The Omnivore's Dilemma - Michael Pollan [148]
Our sense of taste’s second big bias predisposes us against bitter flavors, which is how many of the defensive toxins produced by plants happen to taste. Pregnant women are particularly sensitive to bitter tastes, probably an adaptation to protect the developing fetus against even the mild plant toxins found in foods like broccoli. A bitter flavor on the tongue is a warning to exercise caution lest a poison pass what Brillat-Savarin called the sense of taste’s “faithful sentries.”
Disgust turns out to be another valuable tool for negotiating the omnivore’s dilemma. Though the emotion has long since attached itself to a great many objects having nothing to do with food, food is where and why it began, as the etymology of the word indicates. (It comes from the Middle French verb desgouster, to taste.) Rozin, who has written or coauthored several fascinating articles about disgust, defines it as the fear of incorporating offending substances into one’s body. Much of what people deem disgusting is culturally determined, but there are certain things that apparently disgust us all, and all these substances, Rozin notes, come from animals: bodily fluids and secretions, corpses, decaying flesh, feces. (Curiously, the one bodily fluid of other people that doesn’t disgust us is the one produced by the human alone: tears. Consider the sole type of used tissue you’d be willing to share.) Disgust is an extremely useful adaptation, since it prevents omnivores from ingesting hazardous bits of animal matter: rotten meat that might carry bacterial toxins or infected bodily fluids. In the words of Harvard psychologist Steven Pinker, “Disgust is intuitive microbiology.”
Yet helpful as it is, our sense of taste is not a completely adequate guide to what we can and cannot eat. In the case of plants, for instance, it turns out that some of the bitterest ones contain valuable nutrients, even useful medicines. Long before the domestication of plants (a process in which we generally selected for nonbitterness), early humans developed various other tools to unlock the usefulness of these foods, either by overcoming their defenses or overcoming our own aversion to how they taste.
That’s precisely what people must have done in the case of the sap in the opium poppy or the bark of the willow, both of which taste extremely bitter—and both of which contain powerful medicines. Once humans discovered the curative properties of salicylic acid in willows (the active ingredient in aspirin) and the relief from pain offered by the poppy’s opiates, our instinctive aversion to these plants’ bitterness gave way to an even more convincing cultural belief that the plants were worth ingesting even so; basically, our powers of recognition, memory, and communication overcame the plants’ defenses.
Humans also learned to overcome plant defenses by cooking or otherwise processing foods to remove their bitter toxins. Native Americans, for example, figured out that if they ground, soaked, and roasted acorns they could unlock the rich source of nutrients in the bitter nuts. Humans also discovered that the roots of the cassava, which effectively defends itself against most eaters by producing cyanide, could be made edible by cooking. By learning to cook cassava humans unlocked a fabulously rich source of carbohydrate energy, one that, just as important, they had all to themselves, since locusts, pigs, porcupines, and all the other potential cassava eaters haven’t yet figured out how to overcome the plant’s defense.
Cooking, one of the omnivore’s cleverest tools, opened up whole new vistas of edibility. Indeed, in doing so it probably made us who we are. By making these foods more digestible, cooking plants and animal flesh vastly increased the amount of energy available to early humans, and some anthropologists believe this boon accounts for the dramatic increase in the size of the hominid brain about 1.9 million years ago. (Around the same time our ancestors’ teeth, jaws, and gut slimmed down to their present proportions, since they were