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.