What the Nose Knows - Avery Gilbert [48]
In their tally of thousands of meat-based recipes, Sherman and Billing found that the most commonly used spices are onion (in 65 percent of all recipes) and pepper (63 percent), followed by garlic (35 percent), hot peppers (24 percent), lemon and lime juice (23 percent), parsley (22 percent), ginger (16 percent), and bay leaf (13 percent). Another thirty-five spices appear only occasionally (in 10 percent or fewer of all recipes). They found that the vast majority of the world’s recipes could be made with about four dozen spices—a number remarkably close to the length of Elisabeth Rozin’s world cuisine shopping list. Further, the average meat recipe calls for 3.9 spices, a number that is consistent with Rozin’s flavor-principle concept.
Sherman returned to his cookbook collection and analyzed another 2,129 recipes, this time looking at only vegetable dishes. Compared with meat recipes, these use fewer spices (2.4 per recipe on average). Still, the results supported the antimicrobial hypothesis: the hotter the climate, the more spices, though this relationship proved somewhat weaker for vegetable dishes. Why? Fruits and vegetables come prepackaged with physical and chemical defenses against microorganisms, which makes the health benefit of adding spices correspondingly smaller.
COOKING AND SPICING are behavioral adaptations with biological consequences. They have shaped our face and made mouth-based smelling a defining human trait. Outlandish as it sounds, spicy cooking may even have altered the core of our biological identity—our DNA.
It is often said that a species’s DNA code can be read like a book. If so, some biologists read it like the sports pages—they add up the number of odor receptor genes and rank us against other species according to the results. Rats lead the Mammalian League with the most functioning receptor genes; dogs and mice are a few games behind, while chimpanzees and humans are looking for a wild-card berth; and dolphins—an aquatic expansion team—own the cellar.
Among primates, humans have the highest proportion of nonfunctional receptor genes; we keep a lot of obsolete junk in our genetic attic. Superficially, it looks like the human nose is weak (relatively few receptors) and getting weaker (losing receptor genes at four times the evolutionary rate of other higher primates). Some, such as the science writer Nicholas Wade, see this as a case of use it or lose it. He says that “the price of civilization is that the faculty of smell is inexorably being degraded.” Wade’s gloomy conclusion may not be justified. Humans continue to evolve, and geneticists have identified hot spots in our genome—areas of biological function in which new genes are being born. Olfaction is one such hot spot. In the last 5,000 to 10,000 years, genes for smell receptors, along with genes related to diet and metabolism, have been evolving faster than those in any other physiological system. One new study finds that “many changes in the human olfactory repertoire may have occurred very recently,” the changes in this case being beneficial genetic mutations that have become fixed traits throughout the population.
The human genome responds rapidly to cultural changes. For example, in ancient populations the gene for lactose absorption ceased to function shortly after weaning. With the emergence of dairy farming, natural selection favored individuals in whom the gene stayed active into adulthood. The selective advantage of being able to eat milk products was so great that adult lactose absorption became a widespread trait within 5,000 years, a mere blink of the eye in evolutionary time. I suspect there has been ample time for the aromas of cooked food to influence our odor receptor repertoire in a similar way. If our gut evolved to digest dairy products, why wouldn