Fortean Slips: Sperm Warfare

Every sperm is sacred,
Every sperm is great.
If a sperm is wasted,
God gets quite irate.

-- Monty Python

Sperm Warfare

by D. Trull
Enigma Editor
dtrull@parascope.com

There's a popular misconception about conception, that all sperm are created equal, and every single one of the teeming millions in the average ejaculate stands a fair chance at winning the reproductive lottery. Alas, this democratic vision ain't exactly so.

As frequently depicted in sex-ed films and Discovery channel specials, a large percentage of sperm cells are aberrant and misshapen, bestowed with two heads, a malformed tail, or a listless disposition that drives them to flail around without direction or ambition. These poor guys have always seemed like the pathetic geeks and losers of the spermatozoa world, worthless rejects who'll never have a shot at romancing the glamorous ovum -- thank goodness there are bucketloads of more studly sperm around to take up the slack, right?

Well, some scientists have taken a different view of sperm diversity. They propose that sperm cells can play important roles besides the primary objective of fertilizing the egg, and the legions of seemingly ineffectual "mutant" sperm may be far more valuable to the process of reproduction than previously thought.

The idea is that male gametes are regimented into specialized fighting forces, which work together at all costs to make sure one member of their unit infiltrates the feminine fortress and delivers its payload successfully to the target. The important thing to remember in this theory is where the real conflict is being fought. Love is a battlefield, but in this case, it's not man versus woman. The enemy the sperm army must defeat is another man's sperm.

Robin Baker, a biologist at the University of Manchester, has championed this hypothesis in such books as Sperm Wars and Human Sperm Competition: Copulation, Masturbation and Infidelity. The crux of Baker's philosophy is that human reproduction has been designed for optimum success in a decidedly non-monogamous environment. He believes that sperm from multiple men frequently confront each other in utero, even in our supposedly enlightened era of "safe sex." Ten years ago Baker carried out a study showing that between four to 12 percent of pregnant woman in Britain had conceived while the sperm of more than one man was present in their birth canal.

Baker contends that there are three distinct classes of sperm cells, whose variations have adapted through evolution to make sure it's their team that wins the big prize. The traditional "normal" sperm is what Baker calls the "egg-getter" -- a strong and speedy swimmer, boasting a larger head than the other types. Like all sperm cells, it bears a parcel of volatile enzymes on its head, which are known as acrosomes. The lucky egg-getter that reaches the ovum will burst open its acrosomes upon contact with the goal, helping it to penetrate the egg's membranes. Sometimes a number of egg-getters must pool their explosive resources to enable one of them to slip inside.

It's with the other two categories of sperm that things start to get juicy. Baker says that weaker sperm cells can become "kamikazes" if they encounter sperm from another man. They recognize outsiders and attack them by blasting open their acrosomes. This offensive maneuver causes the kamikaze to die, but his sacrifice might increase the odds for the egg-getters on his team.

The third and lowliest rank in the sperm army are the "blockers," slow, clumsy, dying sperm, some of them spent kamikazes, whose defensive contribution is simply to get in the way of incoming enemy sperm. Blockers have coiled-up tails that are poorly suited for swimming, but ideal for clinging together in masses and getting stuck in the narrow passages that lead to the egg. Even after they die, the entrenched blockers can keep out foreign sperm for several days.

Baker's sperm warfare scenario has its precedents in the sex lives of many other species. It is known that certain invertebrates produce non-fertilizing sperm whose job is to run interference, and the sperm of a wide variety of mammals -- including monkeys, rabbits and rats -- form "copulatory plugs" inside the female that temporarily prevent another male from impregnating her.

But despite this supporting evidence from other quarters of the animal kingdom, Baker's theories are not widely accepted in the scientific community. Detractors have accused him of making weak assumptions with little empirical support. They especially have trouble with Baker's kamikaze sperm, which have been misrepresented in oversimplified news reports as "killer sperm" with "pointy and poisonous heads that bite enemy sperm." The skeptics argue that the kamikaze is more heroic fantasy than demonstrable scientific fact, and they remain firm in the accepted view that irregular, non-champion sperm are simply duds, and nothing more.

Nevertheless, Baker's microscopic microcosm does seem to make a certain amount of sense, and its appeal at a basic level is undeniable. The proud soldiers of the sperm combat corps offer hope to tragic misfits everywhere, rightfully or not, that there might really be a purpose for everyone in this crazy war zone we call life -- no matter how ill-equipped for our personal battles with reality we might be. It would be an inspiration to know that the only kind of loser sperm in the world are the ones that end up in a wad of Kleenex.

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