While we might expect maleness and femaleness to be well defined among most bisexual alien species, intersexuality constitutes a major exception to this rule. Intersexuality is a state in which an organism is neither strictly female nor strictly male. Rather, it displays some alternate, intermediate, or variable condition that lies somewhere in between.²⁴⁹⁴

There are two major classes of intersexes.

The first of these is illustrated by a strain of fruit fly (Drosophila) which has three copies of all its chromosomes instead of the normal two. In most bisexual hereditary systems, each parent contributes one set of genes — including the sex-determining ones — to the offspring. But with three sets, this special strain of fly can attain intermediate states of sexual expression. Using artificial breeding techniques, any desired degree of intersexuality may be arranged: 30% male/70% female, 60% male/40% female, and so forth.

These insects, and various higher animals such as the bovine freemartin (the female of a male-female twin pair in cattle), are called spatial intersexes. They are stuck with their ambiguous constitution for the rest of their lives. They cannot change, and are often sterile.

Hermaphrodites represent an interesting special case of spatial intersexuality. A "simultaneous hermaphrodite" is an organism which possesses at once both female and male sex organs. Ovaries and testes are present together in the same individual. Planarians, earthworms, annelids, sponges, hydras and snails exhibit this form of bisexuality.²⁴⁹³ A few vertebrate simultaneous hermaphrodites are known, such as the banded flamefish (Serranus subligarius).

But the intersexual animal can be a sex-mosaic in time as well as space. There are many organisms, of which the gypsy moth Lymantria is but one example, which start life as one sex and finish it as another. This condition, in which the two sexes are separated temporally, is called temporal intersexuality or "sequential hermaphroditism."

Sequential hermaphrodites come in many varieties. Protoandry is a system where an animal is first male, and later female; proterogyny is the converse, with young females metamorphosing into functional males as they age. And there are many other more complicated arrangements. Populations of sea anemones, for example, consist only of females and simultaneous hermaphrodites, a condition known as gynodioecy.

What would a temporal intersexual extraterrestrial be like? We can take a few clues from the freshwater shrimp Gammarus pulex. Each individual crustacean is both male and female, but not at the same time. Newborn animals spend early life in a neuter stage, after which they pass through puberty and enter the first sexually active phase as functioning males.

After a while, the maleness is exhausted. Latent ovaries ripen into maturity, and the organism spends the remainder of its life as a full-fledged female. Eggs are shed by middle-aged mothers and fertilized by energetic youthful males (who are still in the middle of their first cycle).

It is a magnificent bisexual system, one that works quite well on this planet. No one is excluded from any phase of the reproductive process. Still more significant, each member of the colony plays both male and female roles during his/her life. This cannot fail to have major effects on the intensity and depth of interpersonal relationships among these beings. In the case of such hermaphroditic aliens, the impact on the development of society, patterns of competition and aggression, laws and government, and attitudes toward the young are scarcely imaginable. (Science fiction writers have had a field day with this theme.^{97, 226, 442})

If there exist extraterrestrial hermaphrodites patterned after the freshwater shrimp on some other planet, what would their lives be like? Dr. Norman J. Berrill, Professor of Zoology at McGill University in Montreal, gives us some insight into the lifestyle of a temporal intersexual alien:

[Measured against a human yardstick], all half-grown individuals, about ten years old and weighing about 34 kilograms, would be males, the only males, ready to act as such both sexually and probably in other wayward ways. But as troublemakers like their truly human counterparts they would undoubtedly be kept in place by a closed society of matriarchs, roughly equal in number to the males, each twice the weight and much older and wiser. And not only wiser in a general way, but in the special sense of having each been a male herself, as understanding as a mother with a child and as little likely to put up with any nonsense, perhaps wistfully looking back to her youthful manhood. Girlhood would bud as usual when masculinity had faded, with growth continuing and full female maturity yet to come. Apart from lovelife the only question is, who would do man’s work? Little men browbeaten by large women who once had been little men themselves, or the women themselves, whether full-grown and breeding or not?⁸⁹

Of course, the reverse of the above is also quite possible in ET races, although it appears much less common among the fauna of Earth. There is no reason why bisexual alien hermaphrodites could not develop along a cycle in which young females transformed into old males.

An example of this appears in the sword-tailed minnow (Xiphophorus helleri), a teleost fish that bears live young much as the mammals do. Xiphophorus females typically produce offspring until they are a few years old. Then, during a period of only a few short weeks, they take on the characteristics of the male of the species. They produce sperm and are capable of fertilizing females. Exhaustion of the ovaries is believed to trigger the changeover.

