The Triumph of Seeds (6 page)

The strong ties binding people and grasses date to the roots of agriculture itself, when plant gatherers began to choose and manipulate their staples from the myriad wild species around them. Grains figured prominently in the founding of virtually every early civilization: barley, wheat, and rye in the Fertile Crescent (10,000 years ago), rice in China (8,000 years ago), corn in the Americas (5,000 to 8,000 years ago), and sorghum and millet in Africa (4,000 to 7,000 years ago). Some think the human reliance on grains (and other seeds) began much earlier, but regardless of when it started, our grass habit relies on specific traits found within the seeds. Unlike an avocado pit, where fat cotyledons fuel slow, steady growth in the shade, grass seeds evolved for life on the plains, where a quick start is the key to success. They are tiny and prolific and eager to sprout, traits that make grasses an ideal food crop and a dominant plant on virtually any patch of open ground. No toothpicks or water glasses are necessary to watch grass seeds grow. A woodpile and a January rainstorm will do the job nicely.

E
veryone needs a hobby. Biologists, however, often run the risk of redundancy on their days off. Does it count as a vacation when I head outside to watch birds, catch bees, or look at plants? I do play bass in a jazz band, but anyone tallying my free moments would find one thing taking up more time than any other: firewood. We live in
a 1910 farmhouse that was once sawn in half, loaded onto a flatbed truck, and hauled five miles down a country road to its present location. Patching it back together resulted in a charming but drafty structure that no amount of fiberglass batting can properly insulate. As a result, it’s a rare day that doesn’t find me sawing, splitting, stacking, or restacking some portion of the four cords we burn every year to cook and keep warm.

Finding all that fuel has turned me into a bona fide wood scrounge, combing the roadsides after every windstorm, and pestering neighbors and relations for tips on surplus timber. I’ll take anything, and so I was happy to help clean up the old madrona logs cluttering a friend’s yard. Madrona trees belong in the heather family and look like giant rhododendrons, their curving trunks and branches covered in a beautiful reddish bark. As I set to work, it struck me as odd that this madrona was decidedly green. Looking closely, I soon saw why. Having sat outside for more than a year, surrounded by tall meadow grasses, these logs and branches had collected seeds in every crack and crevice. And now they were beginning to sprout. Swollen with recent rains, each tiny grain had sent up a spear of purest green, giving the surface of the wood a decidedly fuzzy, grassy look. If the Chia Pet folks offered their wares in a woodpile motif, this would have been it.

I pulled up one of the little grasses and found the faintest husk of a seed remaining, a thin, split thing where the base of the green shoot turned pale. Rather than invest in fat cotyledons, grasses endow their offspring with only a modest lunch and rely instead on fecundity—broadcasting droves of seed in the hope that a few will find purchase. Where a pampered avocado tree might yield 150 single-seeded fruits annually, I recently counted 965 seeds on the wispiest looking bent-grass growing in our driveway. The food stored in a grass seed gives that baby plant enough energy for a quick growth spurt, but would never keep it alive for long in the shade. Instead, young grasses depend on finding open,
unoccupied real estate. They prefer soil, but will also germinate on pavement, in gutters, or on the running boards of old pickup trucks. Some species thrive in
sand or on mud flats, or make a quick living colonizing the shifting gravel of riverbanks. To rock climbers everywhere, grass seeds create the constant need for “gardening,” yanking tufts of new greenery from the tiny cracks and crevices that both climbers and plants hope to cling to.

Contrary to popular belief, watching grass grow can actually be quite riveting—a story of derring-do combined with sheer tenacity. Though I hated passing up free firewood, I left a stack of the grassy madrona in place to let the drama unfold. Six months later, the meadow lay baked in summer sunshine. I returned to find the logs in their pile, but with hardly a trace of that promising green fringe. Nearly every seedling had withered in the heat, exhausting its tiny lunch long before a root could stretch down to reliable water. But one plant had survived. From the split end of a log near the bottom of the pile, a tuft of velvet grass now sprouted, its tall flower stalk rising upward to sway in the breeze. I carefully lifted the wood and saw where roots had threaded their way through a crevice to find the soil below. In general, scattering seeds on woodpiles spells a death sentence for the baby plants inside. But this one success story, with the hundreds of seeds it would produce, helped justify the tactic.

