Saturday, February 04, 2006

The journey-work of stars

Everyone is waiting for the bird flu virus to find and exploit the mutation that allows human-to-human transmission. Given the notorious genetic adaptability of viruses it would seem to be just a matter of time. The little stinkers have a huge bag of tricks up their sleeves for sneaking into cells and avoiding defenses. Their very simplicity is key to their plasticity.

A recent article in Nature (12 January) takes the viral story one step further. Evolutionary biologist Patrick Forterre of the University of Paris-Sud, Orsay, thinks viruses invented DNA as a way around the defenses of the cells they infected. Yep, he imagines an early world of cells that used single-stranded RNA as their template for reproduction. Even then viruses were preying on cells, says Forterre, and they came up with double-stranded DNA as a way of avoiding their host's defenses. DNA is more chemically stable than RNA, and better able to resist the enzymes that cells had evolved to break apart viral RNA.

Of course, DNA had another advantage. Its greater stability also made possible larger genomes, and therefore organisms of greater complexity. If Forterre is right, the whole marvelous panoply of life on Earth today started as a viral ploy. Nature red in tooth and claw from day one. Well, ok, day two.

In her wonderful book The Sacred Depths of Nature, my microbiologist friend Ursula Goodenough writes: "The religious naturalist is provisioned with tales of natural emergence that are, to my mind, far more magical than traditional miracles. Emergence is inherent in everything that is alive, allowing our yearning for supernatural miracles to be subsumed by our joy in the countless miracles that surround us."