It was the deadliest epidemic in human history. It circled the globe in a few months, killing more than 20 million people. Some cities and towns saw thousands perish in a few short weeks. In some remote villages, more than half the population died. The epidemic emerged out of nowhere, sickened and killed millions, then disappeared as quickly as it had come. The most deadly plague in human history remains largely a mystery.

Shocking as it may seem, humanity's deadliest epidemic occurred not in the Middle Ages, not in the time of the waves of bubonic plague that devastated Europe centuries ago, but in this century.

The influenza epidemic that traversed the globe from September 1918 through March 1919 left more than 20 million dead-in sheer numbers, far more than any previous plague. In New York City alone more than 33,000 died.

Time magazine estimated that, if a similar killer-flu virus emerged today, modern travel would allow it to spread worldwide in four days rather than the four months it took in 1918. The magazine estimated that some 60 million could die-triple the 20 million of 80 years ago.

Scientists are only now beginning to unravel the secrets of that extraordinary epidemic. How could an influenza virus-known primarily for its ability to produce aches, fevers and coughs-turn so deadly?

In recent years we have begun to see that the world of microorganisms is far more diverse-and unstable-than we had thought. As new technologies have enabled scientists to unveil and study the genetic makeup of living things, some of their discoveries are increasingly disconcerting.

The incredible variety and diversity of life we see around us is mirrored in the microscopic world-also all around us, but largely unseen and unnoticed. Just as humans and animals reproduce and pass on their diverse genetic traits to their offspring, so do the other tiny creatures all around us.

And occasionally something goes wrong.

Scientists think this is what happened in 1918. Several have concluded that a strain of flu mutated and crossed from swine to humans. The strain then spread around the world in the mass movement of soldiers and civilians in World War I.

Somewhere along the way, the virus apparently mutated further. Its particular genetic makeup differed so greatly from other flu strains that many people had no natural immunity and thus were defenseless. The mutated virus claimed millions of victims before it ran its course and apparently disappeared.

This crossover from animals to humans is not without precedent. Some scientists think that such news makers as the Ebola virus and HIV crossed from animals to humans, and our lack of any natural resistance helps explain why they are so lethal to humans.

Some researchers think the flu virus of 1918 first migrated from birds to pigs before it spread to humans-and thus the desperate slaughter of every chicken, duck and goose in Hong Kong when a different flu strain jumped from these domesticated birds to humans and started a miniepidemic there earlier this year.

As Time described the chain of events in Hong Kong, "while the rest of the world was wringing its hands over the remote threat from such exotics as Ebola and hantavirus, the health officials were busy staring down a far more likely global disaster . . ."

Could an epidemic like the 1918 flu outbreak happen again? Some researchers think we came perilously close just a few months ago and that it is just a matter of time before something similar-or worse-comes to pass.

Read the articles in this issue to discover what the Bible has to say about the possibility of future epidemics. But keep in mind that beyond the trauma prophesied to come lies the long-promised world of tomorrow. To discover more about this magnificent age to come, please request our free booklet The Gospel of the Kingdom. GN