So why do only some peppers produce capsaicin? That is the question Professor Tewksbury set out to answer. With the help of an assistant, he collected more than three hundred chili plants from a three hundred-kilometer area in Bolivia. Within this area were different climates. Some plants grew in desert-like conditions, while others were from a very wet climate.

SHIRLEY GRIFFITH: Professor Tewksbury and his assistant found that among the chilies growing in the dry places, only about fifteen to twenty percent were hot. By comparison, one hundred percent of the chilies growing in wet conditions were hot.

They also found that hot chilies growing in dry areas need more water. Because the fungus is less of a threat in dry weather, the chilies in those areas were less likely to produce the heat-making capsaicin. In wet areas, the pepper produced more capsaicin to defend itself.

STEVE EMBER: The researchers tested their findings back at the University of Washington. Three hundred thirty chili plants were grown under the same conditions. Then they were separated into two groups. One received a lot of water. The other plants received the amount of water they would get in a dry climate in Bolivia.

The researchers found that the hot peppers use up more water as a way to protect themselves from fungus. Their findings were published in the Proceedings of the Royal Society B.

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SHIRLEY GRIFFITH: Maybe a little of this … (Music)