AUTHOR: Sarab DATE: 10:23:00 AM ----- BODY:

"One of Paul's most important insights is that AIDS is probably not a new disease, in the sense of HIV being a new pathogen. What we're dealing with is a pathogen that has rapidly evolved a much higher level of virulence because of its environmental circumstances. It may have been an organism that, prior to two or three decades ago, was transmitted primarily from parent to offspring — and maybe rarely between sex partners — and therefore the evolutionary factors acting on its virulence necessarily kept it very nonvirulent. Individuals with this virus had to survive long enough to reproduce, or the virus wouldn't be transmitted.

Now, take people with this virus and move them into a completely different social situation, in which families are disrupted and men are being served mainly by prostitutes who are dealing with hundreds of men per year. You now have a situation in which the opportunity for the transmission of the disease to another individual no longer depends upon the long-term survival of the individual that has it. Therefore the restraints on its virulence are removed. Within an individual, the more virulent the strain, the better it will do, because the more virulent the strain the more of that particular virus there will be for transmission to the next individual. We've shifted the balance of selection on this virus from mainly between individuals — between hosts — to within hosts. Within hosts, there's normally selection for increased virulence. Suddenly the virulence of the HIV went way up. This is just one example. There are many, many examples of human activities that influence the evolution of virulence in our pathogens.

There are many other ways in which evolutionary ideas can be brought to bear on medicine — for instance, in dealing with the mismatch between our evolved adaptations and the environment in which we now find ourselves. This mismatch is probably the main source of medical problems today."

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