Read This: A Planet of Viruses


There are 1,000,000,000,000,000,000,000,000,000,000 viruses in the ocean. There's more virus DNA in your genes than there is DNA that actually creates proteins. Viruses are everywhere. Ubiquitous. Silently shaping human history, and the evolution of life, itself.

With a resume like that, you might imagine that a book about viruses would necessarily have to be thick enough to justify its own zip code. But Carl Zimmer's new primer on the world's smallest life forms, A Planet of Viruses, is slimmer than my MacBook. With chapters that average 8 pages a pop, and beautiful, colored microscope images of viruses fronting each chapter, it's almost like a picture book for grown-ups—a smart, beautiful, and somewhat demented picture book that's likely to give you a case of the willies. In the best way possible.

Framed as a series of short meditations on individual viruses or virus types, A Planet of Viruses actually tells a deeper story—about how humans discovered these things living inside and all around us, and how our knowledge of virus' influence has grown.

Some of this story was stuff I'd heard before. Like almost every book about viruses, for instance, it starts with Tobacco Mosaic Virus—a plant disease which provided the first evidence that there was something else out there, smaller than bacteria, that could make living creatures sick. This introduction, and the first couple of chapters—which cover the common cold and influenza—really didn't add much to my understanding of viruses. But the book picks up steam when Zimmer starts talking about jackalopes.

You've probably seen these whimsical taxidermy projects. Usually, they're just common rabbits with deer antlers glued to their heads—one step up from those shellacked frogs holding little wooden beer bottles that you can buy in any Gulf of Mexico resort town. Less well known is the fact that jackalopes-the-joke are based on reality. Rabbits really can grow "horns", actually tumors, when they're infected with a virus.

In fact, jakalopes exist for the same reason Guardasil—the controversial cervical cancer vaccine— and annual pap smears exist. The virus that causes tumors to grow on the heads of rabbits is related to the one that causes tumors to grow on the cervixes of human women.

I did know that basic fact, but Zimmer does a brilliant job of explaining how viruses cause cancer, and spins that information out over several following chapters to help explain how virus DNA ends up inside our own genomes. The basic information at the beginning turns out to be important build-up, laying the foundation for some much more mind-blowing revelations—like this one:

Endogenous retroviruses [the viruses that can inject their DNA into our genome] may be dangerous parasites, but scientists have discovered a few that we have commandeered for our own benefit. When a fertilized egg develops into a fetus, for example, some of its cells develop into the placenta, an organ that draws in nutrients from the mother's tissues. The cells in the outer layer of the placenta fuse together, sharing their DNA and other molecules. ... Researchers have found that a human endogenous retrovirus gene plays a crucial role in that fusion.

The cells in the outer placenta use the gene to produce a protein on their surface, which latches them to neighboring cells. In our most intimate moment, as new human life emerges from old, viruses are essential to our survival. There is no us and them—just a gradually blending and shifting mix of DNA.

Any writer that can connect that to jackalopes deserves your attention.

While I definitely got a lot out of it (and I've been reading virus non-fiction for almost two decades now), I think it's likely that A Planet of Viruses will be appreciated most by teenagers, and by adults who haven't before read much about the amazing world of viruses. And that's not a bad thing. In fact, a clear, concise primer on what we know about viruses is important, in and of itself. This book would make great reading material for junior high or high school biology classes, and is bound to be remembered as the first inspiration many future virologists ever had.

The downside is the price. For a slim, 94-page primer—wonderful and well-written though it is—A Planet of Viruses is kind of steep. The hardback has a sticker price of $20. In contrast, a 300-page hardback book I'm also currently reading is priced at $27.

A Planet of Viruses is a great book, and a book that is well worth reading, but the price feels a bit off to me, especially given the fact that its biggest fans are likely to be kids, and people drawn in by an un-intimidating introduction to a complicated subject, rather than dedicated science-media consumers. Looking around the Internet, you can buy it for as little as $13, which seems like a better price point for this kind of book.

That said, I really do recommend picking up a copy. Zimmer's writing, the book's size, and its subject matter come together to create an amazing alchemy—a perfect, beach-ready, light-but-deep science read for Summer.

A Planet of Viruses by Carl Zimmer

Disclaimer: I received a free review copy of this book from the author. That said, I receive a lot of free review copies of books. I only tell you about the ones I think you really need to read.

Image: CDC/ Dr. Erskine. L. Palmer; Dr. M. L. Martin. I used a version posted to Flickr by Kat Masback. This same image is used in Carl Zimmer's "A Planet of Viruses".


