David Quammen

measures them, roundish viruses range from around fifteen nanometers (that’s fifteen billionths of a meter) in diameter to around three hundred nanometers. But viruses aren’t all roundish. Some are cylindrical, some are stringy, some look like bad futuristic buildings or lunar landing modules. Whatever the shape, the interior volume is minuscule. The genomes packed within such small containers are correspondingly limited, ranging from 2,000 nucleotides up to about 1.2 million. The genome of a mouse, by con

The capsid shouldn’t be mistaken for a cell wall or a cell membrane. It’s merely analogous. Viruses, from the beginning of virology, have been defined in the negative (not captured by a filter, not cultivable in chemical nutrients, not quite alive), and the most fundamental negative axiom is that a virion is not a

so important I’ll repeat it: RNA viruses mutate profligately.
Mutation supplies new genetic variation. Variation is the raw material upon which natural selection operates. Most mutations are harmful, causing crucial dysfunctions and bringing the mutant forms to an evolutionary dead end. But occasionally a mutation happens to be useful and adaptive. And the more mutations occurring, the greater chance that good ones will turn up. (More mutations also