We see that both male-first and female-first alien intersexuals may be common, if not abundant, among the many intelligent extraterrestrial races in the universe.

What about the fascinating possibility that extraterrestrials might be able to choose their sex voluntarily in some fashion? How much different the world would be if sex were a matter of choice rather than accident or compulsion! It would also matter a great deal whether the decision to switch was made by society, by pressing cultural or environmental exigencies, or by the individual himself (who might exercise his sexual option at puberty).

Xenologists are convinced that optional sexuality is a real prospect for alien lifeforms because of the many times this system has arisen independently on Earth. One common transformation, found among starfish, the slug (Limax maximus), and the molluscan gastropods Crepidula plana and Patella, involves a changeover from male to female. The cause in this case is environmental. When necessary to maintain proper ecological balance, some members of the colony will voluntarily transmute from male to simultaneous hermaphrodite. Soon thereafter, they blossom into full females without any trace of maleness remaining.

Given the relatively major body alterations that occur during puberty in the higher mammals, it is not inconceivable that ETs might be capable of altering sex in response to the environment.

Extraterrestrials may also be able to change sex as a purely personal prerogative.²⁸⁶³ Quite a few terrestrial creatures can switch back and forth between male and female on a regular basis — and at their own pleasure. The most notable examples include the oyster and the clam.

The native oyster begins its life as a male. After a year or two, it may change to female much like a sequential hermaphrodite. But after the animal has "ovulated" (deposited its ova into the mantle cavity), it becomes "white sick" and reverts to maleness.

While still carrying its own embryos, the female oyster can fully retool as a working male in a matter of weeks. Male and female phases typically follow one another, in irregular cycles a few months long. This ensures that all fertilized eggs are the product of different parents, and eliminates the problem of accidental self-fertilization.

Intelligent extraterrestrials modeled after the changeable oyster would probably experience fewer psychological conflicts, in many ways, than humans. Each individual would have the advantage of knowing the world from the viewpoint of either sex. Furthermore, the opportunity to assume the role of either mate at any time could encourage what some earthlings might regard as a promiscuous social and cultural code of liberal sexual behavior. Their political, legal, religious and humanistic traditions would doubtless reflect this added layer of complexity.

While the sexual identity of aliens may be regulatable either by the environment or by the individual as discussed above, it may also be subject to sociocultural management. There is ample precedent for this on Earth. Numerous behavioral adaptations exist which allow colonies to regulate their sex ratio (the fraction of each sex in the population). These systems usually favor the female, and it is easy to see why.

The female carries the egg. This is the basic raw material of reproductive activity. On the other hand, the male’s function is clearly ancillary. He is expendable.

Consider the purely "parthenogenic" species, in which the male is dispensed with altogether. In such systems of virgin birth, eggs develop into full adults without ever being fertilized at all. The sawfly is a case of an all-female species. All of their eggs develop into more insect females, with no males — or sex — required in the process.⁸⁹ This amounts to practical unisexuality.

In less extreme systems, the male is not totally expendable but is still optional. A typical colony of the crustacean waterflea Daphnia is all-female, producing offspring by parthenogenesis like the sawfly. But at the first sign of trouble, such as overpopulation or the approach of winter, an interesting thing happens. The females "panic," and lay some eggs which quickly develop into males.

If the trouble passes without incident, the males have no duties to perform and are ignored by the females — who continue breeding parthenogenically as before. But if major difficulties do materialize, the females deign to use the male stud service to increase variability in the gene pool and ensure survival of the colony. Says one marine biologist of this arrangement: "Males are necessary, but only as a last resort."*

* Parthenogenesis (all-female reproduction) is not limited to insects. Many species of lizards, for instance, commonly reproduce without males.²⁵⁸³

So we might expect that if society has the final say, alien races will consist mostly of females when optional sex is available. Many females can be sexually serviced by a single male, so this choice is hardly surprising. What is striking and unusual is the degree of social stratification which frequently results. Biological caste systems are not uncommon.

Honeybees are a case in point. The focus is on the only fertile female, the queen bee. A hive’s queen mates but once in her lifetime, and then only with a single male and only on her nuptial flight.* All the eggs the queen will ever produce must be fertilized by the sperm stored from that single mating.

