Evolutionary psychologists often assume that the perceived genetic proximity of people in your surroundings affects your behavior towards them; but they are often at a loss to explain how exactly genetic proximity can be perceived. Some genetic proximity cues seem obvious, yet they have never really been shown to be real cues for genetic proximity. Facial similarity can also be a result of living together, as this study showed 20 years ago: photographs of people who spent 25 years living together were judged more similar than photographs of people who just spent one year together - probably as a result of unconscious mimicry of the other's emotional state. Increase in resemblance over 25 years correlated with increase of self-reported happiness in couple, frequency of sharing worries, and greater perceived similarity of attitudes.

This is really bad news for Jean-Pierre Bacri and Agnès Jaoui, a pair of french actors involving a charming, easy-going wife and a sullen and depressed husband. The theory predicts that Agnès will end up sharing some of Jean-Pierre' facial features.

Agnès Jaoui and Jean-Pierre Bacri, who wrote the play "Un air de famille" (Family Resemblance).

So it comes as a surprize that the study featured in the Journal of Vision does not control for time spent by siblings living together! Indeed, it puts their conclusion in jeopardy. The PNAS study is apparently more subtle; it purports to test Darwin's hypothesis concerning the innateness of some core facial expression. They analyse the similarity in simple emotion expressions between blind siblings and their parents. Since the children are blind, imitation could apparently be ruled out, and one would bed faced with the raw power of genetic determinism. But one might argue that empathy is an overlooked hidden factor: blind siblings are as likely as others to share in their kins' worries, griefs and pleasures. Hence they might come to empathize with some fine-grained emotional details of their kins' expression, and end up reproducing their facial manifestation.

Another hypothesis (which I owe to Simon) to account for the PNAS findings could be that the siblings reproduce some phonetico-linguistic gimmicks they hear around them, and that these in turn induce facial expression (think for example of the anthem of blasé adolescents "(sigh) whatEver...", and the looks it gives you).

Perhaps this is just far-fetched, unparsimonious anti-nativism. I don't want to sound like these results mean nothing to me; I am a strong supporter of the nativist program in emotion science; Incidentally, I would recommend this recent long paper about Paul Ekman. But I think the best work along those lines is that which adresses the two questions of empathy (the effect of sharing the same life on facial morphology and expression of emotions) and the the relation between emotion-recognition and face recognition.

Concerning this second question, Cognitive Daily adresses the interesting question of the modularity of face-expression- and face-recognition mechanisms; to what extent are they dependent upon one another? This is also the issue raised by this paper in Current Biology. Their conclusions are opposite: some think that face- and emotion- recognition share the same pathways, but others argue that they're separate processes. It would be presomptuous of me to try to settle the matter, since the litterature looks very complex (well, as usual, I would opt for the modular view, but that's just my advice).

Meanwhile, a widespread suspicion is being confirmed by this study: selective deficits of face perception sometimes run in whole families; this is great news for nativists, since the face-perception module is the closest thing we have to a full-blown hardwired specialised, high-level cognitive device.

So the field of face-perception research seems to be making huge progress, which might enable them to take the issue of empathy and common life into account.

(Concerning facial similarities in couples, theories of assortative mating suggest that it may be present from the start; for example, that's the reason why dog-owners often resemble their dogs - not because of empathy, but because they chose dogs that are similar to them. Proof of that is the fact that only pure-breed dogs - whose appearance can be foreseen by the buyers - resemble their owners. By the way, when do the guys who showed this get their IgNobel Prize?)