It is often said that in the centuries after Columbus landed in the

New World on 12 October 1492, more native North Americans died each year

from infectious diseases brought by European settlers than were born. They

fell victim to epidemic waves of smallpox, measles, influenza, bubonic plague,

diphtheria, typhus, cholera, scarlet fever, chicken pox, yellow fever, and

whooping cough. Just how many died may never be known. For North America

alone, estimates of native populations in Columbus’s day range from 2 to

18 million. By the end of the 19th century the population had shrunk to

about 530 000.

Staggering losses. But why, asked a perplexed French missionary working

among the Mississippi Valley’s Natchez in the 1700s, should ‘distempers

that are not very fatal in other parts of the world make dreadful ravages

among them’? The answer seems obvious enough: because native Americans had

no immunity to the imported diseases. This begs a larger question, however:

why the lack of immunity? And why had native North Americans no deadly diseases

to infect Europeans with in return? Here the answers are not so obvious,

for they have little to do with events after 1492. Rather they are intimately

linked with the peopling of the Americas more than 11 500 years ago.

But let’s start with Columbus. His reports of the New World jolted Europeans:

here was a land of exotic plants, animals and people. The great savants

scrambled to explain who the native North Americans were, where they had

come from, and when they had arrived. One popular idea was that they were

descendants of the Ten Lost Tribes of …