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Strange Sex
Alien Reproduction Through a Biologist’s Eyes—
and What This Could Mean to Science Fiction

Dave Freer

bristle worm

Sabella spallanzanni, the fan worm. Photo courtesy CSIRO Australia

Now: to save time and avoid disappointment, if you were hoping for outrageous and graphic tentacle-porn, read no further. If you think sex is purely for entertainment, you’re also going to be disappointed. On the other hand: I trained and worked long ago as a fisheries biologist. Sex you know means mixing up gametes to produce offspring. This isn’t porn, but describes mating in various real organisms—no, not orgasms (real or faked), just creatures, described in ordinary biological terms. I can’t write about reproduction without them. Of course, there may also be the occasional double entendre, but biologists have to have a sense of macabre humor; it’s how they cope with the pay.

When most of us think of “sex,” it tends to be in the “count the legs and divide by two” sense. For a biologist the answer could be twenty-seven or the difficulty of dividing by zero—which makes it interesting when science fiction meets biology, which it tends to do particularly when we write about aliens . . . and what springs from aliens. No. Not tentacles . . . or not unless you are referring to Eric Flint’s Mother of Demons. I mention this book particularly because Flint seems to have understood that reproduction (without which there is no society) tends to shape that society. When we meet aliens out there, or if one suddenly drops in and demands to be taken to your larder* understanding how that society works will probably hinge on their biology—which, as a biologist (would I lie to you—don’t answer that) would be to some extent shaped by their breeding. And that—simply based on the bizarre differences among Earth’s biota—is potentially both vastly varied and complex, and unlikely to be the same as humans.

I recall reading an essay recently in which some avant-garde soul posited that the future of sf sex was non-binary. My first thought was “well that about wraps it up for computer dating.” Once I’d worked out that this was not “binary” in the sense of binary numbers, 1 and zero, or yes and no, and that they didn’t mean the future of sf also included “maybe,” and instead they were positing that sex in sf would not be heterosexual couples, but “strange sex.” I think I was supposed to be shocked, but instead I laughed a lot. The author had plainly never come across turbellarian copulation with hypodermic impregnation (which gives an entirely new level to penetrative sex), or the copulatory stacks of the slipper limpet, Crepidula fornicata.

slipper limpet

Slipper limpet. Photo by Daniel Davis via Wikimedia Commons

Slipper limpets change sex with age, males becoming females as they grow older and larger. It’s quite common to have stacks with all stages from immature on top to long dead at the bottom. Necrophile to pedophile. Male:male, hermaphrodite, heterosexual and female to female, sometime in multiple combinations, all having what humans would consider sadomasochist sex. Alas, biology has so much truly “strange sex” as a normal part of reproduction, that it’s hard to shock a biologist. It’s pretty good for sf ideas though.

So let me talk about a couple examples which make the most bizarre human variants look tame and dull . . . and actually exist and work. Of course, drawing examples from known biota for your sf to model strange futures and indeed alien society on, has two advantages. Firstly, much of it is weirder than most imaginings, and secondly one has a complete, actually successful and therefore hopefully plausible model.

Maybe I need to rethink the plausible part. . . .Take the annelids (the segmented worms), specifically the polychaetes. No, that is not even remotely related to the fashionable human “polyamorous” or even “poly-cheats,” except that they are both considered to be worms by some people. Sometimes called the bristle-worms, they’re very common in marine environments, show enormous levels of structural differentiation, and vary vastly in size (some getting several yards long, others being barely visible. They also display higher levels of intelligence than many political party caucuses, although I admit this is not what most would consider sentience. Still, they could evolve toward it, and on some alien world, something similar might have. After all, the development of metameres (a repeat series of segments) appears to have evolved successfully at least twice—the second time being in vertebrates.

genus polychaetes

Example of genus polychaetes. Photo by Hans Hillewaert via Wikimedia Commons

Given that, let’s talk about polychaete reproduction. It’s fair to say that compared to polychaetes, the most rainbow-haired polyamorous human . . . has vanilla sex. Really, really boring straightforward vanilla-bland. No, I don’t want try polychaete sex, I like bland, but their mechanisms work, appear long-term stable (the species continue to reproduce and survive, and the offspring do not suffer disadvantages against their competitors that would make them extinct in the short term. Oh and never mind rainbow, some are actually iridescent or luminescent).

