An Edible History of Humanity Read Free Page A

genetic modification ever undertaken. It is a complex technology,
     developed by humans over successive generations to the point where maize was ultimately incapable of surviving on its own
     in the wild, but could deliver enough food to sustain entire civilizations.

    CEREAL INNOVATION
    Maize is merely one of the most extreme examples. The world’s two other major staples, which went on to underpin civilization
     in the Near East and Asia respectively, are wheat and rice. They too are the results of human selective prcesses that propagated
     desirable mutations to create more convenient and abundant foodstuffs. Like maize, both wheat and rice are cereal grains,
     and the key difference between their wild and domesticated forms is that domesticated varieties are “shatterproof.” The grains
     are attached to a central axis known as the rachis. As the wild grains ripen the rachis becomes brittle, so that when touched
     or blown by the wind it shatters, scattering the grains as seeds. This makes sense from the plant’s perspective, since it
     ensures that the grains are only dispersed once they have ripened. But it is very inconvenient from the point of view of humans
     who wish to gather them.
    In a small proportion of plants, however, a single genetic mutation means the rachis does not become brittle, even when the
     seeds ripen. This is called a “tough rachis.” This mutation is undesirable for the plants in question, since they are unable
     to disperse their seeds. But it is very helpful for humans gathering wild grains, who are likely to gather a disproportionate
     number of tough-rachis mutants as a result. If some of the grains are then planted to produce a crop the following year, the
     tough-rachis mutation will be propagated, and every year the proportion of tough-rachis mutants will increase. Archaeologists
     have demonstrated in field experiments with wheat that this is exactly what happens. They estimate that plants with tough,
     shatterproof rachises would become predominant within about two hundred years—which is roughly how long the domestication
     of wheat seems to have taken, according to the archaeological record. (In maize, the cob is in fact a gigantic shatterproof
     rachis.)
    As with maize, proto-farmers selected for other desirable characteristics in wheat, rice, and other cereals during the process
     of domestication. A mutation in wheat causes the hard glumes that cover each grain to separate more easily, resulting in “self-threshing”
     varieties. The individual grains are less well protected as a result, so this mutation is bad news in the wild. But it is
     helpful to human farmers, since it makes it easier to separate the edible grains after beating sheaves of cut wheat on a stone
     threshing floor. When grains were being plucked from the floor, small grains and those with glumes still attached would have
     been passed over in favor of larger ones without glumes. This helped to propagate these helpful mutations.
    Another trait common to many domesticated crops is the loss of seed dormancy, the natural timing mechanism that determines
     when a seed germinates. Many seeds require specific stimuli, such as cold or light, before they will start growing, to ensure
     that they only germinate under favorable circumstances. Seeds that remain dormant until after a cold spell, for example, will
     not germinate in the autumn, but will wait until after the winter has passed. Human farmers would often like seeds to start
     growing as soon as they are planted, however. Given a collection of seeds, some of which exhibit seed dormancy and some of
     which do not, it is clear that those that start growing right away stand a better chance of being gathered and thus forming
     the basis of the next crop. So any mutations that suppress seed dormancy will tend to be propagated.
    Similarly, wild cereals germinate and ripen at different times. This ensures that whatever the pattern of rainfall, at least
     some of