Sperm Like Sperm Why sloppy seconds can be smart
Posted by pozlife on January 5, 2007
By Bill Andriette
A bodily orifice oozing cum (don’t necessarily try this at home) can be a comely sight– entirely on its own terms, not to mention nostalgia-evoking for guys of a certain age. But a spooge-weeping orifice isn’t just attractive to mankind: from a sperm’s-eye point of view it looks pretty inviting, too.
So argue D.J. Hodgson and D.J. Hosken, two biologists from the University of Exeter, England, writing recently in the Journal of Theoretical Biology. Sperm, the duo contend– other things being equal– are happier getting shot into a place recently soaked by another male’s ejaculate. Think how dogs prefer adding their mark to a hydrant already richly tagged. It all points to a curiously queer inner-gear that may help turn biology’s big wheel of heterosexual reproduction.
The milkman comes late
The idea that sperm savor other men’s semen (in the manner some men do) was sparked by an observation. Biologists have long noted that– from yellow dung flies to chimpanzees– the last to mate with a polyandrous female sires a disproportionately large share of the resulting offspring.
To be sure, male genitalia, across the animal kingdom, have evolved crafty devices for sweeping a rival’s ejaculate from a female’s reproductive tract. The curvaceously bulbous glans– the tip of the human penis– is just one example.
But the researchers suggest that more than merely subtracting a rival’s semen, there’s a positive factor at work, too, accounting for the reproductive boost gained by him who comes last. The second guy’s sperm, they contend, enjoy some same-sex action from earlier suitors’ spooge.
In other words, the proverbial milkman– if he’s looking to maximize progeny– should hope the husbands he’s cuckolding spent amorous mornings with their wives before they headed off for work.
What’s semen got to do with it? The milky fluid does some heavy lifting. Carrying sperm cells (some 200-500 million per shoot) may be job one. But as well, seminal fluid buffers the dangerously acid female reproductive tract, suppresses the hostess’s immune system lest it attack the sperm as foreign invader, keeps the energetically-swimming sex cells buzzed on fructose, and hormonally induces uterine contractions to aid their eggward wriggling.
So you can see where Hodgson and Hosken are going. Previously deposited semen is like scouts bushwhacking a trail into virgin territory, with their tracks potentially guiding second comers.
Or say Vladimir Putin wants a chat with Tony Blair. The Russian leader would first dispatch a cadre of Kremlin trusties– to plan the state dinner, schedule the photo ops, and arrange the poisoning of regime critics. Yet that groundwork, once laid, would prove helpful if Putin cancelled, and, say, Chechnya’s puppet president visited London instead.
Hodgson and Hosken speculate that something like this happens with overlaid ejaculations. As a result, the sperm of the last-to-come accrues the benefits of the buffering, nutrition, contractions, and/or immunosuppression provided by the semen previously there.
Shooting a freeload
Are you getting a warm and fuzzy picture of the brotherhood of sperm? An image of sex cells from different men frolicking like dolphins, a microcosmic reflection of what men do in the course of getting off together?
Alas, biologists have a different name for what’s going on here– parasitism.
Latecomers, Hodgson and Hosken contend, are just using the earlier males’ semen for their own purposes, with the donors getting less than nothing in return out of the arrangement– except perhaps a chance to enjoy sloppy seconds themselves on some later, luckier occasion.
Or perhaps it’s really not so different from erotic relationships, after all. A soupçon of mutual parasitism is inevitably part of sex’s game. “I am not just a human being– I am a piece of meat,” Boyd McDonald memorably said. And more than any individual uses sex to his or her advantage, sex uses him or her– casting individuals in their sex-jumbled uniqueness and dooming them to die. Asexual creatures, on the other hand, clone, divide, and potentially live on ad infinitum.
But however ultimately ambivalent animals are about sex, there’s evidence they are attuned to their position in the queue when they’re about to get some. Among ground squirrels, for instance, males line up for coitus with willing females in scenes that recall (adjust for gender) the sling-room of New York’s Mineshaft circa 1979. Male squirrels are in a good position to know where they stand– unfortunately first or felicitously last– and can adjust seminal investment accordingly.
It’s not just the beady-eyed and bushy-tailed who make such calculations. A study reported in 2005 from the University of Western Australia found that a sample of heterosexual men produced better quality (more motile) sperm from masturbation after watching porn with two men and a woman, compared to porn showing only women. Readers may draw other morals, but the researchers concluded the men were unconsciously priming their ejaculate to compete with rivals’ sperm. Yet oddly, the men also produced notably fewer sperm.
That seeming contradiction fits nicely with the Exeter team’s model: if a well-plowed and already spermy pussy is so welcoming a field, then it’s smart to sow the best seeds; and with their prospects so assured, unnecessary to sow many.
Making semen isn’t cheap– Hodgson and Hosken cite the expenditure involved as fully ten percent of a male’s basal metabolism. (Forget the glycemic index and pick up a copy today of Ejaculate the Way to a Slimmer You!).
To be sure, semen freeloading isn’t the only reason why– patrimony-wise– last often comes first. There’s mechanical displacement of a rival’s sperm– think of that engorged, thrusting, plunger-rimmed cock-head. And speaking of poisoning, maybe even chemical incapacitation is involved, suggested by the finding that proteins in semen are coded by the most quickly evolving human genes– indicative of an ongoing arms race.
How these different factors interact, how they vary among species, and what’s optimal timing between ejaculations for sperm parasitism– if that’s what you want to call it– are riddles awaiting their graduate students.
A debate rages since the question was first posed in ancient Greece as to whether male same-sexers are more like straight men or straight women. Certainly squabbles between partners set the stage for rapturous reconciliations irrespective of gender. Is the real driving force behind the push for gay marriage the more passionate– and more seminally rich– orgasms that follow from the (now higher-stakes) suspicions that a spouse has strayed? In any case, the comeliness of the semen-bedripped asshole– which might seem the most refinedly homosexual of tastes– could be an echo of a smart heterosexual mating strategy.
Author Profile: Bill Andriette
Bill Andriette is features editor of The Guide