One of the faithful visitors to this blog recently posted a comment that referred to the "suburban housewife on Mars" motif. The phrase reminds me of the old TV series THE JETSONS. Aside from the robot maid and gadgetry such as personal space shuttles instead of cars, the Jetson household looked like a stereotypical middle-class American family of the 1950s, as seen on dozens of mundane sitcoms. It effect, it simply projected that family structure forward in history just as THE FLINTSTONES projected it backward. In earlier decades, classic SF writers didn't always use any more imagination in this area. The original STAR TREK fell short of its potential in this regard. Except for the occasional standout character such as the Vulcan matriarch in “Amok Time,” many of the adult alien females encountered by the Enterprise seemed to exist mainly for Captain Kirk to seduce. In Robert Heinlein's HAVE SPACE SUIT, WILL TRAVEL, Earth has a permanent settlement on the moon, but the teenage protagonist's mother appears to be a fifties-style housewife. In Heinlein's PODKAYNE OF MARS, Podkayne's mother is a career woman, but female spaceship officers seem to be relegated to supporting rather than commanding roles. His later work allows more scope for experimentation in family structures, however; in the former penal colony of THE MOON IS A HARSH MISTRESS and the distant future of TIME ENOUGH FOR LOVE, all careers are open to both sexes, and various forms of marriage in addition to traditional monogamy are common.
I have no doubt that as long as our species remains recognizably human, we'll have marriage and family in some form, for the mutual emotional and financial support of adults and the care of offspring. The evolution of the Israeli kibbutz system has shown that, given a choice, most people do want to bring up their children in family units rather than a communal arrangement. The biblical book of Genesis contains stories of love and marriage that we have no trouble identifying with. If those social institutions haven't become unrecognizable or extinct over the past three or four thousand years, they aren't likely to vanish in the next century or two as a result of technological changes that are trivial compared to the shift from an economy of desert nomads to the global computer culture of our time. Still, it seems unlikely that marriage and reproductive patterns of future eras will look exactly like those practiced by our parents or grandparents, or even ourselves. In today's Baltimore SUN there's a story about a court decision allowing a birth certificate to be issued with the mother's name left blank (analogous to the way it has been possible to leave a father unidentified all along). A single man had hired an egg donor to conceive and a surrogate gestational mother to bear his baby, and both he and the surrogate wanted to ensure that she would have no legal obligation to the baby. So part of the BRAVE NEW WORLD reproductive future has already arrived. In the imagined future of PODKAYNE OF MARS, it's not uncommon for young parents to conceive and gestate babies as close together as the mother's health allows, then have them frozen (placed in cryogenetic suspended animation) until the parents' career patterns allow them to provide the children with optimal amount of attention as well as material resources; as Heinlein's narrator puts it, this plan resolves the conflict between the best biological stage to bear offspring and the best social and economic stage to rear them. I doubt that any such technological innovations will become the norm for the majority. Compared to the old-fashioned way of pregnancy and birth, they're too much trouble and, for the foreseeable future, will probably remain too expensive for many working parents.
What about alternate marriage patterns? In pre-industrial centuries, "family" comprised all the inhabitants of a household, including apprentices and slaves. We tend to define "family" as the nuclear household unit of parents and children, so we invented the phrase "extended family" to talk about grandparents, uncles, aunts, etc. Polygamy has been legal throughout history over much of the world, usually polygyny (one man with several wives), although a few cultures practice polyandry (a woman with two or more husbands, typically a pair of brothers). In an earlier post I mentioned the potential economic and reproductive advantages of legalizing polyandry in our own culture (not likely to happen outside an SF novel!). Wyo Knott in THE MOON IS A HARSH MISTRESS was formerly married to a pair of brothers. Heinlein's futures include a variety of line marriage and group marriage patterns. Suppose your hero or heroine becomes involved with a lover who belongs to an even more complicated type of household? In the Sime-Gen series of Jacqueline Lichtenberg and Jean Lorrah, anyone who falls in love with a Companion knows that the Channel whose need the Companion serves has priority. The Channel-Companion transfer relationship doesn't necessarily involve sex (indeed, it seems that more often than not each partner in the transfer relationship has a separate love interest), yet in a way it can be more intimate than a marriage. Octavia Butler's short story "Bloodchild" takes place on a world where human colonists, to survive, have accepted a symbiotic relationship with the natives of the planet, who look something like giant centipedes. Typically, a human household gets adopted by an alien female, who lays her eggs within the bodies of the young men of the family, to be removed (if all goes well) before the newly-hatched grubs can devour their host.
Other aliens might look humanoid but have three or more sexes instead of our standard two. Or they might change sex over a lifetime, as Heinlein's Martians in RED PLANET and STRANGER IN A STRANGE LAND (and some Earth species of fish) do. How would a human hero or heroine in a romance handle falling in love with one of these people? The difficulties in loving a member of the symbiotic species in the STAR TREK universe, where the symbiont switches between male and female bodies several times over its very long lifespan, look simple in comparison.