But smell may also play into judgment.

"We know that humans release olfactory signals," said Christine Drea, an associate professor of biological anthropology and anatomy at Duke University who studies scent cues in primates. "The question is to what extent do we use those cues when selecting a mate."

The proof is in so-called armpit studies, or sniff tests.

"A group of women are asked to smell shirts previously worn by a group of men and asked which scents they find most attractive," Drea explained. "There is evidence that women will pick the shirt worn by the man with the best genetic complement to her own genetics."

A good genetic complement is someone whose genome fills in the gaps in your own genome. For example, if your genetics protect you against a certain set of diseases, a good genetic complement will carry genes that protect against another set of diseases, providing your offspring with an immunity double dose.

Scientists have not resolved the complex array of chemicals that make up human scent, but they are inching closer by studying other primates. Last month, Drea and a team of Duke researchers announced that they had mapped the scent chemistry of a distant human relative, the ring-tailed lemur, to an individual's gene pool.

Male lemurs have glands on their shoulders that manufacture a musky scent. When the animals wish to mark their presence, they scratch a tree and then rub their scent into the wood.

Not only does the scent identify the lemur, but it also contains information about that lemur's family tree.

"Diverse genetics are reflected in a diverse chemical signal," Drea said. "In humans and in lemurs, in-breeding has genetic consequences, and diverse genetics are really advantageous."

The quality of a lemur's gene pool is especially important during mating season.

"It's a very intense period of breeding, where they fight over the best mates, and there are very high levels of stress," Drea said. When the male lemurs with weaker genetics experience high levels of stress, it is expressed through their scents.

The question now is to what extent the lemurs use these smell indicators to make their mating decisions. It's the equivalent of an armpit study for lemurs. The Duke research team is working on that now.

Meanwhile, scientists continue to study how human genetics are expressed through scent.

"We do know that people who are related smell alike, just like primates who are related," Drea said. A 1987 study by Dr. Marsha Kaitz of Hebrew University of Jerusalem showed that human mothers can recognize their newborn babies purely by their scent.

But the one thing human odors simply don't play a role in is human sexual arousal.

Dr. George Preti studies the nature and origin of human odors at the Monell Chemical Senses Center in Philadelphia.

"What we can say right now is that odor does play a role, albeit subtle, in mate choice in humans," Preti said.

But mate choice has nothing to do with arousal. Those magazine ads for "bottled pheromones" promising miraculous feats of sex appeal have little or no science behind them, Preti added.

It is more likely that scent guides mate choice through the expression of genetic information, not animal magnetism.