Having attractive friends will make you more popular on Facebook, especially if you are a woman, according to a new study that takes Charles Darwin into the domain of cyber networking.
The findings show that signs of reproductive fitness sway our decisions about friendship, says Dutch researcher Associate Professor Piet Kommers.
The study is published in the International Journal of Web Based Communities.
"People are attracted by other people who look very healthy, happy and productive in a sexual sense. That is an accepted evolutionary law," he says.
"The very pure healthiness aspect is still dominant. It is hard to suppress that."
The University of Twente team created four mockup Facebook profiles using pictures of a man and a woman deemed "neutral" for attractiveness in a pre-test evaluation.
Two profile pages were created for each of them.
One page had photographs of two attractive "friends" - a man and a woman - and the other had two unattractive ones.
The profiles were otherwise identical, listing the owners' place of residence, birth date, interests and favourite movies, music and TV shows.
Scientists then showed the profiles at random to 74 students between the ages of 21 and 31, asking them to rate the profile holder's "social attractiveness".
Participants had to consider such questions as "I think he/she could be a friend" or "He/she would be pleasant to be with".
The respondents were 20 per cent likelier to choose the profile with "attractive" friends, the investigators found.
"The appearance of one's Facebook friends in fact influences the perception of the profile owner," the study said.
"More specifically, the attractiveness of one's associates on Facebook has a direct positive influence on one's own social attractiveness."
Having beautiful friends was especially important for the popularity of women, it found.
The authors note that the opposite is also true. Having unattractive images could harm the appeal of individuals and businesses using social networking sites, they warn.