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There's a Reason We Live in a Spice World

Spicing Evolved as a Way to Kill Bacteria and Fungi on Food, Two Researchers Say


Imagine a world without spice.

Pizza without oregano. Lamb chops without mint sauce. Curry without turmeric.


People have used spices for millenniums, and regional cuisines are largely defined by the arrays of spices used in their preparation. But what is it about spices that makes spiced food taste so good? And why is it that patterns of spicing differ in various parts of the world?

Cornell University behavioral ecologist Paul Sherman and his student Jennifer Billing confronted those questions a couple of years ago as part of a broader look at the evolutionary roots of human behaviors and preferences. Sure, we eat spices because they taste good, the team reckoned. But what exactly happened to make us experience these flavors as pleasant--especially considering that many of the chemical compounds that give spices their flavors are, in larger doses, poisonous?

Now Sherman and Billing have published the results of a major research project that grew out of their casual curiosity.

After an exhaustive review of 4,578 recipes taken from 93 cookbooks of traditional cuisines from 36 countries and an analysis of the spices used in those recipes, the team has ruled out several popular theories about why people use spices--such as that spices are used to cover up the taste of spoiled food, or to provide micronutrients, or to help people keep cool in hot climates by making them sweat.

Instead, Sherman and Billing conclude, spicing evolved as a way to kill disease-causing bacteria and fungi on food.

"The proximate reason spices are used obviously is to enhance food palatability," the researchers write in the March issue of the Quarterly Review of Biology. "But the ultimate reason is most likely that spices cleanse foods of pathogens and thereby contribute to the health, longevity and reproductive success of people who find their flavors enjoyable."

Sherman concedes that the newly published analysis is a mere stab at understanding an enormously complex biological and behavioral phenomenon. But he and others said they couldn't help but be impressed with how strongly the data support the "spice as antibiotic" hypothesis.

"His explanation is the best hypothesis," said Paul Ewald, a pioneer in the field of evolutionary medicine from Amherst College. "It seems quite clear that these compounds are inhibiting bacteria and we get a big benefit from using them."


At the core of the researchers' culinary conclusion is their discovery that spicing varies predictably depending on how hot a country's climate is--that is, depending on how quickly food would rot in the area before refrigeration. Specifically, as average temperatures increased, the percentage of recipes that contained spices also increased, as did the number of spices per recipe, the total number of spices used, and--here was the clincher--the antibiotic potency of the spices used.

Many spices can kill microbes at doses similar to those used in food. "Think about cutting a tomato and leaving it in a jar," Ewald said. "It's pretty rotten in a day or two. But make it into salsa and it can last days or weeks."

Sherman and Billing ranked 43 spices by their ability to kill 30 bacterial species in test tubes. Some, like onion and garlic, can kill all 30 and are found in most cuisines. Overall, one trend became clear: The hotter the climate, the more intensely antimicrobial were the spicing patterns.

"I think that much of what we do in our food preparation is associated with preventing food-borne illnesses, and that includes salting, smoking, drying, thoroughly cooking food and now this idea of adding spices," Sherman said. "It's especially interesting because we're using compounds that plants evolved for the same function--to ward off the microbes that would infest them."

Sherman suspects that in warmer climes, evolution favored individuals who practiced spicing. "The food of those individuals would be safer to eat, and it might be preserved longer. They might be able to eat a mastodon for a week instead of for three days," he said.

Eventually, the trend would spread. "Neighbors would be interested in what you are doing that they are not. They might say, 'You are healthy and all of us over here have the runs.' Humans are very good at imitating success."


Sherman argues that the "stench cover-up" hypothesis makes no sense, since it pays to know when food has spoiled. Spices also are a poor source of nutrients, he said, and there is no evidence that a "chili pepper sweat" significantly cools the body.

Not everyone buys the antibiotic hypothesis. Critics argue that cultural and economic forces can explain most global spice-use patterns.

"There's a great temptation for contemporary people to explain things from antiquity in terms of present-day knowledge," said retired cultural geographer Frederick Simoons of Spokane, Wash.

For example, many people today presume that the ancient Hebrews avoided pork because they recognized that pigs harbored trichinosis, a potentially fatal disease, even though the first recorded discussions of this danger do not appear until the 19th century.

As for spices, Simoons said, "They were rare and they tasted good. They were in demand, and it was probably just a matter of conspicuous consumption."

Paul Rozin, a University of Pennsylvania psychologist who studies food choice, said spices were popular in the tropics because that's where they grew. And tropical diets are more starchy than meaty, he said, so they need more spice to taste interesting.

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