You've paid a small fortune to sample one of the world's great delicacies: truffles. Your waiter ceremoniously shaves a few grams over your pasta. All around you, diners are sighing with delight. But you smell zilch, and your companion complains that the pricey fungus reeks.

It's a fact -- people react to truffles in vastly different ways. Now scientists are closing in on why. Nearly 25% of the population do not smell androstenone, a chemical that contributes to truffle's signature musky aroma (and makes female pigs go into...