The Triumph of Seeds (22 page)

Scientists long ago traced the pungency in chilies to the presence of
capsaicin
, a compound produced in the white, spongy
tissue that surrounds the seeds. It’s what experts call an
alkaloid
, a type of chemical that may be more familiar than you think. Alkaloids all share a similar nitrogen-based structure, a set of building blocks that plants have arranged and rearranged into more than 20,000 distinct combinations. The nitrogen matters because it’s a vital nutrient that plants also need for growth, so they don’t use it on alkaloids without a purpose. Usually, that purpose amounts to some form of chemical defense. And because plants usually need to defend themselves
against animals, alkaloids almost always have an effect on people, too. They can be spicy, like capsaicin, but that’s just the beginning. Even a short list of common alkaloids includes some of the world’s most recognizable stimulants, narcotics, and medicinals, from caffeine and nicotine to morphine, quinine, and cocaine. In Bolivia, however, few mammals seemed interested in chili peppers, even the mild ones. To Noelle, that made the fungus growing on the seeds look all the more suspicious.

“A fungal seed pathogen is the strongest kind of selection pressure,” she explained. “Seeds are progeny—a direct link to fitness.” In other words, if fungi were killing the seeds of mild chilies, it would give the plants a powerful reason to develop some kind of chemical response. After all, there’s hardly a stronger evolutionary imperative than the life or death of offspring. In an elegant series of experiments, Noelle showed that fungi did indeed kill a large portion of the seeds they infested, and that pungent seeds were significantly more resistant than mild ones. Capsaicin slowed or stalled the growth of a wide range of fungi, both in the wild and in Petri dishes back at the lab, strongly suggesting that it evolved for just that purpose. But her success only raised another question. Why weren’t all the chilies hot? If capsaicin was such a great idea, then why did some plants keep producing chilies as mild as an apple?

Solving that puzzle takes us back to the great square dance of coevolution, the same process of give-and-take that led to strong rat teeth and thick nutshells. In this case, the struggle was invisible, but no less imperative. Noelle’s research showed that both chilies and fungi respond to one another—plants produce more capsaicin as the fungi become resistant, and vice versa. “I think of it as a coevolutionary arms race,” she summarized, but running that race had steep costs for both sides. For a fungus to withstand capsaicin, it gave up the ability to grow quickly—a distinct disadvantage anywhere except inside a pungent chili pepper. For the plants, making capsaicin interfered with their ability to retain water, leading to lower seed production in dry weather. What’s more, it took energy away
from the woody material in seed coats, making the seeds more vulnerable to predation by ants. These are serious drawbacks that only made sense under certain conditions, a reminder that the results of coevolution involve more than which partners are dancing. It also depends on where the dance takes place.

Bolivia’s Gran Chaco region stretches from arid savannahs and cactus patches to wet forested hillsides near the borders of Paraguay and Brazil. By sampling chilies across 185 miles (300 kilometers) of mixed terrain, Noelle and her team quickly found a pattern. “In areas of high rainfall, all the chilies are hot,” she told me. “But as rainfall decreases, so does pungency.” For chilies growing in wet forests, where fungi and the insects that move them from fruit to fruit are common, investing in spiciness was a clear advantage. But in arid environments, fungi don’t grow nearly as well, and the potential for water stress and low seed production made pungency a burden. This dynamic of pros and cons put the evolution of pungency in context—a balance between rainfall, insects, fungi, and the physical costs of producing capsaicin. It also helps explain how a change in climate, range, or habitat might have led the ancestors of domesticated chilies to lose their mild forms entirely. When life gets wet and moldy, chilies retaliate with heat.

Most spices will never receive the level of scrutiny that Noelle and her colleagues have given to chilies, but the capsaicin story illustrates a general pattern about the pathway to spiciness. Similar research may one day unravel the mystery behind the myristicin in nutmeg and mace, or the piperine that puts the punch in black pepper. What we perceive as spiciness develops in an intricate coevolutionary dance between plants and their adversaries. Without those relationships, world cuisine would be almost universally bland. This raises a question worth thinking about: Why is it that we add seeds, bark, roots, and other plant parts to flavor meat dishes, and not the other way around?

From pepperoni and pepper steak to pork vindaloo, the zest in our favorite meat recipes always comes from the spices, not from the
meat. There is a fundamental biological reason for this. Meat isn’t spicy because meat can move. When a chicken, a cow, a pig, or virtually any other animal is attacked, its capacity for motion gives it a wide range of options: run away, take flight, climb a tree, slither into a hole, or stand and fight.
Plants, on the other hand, are stationary. Their lot in life is to stay put and endure, a situation tailor-made for the evolution of chemicals. If you can’t flee or fight back physically (beyond the occasional spine or thorn), it makes perfect sense to repel attackers with alkaloids, tannins, terpenes, phenols, or any of the many other compounds invented by plants. It’s true that insects also boast a wide array of chemical defenses, but they often get them from the plants they eat. Some frogs and newts manufacture poisons, too, and there is at least one species of toxic bird. But the only notable exception to the bland-animal rule comes from the ocean floor, where bryzoans, sponges, anemones, and a range of other creatures spend most of their lives glued to rocks, as stationary as plants. Thousands of marine alkaloids have been isolated from these animals, though it remains to be seen if any of them will prove tasty sprinkled on fajitas, souvlaki, or chicken tikka.