As a general rule only female offspring are produced, and the beehive is populated almost exclusively by sisters. Males appear only occasionally in small numbers, whenever a new queen is needed either to replace an aging matron or to found a new colony.

The apian assembly line is faintly reminiscent of Aldous Huxley’s Brave New World. All eggs start in the queen’s ovaries. If they are not fertilized they grow into male bees called drones. Most eggs, however, are fertilized and placed in tiny compartments in the hive. Those which are fed the regular pap of the drones mature into female bees called workers. Larvae raised on a specially enriched nutrient mix (royal jelly) grow into queens.

Notice that the honeybee has a genetically programmed three-caste system. Queens constitute the reproductive caste. Workers, while technically females, are really neuters because their sex organs are degenerate. They represent the laboring caste, able to carry on with the daily chores of the hive without the distraction of sex. The drones, or stud caste, are virile males who lack this admirable detachment and are not good for useful work. They are usually exterminated by the workers at the approach of winter.

* The penis of the male honeybee breaks off during mating, and he promptly bleeds to death. The severed organ remains inside the queen for some time thereafter, serving as a plug to prevent the semen from dribbling out.

Ant and termite societies have four castes — generally two classes of royalty and two classes of industrious eunuchs. As with bees, the queen retains many fertilized eggs in her swollen belly. Kinghood and queenhood is the reward for those few active larvae who are fortunate enough to make an early escape from the maternal womb. For the vast majority, however, the exit is delayed and a horrible thing happens to them: They begin to be reabsorbed back into the body of the gravid female. The longer they delay, the smaller they are at birth. The largest become soldiers, the smallest workers. (All are sterile.)

It is a kind of merit system. The more active the organism, the bigger its body and the higher its social status.

The extrapolation of a breeding system with genetic castes to a race of intelligent extraterrestrials has been attempted by science fictioneers Larry Niven and Jerry Pournelle in their recent collaboration The Mote in God’s Eye.⁶⁶⁸Their aliens, the Moties, have many tens of biological castes, each one specializing in a particular societal function. Depending on the details of birth, there are Engineers, Farmers, Mediators, Warriors, and so forth. Though the Moties are fictional, can reality be much less strange?

As suggested earlier, there is no real limit to the dimensions of bisexual reproduction. To some ETs, optional sex may mean more than mere changeability. It may mean instead the decision to reproduce, the option to mate, the choice between life and death.

Consider the common mole, Antichinus stuarti. These tiny animals have a brief but concentrated rutting season spanning only a few days in June. Shortly after copulation, a sudden surge of hormones automatically kills the male. This makes available greater quantities of food, water, and other critical resources for the pregnant female and, later, for the developing fatherless family.

The price of love is death.

Extraterrestrials patterned after such a scheme may exist on some arid world in our Galaxy. Could humans hope to fathom the psychology of an alien species in which marriage was the culmination of the life of every father, in which only females lived on from year to year and provided social continuity, and in which a single act of sex meant inevitable, almost instant, death? Conversely, could such sentient ETs comprehend our peculiar addiction to erotica, our marriage vows, our complex family life, our political institutions, or our social sexual mores and taboos?

And which of us would better know, and understand, the true meaning of ecstasy?

Table 12.1 Approximate Coition Times for Various Animals

We have examined just a few of the many possible variations in pairwise reproduction. Bisexual aliens, who may comprise the majority of higher lifeforms in this Galaxy, will undoubtedly display an even richer variety of reproductive styles than we can imagine.

But exactly how will biological ETs execute their sexual functions? The fundamental need for a joining of male and female is clear, but the details of this fascinating operation (e.g., Table 12.1) remain indeterminate where ETs are concerned. Of course, it is far too early in our exploration of space to be offering detailed speculations on this matter. Nevertheless, the grand diversity of sexual practices among the fauna on this planet can give us some idea of what to expect from aliens. Earth is typically exotic; terrestrial animals are typically peculiar.

Consequently, we may demolish the age-old myth that it is the male who always chases the female. In crickets, it is the female who courts the male and later mounts him. ETs may conduct themselves in similar fashion.

Another instance of the unusual: humans are not the only beings concerned with the virtuousness of their female mates. While men once fashioned chastity belts to keep their ladies safe, other creatures must improvise without the benefits of technology. The male garter snake, to take one example, is so suspicious of his companion’s attentions that he installs a "chastity belt" inside his mate after copulation. This hardened plug effectively ensures the fidelity and continued continence of the female.

