The World Without Us

Deserts like the Sahara, the Gobi, and Chile’s Atacama, where desiccation is near-total, occasionally yield natural human mummies, with intact clothing and hair. Thawing glaciers and permafrost sometimes give up other long-dead, eerily preserved predecessors of we, the living, such as the leather-clad Bronze Age hunter discovered in 1991 in the Italian Alps.

There won’t be much chance, however, for any of us presently alive to leave a lasting mark. It’s rare these days for anyone to be covered with mineral-rich silt that eventually replaces our bone tissue until we turn into skeleton-shaped rocks. In one of our stranger follies, we deny ourselves and our loved ones the opportunity of a true lasting memorial—fossilhood—with extravagant protections that, in the end, only protect the Earth from being tainted by us.

THE ODDS OF us all going together, let alone soon, are slight, but within the realm of possibility. The chance that only humans will die, leaving everything else to carry on, is even more remote, but nevertheless greater than zero. Dr. Thomas Ksiazek, chief of the Special Pathogens Branch at the U.S. Centers for Disease Control, is paid to worry that something could take out many millions of us. Ksiazek is a former army veterinary microbiologist and a virologist, and his consultations range from threats of biological attack to hazards that unexpectedly jump from other species, such as the SARS coronavirus he helped to characterize.

Grim as those scenarios are, especially in an age when so many of us live in oversized Petri dishes called cities, where microbes congregate and flourish, he doesn’t see an infectious agent arising that could wipe out the entire species. “It would be unparalleled. We work with the most virulent, and even with those there are survivors.”

In Africa, periodic horrors like the Ebola and Marburg viruses have slain villagers, missionaries, and so many health care workers that the rest fled their hospitals. In each instance, what finally broke the chain of contagion was simply getting staff to wear protection and scrub with soap and water—often lacking in poor areas where such diseases usually begin— after touching patients.

“Hygiene is the key. Even if someone tried to introduce Ebola intentionally, though you might get a few secondary cases in families and hospital staff, with sufficient precautions it would die out rapidly. Unless it mutated to something more viable.”

High-hazard viruses like Ebola and Marburg originate in animals— fruit bats are suspected—and are spread among people through infected body fluids. Since Ebola finds its way into the respiratory tract, U.S. Army researchers at Fort Detrick, Maryland, tried to see if a terrorist might be able to concoct an Ebola bomb. They created an aerosol capable of spreading the virus back to animals. “But,” says Ksaizek, “it doesn’t make respiratory particles small enough to be easily transmissible to humans via coughing or wheezing.”

But if one Ebola strain, Reston, ever mutated, we might have a problem. Currently, it kills only nonhuman primates; unlike other Ebolas, however, it is believed to attack through the air. Similarly, if highly virulent AIDS, which is currently passed through blood or semen, were ever to become airborne, it could be a real species-stopper. That’s unlikely, Ksiazek believes.

“Possibly it could change its transmission route. But the current way is actually advantageous to HIV’s survival because it allows victims to spread it around awhile. It evolved into that niche for a reason.”

Even the deadliest airborne influenzas have failed to wipe out everyone, because people eventually develop immunity and pandemics fizzle. But what if a psychotically obsessed, biochemically trained terrorist creatively spliced something together that evolves faster than we develop resistance—maybe by clipping genetic material into the versatile SARS virus, which could spread both sexually and via the air before Ksaizek helped eradicate it?

It would be possible to design for extreme virulence, Ksaizek allows, although, as in transgenic pesticides, results of genetic manipulation aren’t guaranteed.

“It’s like when they breed mosquitoes to be less capable of transmitting a viral disease. When they release these lab-bred mosquitoes, they don’t compete very well. It’s not as easy as just thinking about it. Synthesizing a virus in the lab is one thing; making it work is another. In order to repackage it as an infectious virus, you need a constellation of genes that will let it infect a host cell, then make a bunch of progeny.”

He chuckles mirthlessly. “People trying might kill themselves in the process. There are a lot of easier things to do with a lot less effort.”