Over the centuries, physics, chemistry, and biology have transformed what once was seen as mysterious or even magical—the rotation of the stars, flowers blooming, causes of disease—into well-understood phenomena. Could the same now be happening to love and lust, the most mysterious and magical of all human emotions?

In recent weeks, two companies (Instant Chemistry and SingldOut) have made a media splash with their launch of a new direct-to-consumer genetic testing service to help determine compatibility in intimate relationships. SingldOut is an online dating service that operates via the professional networking site LinkedIn and uses Instant Chemistry’s genetic testing results to match its members. DNA results become part of each user’s profile, and members can search for and evaluate potential matches based on their genetic compatibility.

Instant Chemistry and SingldOut are not the first to promote genetic testing to determine romantic compatibility. In 2008, a company called GenePartner began to offer genetic testing to identify relationship compatibility. Applying a similar concept are “pheromone parties” in which singles sniff well-worn T-shirts worn by members of the opposite sex to facilitate biological matches based on pheromones, the elusive compounds of attraction.

Unlike some direct-to-consumer genetic testing companies (such as those claiming to offer genetically tailored nutritional supplements, which have been subject to enforcement by the Federal Trade Commission for deceptive claims), there is some legitimate science behind the new DNA-matching dating websites.

While genetics seems to play some role in human sexual attraction, it clearly is not the only, or even predominant, factor determining human mate choice. SingldOut claims that genetic tests can identify up to 40 percent of the chemistry of attraction between two people. While not denying that genes play some role in mate selection, Mike Dougherty of the American Society of Human Genetics contends that the research to date does not support quantifying the impact of genetic attraction.

In fact, the research to date is all over the place. It has long been known that other mammals, such as mice, selectively mate with partners having different genetic variants of their MHC genes, which control immune responses. A leading hypothesis is that such “disassortative” mating will produce offspring with greater diversity in their MHC genes that will protect them against a broader range of pathogens.

Given that all mammals display similar genetic mechanisms, one might expect a similar genetic attraction to exist in humans, albeit within the context of the greater complexity of human relationships. Indeed, a 1995 study found that single women, asked to smell and pick from sweaters worn by men, were disproportionately inclined to pick one worn by a man with different MCH alleles from their own. This suggests that our preference for a particular mate is influenced by our sense of smell, as is the case with other mammals. Similarly, a 2006 study found that the more differences in MHC genes between a romantic couple, the more likely the female partner was to be sexually satisfied and committed to her existing relationship.

Yet, as noted above and as is common for most genetic research, especially as it relates to complex human behaviors such as love and romance, the data supporting genetic attraction is highly inconsistent. A large number of studies, involving different experimental methods and populations, have now been reported, and they give discordant results. While some research has supported the theory that MHC gene diversity drives human attraction, other studies have reported different or conflicting results. A few studies have found that humans prefer sexual partners with only moderately different or even similar MHC variants, others have found that MHC diversity is detected by facial shape rather than smell, and still more have found that women in committed relationships are most attracted to men with different MHC alleles. Some studies have also discovered that women on birth control pills tend to prefer men with the same MHC variants, the opposite of their peers not on the pill. As one scientific review of the entire body of data concluded, “the mixed evidence … makes it difficult to draw definitive conclusions, [but] the large number of studies showing some MHC involvement suggests there is a real phenomenon that needs further work to elucidate.”

Into this complicated field now come direct-to-consumer genetic testing companies such as Instant Chemistry and SingldOut. Once the “spit, seal & mail” process is complete and the kit is received, Instant Chemistry goes to work to analyze three specific genes in the MHC complex on chromosome six. In assessing compatibility, Instant Chemistry also considers the impact of the serotonin transporter gene to gain insight into one’s emotional response to encountered situations. Married individuals with two “short” alleles of this gene are less inclined to be satisfied long-term if the initial marital experience boasts more negatives than positives.

Testing for STG variation might be genetic compatibility services’ best bet, because if you or your partner has two copies of the short variant of that gene, it may result in a heightened response to either positive and negative influences on a marriage. This might argue for a heightened awareness of the importance of keeping a relationship on a positive keel.

Genetic affinity testing may also have some marginal benefit for new matches, where singles make choices with limited knowledge about potential partners. Genetics may be one factor to consider, certainly more relevant than astrology, psychic readings, or even material goods—such as the type of car someone drives—that some people rely on. For existing couples, a psychological component is likely at play, in that a high or low genetic compatibility ranking could influence partners’ feelings toward each other. A positive match may bring about “the test says we’re compatible so we obviously are” thinking even if there are red flags indicating otherwise, leaving couples to remain in relationships they might abandon in different circumstances, whereas a low score may create or reinforce doubts in an otherwise solid relationship.

Most importantly, genetic affinity matching is a test case for what will be an increasingly prevalent challenge as we enter the era of widespread whole genome sequencing. Over the next decade, we will have the opportunity to learn about all kinds of predispositions and proclivities buried in our DNA, from health risks to behavioral tendencies to traits affecting abilities such as intelligence, athleticism, and musical talent. Few, if any, of these genetic findings will be deterministic, but rather will be one set of factors that interact with environmental and many unknown factors to produce the unique individual each of us represents. It will be a challenge for each of us, the media, and companies marketing products to put this information in proper context, not ignoring it completely, but also not giving it more weight and significance than it merits. (To its credit, Instant Chemistry isn’t just about genetics—it also relies on a personality assessment as part of its compatibility calculation, which assesses a registrant’s social tendencies, dominant and submissive inclinations, and intimacy.)

Genetic affinity testing provides an opportunity to start exploring some of the genetic influences of our lives that have long been shrouded in darkness and mystery. As we study our own genetic tendencies, the meaning and significance of which will be constantly updated and enhanced by ongoing research, we may eventually have a better grasp of both what causes the spark between two people and keeps it going and the overall significance of genetics in this and other behaviors. In the meantime, if you think you are ready to handle this information, and can afford to drop a couple hundred bucks, why not, just for fun, “spit, seal & mail”?

This article is part of Future Tense, a collaboration among Arizona State University, the New America Foundation, and Slate. Future Tense explores the ways emerging technologies affect society, policy, and culture. To read more, visit the Future Tense blog and the Future Tense home page. You can also follow us on Twitter.