Some online dating sites rely on a mathematical algorithm to match people. Others are based on pure physical attraction and a quick swipe to the left or right.

But a new online dating site promises deeper compatibility by testing users’ DNA. They say they've found the secret to “long-term chemistry” — what makes a relationship last — in people’s genes.

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The Science of Compatibility

Two companies, SingldOut and Instant Chemistry, are working together to match users based on the results of both a personality test (evaluating “diet habits of a mate, how often they exercise, and so on,” according to a company press release) and a genetic test.

“Through intensive research, scientists have found that long-term relationship satisfaction stems from two constants — your DNA and core personality — and how those match up with your partner's,” said Sara Seabrooke, a geneticist and chief science officer of Instant Chemistry, in a press statement.

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Users sign up and receive a DNA testing kit in the mail, spit into a cup, and send the kit back to be tested for mutations in a serotonin transporter gene and a group of three genes that belong to the human leukocyte antigens (HLA) system.

“Theoretically, selection of the serotonin transporter gene does make a little sense,” said geneticist Ricki Lewis, Ph.D., author of “Human Genetics: Concepts and Applications.” The gene gives people either a “long” or “short” component of their serotonin transporter, which recycles serotonin, a neurotransmitter chemical. Variants of the serotonin transporter gene have been linked to issues such as alcoholism, hypertension, and obsessive-compulsive disorder.

HLA testing is generally used to determine compatibility for things like blood transfusions and transplant matches. “People with different HLA variants may be less likely to pass infections back and forth, but those with similar variants would be more likely to be compatible if, say, one wanted to donate blood or part of a liver to a partner,” Lewis said.

“The idea of basing a dating website or service on a handful of genes is absurd. Using the science in this way takes advantage of people who do not know anything about human genetics.” — Ricki Lewis, Ph.D.

Ultimately, Lewis said, the science doesn’t live up to the hype. “Testing for two genes out of 20,000 … is hardly useful — would you select a person to date based on four items on a 20,000 item questionnaire?” she asked. “Even if what those two genes do makes sense, it is simply too little information to have any value.”

No one gene can predict the sort of compatibility required for long-term relationship success.

“I think a shared love of pistachio ice cream or running or Woody Allen films may be more meaningful measures of day-to-day compatibility,” Lewis said.

‘Pseudoscience’ in Online Dating

In November of last year, the Food and Drug Administration (FDA) ordered home genetic testing company 23andMe to stop providing health information “intended for use in the diagnosis of disease.”

Although new guidelines for the FDA regulation of genetic tests are expected by the end of September, the FDA will likely continue to practice “enforcement discretion” for tests like the one offered by SingldOut and Instant Chemistry. 

The companies are careful not to provide any information about users’ genetic health or even details about ancestry, which could tell users if they are related by blood. At worst, users could find themselves out of pocket for the fee: $199 for a three-month membership.

“The idea of basing a dating website or service on a handful of genes is absurd,” Lewis said. “But it is like the many ads for cosmetics that claim to be anti-aging, which of course is impossible without a time machine. Using the science in this way takes advantage of people who do not know anything about human genetics.”

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Online dating has long relied on mysterious algorithms and blind luck to help users decide who and how to date. Enough people have turned to Internet dating that a 2012 study found that more than one-third of marriages in the United States began online.

However, anyone looking for a genetic determinant of true love may be disappointed.

“Let common sense, not a false impression with pseudoscience, guide social choices,” Lewis said.