I'm on pset12 (virus population simulation) and I'm wondering about some ambiguity. Is it normal/expected that the viruses reproduce drug-resistant offspring prior to the administration of a drug? It makes no logical sense really, so are we just supposed to go with it for the sake of simplicity? Or have I done something terribly wrong?

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anonymous · Answer

I haven't done that pset yet, so I can't give you a definitive answer from that perspective, but I just wanted to say that this makes complete sense from a biological perspective. If there were no drug-resistant viruses, they would all be killed by the drug. The drug doesn't induce a change in the viruses so much as it amplifies a specific characteristic that already existed there. So some viruses were already resistant, and now that the drug killed all the others off those become dominant. (You might ask why some were already resistant; basically there's just so many and they're so varied that some will always have a resistance for pretty much any method you use against them). The occurrence of resistance in the population will certainly increase dramatically in the presence of the drug, but it must be there to begin with.

anonymous · Answer

Agreed, it makes sense given the (correct) theories of evolution / natural selection. The same reasoning explains, for example, why some people have allergies to cats but others don't... (I think allergies work this way...)

So, think of this scenario: some super dumb alien race comes to earth and wants to kill everyone off by putting cats everywhere so that everyone who was allergic couldn't escape the cat invasion. Hospitals quickly run out of Benedryl and every allergic person dies from the asphyxiation caused by their allergic reactions. The bros not allergic to cats would be saying to themselves, "WTF are all these cats doing here" but would be very alive and the aliens would be, like, "S**t we r dumb let's just kill them with our photon lazer rockets etc."