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Wednesday, 25 July, 2001, 22:35 GMT 23:35 UK
Why chillies are so hot
Chillies BBC
Chillies fool the brain into thinking the tastebuds are burning
Scientists have discovered why chillies are so hot.

They say the burning taste is an evolutionary ploy to stop mammals eating the pods and destroying the seeds.

However, birds, which tolerate the peppery taste, eat the fruits and disperse the seeds far and wide. This ensures survival of the pepper plant.

The researchers say their work could provide new ways to control populations that do not harm birds.

Spicy snack

A substance called capsaicin gives chillies their distinctive hot, peppery taste. The chemical stimulates areas of the skin and tongue that normally sense heat and pain, fooling the brain into thinking they are burning.

Chillies: the facts
The chilli is a native of Mexico where people started using a wild variety as long as 9,000 years ago
The Spaniards and Portuguese introduced the chilli to the rest of the world in the mid-15th Century
Some types of chilli are used to produce cayenne pepper or paprika
Capsaicin has been found to repel or poison mammals but not birds.

To find out what happens in the wild, a US research team studied the eating habits of animals living around a type of chilli plant that grows in southern Arizona.

The team, from the University of Montana and the Northern Arizona University, observed that desert mice and rats avoided spicy chillies but ate other fruits. However, birds fed on the wild chillies almost exclusively.

Digestive system

Lab studies showed that when birds ate the fruits, the seeds passed straight through their digestive system and were able to grow. This was not the case in mammals.

The researchers - Joshua Tewksbury and Gary Nabhan - suggest that chilli plants have evolved to produce capsaicin as a repellent for animals, while still allowing birds to eat the fruits and disperse the seeds.

"The capsaicin-mediated dispersal of chillies described here provides the first evidence, to our knowledge, that directed deterrence in a ripe fruit may shape plant-vertebrate interactions," the authors write in the journal Nature.

The work could also lead to the development of chilli-treated birdseed as an effective means to control rodent pests without threatening birds.

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 ON THIS STORY
Researcher Gary Nabhan
"Chillies are hot because of evolutionary history"
See also:

10 Jul 01 | Health
Chilli link to bowel disorders
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