This Is Not Just Biology Here--It’s a Mini-Super Bowl
Men’s lust for sports is unparalleled.
Playing sports, watching sports, using sports lingo to explain everything from passion to politics, most men are hooked--from jock-motif baby paraphernalia to T-ball to father-son bonding in the clamor of the Super Bowl.
But this fanaticism may be ingrained even before birth. It may indeed be rooted in male biology.
Research by British evolutionary biologists R. Robin Baker and Mark A. Bellis suggests that, in the primordial struggle to procreate, a man’s sperm goes after the egg with the strategy of a football team--blocking, guarding and flagellating for the victory of the team.
They claim that a man unconsciously adjusts his ejaculate’s lineup of specialty players (sperm types) to fit the situations.
Sperm competition in mammals and insects has been documented for decades. (Damselflies, for example, have penises that sprout barbs and whips that scrape out sperm from previous encounters).
But Baker, at the University of Manchester, and Bellis, a senior scientist at the Public Health Laboratory in Liverpool, are the first to investigate sperm competition in humans.
They questioned the conventional explanation for why as much as 40% of each human ejaculate seems to consist of malformed sperm that spin chaotically rather than racing for the egg. Slackers, many researchers had concluded, a quality control problem.
Not so, the two biologists argue. The spinning sperm are part of the team--running interference against sperm from some other male, which might ace them out in the biological Super Bowl by getting to the egg first.
Considered controversial, Baker and Bellis’ research, much of it published in the journal Animal Behavior, has yet to be widely accepted. Nevertheless, it has won attention among scientists and has landed the biologists contracts for two books: one recently released in Britain and an American version titled “Sperm Wars,” to be published this fall by Basic Books.
Heightened interest in the private lives of sperm is also being generated by a spate of studies showing sperm counts have declined as much as 50% over the past century.
According to the biologists, after a man ejaculates, his sperm play four different positions to help power a teammate to the goal (Fallopian tubes). Like athletes, these specialized sperm vary in shape according to their role:
* Of the 300 million sperm in an average ejaculate, fewer than 1% are “egg-getters” (with slightly larger heads than normal), programmed to fertilize the egg.
* A large proportion are “kamikaze” sperm (with round or oval heads), whose self-sacrificing job is to obliterate other men’s sperm.
* “Blocker” sperm (some with coiled tails and some with two heads) form a barricade at the cervix, or neck of the uterus, to prevent rival sperm’s passage.
* Finally, there is the “family planner” sperm (identified by its cigar-shaped head), which kills off its own egg-getters when fertilizing eggs would be a disadvantage. This sperm appears only in species that show paternal care, such as humans and gorillas, says Baker. Family planners “increase in the ejaculate when a man is stressed,” he says, adding that studies show this type of sperm fails at fertilizing eggs in in vitro fertilization.
The biologists found that the more time a man spent away from his mate, the more ejaculate he produced and the more kamikaze sperm. This, they say, is a defense against the risk that his mate had sex with another man. (This is not just macho paranoia. DNA studies in the U.S. and Britain have found around 10% of all children to be the offspring of someone other than their putative father.)
The scientists believe sperm swim into position for scrimmage. Kamikaze sperm seek out interloper sperm in the Fallopian tubes and in the cervix, head-butting their opponent, which releases a deadly chemical called acrosome, until both die. Blocker sperm post themselves between the uterus and the Fallopian tube in fibrous channels of mucous that are about two sperm heads wide.
“So if you have two sperm sitting in one channel, one can block the other,” says Baker. All this clears the path for the egg-getters.
From a Darwinian standpoint, the team’s goal is to generate as many progeny as possible, says Baker. But even in this sperm-o-centric world view, the biologists concede that a woman’s body ultimately calls the plays. Like an umpire ejecting the best players for fouls, her body can toss an entire ejaculate out on its can. On average, a woman’s body rejects two-thirds of a man’s ejaculate.
All part of the rough and tumble world of love and war.
