New York, June 30 (IANS): The perception of beauty in a romantic partner changes with time as individuals get to know one another better before they start dating, says researchers.

In other words, partners who become romantically involved soon after meeting tend to be more similar in physical attractiveness than partners who get together after knowing each other for a while.

"Having more time to get acquainted may allow other factors, such as another person's compatibility as a relationship partner, to make that person appealing in ways other than the physical attractiveness," said lead researcher Lucy Hunt from the University of Texas at Austin.

"Another person might actually become more attractive in the eyes of the beholder by virtue of other factors," Hunt said.

The researchers looked at data collected from 167 couples -- 67 dating and 100 married. The couples had been together for as few as three months and as long as 53 years, with an average relationship length of eight years and eight months.

The results revealed that the longer the romantic partners had known each other before dating, the less likely they were to be matched on attractiveness.

For example, the pairing of an unattractive woman with an attractive man was more likely to emerge if the partners had known one another for many months prior to dating.

Partners who began dating within a month of first meeting each other showed a strong correlation for physical attractiveness. But the correlation was much lower for partners who had known each other for a long time before dating.

"Friends-first couples were less likely to be matched on attractiveness than couples who were strangers before dating," Hunt said.

Interestingly, the level of match on attractiveness was not associated with relationship satisfaction for either men or women in the study.

That is, both friends-first and stranger-first relationships seem approximately equally happy years later. The findings suggest that length of acquaintance can influence whether we perceive someone as being a desirable partner.

"There may be more to the old saying than was previously thought. Maybe, it is the case that beauty is partially in the eye of the beholder, especially as time passes," Hunt added.

The research appeared in the journal Psychological Science.