A Planet of Viruses (12 page)

Drawing a bright line between life and nonlife can also make it harder to understand how life began in the first place. Scientists are still trying to work out the origin of life, but one thing is clear: it did not start suddenly with the flick of a great cosmic power switch. It’s likely that life emerged gradually, as raw ingredients like sugar and phosphate combined in increasingly complex reactions on the early Earth. It’s possible, for example, that single-stranded molecules of RNA gradually grew and acquired the ability to make copies of themselves. Trying to find a moment in time when such RNA-life abruptly became “alive” just distracts us from the gradual transition to life as we know it.

Banning viruses from the Life Club also deprives us of some of the most important clues to how life began. One of the great discoveries about viruses has been the tremendous diversity in their genes. Every time scientists find new viruses, most of their genes bear little resemblance to any gene ever found before. The genes of viruses are not a meager collection of DNA cast off in recent years from true living things. Many scientists now argue that viruses contain a genetic archive that’s been circulating the planet for billions of years. When they try to trace the common ancestry of virus genes, they often work their way back to a time before the common ancestor of all cell-based life. Viruses may have first evolved before the first true cells even existed. At the time, life may have consisted of little more than brief coalitions of genes, which sometimes thrived and sometimes were undermined by genes that acted like parasites. Patrick Forterre, a French virologist, has even proposed that in the RNA world, viruses invented the double-stranded DNA molecule as a way to protect their genes
from attack. Eventually their hosts took over their DNA, which then took over the world. Life as we know it, in other words, may have needed viruses to get its start.

At long last, we may be returning to the original two-sided sense of the word
virus
, which originally signified either a life-giving substance or a deadly venom. Viruses are indeed exquisitely deadly, but they have provided the world with some of its most important innovations. Creation and destruction join together once more.

A Planet of Viruses
was funded by the National Center for Research Resources at the National Institutes of Health through the Science Education Partnership Award (SEPA), grant no. R25 RR024267 (2007–2012), Judy Diamond, Moira Rankin and Charles Wood, principal investigators. Its content is solely the responsibility of the author and does not necessarily represent the official views of the NCRR or the NIH. I thank the many people who advised this project: Anisa Angeletti, Peter Angeletti, Aaron Brault, Ruben Donis, Ann Downer-Hazell, David Dunigan, Angie Fox, Laurie Garrett, Benjamin David Jee, Ian Lipkin, Ian Mackay, Grant McFadden, Nathan Meier, Abbie Smith, Gavin Smith, Philip W. Smith, Amy Spiegel, David Uttal, James L. Van Etten, Kristin Watkins, Willie Wilson, and Nathan Wolfe. I am particularly grateful to my SEPA program officer, L. Tony Beck, and to my editor at the University of Chicago Press, Christie Henry, for making this book possible.

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