You are in: Front Page > Science and Technology Monday 30 July, 2001

Chillies: The Burning Question



Scientists in the United States have discovered the reason why chillies are so hot. They say that the chilli plant repels animals, which will not spread the seeds, whilst birds, which ensure effective dispersal, are not put off.



But if birds eat chillies and mammals don’t - why do we like them? Science In Action investigates.



To listen to the programme, please click here.

Plant Manipulation



Many plants have ripe, fleshy, coloured fruit in order to attract animals that will eat them and then disperse their seeds in droppings. However, the chilli plant has developed another way of ensuring its seeds are spread far and wide.



What raises the roof of your mouth when you eat a chilli is a substance called capsaicin. This stimulates the areas of the skin and tongue that normally sense intense heat and pain, falsely telling the brain that the area affected is burning.



New research carried out by scientists in Arizona, has discovered that this characteristic peppery taste repels certain animals – which are no good at dispersing the seeds.



Digestion And Dispersal



To find out what happens in the wild the scientists observed the eating habits of the local animals living around a group of wild-growing chillies in Arizona. They found that desert mice and rats avoided spicy chillies, but birds fed almost exclusively on the plants.



The researchers also noted that when birds ate the chillies, many seeds germinated, but there was no germination after mice had eaten the chilli seeds.



This is thought to be because seeds pass through a birds’ digestive systems very quickly and come out unharmed, whereas in mice, rats and other mammals, the seeds don’t make it out in one piece as they are broken down by the acidic juices during digestion.



The researchers suggest that chilli plants have evolved to produce capsaicin as a repellent for animals, which will ensure their future survival, whilst still allowing birds to eat their seeds.



Human Taste



Skilful play by the chilli, but if birds eat chillies and mammals don’t - why do humans like the hot stuff?



According to Paul Sherman from Cornell University in New York, people may have initially eaten spices because they tasted good, but they also recognised their health giving properties. He explains:



‘There is tremendous evidence that spices are anti-microbial. Of 30 commonly used spices, at least half of them kill or inhibit 75% of the bacteria they have been tested on.’

‘Certain ones, garlic, onion, allspice and oregano kill or inhibit everything that they have been tested on in the laboratory.’



Sherman reached his conclusion after he had studied a range of recipes from different parts of the world.



In particular he wanted to see whether different amount of chillies and other spices are used in meat as opposed to vegetable dishes. The idea being that if humans use spices to inhibit or kill food born pathogens, more would be needed to perform the same job in a meat product than a vegetable product.



Sherman details his findings:



‘We went back to all our cook books and looked at the 2,900 vegetable recipes and found that in 36 out of 36 countries worldwide, spices are used less frequently in vegetable recipes. This was across the board in every single country.’



Luckily for those of us with delicate palates, the decision to add a pinch or spoonful of chilli powder to our dishes is also determined by another product of evolution - free will.



Many plants have ripe, fleshy, coloured fruit in order to attract animals that will eat them and then disperse their seeds in droppings. However, the chilli plant has developed another way of ensuring its seeds are spread far and wide.What raises the roof of your mouth when you eat a chilli is a substance called capsaicin. This stimulates the areas of the skin and tongue that normally sense intense heat and pain, falsely telling the brain that the area affected is burning.New research carried out by scientists in Arizona, has discovered that this characteristic peppery taste repels certain animals – which are no good at dispersing the seeds.To find out what happens in the wild the scientists observed the eating habits of the local animals living around a group of wild-growing chillies in Arizona. They found that desert mice and rats avoided spicy chillies, but birds fed almost exclusively on the plants.The researchers also noted that when birds ate the chillies, many seeds germinated, but there was no germination after mice had eaten the chilli seeds.This is thought to be because seeds pass through a birds’ digestive systems very quickly and come out unharmed, whereas in mice, rats and other mammals, the seeds don’t make it out in one piece as they are broken down by the acidic juices during digestion.The researchers suggest that chilli plants have evolved to produce capsaicin as a repellent for animals, which will ensure their future survival, whilst still allowing birds to eat their seeds.Skilful play by the chilli, but if birds eat chillies and mammals don’t - why do humans like the hot stuff?According to Paul Sherman from Cornell University in New York, people may have initially eaten spices because they tasted good, but they also recognised their health giving properties. He explains:‘Certain ones, garlic, onion, allspice and oregano kill or inhibit everything that they have been tested on in the laboratory.’Sherman reached his conclusion after he had studied a range of recipes from different parts of the world.In particular he wanted to see whether different amount of chillies and other spices are used in meat as opposed to vegetable dishes. The idea being that if humans use spices to inhibit or kill food born pathogens, more would be needed to perform the same job in a meat product than a vegetable product.Sherman details his findings:‘We went back to all our cook books and looked at the 2,900 vegetable recipes and found that in 36 out of 36 countries worldwide, spices are used less frequently in vegetable recipes. This was across the board in every single country.’Luckily for those of us with delicate palates, the decision to add a pinch or spoonful of chilli powder to our dishes is also determined by another product of evolution - free will. More Highlights Beetle back juice The Bengal Tiger: spirit of the forest The dinosaur eating super-croc Marrakech climate talks Black Death Aids Left-handed memories Grading anthrax Nobel medicine man Global biological fears Bombing: the long-term fears Mapping the plague India obesity fears Racing to save the environment Family planning in Bangladesh Water tracking bacteria Chemical weapons of war ID cards: Facing the future The threat of asbestos In search of the missing in America New York health fears New York attempts to identify its missing High-tech hunt for low-tech man Black box: finding the perpetrators Super-skyscraper safety Coping with post-traumatic stress disorder Mobile safety fears Aids vaccine hope Gene Pioneers Ancestral lines Mobile phone movement Self repairing teeth Himalayan earthquake forecast Go Digital Starfish eyes Canadian bear necessities Healing hearts World water symposium Rain remover Dam Busters Population Predictions

Burning Issue The sensory nerves, which are affected by the burning sensation caused when eating chillies, can become damaged and die if they are exposed to capsaicin for too long.



This may be why people become less sensitive to chilli the more they eat it. Extra Chillies India is the world's top producer of chillies, exporting an estimated 35 tonnes a year. Related Stories 27 May, 2001

Seven Hurt In Sauce Attack 10 July, 2001

Chilli Linked To Bowel Disorders 2001

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