Two ecosystems--the fragile, naturally evolved net. works of relations among organisms in a stable environment-commingled and clashed when Columbus waded ashore. The reverberations from that historic encounter often called the Columbian exchange-echoed for centuries after 1492.
The flora and fauna-as well as the peoples of the Old and New Worlds had been separated for thousands of years. European explorers marveled at the strange sights that greeted them, including exotic beasts such as iguanas and "snakes with castanets" (rattlesnakes).
Native New World plants such as tobacco, maize, beans, tomatoes, and especially the lowly potato eventually revolutionized the international economy as well as the European diet, feeding the rapid population growth of the Old World. These foodstuffs were among the most important Indian gifts to the Europeans and to the rest of the world.
Perhaps three-fifths of the crops cultivated around the globe today originated in the Americas, Ironically, the introduction into Africa of New World foodstuffs like maize, manioc, and sweet potatoes may have fed an African population boom that numerically, though not morally, more than offset the losses inflicted by the slave trade.
In exchange the Europeans introduced Old World crops and animals to the Americas. Columbus returned to the Caribbean island of Hispaniola (present-day Haiti and the Dominican Republic) in 1493 with seventeen ships that unloaded twelve hundred men and a virtual Noah's Ark of cattle, swine, and horses.
The horses soon reached the North American mainland through Mexico. Over the next two centuries, they spread as far as Canada. Southwestern Indian tribes like the Comanche, Apache, and Navajo swiftly adopted the horse; northern tribes like the Lakota. Shoshone, and Blackfeet somewhat later.
Horses transformed newly mounted cultures into highly mobile wide-ranging hunter-warrior societies that roamed the grassy Great Plains in pursuit of the shaggy buf falo and that suppressed unmounted peoples like the Paiute.
Columbus also brought seedlings of sugar cane, which thrived in the warm Caribbean climate A "sugar revolution" consequently took place in the European diet, fueled by the forced migration of mil lions of Africans to work the canefields and sugar mills of the New World.
Unwittingly, the Europeans also brought other organisms in the dirt on their boots and the dust on their clothes, such as the seeds of Kentucky bluegrass, dandelions, and daisies.
Most ominous of all, in their bodies they carried the germs that caused smallpox, yellow fever, and malaria.
Old World diseases quickly devastated the Native Americans.
During the Indians' millennia of isolation in the Americas, most of the Old World's killer maladies had disappeared from among them.
But generations of freedom from those illnesses had also wiped out protective antibodies. Devoid of natural resistance to Old World sicknesses, Indians died in droves.
Within fifty years of the Spanish arrival, the population of the Taino natives in Hispaniola dwindled from some 1 million people to about 200.
Enslavement and armed aggression took their toll, but the deadliest killers were microbes, not muskets. The lethal germs spread among the New World peoples with the speed and force of a hurricane, swiftly sweeping far ahead of the human invaders; most of those afflicted never laid eyes on a European.
In the centuries after Columbus's landfall, as many as 90 percent of the Native Americans perished, a demographic catastrophe without parallel in human history.
This depopulation was surely not intended by the Spanish, but it was nevertheless so severe that entire cultures and ancient ways of life were extinguished forever. Baffled, enraged, and vengeful, Indian slaves sometimes kneaded tainted blood into their masters' bread, to little effect.
Perhaps it was poetic justice that the Indians unintentionally did take a kind of revenge by infecting the early explorers with syphilis, injecting that lethal sexually transmitted disease for the first time into Europe.