Certainly one of the most outré sexual fashions on this planet is found in a small fish that lives in the upper strata of kelp beds in the sea. Shaped like the head of a chessboard knight, the tiny sea horse challenges our traditional conceptions of normality. In these curious creatures, it is the female who impregnates the male with her eggs, and the father who becomes pregnant and carries the child to term!

German naturalist Herbert Wendt describes how they mate:

Two sea horses ready for mating put on the tenderest and most charming of courtship spectacles. As among the closely related pipefish, the female is an active partner. In her resplendent wedding dress, far showier than the modest male, she dances around her mate and grasps him with her prehensile tail. Both swim through the water, head against head, in a close embrace, like human lovers. They sway to every side, rock back and forth, and then rise to the surface of the sea. Thereupon something altogether extraordinary happens. The male puffs up his abdomen so that it presents a kind of sac, and the female protrudes a sort of penis from her body.

With it, the female gropes about along the male’s body and tries to introduce it into an opening in his abdominal sac. An observer of this process cannot help feeling that the male is being fertilized by the female. But what is taking place is not breeding in the proper sense of the word, but only a transmission of eggs. The female wants to deposit her spawn in the male’s pouch. Again and again she thrusts her organ into the opening in the pouch and drops one egg after another inside. This act apparently exerts an irresistible stimulus upon the male. For at the same moment that the female’s "penis" enters his body, he pours his sperm into the brood pouch.

After a while the couple terminate their embrace. The female swims away, but the male sea horse has been "impregnated" and must now undertake the nourishing and raising of the brood. He continues to behave like a female. The embryos develop in his brood pouch. They hatch out there. And as the small sea horses grow, the father’s abdominal region swells like a balloon…¹⁰²⁸

Actually, some form of copulatory organ, or "penis," has probably been around virtually since the invention of sex an eon ago. This organ has arisen independently in so many vertebrate, arthropodal and molluscan species as to suggest its tremendous utility in accomplishing the designated purpose. (Even the rare male rotifer has a ciliated sperm duct that could be viewed as an early version of the penis.²⁴⁹³)

Using a convergent evolution type of argument, we might advance the proposition that male penises will be common but not universal among alien races.

The vagina has a related, but more involved, evolutionary history. Most female animals which engage in copulation, up to and including the amphibians, the reptiles, most birds and the lower mammals, do not have any distinct reproductive organ.* Instead, these concupiscent creatures accept the male member in their cloaca, an opening which doubles as a passageway for the excretion of intestinal and liquid bodily wastes. Only in the higher mammals has the female evolved a sexual orifice separate from the anal and urethral tracts.

Males of various species, including frogs and many birds, also have a cloaca in place of the penis. The cloaca is a mere rear opening, used in mating as alternative to the penis-vagina combination. Like pressing two pairs of rubbery lips together in carnal embrace, sperm are transferred to the female by the "cloacal kiss."

Multiple organs are quite possible.** Some lizards and snakes exude not one but two penises during mating, although usually only one of these actually passes semen. These copulatory organs are "truly terrifying" in appearance, covered with spines, warts and hooks.

* In some jellyfish, the sperm enter through the female’s mouth and fertilize her eggs. Later, the larvae exit via the same route.²⁴⁹³

** Some male ostracods (mussel shrimp) have a double penis, and the females a double vagina. A few species of flatworm have up to twenty extra penises, although only one is customarily used for reproductive purposes.²⁴⁹³ Another peculiarity is the "pseudopenis" of the female hyena. When approaching a group, she wags it back and forth in a conspicuous display. This is a vital part of the greeting ceremony and pack communication among these dangerously aggressive animals.²⁴⁹⁹

Snakes are also known to attend public orgies unabashed:

Among vipers and adders we will sometimes see a whole knot of males and females in sexual congress. The reptiles which have thus transformed themselves into a Gorgon’s head are attached in pairs, anus to anus, and if disturbed cannot extricate themselves from their tangle. They can do no more than extend their heads from the knot, hiss and strike at the disturber. Courageous foresters and rangers have sometimes amused themselves by gathering the whole hissing lot in a canvas bag and carrying them away.¹⁰²⁸

Alien hermaphrodites may take after the Roman snail in their sex practices. In this Earthly organism, the major sex glands and penis are situated near the top of the body rather than in the lower regions near the sexual orifice. As simultaneous hermaphrodites, snails are two sexes in one, having at once both sperms and eggs. Copulation thus involves two penises (one from each partner) and two "vaginas" (again, one from each).

