A recurring lab-origin argument holds that a bat virus pre-adapted to human ACE2 is unlikely to occur without engineering. BANAL-236 is a counterexample sampled directly from nature and never passaged through a lab before characterization: its RBD binds human ACE2 at SARS-CoV-2-like affinity and it enters human cells. This establishes existence of the phenotype in the wild reservoir, so the receptor-binding/human-infectivity feature of SARS-CoV-2 is not by itself diagnostic of laboratory work. The argument does not touch the furin cleavage site, which BANAL viruses lack; it neutralises only the ACE2/human-infectivity strand of the lab-origin case.
Step 6 verdict — approved, checked
Reconstruction. P1: BANAL-236 was sampled from the wild and characterized without prior lab passage. P2: its RBD binds human ACE2 at SARS-CoV-2-like affinity and it replicates in human cells. P3 (hidden): a lab-origin argument of the form “feature F is too improbable to arise naturally” is defeated by exhibiting a single natural instance of F. C: the human-ACE2-binding/human-infectivity feature is not by itself diagnostic of laboratory work.
Traced load-bearing step. This is an existential counterexample against a universal-improbability claim, the strongest inference form available here: one uncontrived natural instance suffices to remove “no natural human-infectious analogue exists” as a reason. The conclusion is a defeat of a reason, not a positive argument for zoonosis, and the statement says exactly that.
Defeater probe. The natural overreach — “therefore SARS-CoV-2 arose naturally” — is one the argument explicitly does not make; it also pre-empts the scope defeater by conceding the furin cleavage site, which BANAL viruses lack, lies outside what it neutralises. Nothing left that breaks the link without denying P1-P2.