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This negotiation is rather weak since it doesn't recognise the passage of time. Once the viruses have reproduced to their satisfaction, they can renege on the d

This negotiation is rather weak since it doesn't recognise the passage of time. Once the viruses have reproduced to their satisfaction, they can renege on the deal when humans have a weaker negotiating position. That is to say, "Don't negotiate with terrorists." Fortunately the human/mammalian immune system does not typically permit this kind of deal. With a few exceptions: including HIV.

egeozcan 12y ago
If killing you means that the pathogen can spread more rapidly, it will evolve to do so. I don't see the HIV virus gaining anything by killing the host as it depends mostly on sexual intercourse to spread. Correct me if I'm wrong, but, Ebola would have been a better example in this case, I suppose.
- learnstats2 12y ago
  > If killing you means that the pathogen can spread more rapidly, it will evolve to do so. Sure, but killing the host is not generally the goal of a pathogen. Killing the host typically means the pathogen won't spread any further, and that direction leads to the pathogen's extinction. Or, the death of this family line, if you like. But, before worrying about that, if a virus does not address the immune system, it will not be able to spread at all - there will be no family line. The initial goal of a new virus is to evade the (highly advanced) immune system. Ebola apparently has a very naive way of bypassing the human immune system. That is, overwhelm the system, so that the host dies, but you have a small chance of spreading. This works, sometimes, for a little while, but not too much, maybe just enough to gain a few generations of evolution to try and improve your strategy. If you are already a latent virus in a related species, you might get a few attempts at this, as Ebola has. HIV does this in a frighteningly more effective way - a way which is more evolved - hide from the immune system while maintaining a route to spread to other hosts. This has to be a very subtle balance - hiding from the immune system is no mean feat. This is why I used HIV as an example - HIV somehow negotiates its own and the host's survival with the immune system (where Ebola has not been able to). The dance between immune system and virus ultimately leads to AIDS. Death of the host is not ideal for the local strain of HIV, but it had a good chance to reproduce in other hosts, so it's a good result for HIV as a whole. To become an effective and latent human virus, you need to evolve some sympathetic way of defeating the immune system that doesn't have a significantly negative result for the host. It's likely that HIV is still on that path, and Ebola might be on the start of that path. This is why we observe viruses to become less deadly and more easily spread over time. It's not necessarily true that this is the only evolutionary path, but the immune system presents such a huge barrier that you have to overcome this before meeting any secondary goals.
- kale 12y ago
  You are correct, Ebola's high mortality rate is a by-product of how it spreads. Ebola virus is successful at spreading due to the fact that it's in various fluids secreted by endothelial cells (which are everywhere in the body). The virus has mutated to let those tissues start to "leak", which means a person infected with Ebola is more likely to leak fluids (which is why it sometimes causes bleeding out of mucous membranes). Since there is an increase in the endothelial fluids released, there is more exposure to those trying to treat a patient with Ebola.[1] The way the virus spreads (increased discharge of endothelial fluids) is what causes it to be so fatal, which is a by-product. [1] Great overview of the virus: http://arstechnica.com/science/2014/11/understanding-the-ebola-virus/1/ http://arstechnica.com/science/2014/11/understanding-the-ebo...
- mason240 12y ago
  >If killing you means that the pathogen can spread more rapidly, it will evolve to do so. The plague/black death/Y pestis is another is a great example of this. It keeps its rat host just alive enough for just long enough for maximum use of the rats body. The rat then dies, which sends sends it plague-ridden fleas off to infect other rats.
  - abakker 12y ago
    Just an FYI from a thread a few months ago - https://news.ycombinator.com/item?id=7513455 https://news.ycombinator.com/item?id=7513455 It seems that the Black Death was pneumonic as well as bubonic.

egeozcan 12y ago

If killing you means that the pathogen can spread more rapidly, it will evolve to do so. I don't see the HIV virus gaining anything by killing the host as it depends mostly on sexual intercourse to spread. Correct me if I'm wrong, but, Ebola would have been a better example in this case, I suppose.

learnstats2 12y ago
> If killing you means that the pathogen can spread more rapidly, it will evolve to do so. Sure, but killing the host is not generally the goal of a pathogen. Killing the host typically means the pathogen won't spread any further, and that direction leads to the pathogen's extinction. Or, the death of this family line, if you like. But, before worrying about that, if a virus does not address the immune system, it will not be able to spread at all - there will be no family line. The initial goal of a new virus is to evade the (highly advanced) immune system. Ebola apparently has a very naive way of bypassing the human immune system. That is, overwhelm the system, so that the host dies, but you have a small chance of spreading. This works, sometimes, for a little while, but not too much, maybe just enough to gain a few generations of evolution to try and improve your strategy. If you are already a latent virus in a related species, you might get a few attempts at this, as Ebola has. HIV does this in a frighteningly more effective way - a way which is more evolved - hide from the immune system while maintaining a route to spread to other hosts. This has to be a very subtle balance - hiding from the immune system is no mean feat. This is why I used HIV as an example - HIV somehow negotiates its own and the host's survival with the immune system (where Ebola has not been able to). The dance between immune system and virus ultimately leads to AIDS. Death of the host is not ideal for the local strain of HIV, but it had a good chance to reproduce in other hosts, so it's a good result for HIV as a whole. To become an effective and latent human virus, you need to evolve some sympathetic way of defeating the immune system that doesn't have a significantly negative result for the host. It's likely that HIV is still on that path, and Ebola might be on the start of that path. This is why we observe viruses to become less deadly and more easily spread over time. It's not necessarily true that this is the only evolutionary path, but the immune system presents such a huge barrier that you have to overcome this before meeting any secondary goals.
kale 12y ago
You are correct, Ebola's high mortality rate is a by-product of how it spreads. Ebola virus is successful at spreading due to the fact that it's in various fluids secreted by endothelial cells (which are everywhere in the body). The virus has mutated to let those tissues start to "leak", which means a person infected with Ebola is more likely to leak fluids (which is why it sometimes causes bleeding out of mucous membranes). Since there is an increase in the endothelial fluids released, there is more exposure to those trying to treat a patient with Ebola.[1] The way the virus spreads (increased discharge of endothelial fluids) is what causes it to be so fatal, which is a by-product. [1] Great overview of the virus: http://arstechnica.com/science/2014/11/understanding-the-ebola-virus/1/ http://arstechnica.com/science/2014/11/understanding-the-ebo...
mason240 12y ago
>If killing you means that the pathogen can spread more rapidly, it will evolve to do so. The plague/black death/Y pestis is another is a great example of this. It keeps its rat host just alive enough for just long enough for maximum use of the rats body. The rat then dies, which sends sends it plague-ridden fleas off to infect other rats.
- abakker 12y ago
  Just an FYI from a thread a few months ago - https://news.ycombinator.com/item?id=7513455 https://news.ycombinator.com/item?id=7513455 It seems that the Black Death was pneumonic as well as bubonic.