investigation.
In other words, the strength of face recognition does not seem to track other intelligence test results much at all (including tests which measure verbal and visual memory). Rather, it seems to be a domain-specific competency, rather than emerging out of general intelligence. And, the variation in face recognition ability is highly heritable.
What's going on here? A reasonable guess for me is that the ability to recognize many, many, different faces isn't something that came up for most of human history. Even in a pre-modern village you'd see the same people over and over. By contrast, if you work in sales you probably need to juggle a lot of faces & names to be successful.
Remember that if a quantitative trait is highly heritable then by definition that means that directional selection wasn't operating to drive genes to fixation so that the population was monomorphic in trait value. In English that means if there was a huge benefit to being able to recognize hundreds of faces very well in the past, then we would be able to recognize hundreds of faces very well to the same extent. As it is the strongly for face recognition has to be more complex, with the direct selection applicable being some sort of balancing selection.
Citation: Jeremy B. Wilmer, Laura Germine, Christopher F. Chabris, Garga Chatterjee, Mark Williams, Eric Loken, Ken Nakayama, and Bradley Duchaine, Human face recognition ability is specific and highly heritable, doi:10.1073/pnas.0913053107
Going on the results of the twin studies I would say we cannot conclude much about the general population! Twins are more alike than most random members of the community, especially in age and experience- so their brains may cover a smaller range of development and experience than is possible in the broader community. Because their scores on tests of abilities will be closer to each other, they produce smaller ranges and variance and I think there is more chance of a Type 1 error. With face recognition, you have a mix of multiple skills being tested: there is the general recognition that something is a face, not a ball; there is recognition of the spatial proportions of human faces changing with age and the ability to recognise the combinations of facial cues that indicate universal emotions (which seem to be impaired in autism and Asperger's people)- plus lots of others eg. mirroring and imitative skills which allow empathising with emotions witnessed.
Of course, we all see families around us where general facial recognition seems to be inherited when it is in deficit- a friend of mine and his son are pretty hopeless with recognising their own distant acquaintances- so we're also surrounded by people who have inherited some of the ability to be good at this as well. However, I think it's too early in the piece to conclude that human evolution hasn't required us to be pretty excellent at face recognition as a species because we've also lost our smellivision along the way!
A reasonable guess for me is that the ability to recognize many, many, different faces isn't something that came up for most of human history. Even in a pre-modern village you'd see the same people over and over.
Could the ability to recognize lots of different faces have initially been a side-effect of the ability to recognize subtle differences in emotional states of people from their faces?
I think of this in conjunction with the lost of olfactory receptors -- in tribal life we may have identified people at least as much by smell as visually, whereas in a more dense population setting that's less feasible due to all the odor crosstalk.
There is a brain area specifically for face regognition, so it is a discrete neurological function separate from general memory areas. There are people with an inability to recognize faces of those who are familiar to them. Google "prosopagnosia"