[Below is the original script. But a few changes may have been made during the recording of this audio podcast.]

Many say a big part of sexual attraction is scent. But odor can also wreck havoc. Take mice for example. The aroma of a strange male's urine can cause pregnant females to miscarry, and restart ovulation. This is how the male, driven to propagate his own genes, knocks out a competitor's potential offspring.

But the female mice have a remarkable protection that kicks in on day three of pregnancy. Research out of the European Molecular Biology Laboratory has found that the females produce a surge of the chemical dopamine—known to regulate the olfactory senses—and this blocks the scent of urine from a strange male; because she never perceives it, the brain circuit that would cause her to abort her babies never switches on.

The dopamine surge that dulls the olfactory bulb to the abortive aroma is first triggered during mating, and progressively impairs sensitivity to male scent. Researchers found that when they inhibited this chemical surge, the males were able to trigger miscarriages later in pregnancy.

Dopamine is well known as the "reward chemical" in humans—a key to addictive behavior. But it is not yet known if there is a similar link between the olfactory bulb, pregnancy and dopamine in humans.

But the researchers say it may be why a pregnant woman may experience marked changes in her sense of smell.

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