While a grass’s profligacy might not have the cozy, nurturing appeal of the well-stocked lunches found in avocados, nuts, legumes, and other plump seeds, it’s certainly a
successful strategy. Programmed for colonization and survival, the tiny grains of most species can withstand desiccation and long periods of dormancy, traits that help grasses dominate almost every earthly habitat too arid for trees and shrubs. Even Antarctica boasts native grasses, and if you lined up all the flowering plants on earth, nearly one in twenty would be a grass. Ubiquity alone, however, does not a staple make. For all their prolific seed, grasses would hardly be so vital to people without a trick of chemistry. That trick lies in the way they pack their lunch.

D
issecting a grass seed takes steady hands, and if you decide to try it, I suggest skipping the afternoon coffee. My jittery attempts sent
half a dozen wheat grains skittering off the desk before a clean slice finally revealed the pertinent feature: a mass of starch granules that glowed like lumpy marbles in the light of my microscope. Of all the ways that seeds can store energy, from oils and fats to proteins, none makes a better staple food for people than starch. It’s built from long chains of glucose molecules, like sugar beads on a flimsy necklace. Enzymes in the human intestine, and even in our saliva, can break that necklace easily and release the sugars. Tweak the chemistry of starch ever so slightly, however, and you get cellulose, the indigestible plant fiber that makes up stems, twigs, and the trunks of trees. Cellulose and starch differ only in how their glucose chains hold together, a few repositioned atoms that change the flimsy string to an indigestible one,
like a steel wire. Without starch’s weak glucose bonds, and our ability to break them, grass seeds would pass through the human gut like a handful of sawdust. As it stands, the starch content of a grass seed can top 70 percent, quick energy that evolved to fuel plant growth but that now fuels over half of all human activity.

Given the abundance of grasses and their prolific, starchy seeds, it’s not surprising that our ancestors learned to take advantage of them. It seems that wherever people made the switch from hunting and gathering to cultivation, a grass or two lay at the heart of it. The civilizations that followed helped to cement our dependence on grass calories, and those few select species then spread to fields and garden plots around the world. But while historians have long considered the grain diet a relatively recent phenomenon, a product of the agricultural revolution, new thinking puts the seeds of grasses and other plants high on the human menu far into our nomadic, hunter-gatherer past.

“It’s absolutely reasonable to assume that seeds have been part of the diet forever,” Richard Wrangham told me. “After all, chimpanzees eat them.” As a professor of biological anthropology at Harvard University, Wrangham should know: he published his first paper on chimp feeding habits in the early 1970s, and has been studying them in the wild ever since. I first met Wrangham at a primatology
workshop in Uganda, where he and Jane Goodall kicked off the keynote address with a piercing exchange of chimpanzee pant-hoots and shrieks. Two decades later, he still knows how to get people’s attention. I called him at his Harvard office, where in spite of pressing research deadlines and a full teaching load, he sounded eager to explain his unorthodox new theory.

“I used to try and eat what the chimps ate,” he began, recalling his early fieldwork in Uganda’s Kibale Forest, “and I can tell you I was pretty hungry by the end of the day.” At first, Wrangham assumed that he just wasn’t suited to the fruits, nuts, leaves, seeds, and occasional raw monkey that made up the chimpanzee diet. But when he put his observations in the context of human evolution, a profound new idea emerged. It wasn’t the type of food that mattered, but how it was prepared. “I became convinced that we cannot survive in the wild on raw food. As a species, we are entirely dependent on using fire for food preparation. We are
the cooking ape.”

In spite of his bold ideas, Wrangham speaks carefully, building a case with the patience of someone accustomed to long hours of observation in the field. “My perspective comes from working with apes. I see humans as apes that have been modified,” he explained, noting our substantially smaller teeth, shorter intestines, and larger brains. He told me about the remarkable energy gain achieved through cooking—how roasting or boiling meats, nuts, tubers, and other primate foods increased digestibility by anywhere from a third for wheat and oats to as much as 78 percent for a chicken egg. Wrangham’s theory proposes cooking as the critical innovation separating advanced members of the genus
Homo
from their more ape-like ancestors. By shifting to a highly digestible, cooked diet, our forebears no longer needed the massive molars and expansive guts that apes need to process fibrous raw foods. And with so much more energy available, we could suddenly afford the metabolic demands of a larger brain.

