Who Loves Grass Seeds?
Today’s cereals were once wild grasses. The process of wild seeds becoming cultivated varieties is known as domestication. Ancient hunter-gatherers selectively cultivated plants that were the wild progenitors of wheat, oat, barley, maize, rice, etc. They must have been eating wild grass seeds before starting to cultivate. But why? Wild seeds are tiny and difficult to thresh and husk. They are not tasty either. Yet, archaeological records show that several prehistoric societies harvested wild grass seeds, even though they were not in a food crisis.
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The Natufian people lived in the Mediterranean side of the Near East (the land now belonging to Lebanon, Israel, and Palestine and historically known as the Levant) about 13,000–14,000 years ago. The region was then a lush green grassland interspersed with groves of oak and pistachio trees. Plenty of nuts and fruit, as well as game animals, including gazelles, deer, horses, wild boar, goats, and sheep, were available there. The Natufians built semi-subterranean circular houses and lived there like villagers. They were not farmers but used stone-made sickles to harvest wild grass seeds, such as einkorn wheat, emmer wheat, and rye.
Ofer Bar-Yosef and Anna Belfar-Cohen proposed an explanation for why they chose to eat grass seeds. Humans need both protein and energy (calories) in their diet. Nuts provided a lot of calories in the Natufian diet, but those were available only in the fall. If Natufians failed to store enough nuts for the whole year, they could face a calorie shortage in the late spring and summer. Grass seeds could fill the gap if the Natufians compromised on taste. Bar-Yosef and Belfar-Cohen have calculated that a hunter-gatherer band of 15–20 people could live within a 12-kilometer square territory in the Levant if they were willing to eat gritty grass-seed flour. Alternatively, they would have to walk a long distance every day to pick more nuts from a wider foraging area. The Natufians apparently preferred eating seeds to walking longer.
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Cardiologists may praise the hunter-gatherer way of life because of their daily walk. But nomads themselves prefer the physically less straining option, even at some price. This choice conforms to the principle of least effort, first mentioned by the Harvard linguist George Kingsley Zipf. He noticed that when speaking, people often use abbreviations, such as math, for mathematics, to save effort. Although discovered in language research, this rule points to a fundamental human trait—energy conservation. We try to accomplish everything with minimal physical activity, like cutting corners and taking the car to travel only a kilometer.
There are two ways to conserve energy in our food strategy. One may spend less energy obtaining food or eat foods containing more calories. Ordering a meal delivery instead of cooking is an example of the first approach, while choosing a burger instead of a salad is an example of the second. People often find a strategy that gives the best overall efficiency. The Natufians added grass seeds to their diet to achieve that. All species in nature try to follow a subsistence strategy that gives them optimal net energy: calories from food minus calories spent on gathering it. In hunting and gathering, such a strategy is known as “optimal foraging.” Animals have evolved to achieve amazing levels of fine-tuning in their foraging practices.
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Howard Richardson and Nicholaas Verbeek studied the food-gathering strategy of crows that feed on clams found on the beaches of America’s northwestern coast. These crows look for clams buried in the sand. A crow spends some time searching for and digging up a suitable clam, holds it in its beak, and then flies to a rock onto which it can drop the clam to open it up. It takes less energy to search than to fly and break the clam. Ideally, the crow will want to get maximum nutrition in a certain time. Random picking may minimize the search time, but the collected clams may be too small to provide enough nutrition most of the time. On the other hand, if too much time is spent looking for giant clams, the crow may end up carrying too few. The researchers theoretically estimated that the bird should exclude clams under 28.5 mm for optimal foraging. Amazingly, the crows actually follow that selection rule; they rarely pick a clam smaller than the optimal size.
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When an ecosystem changes due to climatic or other reasons, food resources in that environment may alter drastically, so the species living there must find a new optimal foraging strategy. Both climate change and readjustment of diets may take many years to settle, which is why such changes are usually discovered in archaeology, where changes over thousands of years can leave their marks in the ground. For example, the archaeologist Kent Flannery noticed that ancient humans of the Near East began to eat a broader range of foods at the end of the Ice Age. They were hunting smaller animals and eating more wild cereal seeds. He called this phenomenon the Broad Spectrum Revolution.
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It is rare to observe such a broadening of diet in real-time. One such opportunity arose in 1983 in the Caribbean Sea when a sea urchin species known to zoologists as Diadema antellerum suffered mass extinction. The urchin was the favorite food of the queen triggerfish living in the area’s coral reefs. Since the disaster, the queen triggerfish have adapted to a new dietary pattern. Luckily, a study of queen triggerfish was conducted in 1967, so another study done after the disaster could discover the changes. J.E. Randall of Hawaii University conducted the first study. Peter Reinthal and Sara Lewis of Duke University and Brian Kensley of the Smithsonian Institution conducted the second study.[i] Before their depletion, Diadema sea urchins comprised 73 percent of the triggerfish’s diet, followed by crabs, at only 5.4 percent, and bivalve mollusks, at 4.6 percent. After the depletion of the Diadems, crabs moved to the top place at 48.4 percent. The two species, now in second and third place, accounted for 11.1 percent and 4.4 percent of the diet, respectively. This new, somewhat flattened diet curve is precisely what the Optimal Foraging Theory predicts.
This theory helps us understand how grass seeds found a prominent place in the human diet at some point in time. We now know that the Broad Spectrum Revolution happened due to a drastic environmental change, which will be discussed in the next section. With the end of the Ice Age, large animals that once provided a large portion of calories in the human diet disappeared. As we saw earlier, the Natufian people of the period began to eat more cereals, i.e., wild grass seeds, as part of an optimal foraging strategy. As their taste buds adjusted to the blandness of seed flour, something else also happened. At some point, they began cultivating the seeds. Wild seeds became larger and tastier, and finally, the present-day cereals, resulting from centuries of cultivation.
The process is known as domestication. It is a process in which humans and nature work together. Human participation involves repeated cultivation and selective harvesting of crops, sowing only the best seeds. On its part, nature responds by mutating the crop to make it tastier and the yield bigger. A key mutation changed how seeds break away from the stem to propagate. Wild plants shed seeds automatically; the shell covering the seed shatters when ripe. The ground soil and water help the seed germinate and propagate. This natural cycle is inconvenient for farmers because plants shed seeds as soon as they are ripe, so they have a narrow harvest window. The domestication process solves the problem using a biological mechanism. Along with shattering seeds, many wild plants also produce a small proportion of “non-shattering” seeds. These seeds remain attached to the stalk even when ripe. Farmers increased the proportion of non-shattering seeds by selecting and sowing these seeds year after year. In nature, non-shattering seeds are a waste, but in collaboration with humans, these seeds become the vehicles of domestication.
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Ancient farmers must have collected ripe seeds after shattering had begun. With most normal seeds already fallen to the ground, this strategy would give them a harvest with a good proportion of non-shattering variety. Those seeds were resowed for the next crop. Patricia Anderson carried out an experimental simulation of the ancient practice. She found that wild strains would still dominate the ground unless resowing was done in a new plot every time.[ii] This method would help eliminate plants grown from normal seeds that had fallen on the ground.
End Notes:
[i] Peter N. Renthal, Brian Kensley, and Sarah M. Lewis; “Dietary Shift in Queen Trigger Fish (Balistes vetula) in the Absence of it Primary Food Item (Diadema antelerrum)”; P. S. Z. N. I: Marine Ecology, 5 (2): 191-195 (1984)
[ii] Steven Mithen; After the Ice; Harvard University Press; 2006