The loveplay of the Roman snail is shocking indeed:

Its penis is a gigantic, erectile generative tube, and its wooing is more passionate and tempestuous than any human Casanova’s. Moreover, the creature is apparently inclined to sadism. For after a wild love dance in which the partners rear up sole to sole, rock back and forth and even exchange regular smacking kisses, the excited snail suddenly releases a dagger of chalky material from a kind of quiver and drives it into the body of its mate. Other varieties shoot arrows of chalk at their victim-mates, and these are not aimed at the genital orifice, but are merely intended to wound some part of the mate’s body. The wounded snail visibly twitches with pain, and indeed the act seems like the prelude to a veritable sex murder. In fact the love daggers of the Roman and garden snails occasionally penetrate the lung or the abdominal wall of their partners, inflicting deadly wounds.

But so far we have described only one of the mates. The other behaves in exactly the same way during the sex act. It, too, is extremely excited, and its excitement mounts when it is struck by the love arrow. Whereupon the masochist likewise becomes a sadist; it too fires a dart or stabs with a dagger at the body of its partner. It too protrudes a huge penis. And after fierce efforts and writhings, each of the two inserts its member into the genital orifice of the other.

For several minutes the snails remain united in this mutual copulation. The male organ must penetrate as deeply as possible into the female genital canal in order to deposit the semen at the right place, in a bladder-shaped receptacle where it will fertilize the eggs some time later. Each partner in this act is both male and female. And both seem to discharge sperm at the same time. Then they separate and both snails drop exhausted to the ground, where they remain lying motionless for some time. At last they crawl away, each in a different direction.¹⁰²⁸

Snails, then, appear also to experience that strange and wonderful phenomenon known as orgasm, an explosive discharge of muscular tension at the climax of sexual tension. We shall have more to say about this in regard to alien sex life in Section 12.3.1.

One might naturally suspect that hermaphrodites would enjoy even better orgies than the snakes. Since they have both female and male organs, snails, leeches and others are not limited to a single partner during the mating ritual. The European mud snail, and a variety of marine snail called Acera bullata, regularly form copulatory chains of as many as six mates among them selves. In these gastropodal "daisy chains," the lead snail serves only as a female. For the rest, each performs as a male for the one in front and as a female for the one behind. The last in line functions solely as a male.

The American slipper snail Crepidula fornicata has perfected this fine copulatory style:

Grown slipper snails are sessile, like most molluscs, but in their youth the animals are motile and all are males. Once a slipper snail attaches itself to some base for life, it transforms itself into a female. Soon it is mounted by a male and fertilized. The male settles on the female’s shell; a third snail mounts it, and so on until at last a tower of ten to fourteen individuals is established. The lowest and largest specimens in this tower are female; the middle ones will be gradually changing from males to females; and only the topmost indicates by its penis that it has remained a male.¹⁰²⁸

What human sexual mores might regard as "perverted" is a way of life for the slipper snail. Whatever opinions we may harbor as to the propriety of these sexual practices are irrelevant — for the snails, like the intelligent extraterrestrials we may encounter on another world someday, cannot change what they are.

Arthropods, those fearsome looking organisms with jointed legs and hard-shelled bodies, comprise roughly three-quarters of all known animal species on this planet. Carapaced creatures are the most prolific and diverse lifeforms on Earth.

They are also the most ruthless, murderous lovers.

The late French entomologist Jean H. C. Fabre observed two scorpions retiring to the nuptial nest:

The foreheads touch, bend a little to left and right, as if the two were whispering in each other’s ears. The little forelegs flutter in feverish caresses. What are they saying to each other? How shall we translate their silent epithalamium into words?

But connubial bliss hardly lasts until dawn:

The idyll of the evening is followed, during the night, by a hideous tragedy. Next morning, we find the scorpioness under the potsherd of the previous day. The little male is by her side, but slain, and more or less devoured. He lacks the head, a claw, a pair of legs. I place the corpse in the open, on the threshold of the home. All day long, the recluse does not touch it. When night returns, she goes out and, meeting the deceased on her passage, carries him off to a distance to give him a decent funeral, that is, to finish eating him.²⁴⁹¹

The gold ground beetles have been described as "notorious nuptial cannibals." Having observed such a beetle pair mating, Fabre saw the female hurl herself at her mate in a savage attack as soon as the unfortunate suitor had finished his business:

