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Plinz's profile
Joscha Bach
Joscha Bach
Joscha Bach
@Plinz

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Joscha Bach

@Plinz

FOLLOWS YOU. Artificial Intelligence, Cognitive Architectures, Computation. The goal is integrity, not conformity.

San Francisco, CA
bach.ai
Joined April 2009

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    1. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      2. In principle, the virus could mutate in any number of ways, but two of the most important to think about involve VIRULENCE: the amount of harm the disease causes to its host, including mortality risk, and TRANSMISSIBILITY: the ease with which new infections are generated.

      2 replies 46 retweets 296 likes
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    2. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      3. Let's start with transmissibility. Natural selection will favor variants of the virus that are more likely to transmit and initiate new infections. For example, a variant might reproduce better in the upper respiratory tract and thus be spread more in respiratory droplets.

      2 replies 31 retweets 242 likes
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    3. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      4. If such variants arise, we would expect them to spread, because they would produce more new infections than the previous "ancestral" strains. We certainly can't rule out the possibility of this happening, but I don't there is good evidence that it has happened yet.

      1 reply 26 retweets 199 likes
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    4. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      5. It's hard to predict for certain, but my personal opinion is that given the rates at which we seeing mutations in the virus and the structure of its genome, there is not strong reason to expect more transmissible variants to evolve and become widespread over the next year.

      8 replies 48 retweets 277 likes
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    5. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      6. Now let's consider virulence. One argument has it that diseases should evolve not to kill their hosts too quickly, because a dead host doesn't transmit to other people. There are a lot of problems with this argument both in general and for #COVID19 in particular.

      3 replies 28 retweets 215 likes
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    6. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      7. People used to take this reasoning to the conclusion that microbial pathogens should co-evolve with their hosts to cause minimal harm. The problem with that argument is that there tend to be *virulence-transmissibility tradeoffs*.

      3 replies 24 retweets 220 likes
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    7. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      8. To transmit effectively, a pathogen generally needs to make a lot of copies of itself within the host. Doing this tends to cause harm to the host, either directly or as a byproduct of the host's immune response. Of course there are exceptions. Biology always has exceptions.

      4 replies 20 retweets 230 likes
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    8. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      9. So we might expect a pathogen to evolve intermediate virulence. Paul Ewald has proposed this as a reason why we shouldn't worry too much about H5N1 bird flu. It may now kill over 60% of people infected, but if it takes off in humans shouldn't it evolve to become less lethal?

      4 replies 19 retweets 178 likes
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    9. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      10. I've been very critical of this line of thinking: Perhaps in the long run, a pandemic H5N1 would decline in virulence. But to misuse John Maynard Keynes, in the long run we are all dead. Especially in a bird flu pandemic. Beneficent evolution would be little consolation.pic.twitter.com/UZhPbe5H46

      2 replies 39 retweets 274 likes
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    10. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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      11. More generally, predicting virulence evolution is hard, especially for an emerging disease. When a new pathogen enters the human population, it is unlikely to be adapted to maximize transmission. It might be too virulent, or too mild.

      4 replies 27 retweets 212 likes
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      Joscha Bach‏ @Plinz Mar 23
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      Replying to @CT_Bergstrom

      At this point in history, I expect that humanity's response to a pathogen is an important factor in its evolution. If COVID-19 was more lethal, would travel restrictions not have been happening earlier and with greater decisiveness? It may already be too virulent for its own good

      10:36 PM - 23 Mar 2020
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      • Ramzi Nohra Fernando Macías 🕵️🔍 vakibs Jason McCandless Mike Maranto
      1 reply 0 retweets 5 likes
        1. Carl T. Bergstrom‏Verified account @CT_Bergstrom Mar 23
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          Replying to @Plinz

          Well, its virulence affects the *epidemic trajectory* via human responses. But unless it evolves into multiple strains, some of which we tolerate and others of which we fight aggressively, natural selection isn't acting on virulence via human responses.

          0 replies 0 retweets 9 likes
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