Antimicrobial Hypothesis, The
Drawing from the insights that bacterial growth is promoted by higher temperatures and spices can inhibit or kill bacteria, the antimicrobial hypothesis of spices argues that cultures in warmer regions of the world are more likely to include spices in their recipes (and benefit from the antimicrobial properties of spices) relative to cultures in cooler regions.
Pathogenic microbes, such as disease-causing bacteria and viruses, have posed a threat to the health and reproduction of many organisms for as long as microbes have existed, thereby constituting a significant recurring adaptive problem (Thomas et al. 2012). In turn, the selection pressure imposed by pathogenic microbes gives rise to various physiological and behavioral adaptations that facilitate the prevention of microbial infections, such as the immune system, feelings of disgust, and avoidance instincts (e.g., Curtis and Biran 2001; Tybur et al. 2016). The cultural transmission of practices that may help to ward off pathogenic microbes (as well as a corresponding favorability toward those practices) also constitutes another important line of defense. The current entry discusses one such cultural practice – the use of and taste for spices (Billing and Sherman 1998) – as an important accompaniment to humans’ array of antimicrobial defenses.
Spice Use Through the Ages and Across Regions
Spices refer to dried and aromatic plant substances whose primary food function is for seasoning and flavor rather than nutrition. These include seeds (e.g., cardamom), fruits (e.g., chilli pepper), leaves (e.g., cilantro), and roots (e.g., garlic). Spices derive their distinctive flavors from chemicals that are produced in order to fend against pathogens and parasites. Food spicing may have originated from early hunter-gatherers who unwittingly improved the flavor of their game by encasing the meat in certain types of leaves. Over time, early civilizations began realizing the useful properties of spice plants (Rosengarten 1981; Tapsell et al. 2006). For example, the Ancient Indians (approximately second to fourth century BC) documented their discoveries of the antiseptic and digestion-aiding properties of spices such as sesame and cloves, while the Ancient Egyptians (~1500 BC) initiated a classification that grouped spices such as garlic, onion, and thyme as health boosters. The antimicrobial prowess of spices was also well recognized as can be seen from their extensive use in the embalming and preservation of bodies. Spices progressively became high in demand. When the Goths besieged Rome in 408 AD, they demanded a ransom of 5,000 pounds of gold and 3,000 pounds of pepper. Marco Polo, Christopher Columbus, and Hernando Cortes count among the famous explorers who changed history while seeking faster routes to the spice-rich Indies.
Although spices have been used in food preparation throughout the world for centuries, patterns of spice use differ considerably across regions. More specifically, spice use varies as a function of regional temperature such that countries with higher average temperatures tend to incorporate more spices into their recipes (Billing and Sherman 1998). This pattern paints a puzzling picture. First, it is not clear why spices would be popular only in some cuisines despite their health benefits and usefulness as a preservative (Tapsell et al. 2006). Second, given that spices can make people feel hot and perspire, it seems counterintuitive that cultures in warmer regions would exhibit a stronger preference for spices. Third, although the use of spices is most often attributed to their role as a flavor enhancer, this does not address the ultimate, evolutionary question of why people would find foods tastier when flavored with spices. In light of these puzzles, and drawing from the insight that higher ambient temperatures are more conducive to bacterial growth (Genigeorgis 1981), Billing and Sherman (1998) hypothesized that the use of spices arose as protection from food-borne bacteria that are more likely to thrive in warmer climates.
Antimicrobial Hypothesis of Spices
Recipes containing meat products that have been kept for some time at room temperature in hotter, tropical climates exhibit a substantial hike in bacterial concentration (Genigeorgis 1981). Noting both the tendency for bacteria to proliferate at higher temperatures and the antimicrobial properties of spices, Billing and Sherman (1998) argued that spices are popular in warmer regions because they help to kill or inhibit food-spoiling bacteria, thereby contributing to the health and reproductive success of people who find their flavors enjoyable. To test the hypothesis, they examined 4,578 traditional meat recipes from a sample of 36 countries for the number of spices used out of 43 spices. Meat recipes were selected for analysis over nonmeat recipes (e.g., vegetable recipes) because of their greater likelihood of breeding bacteria and carrying food-borne illnesses. The number of spices used in the recipes was then compared between countries with varying average temperatures.
