Enter, a Girl

I was trying, for the second time in four minutes, to lose my virginity by the technical definition of the term. In order to do this, my brain feverishly calculated algebra equations.

While most guys thought about batting averages, it was far more effective for me to concentrate on pitiless abstractions from a class I was failing, imperilling all of my future prospects.

Beneath me, her green eyes lidded and full lips slightly parted, lay a gorgeous 19-year-old Finnish expatriate named Lena. As an infant, Lena had won a Beautiful Baby pageant in her native Finland. As a young woman, she'd become a high-cheekboned reincarnation of Kim Novak in Vertigo. I myself was vertiginous now with lust and shame. Minutes ago, as she'd unzipped my jeans, I had instantly reached the point of no return - what sexologists call "ejaculatory inevitability".

Lena only smiled and kissed me, knowing what I did not yet realize: Soon enough, we'd try again.

The "refractory period," aka, recharge time, varies greatly from man to man, depending on everything from age to level of excitement. All I know is that for me, at age 18, in this circumstance, two minutes proved to be more than enough time for me to steel my resolve once more. It was, if anything, too much rest.

On the second try, at least I managed to achieve insertion. But even with arcane equations running riot in my head, I lasted less than a minute before a second climax. It was, nevertheless, the most enjoyable 47 seconds of my life to that date.

Afterwards, we slipped into sleep. I awoke with another erection an hour later, and used this to nudge her awake as well. She didn't mind. Lasting a full seven minutes, my sexual endurance - in my opinion, at least - now bordered on the epic. Again we fell asleep and again we woke for another round. More sleep, more sex, more sleep, more sex, over and over again, until I coined a term for this state: slex.

By early morning I could finally look at Lena without fear of losing control. I could also listen, touch, smell, taste her - appreciate in every way her many sensual beauties. With lust satiated by slex, rationality began encroaching like a tide.

Over breakfast I asked her a question that hadn't occurred to me in the heat of the night.

"So what kind of birth control did you say you use?"

She regarded me curiously.

"I never said I used birth control."

I'd assumed she knew what she was doing, that she had to be more experienced than I was. Technically, this was true: before me, she explained, she'd had sex only one other time in her life.

"And nothing bad happened then, right?" I asked.

"No, no," she said with that ever-so-cute accent. "Nothing bad. But I did get pregnant."

As one hoary chestnut holds, men reach their sexual peak in youth and women not until middle age. The problem for horny young men, of course, is that fatherhood typically demands more than just successful insemination. Humans are not salmon, after all, where the male's "care" starts and ends with the spilling of milt. Unlike fish fry, our newborns are helplessly dependent on their parents - and for significantly longer than any other species on earth.

"So why do 'men' become capable of producing babies when they're 12 or 13 years old," asks evolutionary biologist Dr Richard Alexander, of the University of Michigan, "a decade before they can reasonably hope to obtain and keep a mate, let alone be good fathers? And why is early male sexuality correlated with very rapid ejaculatory time?

These two things taken together suggest what has been called 'sneaky copulation'." In societies that have allowed polygamy, says Alexander, older, powerful men have traditionally taken almost all the women for themselves. In such a scenario, the reproductive success of younger men likely depended upon a furtive "you're quick or you're dead" approach.

In his pioneering surveys, sex researcher Dr Alfred Kinsey, found that up to 75 per cent of men reach orgasm within two minutes of initiating sex - which was called "premature ejaculation". But rather than being a sexual disorder, the condition may actually be an evolutionary adaptation promoting what one biologist has dubbed the "survival of the fastest".

Eventually, some of these fast young survivors would age to the point where they, too, became powerful enough to start monopolising the women. Our most successful male ancestors apparently reproduced using both strategies - furtive cuckoldings early on, followed by faithful pair bondings later in life. Bondings sometimes coerced, but no doubt also sometimes strengthened, by the aphrodisiac of power and resources.

Our history of competitive copulation is also reflected in the actual length, thickness and shape of the penis. As a 2004 study in Evolutionary Psychology suggests, the human penis evolved not just as a device for depositing sperm but also as a means for suctioning out the sperm of a recent rival. This phenomenon, known as semen displacement, is well documented in many species that have evolved penile barbs, hooks, combs and other adaptations for removing sperm left by another male.

MRIs taken during intercourse show that the human penis swells and expands the vaginal walls, with the head frequently bumping up against a woman's cervix at maximum thrusting.

Unlike other primates, men also sport an oversized glans, or penile head, which features a pronounced coronal ridge. This combination of characteristics led researchers at the University at Albany-SUNY in the US to test a variety of artificial phallus models during simulated sex.

Their discovery: the size and shape of a man's penis during sex is uniquely suited to scoop out the semen of others.

Women's privates have almost certainly evolved their own clandestine adaptations, from selective orgasm with attractive and successful men, to hormone-driven changes in cervical mucus in order to block certain sperm. In many other mammals, from rabbits to pigs, females have also evolved specialised sperm reservoirs for long-term storage. Women, it now appears, provide a similar haven in their fallopian tubes, where sperm can be maintained in a fertile state for up to five days.

It's not yet known for certain whether such traits evolved in part as a way for women to counter men's strategies to control their reproduction. But just as with the continual one-upping technologies of warring armies, it's hard to believe that one gender will ever gain a complete advantage over the other.