Level 14

Stefano Mancuso is a former MAD speaker and founder of the study of plant neurobiology. His work investigates how plants are complex ecological structures and communities that can gather, process, and share important information. He is a professor at the University of Florence, Italy, and a co-founder of the LINV (the International Laboratory of Plant Neurobiology).

Sad was the life of man before cooking. For 98% of the 3,200,000 years that separate us from Lucy, our little—she was 1.2 meters tall—Australopithecus ancestor, man survived without being able to control fire. Sometimes, as a blessing, a thunderbolt would fall from the sky and flames would appear as by magic, darting through the grass of the savannah. In rarer, luckier situations, lightning would hit a tree, securing hours or even days of light, heat, and protection from wild animals. With the exception of these natural fires, man managed for millions of years without the most powerful weapon in the struggle for life: fire.

No one knows the precise moment this extraordinary technological advancement took place. The indications are conflicting. For some authors, man started using fire around one million years ago, but the evidence is not conclusive. We do know that the first remains of hearths appeared around 350,000 years ago at sites in what are now France, Hungary, and China, although they seem related to the use of natural fires. People were capable of finding fire, but not producing it autonomously. For this massive leap, we need to look 50,000 years in the past, when, almost simultaneously in a number of sites in Africa and the Middle East, we can see unmistakable signs of the ability to use fire.

At the site of Jabrud, in Syria, for example, where layers upon layers of human deposits have been continuously stacked since the first Paleolithic Age, there is no trace of fire for hundreds of thousands of years. Then, suddenly, at the fateful “Level 14” (approximately 40,000 years ago), fire materializes so powerfully that all remnants of artifacts found from that level on are distorted by heat. It is an epochal change with vast consequences: the Neanderthal man, not in possession of this technology, was quickly swept away from the history of human evolution.

With fire, people can keep warm, defend themselves more effectively, build new tools, and forge metal. But perhaps the most important point is that fire allows people to cook their food and greatly expand the number and type of nutrients, especially of plant origin, with which they feed themselves.

Why was applying fire to plants so crucial? Don’t experts often say that raw foods, especially plants, are healthier, richer in nutrients, and even tastier? In order to familiarize ourselves with this complex subject, we should step back and talk a bit about how plants work. as we tend to grossly underestimate them; plants are far more complex than what most of us perceive. In many languages, “vegetating” refers to a total lack of sensitivity or calculation capacity. This is completely wrong. Plants are sophisticated beings with characteristics and behaviors that are sometimes significantly more refined than those of animals.

Take the issue of sensitivity. How many of us would guess that a plant is capable of sensing its surroundings in an extremely accurate way? Very few, I’d say. The reality is that plants are far more sensitive than other creatures. When an unexpected noise, a sudden rise in temperature, or an approaching predator comes into the equation, an animal always has the formidable weapon of escape at its disposal. This is such an important response that it doesn’t even need to be activated by the brain. It happens automatically when the potential danger arises.

But plants, as everyone knows, cannot move. Well, it would be more correct to say that they cannot shift from the place where they were born, since they actually do move a great deal. Let’s not dwell on these nuances and move along: if a plant can’t run away, how can it survive the constant changes that occur in its environment? How, frankly, have plants escaped extinction, given that they can’t move away when it gets cold, find shade when the sun is at its worst, or run off when a herbivore wants to eat them? How is it that there are so many still in good health? Despite our continuous attempts on their lives, the amount of plant life on Earth is astounding. Plants account for 99.5% of the biomass on our planet.

Plants may not be able to flee, but they are able to anticipate changes in the environment superbly. Plants can adapt to these shifts anatomically and physiologically. They also have remarkable defense capabilities. There are the obvious mechanical defenses, like sharp spines, thick trichomes, and robust barks, as well as the refined strategies that require alliances with other animals. This is the case with many species that have relationships with ants. The plants provide the ants with food (small fruiting bodies specifically designed to meet all the dietary needs of the ants), housing (huge hollow thorns in which the ants can multiply and thrive), and drink (the so-called extra-floral nectar, rich in sugars and other substances), in exchange for effective defenses from any predator—even a giraffe or elephant—that dares to approach the plant.

The defense that most interests us this weekend, as we discuss cooking, is the potential plants have to produce toxic chemicals for protection. These commonly are secondary metabolites, chemical compounds that the plant purposely produces to repel or deter animals. There’s something for everyone: irritants like saponins that produce foam and are present in about one hundred families of plants; the hemaglutinins that annihilate red blood cells; irritating oils based on cyanogenic compounds produced by the cabbage family or cassava or the cocktail, present in the hairs of the nettle, that is made with acetylcholine, histamine, moroidin, leukotrienes, and formic acid; enzyme inhibitors such as the protease inhibitor present in a number of species; and the remarkable substances in legumes that induce favism and the cholinesterase inhibitors produced by the plants from the tomato family.

Some families of plants are particularly expert in the fabrication of toxic substances. This is the case of the Ranunculacaee family, where it is virtually impossible to find a single species unable to produce poisonous toxins to animals. Among these is aconite, generated by several species of Ranuncolacee and lethal in infinitesimal doses (one milligram can be enough to kill a man). Even species much closer to our food culture, like the Solanaceae, are rich in lethal alkaloids. Thus the deadly nightshade (Atropa bella-donna) produces large quantities of atropine, scopolamine, and nicotine, while the henbane (Hyoscyamus niger) creates a highly toxic alkaloid as the hiyosciamine; even the leaves of the common potato are highly poisonous. Also in seemingly inoffensive families, like the Liliacaee, whose members include onion (Allium cepa), garlic (Allium sativum), leek (Allium ampeloprasum), and chives (Allium schoenoprasum), we can find many poisonous species. The gentle lily of the valley (Convallaria majalis) is extremely toxic, containing saponin and a steroid called convallarin with toxic effects similar to that of digitalin. The same is true for the tubers of tulip (Tulipa) and hyacinth (Hyacinthus).

Toxicity is an intrinsic part of the plant world and it is generally not possible to know at a glance whether a species contains a toxic substance. Throughout the course of evolution, animals have of course developed countermeasures to defend themselves against these substances. The cabbage butterfly is able to metabolize the toxic compounds in cabbage.

But man? To navigate this treacherous terrain, man developed cuisine. With a cultural trait, not an evolutionary process, man managed to overcome myriad restrictions to its diet. Through cooking, many enzyme inhibitors, often proteins or polypeptides, are denatured by heat and rendered completely inert. Many toxic substances are oxidized by heat in non-hazardous substances, or are diluted in water when boiling; solubilized; and safely discarded.

The moment when humans learned to produce and dominate fire—to cook—was an authentic revolution. Yes, with fire we improved our means of defending ourselves, staying active in darkness, and creating tools. But these are not the most important advances that came with Level 14. The most essential one was cuisine. With cooking, mankind won the most vital of wars, the one for food. With fire and cooking, man was ready for agriculture and the birth of civilization.

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