Small and Dangerous Creatures

Thomas R. Tritton reviews Carl Zimmer’s A Planet of Viruses.

By Thomas R. Tritton | December 1, 2011

Carl Zimmer. A Planet of Viruses. Chicago: University of Chicago Press, 2011. 128 pp. $20.00.

Good things come in small packages. This book, for example, weighs in at only 94 pages but, despite its small size, is chock-full of voice, vision, and velocity. Voice because it is finely written and delightful to read, vision because the material is so intriguing you can’t help but be swept into learning, and velocity because you can read the whole thing in one quick sitting and then wish it had taken longer.

Small and Dangerous Creatures - Thomas R Tritton reviews Carl Zimmer A Planet of Viruses

Color-enhanced transmission electron micrograph of herpes simplex virus particles (orange) in the nucleus of a cell.

Color-enhanced transmission electron micrograph of herpes simplex virus particles (orange) in the nucleus of a cell.

Rob Young/Wellcome Images

Bad things also come in small packages—bad things like viruses, which are basically a small chunk of nucleic acid roped off in a protein coat that cause all manner of misery when residing in human bodies. Viruses lack any of the other normal accoutrements of a living cell and therefore may or may not qualify as “alive.” In A Planet of Viruses, Carl Zimmer bravely takes the view that drawing dividing lines in science, while sometimes helpful, often enough ends up being so artificial or arbitrary that progress is impeded. Accordingly, he concludes the book with a call to include viruses among the living because without these small creatures life as we know it would have been impossible. I’m persuaded.

Less persuasive, but no less thought provoking, is Zimmer’s questioning whether we should seek a cure for the common cold. The tiny rhinoviruses that cause so much human misery have proven quite intractable to treatment despite considerable scientific effort. Zimmer speculates that a drug damaging a particular RNA fold that all such viruses share might “stop every cold virus on earth,” but he then questions the wisdom of doing so since exposure to relatively harmless viruses may stimulate the immune system’s alertness for other more dangerous pathogens. The argument seems contradicted by a later chapter on the smallpox virus—now essentially eradicated as a cause of human disease. Smallpox may have killed more human beings than any other disease on Earth, so eradicating the viral scourge seems well worth the effort.

A history of humanity’s contention with disease is contained in this slim survey. You learn how we make discoveries, how we manage conflicts, and how we make sense of the world when it doesn’t seem particularly sensible. You see how fits, starts, digressions, and false leads eventually lead to medical progress. One of the common threads in the history of several of the virus families is how scientists grind up the tissues of diseased animals, filter the sludge to remove large cells like bacteria, and then see whether the resulting fluid causes the same infection. This method allowed the infectious agents to be identified as viruses for influenza, papilloma, and AIDS, among others. These cases are vivid demonstrations of the power of Koch’s postulates—specified criteria that prove a cause-effect relationship between a microbe and a disease—even though they were not explicitly cited in the book.

Diligent readers are also rewarded with the kind of fascinating facts that make you popular at cocktail parties or as a teammate in games of Trivial Pursuit. Did you know that each person on Earth harbors some 100 trillion bacteria? That’s 100,000,000,000,000, making even the national debt seem like a small number. And there are approximately 174 different species of virus in the lungs of a typical human being. Numbers like this make one wonder how we ever manage to stay healthy. If you consider the earth as a whole, the scale is almost incomprehensible. The oceans contain some 1030 viruses with an aggregate weight equaling 75 million blue whales, the largest creature to ever exist on Earth. Too bad the blue whale is facing extinction while viruses just keep on multiplying in seductively welcoming hosts.

A diligent reader can always find flaws in a book. The table of contents is laid out confusingly over two pages. More annoying, antibiotics are labeled as “artificial chemicals.” There probably isn’t a precise definition of this terminology, but if “artificial” means produced in a laboratory, it’s wholly incorrect since most of the early (and many newer) antibiotics are naturally occurring chemicals provided by nature. However, these are small points compared with the pleasures provided by Zimmer’s command of metaphor. My favorite: comparing the 10 genes of a typical virus to the 20,000 found in a human as “a haiku of information.”

This is an informative and fun-to-read book for anyone interested in contemporary life sciences. For the real virus aficionado there is a companion website ( with virus comics, mobile-device apps, and an image bank of pretty drawings of the tiny critters. Also, if the chemically inclined among us have any curiosity about how macromolecules scaffold together to form living beings, the book and website are definitely worth your time to explore.