Similar facial features make people trust, but not fancy, each other, research has suggested.
Some characteristics of the student's face were replicated on the man's face
Of 144 students studied, the majority picked individuals who most looked like them to be the most trustworthy.
But when it came to sexual attraction, most picked those with differing facial characteristics, said psychologists at Aberdeen University, UK.
The results suggest that people steer clear of those who "look like family" to avoid inbreeding.
The students were shown a series of paired faces.
However, they were unaware that shortly before the experiment many of the photographs had been subtly altered by psychologists to resemble the student before they looked at them.
"This supports the idea that people - perhaps unwittingly - detect facial resemblance," said researcher Dr Lisa DeBruine.
"It means to them, on some level, that this person is 'family' and they are more trusting of them."
The similar faces were also described as sexually unattractive by the students.
"These results back the notion that people trust kin but avoid them in a sexual setting due to the costs of inbreeding."
Dr DeBruine carried out the research at McMaster University in Canada and is now continuing her work within the schools of psychology at Aberdeen and St Andrews universities.