The results supported the prediction that countries with higher average temperatures add more spices to their recipes relative to countries with lower average temperatures. The researchers found that in ten of the hot-climate countries, namely, Ethiopia, Kenya, Greece, India, Indonesia, Iran, Malaysia, Morocco, Nigeria, and Thailand, every meat-based recipe included at least one spice. By contrast, in cold countries such as Finland and Norway, respectively, 19 of 62 and 25 of 77 meat-based recipes did not use any spices. The results also showed that higher average temperatures (such that food-borne pathogens would be most prolific) were associated with the use of spices with stronger antimicrobial effects. A follow-up study found that, on average, vegetable-only recipes called for significantly fewer spices than meat-based recipes (Sherman and Hash 2001), thus lending further support to the argument that spice use is aimed specifically at treating food that is more prone to spoilage.
Billing and Sherman (1998) examined the alternative hypothesis that inhabitants of warmer tropical regions eat more spices simply because more spice plants are grown there. They analyzed the distribution of spice plant growth within countries and found no correlation between average temperature and the number of spices grown in a country. This suggests that some warmer regions appear to favor the use of spices even though the inhabitants of those areas do not necessarily have a larger proportion of local spice plants to select from.
The antimicrobial hypothesis can be extended beyond temperature and spice use to other factors that influence the risk of food-borne illnesses, such as raw or undercooked recipes, and the use of other types of seasoning with similar antimicrobial effects, such as olive oil and vinegar (Medina et al. 2007). For example, a study by Ohtsubo (2009) showed that recipes containing uncooked products, such as Japanese dishes consisting of raw fish or meat (e.g., sashimi), are more likely to incorporate the use of vinegar than recipes containing cooked or heated food. Likewise, meat dishes made from raw ground meat, such as the European steak tartare dish, also tend to include more seasoning in their preparation.
Another important contribution of the antimicrobial hypothesis is its ability to account for why humans would have a taste for spices in the first place. Chilli peppers, for example, produce chemicals that create a painful burning sensation when exposed to bodily tissue and are typically avoided by herbivorous animals. Despite the aversive effects of contact with chilli peppers, people can enjoy eating them. From an evolutionary perspective, humans may have adapted a taste for such flavors to motivate the consumption of spices and reap the associated health benefits. That said, considerable variation exists in people’s liking of spicy food. For example, Indian dishes feature strong flavors contributed by the wide variety of spices used, whereas Scandinavian cuisine tends to be bland. Correspondingly, Scandinavians may be less tolerant of spices while Indians enjoy them. This facultative proclivity for spices therefore reflects our ability to adaptively calibrate preferences in response to environmental conditions.
Humans have, for centuries and arguably longer, exploited the chemicals designed to safeguard plants to season food and prevent food-borne illnesses. The antimicrobial hypothesis of spices provides an important evolutionary account for the peculiar correlation between spice usage and regional temperature. Examples of other antimicrobial food preparation practices that extend beyond the use of spices in hot climates, such as the treatment of raw recipes with vinegar, attest to the general validity of the hypothesis. These examples show that under the veneer of cultural differences in taste preferences, which are undoubtedly an important proximate reason for the different varieties of cuisines on offer, lies key survival and reproductive concerns at a fundamental level.
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- Tybur, J. M., Inbar, Y., Aarøe, L., Barclay, P., Barlow, F., et al. (2016). Parasite stress and pathogen avoidance relate to distinct dimensions of political ideology across 30 nations. Proceedings of the National Academy of Sciences of the United States of America, 113, 12408–12413.CrossRefGoogle Scholar