"Every time a bug pokes a hole in the chili fruit, the fungus can get in. And the more times the bugs can poke holes in the fruit, the more likely it is the fungus will start to invade," he said.
Laboratory experiments showed capsaicinoids thwart the fungus invasion—but not the insects.
"It looks like this chili is hot to stop the fungus, and the fungus is sort of mediated by these bugs," Tewksbury said.
Why Humans Eat Chilies
The finding, he said, adds weight to a hypothesis that humans first started to eat chilies for their antimicrobial properties.
He noted that the majority of people who eat chilies live along the Equator, a region of the world where microbes also flourish and cause a range of intestinal diseases.
"We're simply co-opting the result of a very ancient evolutionary arms race between chilies and fungus and saying that will work for us too," he said.
Linda Perry, an anthropologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., said the new research clearly demonstrates that capsaicinoids evolved to thwart the fungus.
But the study does not show that capsaicinoids prevent foodborne illnesses or act as a preservative, said Perry, who is an expert on the domestication of chilies.
Nor, she added, has it been demonstrated that the purported antimicrobial properties of chilies have much to do with their popularity.
"I think people probably adopted chili peppers into their diet just because they taste good," she said.
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