The possibilities range from—at one end of the continuum—some species (including the beautiful sabellid fan-worms) who find relationships hard, but breaking up easy to do. They reproduce asexually, with the adult fragmenting or budding. Each of the offspring grows into a full copy of the parent, and there is never any doubt about who the father was.

Asexuality is quite rare, however—not mixing genetic material is not really long term advantageous to dealing with possibly changing conditions or even getting the edge on competitors. Most polychaetes are dioecious (male and female gametes are produced in separate individuals) although they also do both—but mostly in separate parts of the body.

Of course some species—in the family Syllidae are little double-adapters—asexual and sexual reproducers. They divide their bodies into two parts—becoming two individuals. The posterior end individual goes on to reproduce sexually . . . which is terminal. Yes, to have sex, means to die. But the anterior end can go on living, just budding off more individual posterior ends.

You see for many of the polychaetes, the male and female gamete—eggs and sperm—are not going to meet internally at all. Fertilization occurs outside the body, in the water they live in. You might say it happens largely without parental or even adult supervision—and with all the problems that causes. Internal fertilization leaves a lot less to chance, and a single female gamete can find a male a lot more easily, even without binary assistance. When you are a very tiny gamete in a lot of sea-water, you need to do something to improve your chances, and I don’t mean fashionable dress or makeup (yes, there are many animals which use both).

Perfume is very different matter, as I will explain. Now, not only is this a question “will the gametes get lucky in so much sea-water,” but also this is for many polychaetes a once in a life-time opportunity. You see, the gametes, male or female, are released into the fluid filled cavity (the coelom) of each segment. This is the polychaete version of “gender-fluid” and it can become full to the edge of bursting. Indeed, some polychaetes are closer to humans than most of us realize. They become nothing more than one big gonad. We’ve all met people just like that. Oh, and while I never heard of any blue ones, females are indeed often pink or orange.

There is a serious problem, though, for many of these species. They’re full to near bursting with eggs or sperm in the fluid-filled coelom in the middle of them . . . with no outlet for their desires. Yes. No way to release the gametes . . . except to have a last frantic romantic wriggle in a too-tight skin, and yes, explode.

The best bang since the big one has a whole new meaning here.

The trouble is, of course, that there’s no point in exploding alone. While this may well be pleasure for the individual polychaete: You’re dead and your gametes are wasted. And in the wide open sea, well, the more explosions, the more chances your gametes of getting lucky. This takes “polyamorous” to whole new level, because for a number of polychaetes, when the moon is right, and they are full of . . . desire, they leave their hiding places, and in a night of romance and rapturous rupture, go out together with a bang.

Even if the polychaete species don’t actually die, but manages to shed the gametes through some kind of gonoduct, synchronizing these things may depend on the moon, or the tide . . . or on “perfume”—well, gamones—hormones released by a spawning female, chemical trails through the water, that cause males to join in the blast. And their gamones stimulate females to spawn . . . it is, believe it or not, termed “hysterical spawning.” In other cases, the spawning animals bio-luminesce, to let the partners know. Just think how useful that could be for humans.

Imagine an alien species who had something of the same pattern (and with variations it has plainly evolved several times in the annelids alone) having to deal with humans and the way the two societies would differ (well, I did. It is the basis for one of my short stories, “The War, Me, 17 Million Dollars and a Stripper”—Front Lines, Baen, edited by Denise Little 2008).

Now, if all of this is too much for you, you should stop reading right now—because our iridescent bristle-worms take it quite a lot further.

