The average package - how do you measure up?

Penis, testicles, epididymis and prostate - "male reproductive organs" to the high-minded, "privates" to the polite, and endless crude variations on "package" or "tackle" between friends - these items are the embodiment of maleness.

I can't speak for my brother John, but as far back as I remember, I've been fascinated with, and more than occasionally appalled by, my own urogenital organs. On the "uro" side of this elegant system, I've managed to live unremarkably so far - no kidney stones or urethral blockages, no incontinence or bladder cancer.

The genital side has proved a different story. Basted with an ever-shifting stew of hormones, linked to heart and brain by interconnected loops of blood and spark, it's hard to imagine a more potent driver of male vitality and despair. At times convinced I was the one giving the orders, at other times knowing full well I was the dummy of a barely six-inch ventriloquist, I've followed the rise and fall of my manhood for decades.

But as quixotic and misguided as my male impulses have sometimes proved, I know I'd be nothing without them. I owe the best parts of my life - my ambitions, my family, my capacity for love - to the unceasing inspiration of these drives.

Flush with out weekly pocket money, John and I combed the magazine racks for the latest comics. Spying nothing new, we began grazing through the regular magazines, that is, those intended for readers older than eight, our age at the time. I checked out a Time and a Sports Illustrated. John perfunctorily glanced through a news magazine before opening something called Rogue. Almost immediately he called me over, chortling lowly. "Look at this," he said, pointing to a page labelled "pictorial". It documented, in black-and-white photographs, a blonde who for some reason had decided to enter an Irish pub wearing nothing but her freckles. The camera hovered close on her heels as she sashayed about, ordering a beer, interacting with fully clothed male customers and laughing at their jokes. Her golden hair apparently added to the amusement by ever so lightly tickling her "callipygian" buttocks, whatever that word meant. John and I exchanged glances and immediately started laughing, too. Truth is, neither of us liked girls. In fact, we actively disliked them. Not that this twenty-something was a girl, exactly. Still, whatever she was, we quickly discovered how hard it can be to take your eyes off something you don't see every day or, for that matter, ever.

That night from our twin beds, John and I recapped the day's events before we went to sleep. We briefly dissected the Pittsburgh Pirates' NBL game and the plot of Sea Hunt. At some point in the discussion I remembered an odd quirk I'd meant to mention before. "I got a feely at the newsstand today," I said, using the term we'd coined to refer to that peculiar penile stiffening-and-tingling sensation.

"Me too!" exclaimed John. "And I didn't even have to go!" Both of us understood, of course, that a guy's "privates" had only one function: urination. Waking up in the morning with a feely made perfect sense: it was simply nature's way of telling you your bladder was full. Other feely triggers - such as climbing a rope in gym class - remained to be sussed out by our young scientific minds.


And now this. How the woman in the pictorial might trigger the feely phenomenon was even more baffling. We bandied theories in some detail before concluding that her link to a feely had most likely been some kind of fluke.

Though erections fuelled by erotic stimulation may be the most memorable kind, the vast majority that men sprout in their lifetimes have little, if any, direct connection to sex. Studies in the Journal of Ultrasound in Medicine, for instance, show that erections actually predate birth itself - with male fetuses as young as 16 weeks sporting telltale in utero protuberances that ebb and flow spontaneously throughout the remainder of gestation. With our transition to the outside world, these alternating cycles of tumescence and flaccidity continue, though we remain largely oblivious to them. The reason: they happen when we're sound asleep, by way of a process called NPT, or "nocturnal penile tumescence" - otherwise known as sleep erections.

Thanks to the secret life of the sleeping penis, even the most monastic male becomes aroused for half an hour or longer during each of the 4-6 REM (rapid eye movement) stages of sleep we experience every night. These erections, especially in adolescence, are occasionally associated with nocturnal emissions. But research in sleep labs has shown that the vast majority of them don't seem to be linked to sexual feelings at all.

Researchers have long puzzled over the reason healthy men spend up to 12 per cent of their lives with unconscious, asexual erections. Some have proposed that sleep erections are merely the collateral effect of another quirk of the REM stage - sleep paralysis.

During dream sleep, the sympathetic nervous system, which regulates our fight-or-flight responses, shuts down, temporarily preventing the contraction of our skeletal muscles. This well-documented phenomenon keeps us from acting out our dream, saving us from trying to fly out of a window, for instance.

Erections, on the other hand, are controlled by the parasympathetic nervous system. This system regulates our "rest and digest" responses through its actions on smooth muscles from the gut to blood vessel walls.

In a healthy penis, parasympathetic nerves release nitric oxide, which relaxes the smooth muscles lining the penile arteries. This allows extra blood to flow in and engorge two spongy, parallel chambers called corpora cavernosa (literally, "cavelike bodies"). In the process, the veins that normally drain blood out of these sacs are squeezed down. Hey presto: blood enters and is effectively trapped, putting the magic into your wand

These two nervous systems work in a coordinated, if opposite, fashion. While one serves as an accelerator, the other acts as a brake, and vice versa. As one doctor friend explained it, this is why you can't get an erection when there's a gun to your head.

Conversely, erections may sprout spontaneously, when REM sleep shuts down your capacity for fight or flight.

That might explain part of the puzzle, but other researchers are convinced that night-time erections are so dramatic and lifelong - affecting males from the womb to the nursing home - that they must be more than an accident of our physiology.

"My theory is that the flaccid penis is in a precarious state of oxygen delivery, and erections serve as a way of more or less recharging the battery," says Dr Irwin Goldstein, director of sexual medicine at Alvarado Hospital in California and editor-in-chief of the Journal of Sexual Medicine. To study this possibility,

Goldstein and his colleagues took samples of penile smooth muscle and subjected them to varying levels of oxygen.

The results: during the low-oxygenation levels associated with flaccidity, smooth muscle begins to break down and convert to scar tissue. But at the higher oxygen levels seen during erections, the body naturally produces enzymes that undo the damage.

"The penis is in an interesting balance," says Goldstein, "where it forms scar tissue and then digests it at the same rate later in the day."

If Goldstein's theory is correct, it may help drug researchers find novel ways to counter and possibly help reverse some forms of erectile dysfunction. For now, it's consoling to know that the body in its wisdom is keeping us in shape while we sleep.

There's also one immediate application of this information.

"When I give lectures on this topic," says Goldstein with a laugh, "I tell the men they have a new excuse to have sex. Go home and tell your partner, 'Honey, it's time to oxygenate!'."