Why do we use spices in our foods? In thinking about this question keep in mind that (1) other animals don’t spice their foods, (2) most spices contribute little or no nutrition to our diets, and (3) the active ingredients in many spices are actually aversive chemicals, which evolved to keep insects, fungi, bacteria, mammals and other unwanted critters away from the plants that produce them.

Several lines of evidence indicate that spicing may represent a class of cultural adaptations to the problem of food-borne pathogens. Many spices are antimicrobials that can kill pathogens in foods. Globally, common spices are onions, pepper, garlic, cilantro, chili peppers (capsicum) and bay leaves. Here’s the idea: the use of many spices represents a cultural adaptation to the problem of pathogens in food, especially in meat. This challenge would have been most important before refrigerators came on the scene. To examine this, two biologists, Jennifer Billing and Paul Sherman, collected 4578 recipes from traditional cookbooks from populations around the world. They found three distinct patterns.

1. Spices are, in fact, antimicrobial. The most common spices in the world are also the most effective against bacteria. Some spices are also fungicides. Combinations of spices have synergistic effects, which may explain why ingredients like “chili power” (a mix of red pepper, onion, paprika, garlic, cumin and oregano) are so important. And, ingredients like lemon and lime, which are not on their own potent anti-microbials, appear to catalyze the bacteria killing effects of other spices.

2. People in hotter climates use more spices, and more of the most effective bacteria killers. In India and Indonesia, for example, most recipes used many anti-microbial spices, including onions, garlic, capsicum and coriander. Meanwhile, in Norway, recipes use some black pepper and occasionally a bit of parsley or lemon, but that’s about it.

3. Recipes appear to use spices in ways that increase their effectiveness. Some spices, like onions and garlic, whose killing power is resistant to heating, are deployed in the cooking process. Other spices like cilantro, whose antimicrobial properties might be damaged by heating, are added fresh in recipes.

Thus, many recipes and preferences appear to be cultural adaptations adapted to local environments that operate in subtle and nuanced ways not understood by those of us who love spicy foods. Billing and Sherman speculate that these evolved culturally, as healthier, more fertile and more successful families were preferentially imitated by less successful ones. This is quite plausible given what we know about our species’ evolved psychology for cultural learning, including specifically cultural learning about foods and plants.

Among spices, chili peppers are an ideal case. Chili peppers were the primary spice of New World cuisines, prior to the arrival of Europeans, and are now routinely consumed by about a quarter of all adults, globally. Chili peppers have evolved chemical defenses, based on capsaicin, that make them aversive to mammals and rodents but desirable to birds. In mammals, capsicum directly activates a pain channel (TrpV1), which creates a burning sensation in response to various specific stimuli, including acid, high temperatures and allyl isothiocyanate (which is found in mustard or wasabi). These chemical weapons aid chili pepper plants in their survival and reproduction, as birds provide a better dispersal system for the plants’ seeds than other options (like mammals). Consequently, chilies are innately aversive to non-human primates, babies and many human adults. Capsaicin is so innately aversive that nursing mothers are advised to avoid chili peppers, lest their infants reject their breast (milk), and some societies even put capsicum on mom’s breasts to initiate weaning. Yet, adults who live in hot climates regularly incorporate chilies into their recipes. And, those who grow up among people who enjoy eating chili peppers not only eat chilies but love eating them. How do we come to like the experience of burning and sweating — the activation of pain channel TrpV1?

Research by psychologist Paul Rozin shows that people come to enjoy the experience of eating chili peppers mostly by re-interpreting the pain signals caused by capsicum as pleasure or excitement. Based on work in the highlands of Mexico, children acquire this gradually without being pressured or compelled. They want to learn to like chili peppers, to be like those they admire. This fits with what we’ve already seen: children readily acquire food preferences from older peers. In Chapter 14, we further examine how cultural learning can alter our bodies’ physiological response to pain, and specifically to electric shocks. The bottom line is that culture can overpower our innate mammalian aversions, when necessary and without us knowing it.

Joseph Henrich, The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter, 2015.