A Planet of Viruses: The diseases that drove history

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" A Planet of Viruses " : The diseases that drove history

A compelling new book explores the ways smallpox and other epidemics shaped our

lives, our ideas and even our DNA

By Leonard Cassuto, & Noble Review

If I told you that you have a virus, there's a good chance that you'd go running

to your PC to check that your antivirus software is up to date. Perhaps you'd

discover that your computer had been infected by a highly contagious bug -- a

software microbe that threatened the health of your hard drive.

But a computer virus is just a metaphor for an actual living thing -- the most

abundant form of life on earth. In " A Planet of Viruses, " science journalist

Carl Zimmer goes back to the source and surveys the world of real viruses in

nature. His absorbing account combines epidemiology, marine biology, genetics,

biochemistry, and population history (among other pursuits) as it hops from

virus to notable virus -- only polio is oddly missing -- to tell a story that

emphasizes both the long history of viruses and their fundamental importance to

how humans have evolved and lived.

Take smallpox, for example, the virus that led to the word " vaccine, " whose root

in the Latin for cow ( " vacca " ) points to Jenner's historic discovery that

cowpox immunized people against smallpox. Jenner published a pamphlet in 1798

that announced the results of his experiments, and they eventually made possible

the eradication of smallpox, a historic -- and still unique -- human

achievement. The last recorded case of smallpox was in 1977.

Smallpox took a huge toll before being brought to heel, and it's no exaggeration

to assert that the virus affected the course of human history. The virus killed

hundreds of millions of people between 1400 and 1800 alone, a staggering total

to contemplate. Even during the 20th century, while its territory was being

steadily reduced, smallpox killed an estimated 300 million people and blinded

millions more.

Moreover, as many historians have noted, smallpox was in effect -- if not

intention -- a biological weapon of New World conquest, as it cut down Native

American populations more swiftly than any human warfare could have. The disease

also took the 4-year-old son of lin in 1736. lin was a

proponent of the early and more dangerous form of smallpox immunization, which

involved the use of a smallpox scab to cause a limited infection that would then

confer protection against the disease. Of his son's encounter with smallpox, he

wrote in his " Autobiography " that " I long regretted bitterly, and still regret

that I had not given it to him by inoculation. "

Zimmer's most intriguing point in this slender but compelling book centers on

identity: viruses participate in our understanding not only of human history but

also human definition -- that is, of what " human " means.

Viruses are tiny packets that carry small strings of genes. Unlike cells, they

lack the apparatus to reproduce on their own, and thus require host cells to do

that for them. They enter those cells and redirect the cells' internal mechanics

for their own ends, issuing chemical commands to the cells to replicate the

virus. (The relatively unregulated complexity of this procedure is part of what

leads to so many viral mutations, which in turn makes antiviral vaccines so hard

to devise.)

When viruses don't kill their hosts, they commingle their genes with the host's

own and thus leave their traces in the host's DNA. That means humans are, in

Zimmer's phrase, " an inextricable blend of mammal and virus, " and viruses are " a

genetic archive " that we can use to trace the history of life on earth. Using

detection techniques that we might dub " paleo-virology, " scientists can examine

viral traces to reconstruct the path of a virus -- and also its host populations

-- through history. For example, by examining the particular strain of HIV

carried by Haitians in the early days of the AIDS epidemic (when the entire

Haitian population was demonized by frightened Americans as carriers of this

dread new scourge), scientists have been able to trace the paths of expatriate

Haitians from central Africa after the country then called Zaire gained its

independence from Belgium (which called it the Belgian Congo) in the early

1960s. This insight firms up the theory that AIDS first made a species jump from

chimpanzees to humans (a fact established through the study of chimpanzee

genetics), and then incubated in Africa for generations before greater

development (new roads, increased human contact) led to a tipping point that

allowed the disease to explode throughout the global population beginning in the

1980s.

The idea of a tipping point invokes another viral metaphor, popularized by

Malcolm Gladwell in his book " The Tipping Point, " which suggests that ideas

behave like viruses. And so they can. " Ideas, " writes Nobel Prize-winning

geneticist Jacques Monod, " have retained some of the properties of organisms.

Like them, they tend to perpetuate their structure and to breed; they too can

fuse, recombine, segregate their content; indeed they too can evolve. " Social

scientists have long sought cultural equivalents for biological forms of

transmission, such as the " meme, " an idea introduced by evolutionary biologist

Dawkins to describe a communicable piece of social information. The

underlying structure of a social network like Facebook bears a more than passing

resemblance to a nervous system because our understandings of biology and

culture continually inform each other. " A Planet of Viruses " is a fine brief

introduction to the biological underpinnings of a set of ideas that have, you

might say, gone viral.

http://www.salon.com/print.html?URL=/books/2011/05/17/a_planet_of_viruses_carl_z\

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