Green Planet: How Plants Keep the Earth Alive

Chapter Ten: How Agriculture Changed the World

[196] chapter ten HOW AGRICULTURE CHANGED THE WORLD I wish I was a despot that I might save the noble, the beautiful trees that are daily falling sacrifice to the cupidity of their owners, or the necessity of the poor. . . . The unnecessary felling of a tree, perhaps the growth of centuries, seems to me a crime little short of murder. —THOMAS JEFFERSON Plants keep the world, including the human world, alive in many ways, as explained in the preceding chapters. But there is a particularly special way in which plants maintain our existence and support the entire human economy: agriculture. In prehistoric times, when there were only a million people in the world, hunting and gathering was sufficient to feed the human species. But for thousands of years, most humans have been dependent not on wild foods but on food that they raise on farms. Today, with more than six billion people, the survival of most humans would be unthinkable without agriculture. We tend to think of agriculture as the use of crop plants for human benefit. We think of crop plants as our slaves. But these plants also benefit from agriculture. In fact, crops depend on humans. Agricultural plants have been bred into forms that are unable to survive in the wild. It is just as valid to think that humans serve the interests of the crop plants as it is to think that they serve us. We prepare the ground, plant the seeds, water and fertilize the plants, harvest the seeds, and save some of them for the next year. As science writer Michael Pollan points out, the most successful plants are those that get us to serve them by producing things that we need, or that we simply want. We have turned much of the forest and prairie into an 80 million–acre corn lawn, says CH010.qxd 11/12/08 11:01 AM Page 196 How Agriculture Changed the World [197] Pollan; by creating cornfields, we have swept away all of the other plants with which corn would otherwise have to compete.1 An Agricultural History of the Human Race Historians have long debated how agriculture began. Some scholars used to believe that agriculture was invented by a brilliant man in a tribal society of hunter-gatherers. Other scholars pointed out that, because women gathered most of the plant materials, agriculture was probably invented by a woman. Both the brilliant-man and the brilliant-woman theories are incorrect, however, because agriculture could not have been invented in a single step by anyone. Agriculture had to evolve, because unmodified wild plants, such as the wild ancestors of wheat, are unsuitable for agriculture, in four ways. First, the seeds of most wild plant species are dormant when they are mature. That is, when planted, the seeds will not germinate. Many wild seeds require a period of exposure to cool, moist conditions before the seed can germinate. If a brilliant man or woman planted a seed from a wild plant, it would not have grown, and he or she would have rightly concluded that agriculture was not a good idea. Second, the seeds of many wild grains shatter (fall off of the stem) as soon as they are mature. Because the whole point of the seed is to grow in a new location, shattering is beneficial to the plant, but it is extremely inconvenient for a human harvester. Third, the seeds of many wild plant species contain toxins. And finally, the seeds of many wild grains are small. Furthermore, the advantages of primitive agriculture would not have been immediately apparent to intelligent hunter-gatherers. Agriculture requires intense labor. Modern hunter-gatherers often barely eke out an existence in marginal habitats such as the Kalahari Desert or Great Outback; but these are the habitats to which tribes and nations with more advanced tools have driven them. Before agriculture, many tribes lived in rich habitats in which hunting and gathering in many cases provided a comfortable level of existence. For these reasons also, agriculture had to evolve gradually. CH010.qxd 11/12/08 11:01 AM Page 197 green planet [198] Agriculture, therefore, required a gradual origin, through an evolutionary process, which most likely occurred in the following way.2 Through most of the history of the human species, omnivorous people hunted animals and gathered plants. Because of the toxins and other defenses in the wild plants, humans had...