Though still controversial, the logic of Wrangham’s thinking rings like a bell tone through the din of competing hypotheses. Traditionally, most anthropologists have emphasized the spear and
arrow side of the hunter-gatherer equation, attributing changes in dentition and brain size to better hunting techniques and a protein-rich diet. But Wrangham maintains that no quantity of raw meat (or other raw foods) could adequately nourish modern hominids, let alone spur their evolution. “On a strictly raw diet,” he explained, “you don’t have time for high-risk activities like hunting. If our ancestors ate like chimpanzees, they would have had to spend at least six hours a day just sitting around and chewing.”

By deemphasizing the importance of meat, the cooking-ape theory raises the profile of the gatherers, who brought in a much wider range of foods, from roots and honey to
fruit, nuts, and seeds. “Tubers were probably the fallback,” Wrangham mused, “but any rich seed would have been preferred when they could get it.” He noted how chimps seek out the roasted beans of
Afzelia
trees following forest fires, as well as the common indigenous practice of abandoning hunting during seasonal bonanzas of prime fruit, nuts, or honey. Just when grains became a staple, however, remains uncertain. Their caloric potential is huge, particularly when they are cooked, but they require an organized harvest and considerable processing. A definitive answer requires more evidence, or, as Wrangham puts it, “encouragement from archaeology.” Now that people are looking, however, that encouragement seems to be turning up everywhere.

For anyone interested in early human societies, the habits of recent hunter-gatherers
provide an invaluable comparison. Groups from warm climates traditionally derived between 40 and 60 percent of their calories from plant foods. Many relied on grass seeds, and not just those from the wild ancestors of familiar crops like wheat or rice. In Australia, Aboriginal societies made bread and porridge from grasses as diverse as arm millet, hairy panic, mulga grass, star grass, ray grass, and naked woollybutt. Native Americans near what is now Los Angeles harvested canary grass right up to the Spanish missionary period, and maygrass, a close relative, provided starch to tribal diets throughout the eastern seaboard. People near the Sea of Galilee were using stone tools to grind and process wild barley over
20,000 years ago, and in Mozambique, similar methods put sorghum on the menu 105,000 years ago. But perhaps the most tantalizing ancient grains of all come from Gesher Benot Ya’aqov in Israel, where signs of controlled fire date back 790,000 years. There, nestled amid the scrapers and charred flint, researchers unearthed a tiny handful of burnt seeds: feather grass, goat grass, wild oat, and barley. That discovery puts edible grains by the fireside deep in the era of
Homo erectus
, hundreds of millennia
before our species even evolved.

If Richard Wrangham is right, and this kind of archaeological encouragement continues, we may find that the caloric boost from eating cooked grains played a significant role in human evolution. But regardless of when grass seeds entered the diet, they were firmly established as staples by the time we settled down to farm. When that happened, however, our ancestors did away with the mulgas and woollybutts to concentrate on a few promising varieties. No place on earth illustrates that transition better than the ancient settlement of Tell Abu Hureyra, near the modern city of Aleppo, Syria. What started as a seasonal village for hunter-gatherers grew over time to an agricultural town with 4,000 to 6,000 permanent residents. Each era left behind a clear record of its activities, beautifully preserved in layers of sediment and debris. The early inhabitants enjoyed a diet of more than 250 different wild plant foods, with 120 kinds of seeds, including at least 34 different grasses. By the time farming was firmly established, however, that panoply had shrunk to lentils, chickpeas, and a few
varieties of wheat, rye, and barley.

This same pattern repeated itself whenever and wherever the agricultural revolution took hold: diverse wild diets gave way to ones focused on a few staple grains and other crops. With few exceptions, the chosen grasses share several important traits. They are annuals, an all-or-nothing life strategy that encourages plants to put their
resources into seed production. With only one growing season in which to live and reproduce, annuals have no need to invest in lasting stems and leaves but every reason to produce the kind of large, prolific seeds that make them an appealing target for cultivation.
In fact, the simple availability of large-seeded annuals may be the best predictor for the advent of agriculture. Thirty-two of the world’s fifty-six heaviest-seeded grasses occur in the Fertile Crescent or other parts of Eurasia’s Mediterranean zone, where many of the earliest civilizations flourished. As geographer Jared Diamond has observed, “that fact alone goes a long way toward
explaining the course of human history.”