Angelina Jolie and Marilyn Monroe are classic beauties of the Western world. Experts say it's their symmetrical facial features that give an impression of attractiveness.
In parts of Ethiopia, it's a lip that's been stretched around a plate that's considered desirable. And in one Burmese tribe, it is a long neck wrapped in brass coils.
These standards were all cemented into those cultures over a long period of time. But new research suggests that it might not take generations to hard-wire our brains about what we find beautiful.
"Beauty may be very fluid," said Haiyang Yang, an assistant professor of marketing at Johns Hopkins University's Carey Business School. "Even highly contagious."
The research indicates that a person who finds, say, a woman with a button nose and curly hair attractive will subconsciously start to find, instead, women with aquiline noses and straight hair attractive if it is perceived that the latter is generally considered attractive by others.
Yang used an experiment that allowed people to rank others' dating-site photos on a scale from 1 to 10, and found that, in short, people liked what other people liked.
The participants saw a photo, ranked it, and then were immediately shown the photo's average score. As they continued to rank more photos — thousands of them — the participants began ranking features that they had previously not found particularly attractive as now being very attractive when they learned that others considered them good looking.
Yang said this showed that they were instantly aligning their standard of attractiveness with those of fellow participants.
He repeated the study in his lab, showing that some people became "instantaneously hotter" or less so depending on others' rankings. He even artificially altered scores and got the same result.
In each case, participants denied being influenced by others' assessments of beauty.
Given that attractive people are thought to land better jobs, make more money and enjoy better treatment in general, understanding this influence could have implications not only for dating and other social interactions, but for product marketing and political campaigning and even development of artificial intelligence, said Yang.
For now, Yang's research, published in the journal Advances in Consumer Research, can't say how much people can be swayed or how long the effects would last. He and a partner in Singapore continue to investigate.
Others researchers, however, say it may be "fashion" that is shifting constantly, rather than the more evolutionary standard of beauty in a culture.
Clothing, hairstyle and cosmetics are easy to change and are highly influential, said Robert Provine, a neuroscientist and professor of psychology at the University of Maryland, Baltimore County, who studies human social behavior.
People don't realize that they are constantly pushed to like something new or different, he said.
What's constant across nearly all societies and eras is that "clear eyes, good skin and long, lustrous hair are always signs of beauty," Provine said.
"They are reliable, honest signals because they are hard to change," he said. "When has disease, red, runny eyes, hair that's falling out and skin lesions been attractive? Ultimately, beauty is a matter of good health and the evolutionary product of likely reproductive success. There is nothing arbitrary about beauty."
One woman who scouts beauty for a living acknowledged that those evolutionary elements of beauty are consistently on her list.
Women need a certain height, weight and youthfulness, said Jill Nechamkin Roach, agency director at Model and Talent Management, a national agency for actors, spokespeople and models, which has an office in Timonium.
But perhaps accounting for Yang's fluid theory of attractiveness, Roach said the models also needed a certain trendy look. For example, right now that means men are not too thin, not too bulky and clean cut. Women need great eyes and smile and longer hair.
For promotional work, the models also may need to seem friendly, engaging or approachable.
"They can change everyyear or every other," Roach said about features considered attractive by scouts, though one thing stays consistent: "They tend to always look for symmetrical features on a girls face."
These trendy looks, underpinned with the evolutionary elements, can have a powerful influence on people — though few realize it's happening, said Gary W. Lewandowski Jr., chair of the department of psychology at Monmouth University in New Jersey. He is a co-founder of the website scienceofrelationships.com.
When advertisers hit the mark, "they can sell perfume and soap" he said. But forces are at work in everyday surroundings too, Lewandowski said. People tend to dress alike in an office meeting, having been unwittingly influenced by co-workers to wear a certain kind of suit or tie their scarves a certain way, he said.
More information on just how far the influences can push people and for how long would be even more useful in promoting a person or product. Though Lewandowski figured someone could be made "instantaneously hotter," as in Yang's study, it would be only temporary without constant reinforcement because other social influences would take over.
But Lewandowski said he is sure someone's sense of beauty can be surreptitiously manipulated.
His research has shown that people become more attractive when others are made to believe they are kind, funny or smart. Conversely, they become less attractive when others are made to believe they are mean.
Lewandowski said this isn't always a bad thing.
"This shows you can become a better-looking person by being a better person," he said. "You don't have to wear makeup or go to the gym constantly."