A U.S.-led international team of scientists has solved a long-standing evolutionary mystery involving the spicy hotness of chili peppers.

University of Florida Professor Douglas Levey, one of the researchers, said a plant creates fruit to entice animals to eat and disperse its seeds. Therefore, said Levey, it doesn't make sense for that fruit to be painfully hot.

Now the study led by Assistant Professor Joshua Tewksbury of the University of Washington has discovered the reason is a fungus called Fusarium, which invades the fruits through wounds made by insects and destroys the seeds before they can be eaten and dispersed.

But capsaicin, the chemical that makes the peppers hot, drastically slows microbial growth and protects the fruit from Fusarium.

"And while capsaicin deters local mammals, such as foxes and raccoons, from consuming the chilies, birds don't have the physiological machinery to detect the spicy chemical and continue to eat the peppers and disperse seeds," Levey said.

The study's findings appear online in the Proceedings of the National Academy of Sciences. (c) UPI