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Surprised to read these threads without any reference to the Defuse proposal, documents of which were recently revealed to include even more detailed descriptions of features found in COVID-19 than the ones known previously.

Another thing that continues to surprise me in this discourse is not to have seen spelled out in terms of Bayes factors what to me seems the most straightforward way of thinking about the significance of the Defuse proposal as evidence, namely, that instead of thinking about the likelihoods of the features of the virus, we ask the competing hypotheses to explain the existence of the proposal itself and try to assess the Bayes factor P(Defuse|lab)/P(Defuse|natural).

Specifically, this involves estimating the probability that there exists a grant proposal, written less than 2 years before the outbreak by collaborators of the lab located in the city where the outbreak was first detected, proposing (among other things) to engineer a feature found in the natural virus:

  • not seen before in closely related viruses
  • defined by a 12 nucleotide insert when compared with closest relatives (i.e. the closest know relatives were not in any way close to evolving such a feature)
  • in the same location as the feature appears in the natural virus in the spike protein at the S1/S2 junction

These are not the only detailed correspondences between the supposedly natural virus and the grant proposal, as is made clear in the US right to know piece. To me, the existence of such a plan seems to be a fluke of cosmic proportions under the natural hypothesis and totally unsurprising under a lab engineering hypothesis.

The typical likelihood based argument I have seen argues (correctly in my view) that the likelihood|lab of certain features mentioned in Defuse is vastly elevated when conditioning on Defuse and that therefore P(feature|lab, Defuse) >>P(feature|natural). One thing about this form of reasoning that many people don't seem to get is that the argument for P(feature|natural) being small is not based on some general view of what evolution is capable of achieving; instead it is based on the specificity of the feature in question. With Defuse, the challenge for the natural origin hypothesis is to argue for an elevated probability of a very specific outcome under the natural origin hypothesis. This can't be done by appealing to the general awesomeness of evolution, as this form of argument only underscores the vastness of the sample space of natural viruses of which the subset of the viruses with the specific feature is a tiny subset.

What becomes clearer if instead of P(feature|lab, Defuse) we use up the Defuse evidence by thinking about P(Defuse|Hypothesis) is that the lab engineered virus hypothesis is the only hypothesis H one can think of under which P(Defuse|H) is not tiny.