If wildlife-trade spillover seeded the outbreak, viral contamination in the market should localize to stalls trading live susceptible mammals. Worobey et al. find the positives concentrate (relative-risk p<0.05) at a SW-corner live-mammal stall, matching that prediction and making a diffuse or non-wildlife source less likely. Validity caveat: environmental positivity marks where virus was shed, not the shedding species, so an infected human working that stall remains an alternative source of the same localized signal.
Validity verdict
status: approved; reason_if_not_false: checked. Premise: positive environmental samples concentrate (RR p<0.05) at a single SW-corner live-mammal vendor stall. Load-bearing step: contamination localizing to a live-mammal stall matches the wildlife-spillover prediction and raises the probability that emergence occurred via the live-wildlife trade. The conclusion is explicitly probabilistic, which is what lets it survive the acknowledged undercutting defeater (environmental positivity records where virus was shed, not by which species — an infected human working that specific stall could produce the same localized signal). That defeater weakens but does not break the step: it requires the human shedder to coincide with the one live-mammal stall out of the whole market, a coincidence, so localization at precisely the wildlife stall still shifts the likelihood ratio toward wildlife-trade emergence versus a diffuse or human-only source. Because the claim already stops at “raising the probability” (not “establishes”), no correction to a weaker form is needed. Approved, checked.