Do I know you from somewhere? How humans recognise kin

Humans can tell if two strangers are related, even if they are generations apart, just by looking at their faces. So say scientists writing today in the journal Proceedings of the Royal Society B , who believe this ability helps us to interpret situations and understand the motives of others in a social setting.

It is well documented that humans have the ability to recognise their own relatives an important tool if we are to promote our genes whilst avoiding the damaging impacts of incest. But this is the first study to actually show that humans are capable of indentifying which individuals are related, even in cases where they are more than a generation apart and have presumably not lived together.

The team of researchers from Grenoble University asked 59 subjects to look at pairs of images of faces and decide whether or not they are related. The pairs we made up from a database of images collected from 32 different families. They also timed how long it took the subjects to make the decision, as this indicates how hard they find the task.

The results showed that people can tell that even distant relatives have family ties for example a grandparent and grandchild yet we tend to find it harder to spot relatives the more distant they get.
The similarities in peoples' faces that help us to make a link between relatives can come from genetic makeup and also from environmental factors which are common to people who live together. Siblings raised on the same diet might have a similar complexion, for example.

Because people are more likely to help relatives than those who aren't kin, there is an evolutionary advantage to being able to tell if strangers are related, say the authors. The knowledge can help us to resolve or avoid problems in a range of social contexts: "Anticipating hostile alliances, enlisting aid, pacifying conflicts amongst kin, forming coalitions, punishing people or eliciting sexual favours&even trying to flatter someone may be indirectly achieved by addressing a related individual," they add.

Source: The Royal Society