New Delhi, Oct. 1: The timeless adage that beauty lies in the eyes of the beholder has received fresh scientific endorsement through a research study that has found even identical twins sharply disagreeing over the attractiveness of faces.
The study by US researchers has suggested that people's unique life experiences determine their preferences for one face over another, and provides a scientific basis to explain why people often fiercely, endlessly and futilely debate about someone's attractiveness.
Their findings bolster long-standing wisdom articulated by poets, parents and peers that individual preferences strongly influence decisions about beauty - although people across cultures also appear to use a set of so-called universal features linked to facial biology and geometry to assess attractiveness.
But the results have also surprised sections of scientists because they suggest that while genetics substantially contribute to virtually all known psychological and behavioural traits, it appears to play a much lesser role when people judge facial attractiveness.
"Genes play a critical role in almost every psychological trait we know - even the capacity to recognise faces efficiently is linked to genes," said Laura Germine, a post-doctoral researcher in psychology at Harvard University and the lead author of the study. "But when people judge faces for attractiveness, we find that it is mostly their unique experiences at play and not their genes," she told The Telegraph over the telephone from Boston.
Most previous research on what makes some faces more attractive than others has focused on what biologists would consider universal features of attractiveness - symmetry, average-looks or faces with healthy-looking skin tone and fat.
In their study, Germine and her colleagues from collaborating institutions in the US and Australia focused not on universal features, but on as-yet unidentified sources of disagreement or divergence, among people over facial attractiveness.
"If people say Brad Pitt is more attractive than Donald Trump, they're relying on universal features to make that judgment, but if they debate over Tom Cruise and Brad Pitt, it is their disagreements showing up," Germine said.
The scientists analysed face preferences among over 35,000 volunters through a website and then tested preferences of 547 pairs of identical twins and 214 pairs of non-identical, but same-sex twins by asking them to rate 200 faces.
Many studies on twins have earlier shown that virtually every psychological trait - from personality to interests - is genetically passed down from one generation to the next and, thus, is shared by twins. Pairs of identical twins, for instance, have very similar capacities to recognise faces.
The new study, published today in the journal Current Biology, found very little similarities in twins' preferences for facial attractiveness.
"Many pairs of the identical twins did not have the same preferences for faces - so genetics or family environment are not key contributors to judgments about faces," Germine said. "An individual's life history and experience are likely a major driving force behind individual's face preferences."
Some scientists say the role of personal experience could be even more pervasive than estimated.
"Consensus can also be reached from experience," said David Perrett, professor of psychology at St Andrew's University in the UK, who has spent nearly two decades identifying geometric and biological features that contribute to facial attractiveness.
"Common experience that happy healthy people are nice to us can lead to common judgments of attractiveness of people with slightly smiling expressions and health indicators," Perrett told The Telegraph.
"Our individual experiences may also be important to explain the kind of deviations from average faces that we find appealing," said Lynda Boothroyd, a senior lecturer in psychology at Durham University in the UK whose research interests include attraction.
Scientists say while they cannot yet pinpoint the exact sources of disagreement over faces, the experiences and interactions that people have over time with others can influence decisions on attractiveness of faces.
"This is speculation, but earlier research has suggested that the faces of people we know such as friends, colleagues or spouses can shape the sorts of faces we find attractive," Germine said.
"So if there is a face you have positive associations with, then you're likely to find similar faces more attractive. Likewise, someone you have a negative relationship or experience with might cause you to find faces similar to that person less attractive - over time, such experiences cause us to find people more or less attractive."
