You might credit the legendary Scottish male virility of past time to single malt whiskey, or the sometimes brutal weather, or the fact that haggis is the national dish, but a Dutch researcher is proposing another answer:

Chuck Burton / AP "Men wearing a kilt experience a strong sense of freedom and masculinity," says a researcher. Here Tim Propst, of Lincoln County, N.C., throws a hammer during the Grandfather Mountain Highland Games in Linville, N.C. in July 2012.

It was the kilts.

Kilts, worn as they were meant to be worn, without underwear, lets our laddies swing freely in the breeze, creating, according to researcher Erwin Kompanje, the “ideal physiological scrotal environment.” Exposed to the bracing Highland coolness, testicles will make robust sperm.

The modern man’s “scrotal environment” is pretty confined these days, what with underwear and pants that hold our testicles close to the body and its 98.6-degree heat, Kompanje, a senior researcher in the department of intensive care at Erasmus University in Rotterdam, told NBCNews.com. But as he pointed out in a paper published online in the Scottish Medical Journal, “adequate spermatogenesis requires a temperature about 3 degrees [Celsius] lower than normal body temperature.” (That would translate to about 93 degrees Fahrenheit, compared to the normal body temperature of 98.6 Farenheit.)

Testicular temperature is regulated by the cremaster muscle – the muscle that covers the testicles -- that raises and lowers the scrotum in response to heat and cold. “The cremaster reflex only works, and has any sense, when the scrotum is hanging free,” Kompanje said. “In tight trousers it cannot work. In a naked man, or a man wearing a kilt, it can and will.”

Kompanje stresses that he’s only proposing a hypothesis based partly on his own fascination with things Scottish – he sometimes wears a kilt for special ceremonial occasions – and anecdotal evidence that kilt-wearing is good for sperm, and scientific evidence that sperm production wilts under high scrotal temperatures.

“I searched the scientific literature, and I found nothing on the subject,” he said. “Then I searched on sperm quality and found many scientific papers related to high scrotal temperature and tight clothing. So as 1+1=2, I formed the hypothesis that wearing a skirt-like garment (as a kilt) without underwear would help to improve sperm quality.”

There’s been a lot of debate in science about whether modern western men have poorer sperm quality and fewer sperm overall than they did 50 or 100 years ago. Environmental toxins, stress, smoking, diet, have all been implicated in the decline.

Temperature is often blamed, too, which is why doctors advise men not to put laptop computers on their laps. When doctors in Germany experimented with a “nocturnal scrotal cooling” device – crotch air conditioning – in men with fertility problems, they found “a significant increase in sperm concentration and total sperm count…after 8 weeks” according to a 2005 journal article.

So Kompanje may well be correct when he proposes kilt wearing as a possible solution to dropping sperm quality.

This raises the question, however, of whether a man wearing a kilt will get any opportunities to send his swimmers into the pool.

Kompanje isn’t worried. “I found literature, and I have experienced this myself, that women like to see a man wearing a kilt. It can be very masculine and sexy.”

“Wearing a kilt has strong psychological benefits,” he writes in his journal article. “A kilt will get you noticed no matter where you are. Research indicates that men wearing a kilt experience a strong sense of freedom and masculinity…The kilt gives a man a sensuous awareness of his own body and how it will be seen by others.”

Kompanje acknowledges there’s no proof testicles will be happier under kilts, so he proposes a controlled trial with regular scrotum temperature taking and sperm quality monitoring of some men wearing pants and others wearing kilts. One incentive to volunteer might be what Kompanje argues is the “positive attention from sexual admirers” associated with kilts.

Brian Alexander (www.BrianRAlexander.com) is co-author, with Larry Young Ph.D., of "The Chemistry Between Us: Love, Sex and the Science of Attraction," (www.TheChemistryBetweenUs.com), now on sale.