A vain struggle to break away — that is all the male undertakes toward his salvation. Otherwise, he accepts his fate. Finally the skin bursts, the wound gapes wide, the inner substance is devoured by his worthy spouse. Her head burrowing inside the body of her husband, she hollows out his back. A shudder that runs through the poor fellow’s limbs announces his approaching end. The female butcher ignores this; she gropes into the narrowest passages and windings in the thoracic cavity. Soon only the well-known little boat of the wing sheaths and the thorax with legs attached are left of the dead male. The husk, sucked dry, is abandoned.²⁴⁹⁶

The most hideous of all is the praying mantis, a ferocious centaur-like carnivorous insect that can grow to more than nine centimeters in length. These arthropod monsters have been known to attack and devour small frogs, birds and lizards, so it is hardly surprising to learn that their mates receive no better treatment:

I find, by themselves, a horrible couple engaged as follows. The male, absorbed in the performance of his vital functions, holds the female in a tight embrace. But the wretch has no head; he has no neck; he hardly has a body. The other, with her muzzle turned over her shoulder, continues very placidly to gnaw what remains of the gentle swain. And, all the time, that masculine stump, holding on firmly, goes on with the business!

Love is stronger than death, men say. Taken literally, the aphorism has never received a more brilliant confirmation. A headless creature, an insect amputated down to the middle of the chest, a very corpse, persists in endeavoring to give life. It will not let go until the abdomen, the seat of the procreative organs, is attacked….

The Mantis, in many cases, is never sated with conjugal raptures and banquets. After a rest that varies in length, whether the eggs be laid or not, a second male is accepted and then devoured like the first. A third succeeds him, performs his function in life, is eaten and disappears. A fourth undergoes a like fate. In the course of two weeks I thus see one and the same Mantis use up seven males. She takes them all to her bosom and makes them all pay for the nuptial ecstasy with their lives.²⁴⁹⁶

(Apparently the reflexes of male mantis copulation are restrained by the brain ganglia, so the organism must be decapitated to copulate.)

As enlightened and rational sentients, we are urged to ignore the wanton brutality and utter callousness of such mating behaviors. Cannibalism, the experts tell us, is a purely instinctual act. The mantis, the gold ground beetle and the scorpion are compelled to eat their-mates, not by cruel premeditation, but rather because of a biological urge that is simply irresistible for them — "protein hunger."

But are humans capable of displaying such stolid, rational objectivity in the face of intelligent extraterrestrials known to eat their mates while copulating? Would we, could we, ever feel truly comfortable in the presence of such creatures? Will man be able to retain his sanity and businesslike demeanor long enough properly to conduct interstellar commerce with these beings?

Of course, not all animals are as deadly serious about their sex as the arthropods. Others consider it the purest of fun, such as the spritely orangutans:

Making smacking sounds with her tongue, the female loudly greeted the orang male sitting in the bed of straw. She put her arm around his shoulders and caressingly scratched his abdomen. Then she climbed up to the ceiling of the big enclosure and hung with all fours from a crossbeam, her hind legs straddled. The jungle giant straightened up to his full height and looked up longingly. One rapid movement and his hands grasped the beam. Body dangling, he swung toward his mate, who for her part loosened the prehensile toes of her spread legs and affectionately embraced him. He too now clasped her with his thighs and feet twined around her back. Breast to breast they mated, hanging by their hands and rocking back and forth.^{2497, 2498}

If there are sentient primate forms on other worlds, humans may find them selves at once embarrassed and challenged by the limberness of these distantly-related sexual acrobats.*

* Man has no monopoly on face-to-face copulation.
Young chimpanzees often experiment with this position, although they soon give it up in favor of the more classic mammalian posture.

Whales and other cetaceans, due to the turbulent nature of their watery medium, also must copulate belly-to-belly. Sailors have spotted pairs of blue whales leaping from the water, their midsections pressed tightly together in a few brief moments of airborne ecstasy.

Beavers, too, sit upright in shallow water to copulate, facing each other and embracing with their arms like human couples kissing. Alternatively, beavers can drift along the surface of the water, holding each other lovingly breast to breast. Finally, most male crabs, crayfish and lobsters make love with the female lying on her back, and in many species of millipedes the couples lie abdomen to abdomen and hold each other with all of their many legs.

It is unknown at present whether these examples constitute sufficient evolutionary convergence with humanity to warrant any conclusion as to the probable mating posture to be assumed by highly advanced alien lifeforms.