What to do? The best solution is to rotate starships, creating an artificial gravity. This was beautifully envisioned in Stanley Kubrick’s 2001: A Space Odyssey and is a known technology. But even as interstellar arks make this motion, the central hub of the hurtling star-cities would remain zero-G sites likely to bear witness to every imaginable experiment in human sexual delight. A Massachusetts medical school space biologist recently stated that, “Sex is very difficult in zero gravity … you have no friction,” but this seems particularly unimaginative. Remember, space migrants won’t be astronauts programmed to follow strict minute-by-minute schedules for 90-day flights; they will be normal people living out their entire lives. Sexual experimentation in the future will be nothing new—except that it may well include floating in the central hubs of immense interstellar craft.
What larger issues of sexuality will play out in the vast interstellar spaces? Population genetics tell us that healthy interstellar populations should be in the tens of thousands; one configuration would be eight, 5,000-person villages. Sexually speaking, what do we see in similar demographics on Earth today and in the past? We see everything. Humanity has invented a wide variety of solutions to the questions of sex and sexuality. Even among the most outwardly conservative settlements and communities worldwide, every shade in the spectrum of human sexuality and sexual activity remains alive: multiple genders are known in traditional Samoa, for example, while the marriage arrangement of polyandry—a woman having multiple husbands—is common in highland Tibet village life. There are many ways to be human.
As on Earth, I imagine that so long as domestic arrangements are harmonious in caring for the interstellar young, all will be well and variable. Earth-bound norms regarding homosexuality, heterosexuality, monogamy, or plurality could either erode or become entrenched among interstellar migration cultures. There is no saying exactly how this will play out—could we have predicted the differences in human sexuality between 16th-century and modern England?—but the fact that interstellar ships will be closed ecosystems has one important implication. Even migrant populations as large as 50,000 will have to suppress a cultural imperative that has been with agricultural civilization for the last 6,000 years: to produce as many offspring as possible.
For agriculturalists, children are valuable laborers, but for most of human existence, population was strictly regulated to remain in line with the carrying capacity of, say, the Outback or the Arctic. We can learn from extant foraging communities and from the archaeological records of their ancestors. Their rituals and taboos, their regulations of sexuality to keep populations low, might once again be of great value to our species.
Once space colonists arrive at their desired exoplanet, however, things will change yet again. The migrant population will be expected to explode upon arrival because—as we have learned in conservation biology on Earth—larger populations of any organism are always safer from extinction (local or general) than smaller populations. This will drive yet another shift in the cultural details of sex and sexuality, re-enacting the demographic shift from foraging to farming that occurred millennia before, back on Earth.
How will sexuality play out in space? Take your pick, so long as it doesn’t interfere with maintaining a healthy population or exceeding the limits of the space ark. Wherever we go, humanity will be characterized by change; for millions of years, our behavior has been decoupled from our biology by powerful cognitive processes and tool use. This adaptive ace up the sleeve gives us tremendous behavioral variation, allowing us to proactively adapt to new conditions by mind rather than reactively, by body. For humans settling a new planet, cultural variables related to sex and sexuality will all shift, differing from that of their ancestors long left back on Earth and from that of the generations that crossed the gulfs of interstellar space. Sex will continue—it will have to—and the solution to questions of sexuality will be to have many solutions, as it does on Earth.
We have, more than any other species on the planet, found a way to simultaneously incorporate sex and sexuality into the very fabric of our daily lives. In this way, no matter how far we travel, we’ll carry our cultural history with us, a kind of sexual ripple that recycles over generations. Like the adolescent who moves away from home to establish himself or herself as a new, independent person, how will the diverse body of humans who set sail to a distant star evolve their sexuality over hundreds of generations away from “home”? We won’t know until we try it.
Fortunately, that kind of anthropological experiment can be a lot of fun.
Correction, Sept. 26, 2013: This post originally discussed how sex would take place on a space ship that travels faster than light, which is a scientific impossibility. We have changed it to reflect that sex in space would likely take place on a ship that travels near light speed.
More from Slate’s series on the future of exploration: Is the ocean the real final frontier, or is manned sea exploration dead? Why are the best meteorites found in Antarctica? Can humans reproduce on interstellar journeys? Why are we still looking for Atlantis? Why do we celebrate the discovery of new species but keep destroying their homes? Who will win the race to claim the melting Arctic—conservationists or profiteers? Why don’t travelers ditch Yelp and Google in favor of wandering? What can exploring Google’s Ngram Viewer teach us about history? How did a 1961 conference jump-start the serious search for extraterrestrial life? Why are liminal spaces—where urban areas meet nature—so beautiful?