Before the end of our conversation, I asked Noelle what remained to be learned about capsaicin and chili peppers—what were she and her colleagues working on now? The discussion immediately veered into whole new topics, each one as potentially groundbreaking as Noelle’s dissertation. The birds that disperse chilies, for example, appear to be utterly immune to their pungency. They gobble the fruits at will, and the seeds pass through unharmed, or even enhanced, since it appears that moving through a bird helps clean them of fungi. Capsaicin also slows the digestion of birds, forcing them to carry the seeds farther. Noelle told me that the insects moving fungi from fruit to fruit may be chili pepper specialists, and she talked about a student studying how ants differentiate pungent seeds from mild ones. Then she mentioned that someone had recently discovered a fungus capable of making its own capsaicin—though why on earth it would want to is still anyone’s guess. But perhaps
the most fascinating line of study has to do with the effect of capsaicin on mammals, which is, after all, the reason that Christopher Columbus packed his hold with chilies, and why they quickly found welcome in spice drawers around the world.

When capsaicin touches the human tongue, sinuses, or other sensitive areas, it produces what chemists describe as “a sensation of
intolerable burning and inflammation.” Chefs and fans of hot sauce might describe it differently, but the cause is the same: a chemical sleight of hand that confuses the body’s natural system for detecting heat. Normally, burn sensors in the skin activate only above 109°F (43°C), a temperature that can begin causing physical damage to cells. When you scald your mouth on hot soup, for example, the pain you feel is an honest use of this system. Biting into a pungent chili, however, triggers that response at any temperature. Capsaicin molecules target those same burn receptors and open the floodgates, tricking the body into the kind of pain and rush of endorphins that would normally accompany a serious wound. From the brain’s perspective, the mouth is on fire. The feeling may last for seconds, minutes, or even longer at high doses, but eventually the capsaicin dissipates and the body recognizes that no harm has been done.

For people, this sensation can be enjoyable, the culinary equivalent of a roller-coaster ride or a horror movie—scary, without actually being dangerous. According to some studies, exhilaration from the endorphins peaks only after the burning sensation fades, which raises the paradoxical possibility that we eat chili peppers precisely because it feels so good to stop eating them. Noelle likes spicy food well enough to keep hot sauce on hand at all times, even at the office. But she thinks people developed a taste for pungency only out of necessity, and that chilies entered the human diet for another purpose. “Adding small quantities to food is a pretty good preservative,” she said, noting that capsaicin deters a whole range of microbes in addition to fungi. It’s telling that chilies—and so many other spices—were domesticated in the humid tropics, where meat and fresh vegetables spoil quickly. For thousands of years before
refrigeration, having a burning tongue was small price to pay for thwarting mold and harmful bacteria. If Noelle is right, then people started eating capsaicin for the very same reason it evolved: to ward off the fester of fungus and rot.

Without the need to preserve meat stews or pots of beans, no other mammals have developed the chili pepper habit. They feel the same burn that we do, but to them, pain is simply pain. So while pungency may have gotten its start fighting fungi, it’s also extremely good at deterring rats, mice, voles, peccaries, agoutis, and all the other mammals that would otherwise happily devour a chili seed. Where these gnawers are common, that’s an important evolutionary advantage for the chilies, and it almost certainly played a role in determining why pungency became dominant in so many chili species. It also creates a brilliant dispersal strategy: repel the animals that chew and destroy your seeds, leaving more available for the birds, whose pain receptors don’t respond to capsaicin, making them physically incapable of feeling the heat.

When I said goodbye to Noelle, my head was still swimming with chili questions. But that’s the way with science—new information simply feeds the curiosity. The complexity of the chili pepper’s story explains not only how seeds can become spicy, but why spices have so many uses in addition to seasoning. If they evolved to interact with everything from bacteria and mushrooms to squirrels, it’s no wonder that people find spices useful in a lot of situations. In Columbus’s day, they certainly found their way into food, but they also served as popular medicinals, aphrodisiacs, preservatives, and oblations. (Contrary to popular myth, exotic spices were never used to cover up the taste of rotting meat. They cost a fortune and signified status—the people who bought them could easily afford fresh, high-quality ingredients.) In modern times, things haven’t really changed all that much. Capsaicin from chilies—to take just one example—forms the basis of everything from arthritis creams and weight-loss pills to condom lubricants, bottom paint for boats, and the self-defense spray marketed as Mace. Olympic show-jumpers have been disqualified
for rubbing it on the legs of their horses, and wildlife rangers in Africa fire it from drones to herd elephants away from poachers. But in China, people use capsaicin for something that most of us associate with a different seed product, one perhaps even more famous than chili peppers.

Chairman Mao Zedong promoted an austere lifestyle with simple peasant foods, but he harbored a famous love of chilies. Even while living in a cave, he ordered them baked into his bread, and reportedly ate whole handfuls to boost his energy while working late at night. Now, police officers in Mao’s native Hunan region regularly distribute hot chilies to sleepy drivers in an effort to reduce traffic accidents. For most night owls, however, the stimulant of choice comes in liquid form, extracted from the seed of an African shrub. Like spices in their heyday, it has spawned vast fortunes, influenced world events, and inspired at least one sea voyage worthy of an adventure story.

*
Nutmeg and mace both come from a tree native to Malaysia. Nutmeg is the seed itself, while mace grows as a fleshy red seed appendage called the
aril
. Pepper comes from a rainforest vine native to the west coast of India. Black pepper includes the seed and a thin layer of shriveled fruit tissue; white pepper is the same thing with the fruit layer removed.

CHAPTER TEN