For ecology graduate student Joshua Tewksbury of the University of Montana in Missoula, the hot pain of biting into a chili pepper is one of life's great pleasures. He's also come to think of it as a lesson in evolutionary manipulation. > Chill plants pump their fruits full of capsaicin, a chemical that stimulates pain-sensing neurons in the mouth.
After field studies in southern Arizona, Tewksbury may have discovered why the plants go to such great lengths. Mammals such as cactus mice and desert pack rats find capsaicin unpalatable--a good thing for the plant, because the animals' digestive systems would destroy the seeds within the chilies. Birds can't taste the chemical, however, so they freely eat the chilies. Chili seeds eaten and then expelled by birds are three times more likely to germinate than those that fall off the plant naturally. In lab tests, Tewksbury found that rodents greedily eat specially bred, capsaicin-free peppers. "Chilies clearly benefit from knocking mammals out of the picture," he says.
And for fun: Naga Jolokia
In 2000, scientists at India's Defence Research Laboratory (DRL) reported a rating of 855,000 units on the Scoville scale, and in 2004 an Indian export company called Frontal Agritech obtained a rating of 1,041,427 units, which would mean it is almost twice as hot as the Red Savina pepper and roughly equal to the similar-looking Dorset Naga, which is derived from the Naga Morich. For comparison, pure capsaicin rates at 15,000,000–16,000,000 Scoville units.
In 2005 at New Mexico State University Chile Pepper Institute near Las Cruces, New Mexico, Regents Professor Paul Bosland found Naga Jolokia grown from seed in southern New Mexico to have a Scoville rating of 1,001,304 SHU by HPLC.
In February 2007, Guinness World Records certified the Bhut Jolokia (Prof. Bosland's preferred name for the pepper) as the world's hottest chili pepper.
The effect of climate on the Scoville rating of Naga Jolokia peppers is dramatic. A 2005 Indian study that compared the percentage availability of capsaicin and dihydrocapsaicin in Naga Jolokia peppers grown in both Tezpur (Assam) and Gwalior (Madhya Pradesh) showed that the heat of the pepper is decreased by over 50% in Gwalior's more arid climate (similar temperatures but less humid, much lower rainfall).
For comparison, your average Jalapeño has a rating of only 2,000.