GUNS, GERMS AND STEEL - Cloverport Independent Schools

APPLES OR INDIANS • 1 3 7
tional changes had to be made in them under cultivation. As we discussed
in the preceding chapter, the principal changes—the breakdown of the
natural systems of seed dispersal and of germination inhibition—evolved
automatically and quickly as soon as humans began to cultivate the seeds
in fields. The wild ancestors of our wheat and barley crops look so similar
to the crops themselves that the identity of the ancestor has never been in
doubt. Because of this ease of domestication, big-seeded annuals were the
first, or among the first, crops developed not only in the Fertile Crescent
but also in China and the Sahel.
Contrast this quick evolution of wheat and barley with the story of
corn, the leading cereal crop of the New World. Corn's probable ancestor,
a wild plant known as teosinte, looks so different from corn in its seed and
flower structures that even its role as ancestor has been hotly debated by
botanists for a long time. Teosinte's value as food would not have
impressed hunter-gatherers: it was less productive in the wild than wild
wheat, it produced much less seed than did the corn eventually developed
from it, and it enclosed its seeds in inedible hard coverings. For teosinte to
become a useful crop, it had to undergo drastic changes in its reproductive
biology, to increase greatly its investment in seeds, and to lose those rocklike
coverings of its seeds. Archaeologists are still vigorously debating how
many centuries or millennia of crop development in the Americas were
required for ancient corn cobs to progress from a tiny size up to the size
of a human thumb, but it seems clear that several thousand more years
were then required for them to reach modern sizes. That contrast between
the immediate virtues of wheat and barley and the difficulties posed by
teosinte may have been a significant factor in the differing developments
of New World and Eurasian human societies.
A third advantage of the Fertile Crescent flora is that it includes a high
percentage of hermaphroditic "selfers"—that is, plants that usually pollinate
themselves but that are occasionally cross-pollinated. Recall that most
wild plants either are regularly cross-pollinated hermaphrodites or consist
of separate male and female individuals that inevitably depend on another
individual for pollination. Those facts of reproductive biology vexed early
farmers, because, as soon as they had located a productive mutant plant,
its offspring would cross-breed with other plant individuals and thereby
lose their inherited advantage. As a result, most crops belong to the small
percentage of wild plants that either are hermaphrodites usually pollinating
themselves or else reproduce without sex by propagating vegetatively