When Dan Slater wrote in The Atlantic that online dating was threatening monogamy, it caused a minor sensation. But in the book on which his article was based, Love in the Time of Algorithms, he proves more reticent about how technology will change our relationships.

Slater covers the history of computer-aided dating while filling in the larger historical context of American courtship. Along the way, he probes as many wacky corners of the Web-powered dating universe as he can find. He attends online-dating awards dinners (for the site bosses, not the users). He meets the first computer-based matchmakers, including a man in an open marriage who dreams of building a dating-site aggregator for which women might provide intimate body measurements. He follows the ongoing competition among the men behind the two most popular, free, online-dating sites (Plenty of Fish and OKCupid) and other, paid sites like the blockbuster Match.com. He travels to Colombia with a group of American men seeking international brides. And he talks to lots of online daters, from the man who unexpectedly wound up dating a smoker, to Alexis, a young New York fashion student and Phish fan whose experience with online dating he intersperses throughout the book in short vignettes.

Both a product and user of online dating—his parents met through Operation Match, a 1960s forerunner of today's sites—Slater spins an entertaining and largely unflinching tale of all that's good, bad, and ambiguous in computer-aided romance. Even those who don't think themselves interested in the subject matter would likely be intrigued by his storytelling. And despite the juicy excerpt that The Atlantic ran, his book is not one of those whose best bits were all teased beforehand, in the manner of some movie trailers.

Indeed, Slater's most intriguing scenes occur in places like Mango, a bar in Medellin, Colombia, that features in a "romance tour" for men who've turned to the Internet and women abroad in their search for love. There he follows customers of the website Amo Latina, who have traveled from places like Alabama and Brooklyn to meet potential brides at a series of prearranged "socials" boasting translators, European support staff and female-male ratios of 20-1. (Slater also interviews the director of a New York-based anti-trafficking group, but he doesn't seem entirely persuaded by her account of the modern sex trade; for her part, she expresses "shock" at his account of the tour group's youth—nearly half the men are in their 20s or 30s.)

And then there are the conversations between Alexis and other users on Phantasy Tour, an online Phish fan forum that becomes her primary sounding board for romance. These interactions provide a sometimes wrenching inside look at online dating. With the rise of online communication and connection come new perils: Facebook stalking, elaborate deceptions, discovery of one's relationship blog by a lover. And yet, the underlying desires, emotions, and motives are not new. "Monogamy is not going away, and neither is infidelity," Slater writes. "Rather it is the way we make sense of these behaviors, the values and labels and portent we place on them, that will evolve."

While Slater focuses mostly on the technological pressures and boons relationships face, the authors of Mating Intelligence Unleashed are more interested in biological factors, which they see as fairly consistent over time. Both evolutionary psychologists, Glenn Geher and Scott Barry Kaufman have written a fascinating, if frequently dense, book that pulls together a host of studies related to how men and women pursue romance. Even with the advent of birth control, they argue that procreation remains the ultimate end of romantic relationships, citing Darwin's conclusion that "reproduction is, ultimately, more important than survival."

The authors aim for more than proving Darwin right, however. Geher and Kaufman assemble their research survey, which includes some studies of their own, to argue that people exercise a specific reproductive or mating intelligence that should take its rightful place alongside general, spatial, emotional, and other accepted forms of intelligence.

Although "mating intelligence" as they frame it entails a number of skills and cognitive processes, ranging from courtship displays to "cross-sex mind reading" (i.e., accurately determining a man or woman's interest and intentions) to personality traits, Geher and Kaufman particularly emphasize two key approaches: short-term and long-term mating strategies. The distinction has its roots in the work of an evolutionary biologist whose theory of "parental investment" showed that species' approach to mating was tied to the fragility of their young. Produce a baby that quickly develops basic skills and independence, and the parents are more likely to find new mates next spring. But in the case of species such as robins—and humans, it turned out—whose offspring require intense, long-term care to survive their first few months, long-term mating is the norm. Though the earliest research wasn't trying to explain human behavior at all, the ultimate theory made just as much sense of how we mate as it did for robins and rabbits.

What's more, parental investment explains why, "in most sexually reproducing species, females invest more in parenting than do males." For Geher and Kaufman, this explains why women are generally more apt to pursue long-term mating strategies—a tendency amply born out in the studies cited throughout the book. They are quick to note that both men and women generally pursue long-term mating strategies, but of the two sexes, men still tend to desire more partners than women. Even in the section on "hook-up behaviors," the epitome of a short-term mating strategy, they find that men "overestimated women's comfort levels" with both hook-ups in general and certain riskier acts. On the strength of Geher and Kaufman's evidence, then, no amount of technological innovation will likely override the biological imperative to mate in a relatively long-term, monogamous fashion.

As strong as their case seems to be, however, their thesis depends on some-what-dubious premises. First and most obvious is the Darwinian reduction of sex to reproduction. Though this should raise immediate problems for the Christian, Geher and Kaufman must also reckon with the remarkably and often deliberately unproductive nature of much modern sex. Yet though they acknowledge the changes contraception has brought, they never explain how evolutionary biology accounts for our peculiar modern war on procreative sex. Homosexuality, too, merits only scant attention.

Possibly these silences owe to their definition of success. "As scientists studying human psychology from an evolutionary perspective, the best we can do … is to approximate reproductive success," they write; " … we essentially need to think about tapping outcomes that would have been associated with ultimate reproductive fitness under ancestral conditions" (emphasis theirs). Perhaps such a methodology may not require explanation within their field, but I very much wanted to know why "ancestral conditions" entailed the best time and framework for assessing modern sexual behavior.

