When people searching for love find their perfect mate, they often liken the convergence to “chemistry” — that special something that brings one certain individual to the head of the class.

According to U.S. biological anthropologist Helen Fisher, whose research on body chemistry is behind a personality test on a new Japanese online matchmaking service, science can be used to quantify this formula that leads to a successful relationship.

And in the case of mate-hunting services, it can explain why one person is chosen over another, even if both seem to check the right profile boxes.

“You can walk into a room and everybody is from the same basic background and same level of intelligence, and you don’t fall in love with all of them,” said Fisher, a visiting professor at Rutgers University in New Jersey and chief science adviser to Match.com, the world’s top dating Web site, with 15 million members in 24 countries, including 1 million in Japan.

“So I tried to add the second half of the puzzle, which is your temperament, your body chemistry. Certain people will trigger the brain system for romantic love, while others won’t,” Fisher said.

Riding the “konkatsu” wave of marriage-hunting, Match.com launched the spouse-search service Match.com Marriage on June 11. It features a science-based personality test Fisher created that categorizes members into four broad personality types and suggests which type they would be most attracted to.

Based on her previous research on the biology of love and relationships as well as academic literature, Fisher concluded romantic choice could be affected by the brain chemicals associated with personality traits, in addition to other factors discovered by psychologists, including socioeconomic background, values, education, income and appearance.

She tested her theory on 28,000 people on U.S. Match.com and found that there was a natural pattern of personality type attractions.

Those with traits associated with high levels of dopamine and norepinephrine tend to be novelty-seeking, risk-taking and spontaneous with broad interests, or in Fisher’s parlance, the “explorer.”

Those who express activity in the serotonin system, referred to as the “builder,” are traditional, cautious, community-oriented and respectful of authority. These two types are each drawn to someone of the same type, she said.

Meanwhile, those with the temperament linked to high levels of testosterone are analytical, competitive, tough-minded with good spatial skills, a type Fisher calls the “director,” while “negotiators,” who express activity in the estrogen and oxytocin systems, are intuitive, compassionate, expressive and take a holistic approach.

Fisher discovered that builders and negotiators are often attracted to each other.

Based on these patterns, she created the Match.com Marriage personality test, which attempts to gauge someone’s inclination based on the aforementioned types, and suggests a suitable match among its members.

The test was originally featured on Chemistry.com, a U.S. sister site of Match.com that also aids singles seeking long-term relationships.

Questions on the test include the comparative lengths of a forefinger and ring finger, the type of doodling one scribbles when bored and clicking on the description that best suits a particular picture.

Fisher admitted she has yet to do biological tests to confirm these personality-matching patterns and said she is waiting to collect enough blood and urine samples before analyzing the data.

“But whether we will achieve anything is highly questionable, although I am confident the constellation is there. These neurotransmitters and hormones vary during the course of the day, the month, they vary if you take drugs, have sex, and at exam time.”

Fisher said she then plans to test with genetic samples, although at the current stage of modern genetics it will take years to collect data from a large enough sample.

The patterns of attraction should be interpreted from the Darwinian perspective as various adaptive ways to spread DNA, according to Fisher.

“The ‘director’ and the ‘negotiator’ have very different traits, but they complement each other. The director needs the compassion of the negotiator, while the negotiator needs the decisiveness of the director. I think the attraction of the ‘director’ and the ‘negotiator’ evolved millions of years ago to pull their resources together to raise children,” she said.

“Builders” are drawn to each other to capitalize on their child-rearing traits, while “explorer” couples are more likely to have a series of relationships and create more genetic variety, she said.

It is no surprise to Fisher that the trends are so clear.

“Nature has had millions of years to perfect this. When you’re studying something like love, you’re really studying something that’s central to the human being because there is such strong selection against bad types,” she said.

But any combination of the four types is possible, and the importance of a personality match depends on individual priorities, she said.

“I think some people are more flexible than others. Some people want a traditional person (who shares the same values) and are willing to put up with someone who doesn’t have their interests,” she said.

While Fisher is confident men and women around the world prioritize romantic love when looking for a partner, journalist Toko Shirakawa, who had a hand in coining the term “konkatsu,” said Japanese are more practical when making a selection.

“When you take a survey (on what people look for in a partner), both men and women first say personality, but I don’t think this is their true opinion,” Shirakawa said during a discussion with Fisher.

Japanese men tend to go for young women, searching by age and looks, while women look for someone with enough income to sustain the household while they are pregnant or rearing children, she said.

Some social commentators have recently identified a growing number of “soshoku-kei” (herbivorous) men in Japan, who are not interested in sex or marriage. But Fisher is dismissive of the idea that this trend can affect marriage-hunting inclinations of either men or women.

“These plant-eating boys are all in their late teens and early 20s. They’re not ready to get married, they probably don’t know what their career is, they’re at home tinkering on their computers. What’s the news here? These are just young men,” she laughed.

“It’s as if Japan is worried that they’ll turn into plant-eating middle-aged men. They won’t. Not everyone enjoys the dating scene, especially ‘directors.’ Men are just being allowed to be who they are, as women are allowed to be who they are, by being aggressive if they want to,” she said.

Match.com Marriage gives support to those who may be unsure of how to communicate with a potential partner, according to Carl Leubsdorf, senior vice president of the Asia-Pacific operations of Match.com International. It suggests questions members can ask each other, provides a template invitation so interested parties do not have to ask each other out personally and mediates feedback after a date.

Although the new service is being launched during economically troubled times, feelings of instability encourage people to look for love, according to Fisher.

“In the U.S., the economic crisis has led to a 20 to 25 percent increase in the number of people who come on to Match.com, and I believe in Japan there is an 11 percent increase,” she said. “In a time of real threat and fear, people pull back to the basics in their lives, and love is one of the basic things we do. Love is a survival response in an economic downturn.”