"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.
Darwinian Medicine
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?"
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