I’m breathing fire after adding a few drops of scotch bonnet sauce to my lunch, and it got me wondering: When did adding capsaicin-rich spices become prevalent in certain cuisines? Why was ‘spicy’ food so quickly and decisively adopted in some cultures, and mostly ignored in others?

The short answer is that we don't know for sure.

The longer answers veers away from what I would typically label as the purview of "historians" and into the realms of biology and sociology—in particular, evolutionary gastronomy.

First, let me set the stage. Chili peppers (the only natural source of capsaicin) are native to the Americas, and did not exist in the Old World before the Spanish/Portuguese started bringing them over in the last ~500 years.

It's a little crazy to realize that all of the cultural cuisines that are so deeply ingrained with chili peppers and spiciness—Indian, Sichuan, the paprika of Turkish/Hungarian, Korean, etc.—only got that way in the last couple hundred years, other than Mexican food. Imagine going from never having seen a plant to making it a defining characteristic of your entire culinary repertoire in so short a time.

(Tomatoes, which are also native to the Americas, follow a similar story, as well as a few other items—see "Columbian Exchange". I think it's interest to think about why similar patterns of culinary adoption never emerged from the discovery of Australia, which also sports a wealth of biodiversity. But that's a separate question.)

So why did chili peppers blow up so quickly in so many places, and get ignored in others? More broadly, why do groups of people have similar taste preferences at all? There are a lot of possibilities here, and this is an amazingly complex issue, but let me highlight a few of the most interesting and relevant ideas, and ignore the boring ones like availability, which are less likely to matter here. In particular, let me expand your question a little bit to one that is more commonly debated, and then we'll come back to chilis.

It has been noticed that cultures that are closer to the equator generally employ a greater use of spices (not just chilis) than those in colder regions. Think about an Ethiopian beriberi sauce compared to the very "subtle" (read: "bland") flavors of Nordic cuisine. Why might this be true?

In general, one of the biggest reasons a person likes what they do is because they grew up eating that food. This is even true prenatally—scientists have shown that the flavors of food a mother eats while pregnant influence flavor preferences of their child; infants with prenatal exposure to carrot juice enjoyed carrot-flavored food more than infants who were not.

Notice that this doesn't really explain why cultures use spices differently—it just turns it into a "chicken and the egg" problem. However, also notice that inheriting flavor preferences from your parents seems like it could have some parallels to genetic inheritance. Imagine that a family whose cuisine involves eating a lot of raw meat without doing anything to fight bacteria. The chance of people in that family getting sick and dying before they can have children (and pass that cuisine on to the next generation) is greater than for a family that cooks its meat. In that way, you could imagine culinary traditions spreading evolutionarily, which generally forms the basis of evolutionary gastronomy. But most everybody cooks their food to some extent, so what does that have to do with the equatorial pattern in spice use we see?

Well, the time it takes for raw meat to go bad in India is radically shorter than it is in Scotland, for example. I can't seem to find the hard numbers, but if I recall it's a number of minutes versus a number of days in the right circumstances. Bacteria loves warm wet climates, and food spoilage is a much more prevalent problem in equatorial climates. And as it just so happens, many spices have antimicrobial properties.

If you want a more thorough scientific analysis, check out "Antimicrobial Functions of Spices: Why Some Like it Hot" (Billing and Sherman, 1998), which looks at a corpus of traditional cookbooks across a wide range of cultures and locations, and analyzes their use of spices. To me, their results are relatively compelling, and suggest that the uses of spices in these different cuisines are driven by spices' antimicrobial properties. For example, some spices have synergistic effects, where they inhibit bacterial growth better together than separately, and they find that these combinations are more frequent than you would expect by chance, and spices that are more inhibitive are found more often in general.

They also look at a few alternative hypotheses—nutrition, disguising taste/smell of spoiled foods, increasing sweating to cool people off (weird, I know)—and don't find evidence for any of those.

Chili peppers likewise have antimicrobial properties, but such evolutionary gastronomy is unlikely to have directly led to their rapid adoption—the timescales are just too short. The reason that some cuisines seem to have adopted the chili pepper so quickly seems to be that they were already using lots of piquant spices to begin with.

For example, before chili peppers were introduced into India, many of its cuisines were already using loads of pepper (black pepper and "long" pepper) and heaps of biting ginger and the like. For them, it would be as if chili peppers were born for their cuisine, and represented the "Platonic ideal" of spiciness that they had been approximating with other spices. Even very traditional Ayurvedic recipes (basically India's ancient medicinal / nutritional practices) began substituting in chili peppers for black pepper, etc. There's a reason why Columbus mistook chilis for black pepper, after all!

So in a sense, I would argue that the reason why some cultures adopted chili peppers into their cuisine and others didn't primarily comes down to whether the chili pepper fit into the pre-existing cuisine. But why different cultures had cuisines that worked better with chili peppers seems to be due to evolutionary pressures based on spice use.

Obviously, there's a lot more that could be said about this topic, and I think some may disagree with the evolutionary gastronomy hypothesis, but these questions can be very hard to answer firmly.

References:

Billing and Sherman. 1998. "Antimicrobial Functions of Spices: Why Some Like it Hot". The Quarterly Review of Biology

Collingham, Liz. 2006. Curry: A Tale of Cooks and Conquerors.

Mennella, Jagnow, and Beauchamp. 2001. "Prenatal and Postnatal Flavor Learning by Human Infants". Pediatrics.

Sherman and Billing. 1999. "Darwinian Gastronomy: Why We Use Spices: Spices taste good because they are good for us". BioScience