Rise of the Bugs

The most important question not raised during the swine-flu panic could have been asked by a 6-year-old: where do viruses come from? The answer, it turns out, is simple, and scary: viruses come from a giant wellspring of diseases—also known as the environment—that grown-ups should be very careful not to disturb. Pathogens—viruses, bacteria and a wide variety of other parasites—appear in nature as unpredictable, minimalist terrors equipped with little genetic material of their own but the ability to make things up as they go. A bird-flu virus can rest coolly in pigs, then flare up in humans, scrambling genes from all three species in ways impossible to fully anticipate with vaccines. The SARS virus bided its time among palm civets (a kind of mongoose) and horseshoe bats before killing humans in 2002. And possibly the most diminutive of all, the retrovirus HIV emerged from the blood of wild monkeys to become the most efficient destroyer of the human immune system. With strong enough poison and infinitely transmutable genes, a single pathogen could lay deadly siege to the rest of the living world.

The reason this has yet to happen in our lifetimes is that, brilliant as nature is at devising ways to kill, it has also come up with countless ways to cope and survive. Put all the living species together and you have an impressive array of mechanisms to fend off pathogens or contain them in particular ecosystems that have defenses built in. This arrangement, however, is now under serious threat: humans, moving ever deeper into the wild to level forests, extract minerals and plant crops, are changing the balance of ecosystems the world over and taking these defenses apart. These warped ecologies become ground zero for new and deadly infectious diseases, which emerge and spread at an ever-greater rate. This amounts to "Armageddon in slow motion," says Eric Chivian, head of the Center for Health and the Global Environment at Harvard Medical School. Chivian, who shared the Nobel Peace Prize in 1985 for alerting the public to the dangers of nuclear proliferation, now says the danger to human health posed by a degraded planet is "no less devastating than a nuclear war … the ultimate impact might be just as catastrophic."

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