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Why Some Like It Hot: Spices Are Nature's Meds, Scientist Says
for National Geographic News
November 11, 2005
People who live in warm climates are attracted to spicy foods because the red-hot seasonings keep people healthy, according to a scientist who takes a Darwinian approach to medicine.
"The Darwinian approach asks the question, Why are certain things the way they are, which is a complement to the approach of asking, How do things work?" said Paul Sherman, a professor of neurobiology and behavior at Cornell University in Ithaca, New York.
Sherman's research shows that people in warmer regions of the world benefit from eating spicier foods, because spices are natural antimicrobials. Food-borne pathogens and parasites are more prolific in warmer climates, and spices can kill or inhibit their growth.
When people in a country like Thailand, for instance, eat a spicy meal, they are much less likely to spend the next day with a bout of diarrhea than people in that region who eat bland foods.
"Humans do what makes them feel good, and they learn from each other," Sherman said, adding that people in hot climates learned that spicy food is less likely to make them sick and thus developed a preference for it.
"The simple mechanism is they felt better after eating food that was spicy, and since they felt better they learned to like that stuff," Sherman said. "Over time, word-of-mouth spread the news."
In cooler climates such as Iceland, a steak left outside overnight might freeze. The cold would slow germ growth in the meat, rendering the use of spices unnecessary. As a result, Icelandic dishes tend to be bland.
But that's not a bad thing, Sherman said. Why take antimicrobials when they are not needed?
Randolph Nesse is the director of the Human Evolution and Adaptation Program at the University of Michigan in Ann Arbor. He said Sherman's research is a fine example of how behavioral traits are shaped by both natural and cultural selection.
To prove his hypothesis about the climate-dependent evolution of spicy foods, Sherman and his colleagues compared recipes for more than 4,000 meat dishes and 1,000 vegetarian dishes among 36 countries.
As predicted, countries with the warmest climate have the spiciest food. Meat dishes in particular are always the spiciest because a piece of meat lacks defenses against pathogens and parasites. Plants by contrast are where the antimicrobials originate.
"The plants have a recipe for survival," he said. "We are just borrowing the plants' recipes for use in our own recipes."
In all countries studied, spice use was greater overall in dishes from warmer regions.
The University of Michigan's Nesse said it's possible that cultural differences in spice preference are reflected in people's genes, a hypothesis that could be tested in by studying twins raised in separate cultures.
Sherman's spicy research is part of the emerging field of Darwinian medicine, an approach to understanding the "why" behind bodily functions, ailments, and diseases that complements traditional medicine.
"If you are going to fix something, it's important to know what it's designed to do in the first place," Sherman said.
For example, he said fever is an evolved defense deployed to fight unwanted bacteria in the body. Increased body temperature makes it harder for parasites and pathogens to reproduce and kicks the host's immune system into overdrive.
This is useful knowledge when treating a mild fever, Sherman said. Instead of prescribing medicine to reduce the fever, it may be in the patient's best interest for the doctor to prescribe medicine that works with the fever to combat the parasites and pathogens.
According to Nesse, Darwinian medicine is not "alternative" medicine, nor does it recommend treatment. Rather, he said, "it is simply using evolutionary biology as a crucial tool in mainstream medicine," including nutrition.
"In general the human tendency is to eat exactly what's going to kill us," such as fatty, salty, and sweet foods, "because those were in short supply in our evolutionary history," he said. "So we are determined to eat fats, salts, and sweets."
In future research, Sherman plans to examine how spice use changes with altitude. He predicts that spices will be used less in higher, drier climates than in lower, warmer, wetter places where food-borne bacteria present more culinary problems.
He is also studying whether certain spices fight pathogens and parasites on some foods better than others.
"For example, if I said, Let's have salmon and use lemon and pepper on it, you'd say, OK. But if I said, Let's smother it with ketchup and oregano and vinegar you'd say, What?
"The question is, Why are specific spices associated with particular dishes?"