I don’t know why I read the ScienceDaily newsfeed, because it drives me crazy every single day.  I had naively thought that whoever massages the press releases they receive would have, maybe, a teeny tiny clue about what’s gone on in the field before, but they seem to have the historic awareness of tree squirrels. Today’s gem:

It’s a paradox that has confounded evolutionary biologists since Charles Darwin published On the Origin of Species in 1859: Since parasites depend on their hosts for survival, why do they harm them? … The study, published in the early online edition of the journal Proceedings of the National Academy of Sciences, provides the first empirical evidence in a natural system of what’s called the trade-off hypothesis.

It’s not a “paradox” at all, and while it may “baffle” the marketing department that wrote the press release ScienceDaily regurgitated, it certainly hasn’t baffled evolutionary biologists for a long time.  I’ve talked about this exact subject here:

… if there’s a link between increased transmission and increased virulence, then the balance will not favour the pathogen becoming benign.


I’ve previously talked about the common misconception that viruses evolve toward benignity. This is usually phrased something like, “Natural selection favours viruses with low pathogenicity/virulence (so they don’t eradicate their hosts)“, or “Viral pathogenesis is an abnormal situation of no value to the virus”. This claim is clearly wrong –clearly both through common sense, and through observation.

And here:

I’ve observed before that the common belief that viruses evolve toward avirulence is not particularly true. It’s more accurate to say that viruses evolve toward improved transmission. Some viruses are better transmitted if they let their host survive longer, but other viruses have to be virulent in order to spread. The former may evolve toward reduced (though not necessarily loss of) virulence, but the latter would “want” to maintain stable virulence.