My slender waist and thighs
Are exhausted and weak
From a night of cloud dancing.
—Huang O. (1498-1569), translated by Kenneth Rexroth and Ling Chung
The near-light-speed drive is engaged, and a sliver of humanity is finally moving away from our sun toward a distant new home.* While the space colonists initially play out their lives in a close approximation of life on Earth, a new branch of humanity is already evolving aboard the interstellar ship. Leaving the planet is new for our species, but the evolutionary processes that resulted in this astounding migration are as ancient as life itself: reproduction, variation, and selection. Over the course of generations in interstellar space, the genome of the starship community will be subtly reshaped. The culture, too, will rearrange its norms to make for pleasurable life in such a new reality.
While multigenerational human life in space is still science fiction, many research groups worldwide are already sketching out the required technologies. At Icarus Interstellar, a nonprofit research organization dedicated to achieving interstellar flight by 2100, for example, physicists work on the arcana of near-light-speed propulsion; I work on the population genetics for voyages such drives would make possible. After all, although the success of interstellar voyages will depend on technology, it will also hinge on humanity’s ability to succeed in new social and demographic arrangements. The human co-evolution of genes and culture is diabolically complex; a century of anthropology has come to little agreement about historic patterns in cultural evolution, much less predictions for the future. But we must begin somewhere. So let’s start with something interesting.
Let’s start with sex.
After all, wherever you sit on the spectrum of nature versus nurture—another question anthropology has yet to resolve, perhaps because it is a false choice—sex, as in biological procreation, is going to have to continue to work beyond Earth. And sexuality, as in how sex is manifest interpersonally, cannot be considered much less than secondary to this most imperative of human concerns.
Where do we begin with sex and sexuality in space? The postmodern, post-structural, post-everything French intellectual titan Michel Foucault famously asked how and why sex shifted from a purely biological function in the nonhuman world to a political and economic entanglement in the human one. In the generation since that immense question was posed, few compelling answers have arisen, aside from the obvious commodification of something almost universally enjoyed. Voyaging in Foucault’s seas of postmodern mirage can be a thrill, but for the moment, we have basic issues to sort out, and I will stick to more Newtonian shores.
We can start with sex biology. Roughly 1 billion years ago, a new form of replication appeared on Earth. Rather than producing the next generation by budding off near-clones from individuals, some life forms began to produce it from the combined DNA of two individuals: the sexes. Shuffled DNA resulted in offspring differing enough from their parents and siblings that even new forms of natural selection evolved. Ages later, with the evolution of complex culture in our lineage, Homo, all manner of sexuality appeared as elaborations on the core issue of reproduction.
Will this essential aspect of being human—having two discrete sexes—change radically on the centuries-long timescale of interstellar migration? Not likely. The essential fertilization of the egg cell by the sperm cell will continue. Some superfuturists would like to change that, envisioning, for example, radical experiments such as sending female-only crews on a journey in which they would be artificially fertilized from sperm banks. But a stellar ark with an all-female population, likely just as dysfunctional as an all-male population, would be a long-term disaster, because evolutionary processes are generally intolerant of such radical change to established systems. We are much more likely to succeed with a more tested method of fertilization. For centuries and longer the fact of two biological sexes in our species will remain and will continue to influence sexuality.
Fair enough; now, how will we procreate beyond Earth? Science-fiction authors have often lingered on the titillating prospects of zero-gravity sex, but we’re unlikely to undertake any long-term journeys in the microgravity environment of low Earth orbit where humanity has spent most of its experience in space. That’s because all the research has demonstrated that a low-G environment is crippling to the human body and its processes. It is simply not an option for multigenerational voyages.
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?