Evolution

The disease, as it happened, had been measles.

Mankind had always been prey to some diseases, of course: leprosy, yaws, and yellow fever were among the most ancient blights. Many of them were caused by microbes that would maintain themselves in the soil, or in animal populations — as yellow fever was carried by African monkeys. But people had had time, evolutionary time, to adapt to most such diseases and parasites.

With the coming of the new, dense communities had come new plagues — crowd diseases, like measles, rubella, smallpox, and influenza. Unlike the older illnesses, the microbes responsible for these diseases could only survive in the bodies of living people. Such diseases could not have evolved in humans until there were sufficiently dense and mobile crowds to allow them to spread.

But, if they infected crowds, they must have come from crowds. And so they had: crowds of animals, the heavily social herd creatures people now lived close to, animals in which the diseases had long been endemic. Tuberculosis, measles, and smallpox crossed to humans from cattle, influenza from pigs, malaria from birds. Meanwhile, with the building of grain stores, the vectors of infectious diseases — rats and mice and fleas and bugs — reached populations of unprecedented density. Still, those who survived developed resistance of some kind, though some of these mechanisms were clumsy, with damaging side effects. The mechanisms of adaptation operated too slowly, compared to the frenzied rate of change of human culture, to iron out the deficiencies.

But the hunter-gatherers at the farms’ expanding borders had no resistance. They were devastated, even as their lands were overwhelmed by their farmer neighbors.

This transition, from the old way of living to the new, was a crucial moment in human history. A mass, unconscious choice was being made between limiting population growth to match the resources available, as the hunter-gatherers of the past had done, or trying to increase food production to feed a growing population. And once that choice had been made, the farmers’ expansion could only accelerate. Henceforth the folk following the older ways would survive only in the most marginal environments, the fringes of deserts, the mountain peaks, the densest jungles — places the farmers could not tame.

It would happen in Africa, where Bantu farmers equipped with iron weapons would spread out of the western Sahara, overwhelming peoples like the pygmies and the Khoisan — ancestors to Joan Useb — at last marching all the way to the east coast of South Africa. It happened in China, where farmers from the north, aided by China’s interconnected geography, would march south to repopulate and homogenize much of tropical southeast Asia, driving existing populations ahead of them in secondary invasions that hit Thailand and Burma.

And the great east-west span of Eurasia proved especially conducive to expansion. Farmers spread easily along lines of latitude, moving into places with a similar climate and length of day to their origin, and so suitable for their crops and beasts. With their cattle and goats and pigs and sheep, their highly productive wheat and barley, and their swelling numbers, the descendants of the farmers of Cata Huuk would build a mighty dominion of wheat and rice. The pyramids of Egypt would be built by workers fed by crops whose ancestors had been native to southwest Asia. They would take their Indo-European language with them, but it would splinter, mutate, and proliferate, generating Latin, German, Sanskrit, Hindi, Russian, Welsh, English, Spanish, French, Gaelic. At last they would colonize a huge east-west band stretching from the Atlantic coast to Turkestan, from Scandinavia to North Africa. One day they would even cross the oceans, in boats of wood and iron.

All across this immense span of cultivated land cities would burgeon, and empires would flourish and decay, like mushrooms. And everywhere the farmers went they carried the great diseases with them, a vicious froth on a tide of language, culture, and war.

Juna said impulsively, "Sister, come with us."

Sion glanced at Keram and Muti, and laughed. "That will not be possible." With an expression of anguish, she peered at Juna’s children, who slept in the arms of Muti and Keram. Then she whispered, "Good-bye," and hurried back to the huts.

Juna made to call good-bye after her, but, she thought, that would be the last word I will ever speak in my own tongue. For I will never come back here. Never.

So, without speaking, she turned her face away and, with her children, resumed her steadfast walk to the west, and the new city on the coast.

CHAPTER 15 The Dying Light Rome. Common Era [CE] 482.

I

In Rome, the sun was bright, and the Italian air felt liquid to men used to the milder climes of Gaul. Everywhere lingered the immense stenches of the city: of fires, of cooking, and, above all, of sewage.