An alarming tide of new and resurgent diseases has been rising around the world for decades.

Diseases now advance faster than ever and this signals a crisis in the history of the human species.

Humans have brought it on by rending the fabric of our environment, changing our behavior, and ironically, by our inventiveness in increasing the length and quality of our lives.

For each new disease known to the general public, there are a dozen others because the wheels of biological changes keep turning faster.

The shared evolution of humans and microbes has accelerated to a frenzied pace, because of changes we have made in our environment and our lifestyles.

The scientific and historical research regarding diseases is fragmented, like pieces of a mosaic rarely assembled in more than bits and patches.

We have been slow to understand that we live in a new biocultural era. For decades, we cherished the myth that infectious diseases were fading forever.

This was a posture born of inherited optimism, The nineteenth century generated an almost religious faith in social, scientific, and technological progress.

Such optimism enabled people to call the slaughter of 1914-1918 a war to end all wars. The two great global epidemics of that era, typhus and type A influenza, each killed 20 million people or more, dwarfing the toll of combat, without blunting popular faith in medical progress.

At first, events seemed to justify such optimism. More than a half century would pass before the arrival of AIDS, another epidemic that kills by the millions.

Those decades brought cleaner food and water, better living conditions, polio vaccine, antibiotics, the eradication of smallpox, and huge reductions of such killers as tuberculosis, cholera, and syphilis. Life spans increased, and in some places almost doubled. World War II was the first major war in which epidemics took far fewer casualties than battle.

Now, just a few generations later, it is difficult to appreciate how astonishing all this was

For 10,000 years, since the first hunter-gatherers settled in villages, infections had killed more people than war and famine. Suddenly, by the 1930s, a new era of fitness and longevity was arriving; to many, it promised an end to all infectious diseases.

Cities of the future were portrayed as sparkling under plastic bubbles no germ or poison could penetrate. From now on, medicine's great task would be treating cancer, clogged arteries, stress, and the other so-called diseases of civilization and of aging.

In 1969, the U.S. surgeon general, Dr. William H. Stewart, told the nation that it had already seen most of the frontiers in the fields of contagious diseases.

A decade later, the governments of the United States, Canada, and Great Britain announced that their citizens must recognize a radical transformation; they were threatened no longer by microbes but by their own heedlessness.

Drinking, smoking, and driving without seat belts had replaced bubonic plague, smallpox, and cholera. The authorities had a point, but they failed to mention such expanding avenues of infection as drugs, sex, rapid world travel, new medical procedures, and environmental degradation.

As "developed" nations indulged visions of an antiseptic age, new diseases were already appearing

At first, they arose mostly in remote parts of Africa and Asia. In the 1960s and 1970s, new diseases struck with greater impact and visibility.

The 1980s brought more reports of new diseases, drug-resistant bacteria, and thriving disease carriers, from mosquitoes to household pets.

Infections once limited to small areas were spreading; Lyme disease and Rocky Mountain spotted fever, once local concerns, ranged from coast to coast.

AIDS became, inevitably, a national obsession. At the same time, a trickle of environmental warnings swelled to a dire stream.

Pollutants, carcinogens, and ecological threats from the groundwater to the ozone layer were said to threaten the health of the entire biosphere. Yet, few people made the connection between environment and epidemiological changes.

In the 1990s, we saw that for each disease conquered, another emerged or re-emerged. Scores of infections shattered the dream of a sanitary utopia, where only genetic controls on aging limited the human life span.

Part 2 of 4.