Epitokes . . . well the best explanation might be that an epitoke is either to turn the whole body into a new creature entirely designed for reproduction, or part of it, which then snaps off and becomes a free-swimming organism in its own right. They change shape and form, and often develop oar-like paddles to swim (many of them are sedentary feeders or live in the mud or rocks. They appear so different that some were originally thought to be a separate species. What’s more, they evolve an eye-spot. Think of it as your testes and ova developing an eye and fins and then deciding to go off to an orgy without you.


A polychaete budding epitokes for the purpose of sexual reproduction.

Photo by Megan McCuller via Wikimedia Commons

I mean an orgy. The best known of these polychaete orgies is that of the Samoan Palolo worm—Palolo fucata (synonymous with Eunice fucata) a large bristle-worm that lives a secretive life hidden in the coral and rocks . . . until the last lunar quarter in October (or November) when the epikotes are released and swarm, swimming in a spiral toward the surface. The Samoans consider them a great delicacy and collect buckets of them—the sea is seething with them . . . until, at sunrise, they rupture together. There are so many that they turn the sea-water in the area into a glutinous slurry of gametes doing what gametes do. The result is acres and acres of fertilized eggs, floating, which fairly rapidly develop into larvae, and settle to the bottom.

Of course some kind of internal fertilization is less wasteful, and inevitably there are species of polychaete that do just this. Now, to put it bluntly, internal fertilization requires an internal ‘container’ to keep the egg or eggs in, and possibly some kind of organ—or multiples of the same (yes. Indeed. Humans are under-equipped, comparatively.) designed for making sure male gametes get in there. We know the human analogues. But there are other possibilities. The female Platynereis megalops apparently has her gut undergo regression . . . and her whole body becomes that “container.” It doesn’t end there, however. Well, the male end does end there. The male Platynereis megalops has special anal apertures to allow the gametes to be released from his coelom. While entwined about his partner in a passionate worm-embrace . . . yes. You guessed. In her mouth. Biology is strange. Bizarre though this may be, it’s a working strategy for that species.

Into the current fuss about which bathroom people ought to use let us add a number of the fan-worms, who would have the anterior half enter the “ladies” and posterior enter the “gents.” There are some of the genus Branchiomma who have both male and female gametes in the same body-segment, however. I have no idea if or how they prevent incest.

Of course what happens immediately after fertilization is just as varied—ranging from eggs floating in rafts or dropping to the bottom, being imbedded into a mucous coated egg-mass and attached to things, or even attached externally to the back of the animal like sticky confetti, or kept in a ball of eggs, around which the parent is rolled. There is even reported vivipary (live birth) where the young larvae of Ctenodrilus are reported to be nourished by maternal blood vessels.

The biology of a barely known family of invertebrates is stranger than many science fiction aliens. How strange will the real thing turn out to be?

Stranger than we can imagine, I suspect.

*which if it is about to lay eggs it may need to do. Newly hatched alien grubs need grub . . . well, food, if they’re to grow into healthy young interstellar space-travelers. Don’t take them to meet your leader, and especially not the UN unless the dietary requirements of young alien grubs are toxic to human life. It’s quite possible such a diet may shape them evil hordes of ravaging alien planetary conquistadors, or worse, politicians.)

Copyright © 2016 Dave Freer

Dave Freer is an ichthyologist turned author who lives on Flinders Island (between mainland Australia and Tasmania) with his wife, four dogs and four cats, and two sons. He has coauthored a range of novels with Eric Flint (Rats, Bats and VatsThe Rats, the Bats and the UglyPyramid SchemePyramid Power, and Slow Train to Arcturus), with Mercedes Lackey and Eric Flint (The Shadow of the LionThis Rough MagicThe Wizard of KarresMuch Fall of Blood, Burdens of the Dead, and Freer’s solo entry in the series, A Mankind Witch) as well as writing the Dragon’s Ring fantasy novels Dragon’s Ring and Dog and Dragon. Dave’s latest novel is young adult contemporary fantasy Changeling’s Island.