Another problem with much of the data—which the authors themselves acknowledge—is the reliance on college undergraduates in so many of the studies. As they note, this could undoubtedly distort some of the findings. What of the motives, interactions, and strategies that characterize the elderly and infertile? Do such couples only make love as a kind of irrepressible biological habit? Or does the phrase "make love" in fact provide a clue to the larger meaning and purpose of intercourse?

I doubt that Geher and Kaufman would deny the larger emotional and relational significance of sex, in most cases, yet even the long-term mating explanation seems incomplete in its emphasis on the reproductive motive to bond with another person. Nor, for that matter, can they fully account for the preponderance of mostly sterile hook-ups that increasingly characterize the college relationship scene. What's the evolutionary explanation for this phenomenon?

They primarily explain short-term mating strategies as a response to less-stable, more chaotic childhood conditions, particularly those characterized by paternal absence or neglect. Not only does this seem to prompt a more short-term, risk-associated "fast life strategy," it also triggers earlier sexual maturation, particularly for girls. By contrast, those who grow up amid more stability, less stress, and greater parental involvement tend to be better primed for the long-term planning and self-control associated with a "slower reproductive strategy" (emphasis theirs).

Yet if the very qualities associated with a long-term mating strategy are also associated with securing a college education, why do so many college students engage in hook-ups? Though Geher and Kaufman don't explain what ancestral condition this trend relates to, one study they cite found "pluralistic ignorance" partly to blame. Essentially, when people think certain actions are normal or widely enjoyed, they participate despite whatever misgivings they themselves have.

At this point it's worth noting another difference Geher and Kaufman describe between short- and long-term mating strategies. Not only does one's childhood environment tend to affect one's mating strategy, but also that strategy influences the sort of qualities one seeks in a partner, however subconscious the process may be. The primary quality valued in short-term mating? Physical attractiveness, which Geher and Kaufman report often corresponds with greater genetic fitness (for example, most of the qualities deemed attractive in women also indicate fertility; in some ways, women also become more attractive during ovulation, the window when they are most fertile!). For long-term mating, however, people tend to place more emphasis on qualities like kindness and agreeability—indications of a likelihood to help care for offspring and stick around to see them to maturity.

Unexpectedly, this insight made sense of a parenting strategy my father employed with his daughters, which I felt frequently hurt by during my youth. As my sister and I were growing up, Dad frequently de-emphasized physical beauty, stressing that character mattered much more. Since we were growing up in a world that clearly valued beauty, however, I often took Dad's reluctance to call us "beautiful" as a sign that we lacked value and the key trait necessary for relational success. Though I've subsequently worked through a lot of the identity issues underlying my distorted perspective, something clicked while reading Geher and Kaufman. Dad wanted us to pursue a long-term relational strategy. That's what he was after.

The fact that I could so grossly misunderstand him speaks not just to his imperfect parenting and my own fallible judgment, but to the power of a culture that overwhelmingly stresses the traits most valuable for short-term mating. Its power to do so may partly stem from the sort of technological changes that interest Slater. As Neil Postman noted in his classic jeremiad, Amusing Ourselves to Death, you can't do philosophy by smoke signal. For the same reasons Richard Nixon lost his first televised debate, youth and beauty trump character in the ascendant media of our day (not to say that Nixon provided the character to JFK's youth!). Thus, even if we were to regularly encounter an equal number of messages promoting short-term and long-term mating strategies, we would likely find the former more compelling. Just think about how many Facebook links you've clicked because the preview included an interesting image. Do you click image-free links as often? Probably not.

If one extends this reasoning to online-dating sites, it's not hard to see which type of relationship fares best. Despite sites like eHarmony, and online dating's conduciveness to finding like-minded singles, the medium is inherently better suited to showing physical attractiveness than the character that matters for the long-term. Not surprisingly, mobile-based dating's first big success, the app Grindr, has "a reputation for facilitating sex on the fly," Slater says. And why wouldn't it? Smartphone users are notoriously impatient in their web browsing, a trait likely to discourage the wordier profiles most valued by long-term mating strategists. By dint of the medium, apps built for short-term mating are more likely to succeed.

What does all this mean for relationships? As with many shifts tied to the digitization of culture, no one can say with certainty. In my own life, I find myself wanting books (books with paper and binding and heft) and CDs or even LPs for things I plan to regularly consult for a long while. For shorter-term experiences, though, such as reading the morning news, I confess a keen preference for the dustless online format that won't accumulate in a large, mostly unread recycling pile. Perhaps, too, online dating sites will evolve to become the preference of those seeking short-term mates. Maybe sites for those seeking long-term partners will find ways to showcase character, such as video testimonials from friends.

Though one could easily fret over all this change—I certainly mourn the decline of handwritten correspondence—I tend to agree with Slater that "technology is neutral"; how it facilitates good and bad outcomes depends on us, the people using it. And while, as a Christian, I believe that all of us are fallen, sinful creatures, I also believe that nothing can remove the divine imprint spurring us to make music, tell stories, and form rich and lasting communities.

Anna Broadway is the author of Sexless in the City: A Memoir of Reluctant Chastity (WaterBrook) and a contributor to the anthology Faith at the Edge (Ave Maria). She also writes for the Her.meneutics blog. She lives near San Francisco.

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