People tend to trust those whose faces resemble theirs, but members of the opposite sex who look too much like them are a big turn-off sexually, shows a new study.
Conducted by researchers at the University of Aberdeen, the study suggests that when it comes to attractiveness, people prefer individuals who do not remind them uncomfortably of their own image.
During the study, the research team used computer software to "morph" some images, so that they would look more or less like the study participants.
"The same was not true for judgments of sexual attractiveness. In that case people disliked people who looked like them.
"You could say self resemblance is trustworthy but not lustworthy," the researcher added.
Speaking at the British Science Festival at the University of Surrey in Guildford, she said that the study showed how people thought "incest is bad".
Referring to another finding of the study, she further said that when members of the opposite sex looked too different, they were also repelled from each other.
"People choose partners who are not too intimately similar but it also seems that being too different isn't good. That will be the subject of the next step in our research. We want to look at whether there's a happy medium," Lisa said.
"Big levels of self resemblance seem to be really unattractive but we predict that a little self resemblance might be a good thing," she added.
The theory was borne out by a study in Iceland that showed that married third or fourth cousins produced more children than couples who were either less or more closely related.