  1. That image is totally haunting. I could imagine someone making a complete art exhibit by knitting and/or crocheting those images; they really lend themselves to that form.

  2. jr high bio classes- that might be about right, but doubt you’d see it in schools teaching to a NCLB bottom-line curriculum

  3. Does anyone else think that 1×10^30 viruses sounds incredible? The number of stars in the observable universe has been estimated at 3×10^23, meaning that in tiny droplet we call an ocean on the mote of dust we call Earth floating through the vast expanse of space, there are ~10 million times more viruses than there are stars? If that’s so then I just blew my mind…

  4. yeah that would have been a cool book to read for my HS biology class. i haven’t touched biology since then (i went the chemistry-physics route) but it looks really interesting.

  5. 1,000,000,000,000,000,000,000,000,000,000? Sounds like an estimate to me. I want an actual count.

  6. Now just wait a minute here. A nonfiction book that offers yet more proof of the fact of evolution – illustrated with color plates – and you’re quibbling over the price?

    $20 is more than reasonable.

  7. How is Gardasil controversial? Is it opposed by the general “no one should have sex, ever”/”Planned Parenthood is an abortion factory” crowd? My wife and I were very happy to hear that it’s been approved for use on boys. We plan to have our young sons vaccinated when they hit the appropriate age.

  8. Ok I’ll admit you sold me on this book. (Bought it for $13 @ Amazon)

    I confess to a somewhat lacking biology education, and a typically short attention span, so this sounds pretty much right up my alley.

    As for viruses specifically, I recently had a bout with shingles, luckily caught it early and got some anti-viral medications. The ordeal did renew this thought that viruses are really kind of weird things – they are kind of amazing; it’s just a pity they all do seem to want to hurt me so.

  9. “the world’s smallest life forms”

    By what definition is a virus living? Is this discussed in the book?

  10. We humans (not-so-hairy apes) may like to think that we are individuals. In the USA, that’s “rugged individuals”. Wrong. We are communities. We are vast agglomerations of organic entities, each with their own DNA and their own interests. We are carriers. Our biomass is most bacterial and viral. Our perceptions are filtered, mediated by our memories and expectations. We are peripatetic nodes in distributed networks. (Uh oh, jargon! Shoot me now!) But really, folks — you’re buggier than hell!

  11. @mikelipino

    Considering that viruses are significantly smaller than bacteria and have the ability to turn living cells into “virus factories”, whereas stars are significantly larger than planets and do not have the ability to replicate at all, the numbers don’t really sound that far off.

    @Anon (#5)

    Indeed it is. Read Zimmer’s outstanding “Parasite Rex” for a better view of just how cootie-filled and cootie-manipulated our world really is. (Spoiler: extremely filled and manipulated.)


    I tend to agree with you that viruses do not fit any of the criteria for life, having no metabolism nor independent mechanism for reproduction. However, from what I’ve read in the popular science press, it seems as though viruses are getting a “pass” for being alive. (I’m guessing the hypothesis of “virus as biological robot” is too far-fetched for mainstream consumption, even though it is an entirely accurate description.)

  12. OK – the remarks about scale & the actual number got me going…
    So viruses are between 20 and 300 nm (according to ), so in rough terms, if we make a cube of solid virus averaging 100nm diameter, it should, well-packed, measure on each side:

    # of viruses ^(-3) * # of meters per virus

    10^27 * 10^(-7)


    so the solid mass of viruses on earth is 10^17 kilometers per side?

    Good book so far. I am now skeptical of both the claim and my reasoning.. and I haven’t even bought it yet.

    1. Uh, not quite.

      Let’s stick with your assumption of a 100nm-per-side cubic virus (cubivirus?).

      That has a volume (Vc) of 10E-7 ^ 3, which is 10E-21 cubic metres.

      To get the number of cubic metres that 10E+30 cubiviruses (Ncv) would occupy, we multiply Nc by Vc:

      10E-21 * 10E+30

      Which gives us the total volume (Vt) of 10E+9 cubic metres, which is a solid cube of cubiviruses measuring 1km per side.

      Ick. That is a LOT of viral protein.

      1. If you want to put that in context, if you assume the average human weighs about 70kg (7E+1kg), given that our density is about that of water (1E+3kg per cubic metre), a human occupies a volume of about 7E-2 cubic metres (Vh). The human race currently numbers about 7E+9 (Nh). The entire human race would occupy a volume of about 5E+8 cubic metres, which is a cube measuring about 800m per side, half as much than just the seaborne viruses.

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